Minnesota Astronomical Society August 2021 a publication of the Minnesota Astronomical Society Volume 47 Number 4 In the pages of Feint Preys By Dave Tosteson the Gemini Not long ago the elegant structures called globular clusters, those spherical, glittering balls of hundreds of thousands of stars, were all considered remnants What? Two 30-inch scopes? of our galaxy’s formation. Thought to be produced at the same time as the Milky By Dick Jacobson…Page 5 Way twelve-billion years ago, they were like stately, never-changing reminders of a bygone era, antebellum mansions surviving the social and military upheavals of MAS Patron Members…Page 10 a turbulent time. Now we know differently. Not only has our galaxy gained and MAS Board Minutes lost numerous clusters, but we understand globulars to be far from unchanging By Trena Johnson, Secretary…Page 10 remnants. Likely, all have been altered by tidal gravity and interaction with galactic structure. Some estimates place up to forty-percent of our present globulars as We Live in the Stars extragalactic addressees before “adoption” by the . Here is a group of By Aaron D. Raines…Page 11 recently recognized Milky Way globulars which can be visually observed, and one I have my eye on. Variable Star of the Month By Jim Fox…Page 12 MAS 2021 Star Party Schedule…Page 12 Loaner Scopes & Astronomy DVDs Available to All MAS Members…Page 14

Fornax dwarf galaxy & globulars In 2002 Alan Whiting and his colleagues published information on their search for faint dwarfs in our galaxy. In the dozens of objects recovered from their Cerro Tololo imaging were galaxies, planetary nebulae and a small collection of faint stars in central Cetus thought to be an open cluster. Three years later, Giovanni Carraro of the University of Padua (Italy) used the VLT to determine Stories Wanted: Gemini is written entirely spectrograms and radial velocities to place this cluster in our galaxy’s halo, thirty by our members, for our members. Gemini needs kiloparsecs from the center. Its metal content profile (of elements heavier than your stories: how you first became interested in helium) and its position and velocity suggested it was a member of a class of astronomy, how your interest has evolved over the six known tidally stripped globulars added to the Milky Way’s retinue from the years, equipment you use, projects or activities captured Sagitarrius (Sag dSph). Before its accretion, you have worked on, star parties or events you’ve its case may have been similar to the Fornax Dwarf galaxy, one with a half-dozen attended in this state and elsewhere, how you’ve globulars that, for amateurs, are much easier to see than the galaxy itself. Fornax’s encouraged others—especially young people—to brightest globular, NGC 1049, was found a century before the galaxy was spotted get involved in this fascinating hobby. Submit your by Shapley in 1938; it could be considered a correlate of M54, the former core of stories to [email protected] the Sag dSph galaxy. It and Fornax represent dwarf galaxies that have succumbed If your e-mail, phone number or street to and resisted the Milky Way’s take-out menu. The idea of interacting dwarfs address has recently changed, please fill out contributing to our census of globular clusters dates to Searle and Zinn in 1978. the “Update Member Information” Web form Whiting-1 was named in honor of its discoverer, Alan B. Whiting of the at mnastro.org/update-member-information to Cerro Tololo Interamerican Observatory. This small (one arcminute/three update your contact information in the MAS ) cluster has a loose structure. Its brightest star is magnitude (v) 18.0 member records. and its horizontal branch, where resolution would start to GEMINI INFO occur in the eyepiece, is 20.4. Editors At 6.5 billion years old it is the Brian Litecky and Eugene Brown youngest Sag dSph globular and one of the youngest in the Webmaster/MAS Web Committee: Milky Way. At the Okie-Tex [email protected] Star Party in September, 2006, Forums Administrator I used my newly acquired 32'' Russ Durkee reflector to spot several of the Whiting-1 stars in a near-dawn Monthly Meeting Presenter observation with the Moon up Coordinator and the object at an altitude of Ahmed Reda only thirty degrees. Its position of 02h 02m 57s, -03d 15m 08s Astronomical League Coordinator (ALCOR) sits on the SE edge of Abell Jerry Jones Galaxy Cluster 296 and 4.1 degrees west of Omicron Ceti, Outreach Coordinator Mira. Catching the cluster at Lilah Blinkman its culmination would provide a view fifty degrees above the Gemini is published 6 times annually Koposov-1 horizon from that latitude, by the Minnesota Astronomical Society. offering improved chances for Electronic submissions for seeing its fainter stars. Gemini may be sent to: In the first years of the new Millennium, searches by Whiting and others using [email protected] the Sloan Digital Sky Survey (SDSS) produced a spate of objects that orbited the Hardcopy items should be sent to: Milky Way. Simulations to help explain the “missing mass” problem had predicted Minnesota Astronomical Society thousands of such galaxies and clusters, but researchers were finding only a few- Attn: Gemini dozen dwarf galaxies. Reevaluation with computer programs that added gas and stellar P.O. Box 14931 components to the previous dark-matter-only scenarios reduced the number by an order Minneapolis, MN 55414 of magnitude. Fewer than a dozen in the “FIRE” simulation were predicted to form stars within the dark-matter component. Interaction with our galaxy’s halo appears to have interfered with stellar production in some of these proto-clusters, leaving only MAS Board Members starless, dark-matter clumps. Searches in the halo of the Andromeda Galaxy, which in some ways are easier to perform than in the Milky Way, found globulars to distances President: Mark Job of 650,000 light years from its center, exemplified by Martin GC1. Some predict that E-Mail: [email protected] intermingling of halo globulars between the Milky Way and our sister galaxy will be Vice President: Valts Treibergs discovered. E-Mail: [email protected] Factors differentiating the new finds into either globular clusters or dwarf galaxies include mass, luminosity, size, mass/light ratio, ellipticity and the spread of metal Treasurer: Matt Dunham content within their stars. A key difference is that dwarf galaxies seem to possess large E-Mail: [email protected] amounts of dark matter and globulars do not. This unseen mass allows them to withstand Secretary: Trena Johnson the disruptive forces of gravitational tides and supernovae and increases the spread E-Mail: [email protected] of by incorporating heavier elements made by subsequent generations of stars. Most clusters are thought to have formed concurrently with their parent galaxies, Board Member at Large: and theoretical work at the University of California, Riverside, suggests 50-60% of Gunnar Isberg these early globulars formed within their own dark-matter halos, which were later E-Mail: [email protected]. removed through processes such as dynamical friction, mass segregation and tidal Board Member at Large: stripping. Waves of star formation within galaxies and accretion of external objects Conrad Sanders may be represented by the differing ages of any particular galaxy’s cluster population. E-Mail: [email protected] Most Milky Way globulars have stars with ages commensurate with that of their galaxy. But there are outliers within that group, both in characteristics and position. These objects that don’t fit the usual profile are of great interest to researchers, as they hold clues to their origin and evolution. Palomar-15 shows strong evidence of tidal stripping, with a stream of stars trailing behind it. Messier’s same number shows signs of internal reshaping. The Sloan Digital Sky Survey (SDSS) imaged one-quarter of the sky from its New Mexico site and has been a discovery source for many faint objects in and around our galaxy. In 2007 Sergey Koposov (then at Max Planck Institute in Heidelberg, Germany, later at Cambridge University, UK) and his colleagues announced the discovery of two faint, halo globular clusters (ApJ, 669, 337) at galactocentric distances of 40-50 kpc, subsequently named Koposov-1 and Koposov-2. At the time, GEMINI • www.mnastro.org 2 Koposov-2 beat out AM-4 for the title of lowest luminosity for stellar population of twelve-billion-year-old stars and contained a Milky Way globular, with an (Mv) of no dark matter. Stellar members found at large distances from -0.35 (compared to -1.4 for AM 4). Koposov-1 came in third at its center suggested ongoing mass loss. The SEGUE project’s -2.0, later adjusted to -1.35. For comparison, Omega Centauri, first named find was an Ultrafaint Galaxy called SEGUE-1 that our galaxy’s largest and brightest globular, has an Mv of -10.3, contained only a few hundred stars, with the highest mass-to- several thousand times brighter. Of great interest about these light ratio of any known object at the time—over three-thousand. newly discovered globulars is their short “evaporation time,” the It was basically composed of only dark matter, but I was able period expected for them to lose all their stars into the halo and to spot a few of its identified stellar members in 2009 using my intragalactic medium. This estimate for the Koposov clusters is 32'' scope. There are likely numerous dark-matter-only objects a little over a billion years, which suggests misfortune in both orbiting our galaxy and within the Local Group, but since they their affairs and that of the primordial globular population of our would produce no electromagnetic radiation, they will be very galaxy—a flood of clusters lost through tides since the Milky hard to detect, offering amateurs nothing to see. Way’s formation twelve-billion years ago. Palomar-5 has only about 10,000 stars left from multiple interactions with the dense central plane of the Milky Way. Its preceding and following tails stretch over 13,000 light years, and estimates predict complete dissolution on its next pass through the galactic plane. Our galaxy’s globular population was not staid at home. It has been dynamic, with losses and gains of many objects over its lifetime.

Milky Way stellar streams In 2007 a group headed by Vasily Belokurov of Cambridge University (UK) identified a new Milky Way substructure they named the Hercules-Aquila Cloud. It was an over-density of stars lying between 10 to 20 kpc from us, stretching eighty degrees in longitude and with a projected size of 20 by 15 kpc. Several of these types of structures have been found since the start of the Millennium, including the streams of stars associated with accreted and disrupted globulars such as Pal-15 and Pal-5. The most famous image of this process is of the streams encircling Leavens-1, Cluster NGC 5907 in Draco, several of which were visible in my 32'' My late friend Barbara Wilson was an inveterate globular from the dark, west- Texas skies. hunter; we observed Koposov-1 together at the 2011 Texas Star The faint globular SEGUE-3 lies 41 arcminutes south of Party (TSP). It is at 11h 59m 18.5s, +12d 15m 36s (2000.0). fourth magnitude 1-Pegasus, at the ’s western border Through her 20'' f/4 reflector at 650x, we saw the three bright stars with Vulpecula. It is 28’ NNW of NGC 7056 and sits 55,000 light to the SSW, NNW and west. There is a foreground star within the years from us. At the 2014 Okie-Tex Star Party, using my 32'' confines of the cluster, but the globular’s stars are visible in a 0.5’ reflector at 650x in moderately poor seeing, I saw this cluster as circle, most within a few arcseconds of the center. Conditions a faint haze less than an arcminute in diameter, with a triangle of were poor, with seeing of 5/10 and transparency a 3/10 with stars just north and a string of stars to its south. With an absolute many clouds. I saw Koposov-2, located in eastern Gemini at 07h magnitude of 0.0, Fadeley called it “the least luminous old stellar 58m 17s, +26d 15m 18s, at the same event on June 1st, but this system known” in 2011, shining with the brightness of only 100- time using my 32'' reflector at the same power. The object was 200 Suns. Its brightest star, at magnitude 19.5, should be visible low in the west and seeing was a 6, transparency a 5. It was seen with my 32'' scope in excellent conditions. SEGUE-3 appears as a small, unresolved area 2’ north of the brightest of three field to be involved with the Hercules-Aquila Cloud, a likely dwarf stars in the 7.5’ FOV. galaxy with a new Milky Way address. Koposov-1 is a member In 2010 the Sloan program found another globular with its of another, similar halo subsystem. Sloan Extension for Galactic Understanding and Exploration As new globulars were being found in halo surveys, one (SEGUE) project that explored the Milky Way’s outer halo. This group decided to go the other way and delve into the depths of cluster was even dimmer than the Koposov pair, with an Mv of the galactic core, looking for known objects that may have been 0.0. Named SEGUE-3, it appeared to be composed of a single misclassified. Pfleiderer-2 was discovered in 1977 and called an

3 August 2021 open cluster. It is located in a dense, eastern Ophiuchus starfield eight arcminutes from UKS-1 is another cluster that looks to be near the Serpens border. The closest bright star is Zeta (57) a much smaller and fainter globular, at 17h 54m 42.5s, -24d 00m Serpens, 1.5 degrees to its NNE. In 2009 a group led by Sergio 53s. It appears to carry only 1-2% of the mass of UKS-1 and is Ortolani of the University of Padua, Italy, studied this object with possibly associated with it gravitationally. The uncertainty arose the 3.58 meter Galileo telescope at La Palma and concluded that because data did not allow an accurate distance measurement. it was a small and faint globular, similar in size to NGC 6522 and Their findings were published in A&A 527, A81, 2011. On the NGC 6528 and in mass to the Palomar clusters 12 and 13. For POSS there is only the faintest hint of a few stars at its position. amateur observation, dust around the galactic center reddens and At the 2016 Okie-Tex Star Party I used my 32'' reflector on dims Pfleiderer-2 by over three magnitudes as its light courses consecutive nights at 650x in moderate conditions and saw anear. I viewed it in the fall of 2010 with my 32'' reflector and a hazy patch in the area of the cluster, just NE of an “arrow” found it to be 5-6’ in size, slightly concentrated to the middle, asterism of stars one cluster diameter away. with individual stars seen within it. Its brightest red stars come in at mag 18.5 (Ortolani), within the capability of my telescope, but the cluster lies within a crowded Ophiuchus starfield, so individual stellar data would be needed to know which belong to the cluster. It stood out from the starfield, and I described it as “sparse.” There was a small cluster of stars seen a few minutes NW.

NGC 5907 stellar streams Despite the success of the Sloan projects, that survey covered only one-quarter of the sky, and its limiting magnitude of r~22.5 meant it could only search the out to a few tens of kiloparsecs. Astronomers are eager to explore areas outside the footprint of the SDSS and to greater depth within the galactic neighborhood. In 2012 Ricardo Munoz (Yale University) and his Munoz-1 & UMa dwarf galaxy colleagues used the Canada-France-Hawaii Telescope (CFHT) In the mid 1990s, amateurs were pursuing observations of on Mauna Kea to discover a new Milky Way globular. With its the faintest Milky Way globulars. Wilson had viewed all the larger mirror (3.6 m vs. 2.5 m for Sloan) and world class site, Terzan globulars and wanted to see the faintest known globular the CFHT was able to image to magnitude 26 (g), significantly in our galaxy, UKS-1. Discovered in 1980 by Longmore and expanding the available search volume. As often occurs, the new Hawarden, their private findings using the 48'' UK Schmidt object was a serendipitous find, as they were studying the nearby instrument were published by Malkan, et al., in ApJ 237, 432 Ursa Minor Dwarf Galaxy (UGC 9749). The Mega Cam imager that year. No images were given, as this was an infrared object, carried a field of one square degree and overlapping fields allowed not visible on the POSS images. Wilson had two friends take the new cluster, called Munoz-1 and 45’ SW from the center a deep exposure of the area to render the globular visible. In of the dwarf galaxy, to be spotted. Later data showed velocity July, 1997, she used Larry Mitchell’s 36'' f/5 reflector and that differences between them suggesting they were not associated. image to make and confirm her observation. The next spring at The group’s tentative initial conclusions were that the cluster had the Texas Star Party I heard of this recovery and searched the an age of 12.5 Gyr, a distance of 45 kpc and a size of 7 pc. Its area using my 25'' reflector. With drawing in hand, I surprised absolute magnitude of -0.4 placed it just behind SEGUE-3 as the her with my sighting, demonstrating the common practice that faintest intrinsic Milky Way globular. once an object has been sighted it can often be seen in smaller For observers, the cluster is located at 15h 01m 48s, +66d apertures. This globular that held court as the “faintest in the 58m 07.3s in southern Ursa Minor just 1.4 degrees from the Draco Milky Way” for almost three decades is at 17h 54m 27.2s, -24d border. A pair of PGC galaxies, 53664/5 (mag 17.9 and 16.6, 08m 43s (Galactic Globular Database, William E. Harris). respectively), lie just 3’ to the north and appear to be the central Dante Minniti of the Catholic University of Santiago, Chile, ellipticals of a galaxy cluster 6-7’ in diameter. Three arcminutes headed a group that used the 4-meter Paranal Observatory north of them are two moderately bright stars, one of which telescope to search the central regions of the galaxy in the is mag 11.4. At the 2015 Texas Star Party, in moderately poor infrared for new evidence about known globulars and to find conditions (seeing 4/10, transparency 5/10 and high humidity), I used my 32'' reflector to recover the brightest star of Munoz-1, at those not yet known. Their study was called Vista Variables in th Via Lactea, or VVV, and they quickly struck paydirt. Sitting only 18 magnitude. On the discovery paper image there is a spiral of

GEMINI • www.mnastro.org 4 fainter stars with a diameter of half an arcminute, but those could Recent research on M31 has shown halo globulars extending not be seen. The POSS-2 (R) image displays a haze of stars in an to over half a million light years, many times the diameters of oval about 25'' wide and 30'' high at the position, that lacks the the visible galactic discs. HST studies of distant quasar light resolution into stars on the CFHT image. I would like to try this passing through M31’s halo, published in August, 2020, show its object again in better skies to get the impression of its larger size. outer regions extend up to two-million light years from the core. An interesting object found in Crater in 2014 that goes by The two galaxies are therefore in contact, and member globular the names Laevens-1 and the Crater cluster has sparked debate clusters may be found in that overlapping space. The Crater for several reasons. It was initially thought to contain massive cluster appears to be similar to the SMC globular Lindsay-38, blue stars, suggesting star formation within the cluster in the last whose position and velocity agree with known parameters of the billion years. But improved data showed that these several stars Magellanic Stream. But the initial conclusion that it was a captured were likely in the foreground, not associated with the cluster. SMC globular was thrown in doubt when age and metallicity Its smaller spread of stellar metal content and velocities also data showed that those properties more closely matched certain pointed toward a “baryonic” object (one devoid of dark matter), dwarf galaxies, such as Leo-I and Carina. Jimi Lowrey posted suggesting it was most likely a . Daniel Weisz of observations of Laevens-1 on the Deep Sky Forum in 2014, the University of Washington (Seattle) studied this cluster with using his 48'' reflector. Barbara Wilson showed me a nice view Hubble and published data in 2015 (arXiv: 1510.08533v2, 29 of this globular in her 20'' scope at the 2015 TSP. It was easily Oct 2015) showing it to be very young, at 7.5 Gyr. It had a half- seen as an unresolved haze 20-30 arcseconds in diameter, held light radius of ~20 pc, no evidence for tidal disruption, an Mv of with averted vision and almost held with direct vision. There is a -5.3 and a mass of 10^4 solar. star at its SW corner, with two brighter ones several arcminutes in a line to the NW. It can be found 1.1 degrees south of 4.7 mag Theta Crater, the star at the top of the “Cup.” Its coordinates are 11h 36m 16.2s, -10d 52m 38.8s. Several galactic globulars have been found in the last fifteen years that radiate to us only in the infrared, hidden as they are behind the veil of dust and gas that separates us from their positions nearer the galactic center. Glimpse CO1 and CO2, and the two 2MASS clusters are apparently not visible at any wavelength our eyes can see. I have tried several times to observe each of these, to no avail. Powerful infrared amplifiers may show them, but that is not visual recovery. With all the recent UKS-1 & VVV CL001 interest and success in cluster discoveries, it seems likely that At a distance of 145 Kpc, or almost half a million light years, amateurs will soon have several more faint Milky Way globulars Laevens-1 was, at the time, the most distant Milky Way globular. to challenge their skills.

What? Two 30-inch scopes? In the Beginning By Dick Jacobson Like many children, I was fascinated by things that are big. For many, it’s dinosaurs; for me, it was the numbers in astronomy. This is the story of how I designed and built two 30'' I eagerly devoured every book about astronomy that I could get Newtonian telescopes. Perhaps more importantly, Why? my hands on. When I was about 10 years old I saved my nickels Arguably, this is two more than anyone in the world needs. and dimes and purchased my most treasured possession, a 4'' I can briefly explain the “why”; the “how” will take a Newtonian. Though I never use it anymore, I still can’t bear to little longer. I am fascinated by telescope construction. As the part with it. aperture increases, the problems multiply rapidly. When the Eventually I grew up and pursued a career in computer diameter reaches 30'', it’s nearly impossible to make a telescope programming, where I could make actual money. Astronomy that performs well and is reasonably portable by one person. I faded into the background. The views from the suburbs through had some ideas for improving on existing designs and couldn’t my 4'' were unimpressive and I seldom did any observing. I resist trying them out. started grinding an 8'' mirror many decades ago but it still isn’t finished. Pushing glass just isn’t “in my blood.” In the early 1990s I became obsessed with the idea of building an equatorial mount for an altazimuth Dob. I purchased my first serious telescope, a 10'' Dob, and started constructing a portable equatorial mount. It was more difficult than I expected, but eventually I got it to work reasonably well. Soon I contracted the astronomer’s disease, Aperture Fever. When observing I often asked myself, “What would this look like if I had twice as much light-gathering power?” This led me to build Newtonians of 14'' and 20''. These both had equatorial mounts and went through repeated tinkering and rebuilding. In 2007 an anonymous benefactor donated a magnificent 30'' Obsession telescope to MAS. Can it possibly be 14 years 30-inch Obsession

5 August 2021 ago? I surfed through the MAS forum and back issues of Gemini aluminum is a better material, being seven times as strong as and found Greg Haubrich’s article confirming this date. I well wood, which is four times heavier. In addition, its strength is remember being invited over to John Marchetti’s house, where the uniform (no cracks, knots or grain), can be bent into the necessary scope was temporarily stored, for a training session. In particular shape, and is nearly indestructible by weather or other reasonable I remember struggling side-by-side with another MAS member, forces. You can obtain aluminum in just about any shape and pushing the massive mirror box up the ramp into the trailer. This size imaginable from local companies like Coremark Metals experience convinced me that owning a 30'' would be impossible (formerly Discount Steel). On the negative side, it doesn’t absorb for me unless it was permanently housed in an observatory. I had vibration as well as wood, is not beautiful like well-finished wood, thoughts of building an observatory in a dark-sky location, but scratches easily unless anodized, and paint adheres very poorly this was a level of commitment that was beyond me. to it. I don’t care what the telescope looks like and am pretty careless in handling my equipment, so aluminum suits my needs quite well. It’s harder to cut and drill aluminum than wood, but I have the necessary tools and experience so this isn’t a problem. My inspiration for the mirror box was a cardboard shipping box. Although the cardboard sides might be flimsy (easily bent), the entire box is a very rigid structure as long as all 12 edges are folded or securely taped. I would build an aluminum box with flimsy sides but strong edges and corners. The finished box, without the mirror but including the cell and frame that support the mirror, weighs 70 pounds, about half the weight of a plywood box. It seems very solid; in fact I believe that it’s overbuilt. Besides the aluminum construction, there are two other reasons for the reduced weight. One is that it does not have the semi-circular altitude bearings that you usually see on large Dobs. Instead, the box is supported by a pair of bolts in bronze bearings at the top of the box. My equatorial mounts are also built this way. The bronze bearings are virtually frictionless, so to provide adequate friction for altitude motion I use small My First Lightweight polyethylene pads rubbing against the sides of the mirror box. The combination of polyethylene against either aluminum or The First 30'' is born stainless steel is magical. It provides smooth, buttery motion My Aperture Fever was in deep remission, but it never with almost no “stiction” (static friction). It is even better than completely died. After countless hours daydreaming, I convinced the combination of Teflon and Ebony Star laminate, I think. I’m myself that I could build a 30'' that was light and compact enough talking about ordinary low-density polyethylene, the kind used for me to transport and set up without any help. Despite having in food containers and millions of other products. a weak back and rapidly approaching retirement age, I believed that I could finish it soon enough that I’d be able to enjoy it for many years. Giant portable Newtonian telescopes have many problems, but two loom above all the others: the massive size and weight of the mirror box, and the terrifying height of the eyepiece. I believed that I had found answers to both of these problems. Taming the Giant Mirror Box First, the mirror box. The classic design used by market leaders Obsession and Starmaster is a plywood box that is tall enough so that the entire telescope balances at the top of the mirror box. For a 30'' I estimate that the empty mirror box would weigh in the neighborhood of 150 pounds. Add another 100 pounds for the mirror. The mirror box would be about 27 inches high. Add several inches for the rocker box and ground board, which are usually transported as a unit with the mirror box. It would not come close to fitting inside the vehicle that I owned at the time, a VW Passat wagon. Even a minivan or SUV would be Ultralight scope a dicey proposition. I would likely need a trailer. Setting all this up at a dark-sky site would be so exhausting, if even possible, The other reason for the reduced weight of the mirror box that I’d be too tired to observe. is that I made it shorter so it would fit in my car. Since the box is about 10 inches shorter than usual, I knew that the telescope I tried to think of ways to build a mirror box that would be wouldn’t balance properly on the altitude axis, so I made a just as strong as the Obsession/ Starmaster design but lighter removable counterweight bar that runs across the back of the box. and smaller. In constructing other telescopes, I had increasingly After attaching the bar, I hang individual steel counterweights on used aluminum instead of wood and other materials. On paper, it. This makes it possible to precisely balance the telescope with

GEMINI • www.mnastro.org 6 any combination of eyepieces and other accessories. The idea behind the periscope is pretty simple. It’s similar to Since the usual big altitude bearings are missing, a rocker a periscope on a submarine or tank. A diagonal mirror outside box wouldn’t work. Instead, I built a vertical fork. The bronze the top of the telescope, where the eyepiece would normally be, altitude bearings rest in V-shaped aluminum plates at the top of directs the light downward parallel to the outside of the tube. the fork. The base and arms of the fork are thin aluminum boxes As the light passes downward, it goes through a lens that makes made of two sheets of aluminum on opposite sides of square the light rays parallel again. At the bottom of the periscope is aluminum tubes around the perimeter, tightly bolted together. a second lens that re-focuses the light. Finally, the light hits a This results is a panel that is about the same weight as solid wood second diagonal and goes through a standard eyepiece. but many times stiffer. There are a lot of details to work out; this would fill another The rocker boxes of most big Dobs rest on a ground board, article, so I’ll skip all that. After a lot of tinkering, I got my typically a circle of thick plywood. Instead of a ground board, I periscope to work for my 20'' Newtonian. The view through the built a triangle of (you guessed it) aluminum tubes. On top of this periscope is almost identical to the view at the usual eyepiece triangle is attached a giant 29'' diameter Lazy Susan bearing. The location. The field of view is slightly smaller, depending on vertical fork rests on this bearing. Similar bearings are used in the lenses used and the length of the periscope. I estimate that some swivel rockers and other large rotating pieces of furniture. about 10 percent of the light is lost, though it’s hard to see the The telescope and fork rotate on top of this bearing with very difference, and state-of-the-art optics could do better. I built a little friction. Since a slight breeze would rotate the telescope, I scaled-up periscope for the 30'' and am very pleased with how built an adjustable brake using a piece of polyethylene rubbing it works. I do almost all of my observing using the periscope, against the rim of the bearing to control the azimuth motion. though sometimes when viewing objects close to the horizon I use the standard eyepiece location to get the best possible view. When I first built the scope, the base triangle rested directly There is a second focuser at the top of the periscope so I can on the ground. There was no motorized tracking. I’ve always quickly slide the periscope out of the optical path and the upper hated the ceaseless “nudge-nudge” of Dobs. I had previously focuser into the path. built an equatorial platform for my 10'' and it worked well, so I scaled it up for the new scope. (Equatorial platforms are clever More Gory Details motorized devices that enable anything sitting on top of them to The top end of my telescope, the secondary cage, is also track the stars.) Since my platform was custom designed for this unusual. Historically, most big Dobs have a secondary cage scope, I was able to make it very lightweight. constructed of two plywood rings connected by several struts. On this structure is mounted the spider holding the secondary mirror and a focuser board holding the focuser and finder. The structure is surrounded by a ring of black material such as Kydex. Some newer ultra-compact designs feature a single ring at the top that supports all the other components. I wanted to make my secondary structure as lightweight as possible. The heart of the structure is a piece of one-inch- diameter aluminum tube, bent into a circle. To make this, I used a “Tubing Roller” which is sold by Harbor Freight Tools. This hand-powered but tremendously powerful tool makes it easy to bend metal into circles. Anyone who is serious about building big telescopes should have one of these. With the help of this tool, I made a 33'' outside diameter ring that is extremely strong but weighs less than three pounds. The spider and secondary mirror are attached to the ring, with a total weight of nine pounds— Mirror of Ultralight Scope exceptionally light for a secondary of this size. The focuser board Ditching the Ladder and a light shield opposite the focuser are attached separately. The other big problem with giant Newtonians is the great eyepiece height. At zenith, my eyepiece would be more than 10 feet off the ground. I’ve built ladders with half-step positions which improve observing comfort, but that solves only part of the problem. Endless trips up and down the ladder to change eyepieces, look at charts, re-position the ladder to track the rapidly moving eyepiece, and so on, make for a very fatiguing night. Many years ago someone posted a question in the Cloudy Nights astronomy forum to the effect, “Isn’t there some optical system that could bring the eyepiece down closer to ground level?” Of course there are numerous Cassegrain type optical designs that fold the optical path, but he was looking for an accessory that could be mounted on a Newtonian. After thinking about this for many hours, I had convinced myself that I could build such a device. Thus was born what I call a “periscope.” This Shows One of the

7 August 2021 Another unusual feature of my scope is the truss. Almost pounds. All of the components of my scope weigh 50 pounds every big Newtonian tube is a truss made of either six or eight or less, except for the mirror box. With the mirror, it tips the separate poles. Usually each pole has to be clamped individually scales at 165 pounds. Even with a strong helper, it would be very to the mirror box and secondary cage when the scope is difficult to hoist the mirror box onto the fork. Most big Dobs assembled. For many years I’ve been using a slightly different employ wheelbarrow handles that attach to the rocker box. This design for my trusses. The poles are permanently bolted in pairs wouldn’t work for my scope since there is no rocker box. Instead, to a small aluminum plate at the top. One pole is rigidly bolted to I built a cart modeled after two-wheel hand trucks. I attach one the plate using two bolts; the other is attached with a single bolt side of the mirror box to the cart and roll it along with the mirror and is free to pivot so that the two-pole assembly folds together pointing upward. By a happy coincidence, the 24'' deck height and takes little more space than two separate poles. This speeds of my minivan is about the same as the bottom of the mirror box up assembly since there is only a single attachment point between when it is resting on the fork and equatorial platform, so I can the top plate and the secondary cage. When each pole pair has lift the box out of the back of the van and set it gently onto the been attached to the mirror box, it makes a rigid triangle, and it’s fork without a lot of effort. No ramps are needed, as is usually the easy to attach the secondary cage to the plates at the top of the case when loading conventional Dobs into a vehicle. three or four pole pairs. With construction well under way, there was just one more The other unusual thing about the truss on this scope is that detail to fill in… the mirror! I know myself well enough to realize there are separate lower and upper trusses. Between the lower that I didn’t have the talent and motivation to make a decent 30'' and upper trusses is one of my lightweight aluminum rings. mirror. After some online asking around, I found a used 29'' There are several advantages to this design. The long, skinny mirror for sale for the bargain price of $4,000. The seller didn’t triangles of most telescope trusses are mechanically inefficient. have any kind of test results to quote me but said that it was a They put excessive stress on the poles. The amount of deflection “really nice” mirror. So I took a chance on it. In 2015 my wife at the top of the triangle increases as the cube of the pole length. Helen and I took a trip to Pittsburgh to pick it up. The results In most lightweight structures constructed of triangles, such as were, well… less than stellar. I couldn’t get stars to focus sharply. towers, bridges, and crane booms, the triangles are approximately The mirror had rather serious astigmatism, meaning that a bright equilateral, which is the most efficient design. The triangles in star focused to a short line which alternated in perpendicular my truss are close to equilateral and because of this I was able directions when the focuser was racked in and out. I was able to to use one-inch diameter poles instead of 1.5-inch diameter. This eliminate a lot of the astigmatism by building a system to bend saved a little weight and, at least according to my calculations, the mirror slightly, but later I built a Ronchi tester that revealed produced a more rigid truss than the usual design. Another that the whole surface was quite irregular. The view of star advantage is that I can put the truss together without using a clusters was very disappointing, but at least it had a lot of light ladder. The lower half-truss and mid-tube ring are low enough to gathering power for a good view of fuzzy things like galaxies assemble while I am standing on the ground. Then I tip over the and nebulae. half-truss and weight it down so it’s nearly horizontal and attach After using the scope for a few years, I decided to bite the upper half-truss and secondary cage. The center ring provides the bullet and ordered a new 30'' mirror from virtuoso mirror- a strong point where I can attach the periscope. The truss pole maker Mike Lockwood. I’m happy to report that after coughing pairs are about half as long as the poles of a conventional truss. up $16,800 for this mirror, plus another thousand for a new If the whole truss was put together with individual tubes, secondary, I’m finally seeing sharp star images. (See, you there would be 16 poles to assemble, but instead I have eight pole imagers aren’t the only ones who spend crazy amounts of money pairs, which isn’t too bad. Even so, it takes 20 knobs to put the on this hobby!) truss together, plus three for the focuser board and three for the The Birth of the Ultralight periscope, so I’m an expert in spinning knobs. After all this investment of money and labor, my 30'' scope was finally performing pretty much as expected. The views through the eyepiece were sharp and bright, whether using the periscope or at the conventional focus. I was pleased with the mechanical performance. Despite about 400 pounds on the axes, it takes only about a pound of force to move the scope when at the conventional focus. A little more force is needed at the periscope eyepiece since it is much closer to the axes. The telescope and mount are very solid. A “thump” on the tube produces a small vibration that dies out in about a second. I haven’t attempted to attach digital setting circles or a Go- To system, though I think it could be done without too much complication. I’m happy with old-fashioned star-hopping, though it’s more challenging with such a big scope since the field of view is smaller and it’s more effort to move the monster. So now I had a mediocre 29'' mirror left over. What to do with it? Sell it cheap? Give it away? The thing weighs 75 pounds Here Is the Mount not including its wooden storage box, so shipping would be There’s one more important feature that I haven’t covered expensive. Make it into a birdbath? After a few months I hatched yet. I have a weak back and try to avoid lifting more that 50 a plan. I would try building an ultra-light scope out of it. My GEMINI • www.mnastro.org 8 biggest unhappiness with the 30'' is that it takes about an hour One problem that I’m thinking of fixing is stray light. When of fairly hard work to set it up and the same to tear it down and the scope is set up where there is a lot of light in the environment, load it into the van. This isn’t too bad if I get to the observing site as in my driveway, a lot of light leaks around the rim of the mirror before sunset and can set it up at a leisurely pace, stay overnight, and into the field of view. For serious observing I usually set the and tear it down after a night’s rest. But it’s not so good if I’m scope up on green grass, which looks much darker than the night just observing for a few hours and have to pack it up when I’m sky, so stray light isn’t much of a problem. Ideally there should already very tired. Because of this, I use the scope mostly at be some black material surrounding the rim of the mirror. I’m LLCC and rarely at Cherry Grove. thinking of replacing the open frame with a very minimal mirror The New Plan box, only tall enough to cover the rim of the mirror. I decided to make the new scope as lightweight, simple to At first, to keep things simple, I did not include my periscope construct, and simple to set up, as possible. With the original in the design. But since the scope worked so well, I added some 30'', my goal was to make it just as sturdy as any Dob of that more hardware so I could set it up either with or without the size while reducing the weight and size. With the new scope I periscope. decided to throw caution to the winds. It might be a total failure, The thing that pleases me the most about this ultralight scope but at least I already owned the mirrors so I wasn’t risking a lot is that I’ve reduced the assembly/ disassembly time from about of money. one hour to a half-hour. The total weight is less, so it doesn’t tire The most radical idea was that I would completely eliminate me out so much at 2:00 a.m. the mirror box. Instead, the mirror is supported on a rectangular The flip side of the lightweight construction is that it’s more frame of four square aluminum tubes. Two tubes run crosswise vulnerable to damage. I’ve had disasters with both scopes. In supporting the mirror cell while two others are bolted to the 2016 I brought the original scope to the Nebraska Star Party. crosswise tubes, making a rectangular frame. As with the original There was a ferocious thunderstorm the first night. I had made 30'', I used a pair of bronze bearings for the altitude axis. Four the mistake of letting the scope rest in a vertical position, thinking additional aluminum tubes connect the altitude bearings to the that the wind wouldn’t catch the open truss too badly. Wrong! It rectangular frame. blew over, but there was very little damage. When I am observing, the mirror hangs completely out in I repeated the same mistake with my new scope very recently. the open. This is a little scary, but I figure that there is minimal An unexpected gust of wind blew the scope over (fortunately, in risk of damage while looking at the stars. Most star parties aren’t my back yard). There was a lot of bent metal and a chip in the particularly rowdy. I made a sturdy cover that extends down over mirror. I’ve learned my lesson. With the original scope, I now the rim of the mirror, so it should be well protected while loading weight it down so the tube is horizontal and hopefully can resist and unloading. The lack of a mirror box should be beneficial the wind. With the ultralight, I’m letting it “windmill” freely optically since it promotes cool-down of the mirror and there is around the azimuth axis. no structure to trap unstable warm air. The Future To make assembly quicker, I abandoned the two-stage truss It makes very little sense for me to own both of these scopes. that I used in the original 30''. Instead, I went with a conventional The ultralight is still a work in progress, but the way it looks now, eight-pole truss, with each pair of poles permanently connected I’ll probably move my good mirrors into the new scope and scrap at the top. I still wanted to avoid the use of a ladder to connect the old one. The birds might finally get their fancy birdbath. the secondary cage, so I came up with a different assembly I’ve occasionally daydreamed about a scope in the 40'' class, technique. First I connect the pole pairs on the two sides, making but I’m neither young nor ambitious nor crazy enough to tackle rigid triangles pointing vertically. Next I attach a temporary a project of that size. It would almost certainly require a trailer. support to the center of the mirror frame. I pull the side poles My Aperture Fever is in serious remission and I have other more downward until they are nearly horizontal, with the temporary interesting projects in mind. I’m happy to own a 30'' scope that support holding the mirror frame in place against gravity. Finally is truly portable. I believe there are very few, if any, telescopes of I attach the secondary cage to the side truss pole pairs and then this size that fit easily into a minivan, can be set up in less than the final upper and lower truss pairs, so the tube is complete and an hour by one person, and can be used without a ladder. The nearly balanced. idea that a truss scope requires a big, very rigid mirror box is, Latest Results I believe, a mistake. Many other telescope makers, amateur and So how did it turn out? My main fear was that the ultralight professional, seem to be coming to the same conclusion. structure would shake like a leaf, and at first it did, but with a It is ironic that smaller scopes perform well under bright few improvements it has become reasonably sturdy. After a city skies when used for bright objects or imaging, while giant “thump” on the tube, it vibrates for about five seconds, but the scopes need to be hauled to dark-sky locations to perform best. vibrations are small and not a serious problem for observing. I For those of us who want to do visual observing of deep-space think the optical performance matches the original scope when objects, finding ways to downsize our big Newtonians seems to the crummy 29'' mirror was in it. be the best strategy.

9 August 2021 MAS Patron Members Patron memberships are available to those who wish to contribute a little extra to support MAS activities. Patron memberships are established by constitution at 2-1/2 times the Regular membership rate—currently $65 annually for a patron membership. The $39 additional contribution is tax deductible. Patron memberships help fund equipment acquisitions, facility improvements, outreach activities and more. We would like to thank the following patron members as of July 1: Tom and Arlene Alm David Dennis Angela Heins Family Rebecca Messer Loren Schoenzeit Scott Anderson Mark Dietzch John Hill Matt & Jessica Meyer David Schultz Jack Atkins Courtney Dietzmann Merle Hiltner Gerald Miller Erica Scott Steve Baranski Thomas Dillon Lauren Hoen Robert Miller Jon Seilkop Greg Baril Molly Duffin Nadia Hoffman Scott Morgan Collin Semb Jeff Bauer Matt Dunham Greg Hokanson Bradley Nasset Kristopher Setnes Max Beehler Dave Eckblad Ken Hugill Brian Nelson Mike Shaw Bradley Beisel Steven Emert Chris Hunt Douglas Nelson Jeff Shlosberg Mike Benson Kevin Engebretson Ron Hunt Jacquelyn Nelson Bernie Simmons Yevgen Berezhanskyy Maram Falk John Hurley Brady Nesvold David Sjogren Denise Beusen David Falkner Dick Jacobson Doug Neverman Dennis Sjogren Scott Billeadeau Robert Farrell Bharathi Jagadeesan Tracy Niebeling Eric Smestad Ray Birkenkamp Allan Ferber Len Jannusch Zachary Niebuhr Andrew Smith Lilah and Chris Blinkman Jon Forsberg Mark Job Jennifer Niessen Gerald Smyser Katie Bloome Robert Foucault Julie A. Y. Johnson Aaron Niskode-Dossett Katherine Sproll Wayne Boline Andrew Fraser Kurt Johnson Douglas Oines Bernie Stinger Ned Bouril Alan Fuller Trena Johnson Thor Olson Jack Storms Natalie Broshar Paul Gade Jerry Jones Derek Overdahl Peter Sullivan Rev. Eugene Brown Jim Gerrity Michael Kauper Christopher Paola Tony Thomas Jay Bruesch Gregory Gibbons Bob Kerr Joel Papa Mitch Thompson Donald Bryan William Glass Kenneth Kerrick John Payton David Tosteson Jeff Bullard Martin Godfrey Michael Knowlen Andrew Perez Valts Treibergs Jonathan Burkhardt Bradley Gordon Jim Knudsen Chris Peterson David Truchot Jeff Burrows Martin Gormanson Bill Kocken Chris Polston Iakovos Tsoukalas Earl Bye Steven Grabarkiewicz David Kocken Solomon Portesky Trevor Turner William Bynum Zdenko Grajcar Shremattie Kokotovich Aaron Raines Hayden Uihlein Larry Cain Antone Gregory Robert Kowalski Ahmed Reda Steve Ulrich Craig Carlson Jere Gwin-Lenth Parke Kunkle Michael Regouski Bob Vangen Ken Carlson Dale Hagert Michael Kutzke Chaz Rice Paul VanNorman Kurt Casby Jake Hairrell Greg Larson Stephen Riendl Balaji Vatsavaya Stuart Chastain Nina Hale Christine Laughlin Eric & Rebecca Robinson Lawrence Waite Mary Chilvers Eric Hall Louis Leichter John Rosenberg Joel Waldfogel Cara Clark Brandon Hamil Michael Lilja James Rowan Paul Walker Deane Clark DouglasHansell Clayton Lindsey Derek Rucker Craig Weinert Bruce Coleman Ryan Hanson Edward Malinka Theodore Sadler Robert Williams Mark Connolly Andrew Harwood John Marchetti Jack Sandberg Neil Worthingham Michael Daniels Greg Haubrich Bruce McDonald Roy Cameron Sarver Robin Wright Gary Davis Michael Haydock Duane McDonnell James Schenz Gene Yates John Davis Jonathan Hayman Zach McGillis Ronald Schmit John Zimitsch Mary Beth Smith & Ted Kale Hedstrom Javier Medrano Steven Schmitt Mark Zimitsch DeMatties Victor Heiner Zachary Melby Anna Schoeneberger Neal Zimmerman MAS Board Minutes for May/June Joe Timmerman passed away. His family is offering By Trena Johnson, secretary his gear for sale on the forums. Contact Valts or Conrad. Monthly Meeeting: A new location for the general meeting is May still being discussed. Eisenhower Community Center in Hopkins Attended: Mark J., Valts T., Matt D., Trena J., Conrad has been proposed as one possible location. Send ideas to S. Membership is at 641. We welcome new members and [email protected]. Any venue will need to accommodate thank them. Site Reports: JJC-Metcalf: The committee is 100 people and be available the first Thursday of the month exploring options at the ballfield for star parties. A program throughout the year. manager has been hired. The board recognized David Schaff and new additions to the LLCC committee; welcome on board. June NNSF is Sept 1-6. ELO: New chairs and cabinets have been Attended: Mark J., Valts T., Matt D., Conrad S., Trena delivered to the hotspot and Onan. Work is being done by the J., Merle H. Membership is at 644. Site Reports. ELO: board to update phone line and voice mail systems. CGO: The Discussions between Merle and the board: Paving tile is to be PortaPotty has arrived. The north fence work is being planned. added around Mama Bear; motorized roof plans; power vent to NGT was sold to a person in Oregon. Website: This is coming be added to Baby Bear; plans for Camping with the Stars. Items along with new committee email addresses. We are updating for were reviewed and approved by the board. No changes were user safety along with switching to Slack for more functionality. noted from the other sites. Website/Forum Update: The new ALCON will be virtual this year with hopes for in-person next website is moving along. Valts, Darin and Trena are working on year. Updated COVID restrictions are on the website/forum. the website.

GEMINI • www.mnastro.org 10 We Live in the Stars: To Go Outside and Look Up Gives reason to get interested in astronomy. To begin an adventure into Us Perspective astronomy we only need two things: An open mind to discover By Aaron D. Raines something incredible, both out there and within ourselves; as well as the patience to develop this astronomical skill. Contemplating the heavens can fill us with all sorts of emotions that can range from the overwhelming realization of the magnitude of the universe to the awe-inspiring admiration of its beauty. To start our experience of the cosmos, we can begin going outside with a few astronomical tools (most of which our phones are equipped with). As we progress in our journey of viewing and taking in the big picture, we can continue to upgrade our tools.

Full Moon as seen from Minneapolis June 23, 2021 Take a step back, breathe. Every once in a while, it is important for us to give ourselves some time and space, to see and appreciate the big picture. After the year 2020, it might be just the right time to do exactly that. Whether it is metaphorically, as more people in fortunate countries like ours are beginning to get vaccinated and we start thinking about going back to a new normal in this world; or perhaps something a bit more literal, like stepping outside and Partial Solar Eclipse as seen from Minneapolis June 10, 2021 looking up to contemplate the wonders of the universe. By simply grabbing a compass, a star map, a camera, and maybe a notebook to take notes, or our phones (which can serve as all of these), we can head outside fully equipped for the adventure. Depending on the hour, the day, the month, the season, the year, the weather, we might be lucky enough to catch a beautiful sunrise or sunset, or perhaps we could catch a magnificent moonrise or moonset. Maybe if we do it at just the right time a planet may present itself, shining at unconventional times of the night and day.

The telescope pointing toward a Waxing Gibbous Moon Go out and see the sky. If one takes some time to go out and look up, no matter what Sunrise as seen from Sheridan Memorial Park, Minneapolis time of the day or night it might be, one will probably find a 11 August 2021 (Luna) and maybe catch a glimpse of Jupiter’s largest moons. Once we start advancing and investing more in our astronomical pursuits we can move on to learning how to use a more expensive Newtonian/reflector telescope that can give us a more detailed image of the wonders of space, such as the marvelous view of Saturn’s rings.

Astronomical tools I use, including telescope, compass, sextant and notebook in black and white Sunset as seen from the Stone Arch Bridge, Minneapolis Once we start discovering the magical patterns in the Gazing Through Space and Time dance of the heavens, we may want to start learning and using As we begin to create the habit of stepping outside and the mathematical and astronomical tools that great minds all looking into the dimensions of space-time, we will find ourselves throughout history have left us since the beginning of civilization here and now standing in our beautiful spaceship called Earth. We and which society has kept improving as technology advances. will start discovering the breathtaking patterns of our universe From understanding Kepler’s Laws of Planetary Motion in order and feel the spark of admiration within us. So remember to to know when to see certain objects in the night’s canvas; to occasionally give yourself some time and space to go outside, perhaps using a cheap and simple Galilean/refracting telescope breathe, and look up. Take in the big picture! so that we can observe the astonishing details of our Moon Variable Star of the Month its brightness. The image is not inverted, so it is suitable for binoculars. R Aquilae is the highlighted circle. Magnitudes are By Jim Fox, AAVSO and MAS in tenths with the decimal point omitted so as not to be confused August: R Aquilae with a star; so, 52 = 5.2. Chart is courtesy of AAVSO. Many, if not most, of the stars we see change brightness over various periods of time for various reasons. Sometimes a star can dim, brighten and dim again in less than a second. Other stars can take years to complete a cycle of brightness variation. These stars are called “variable stars.” One variable star that you can see this month is R Aquilae. Located just off the trailing edge of the western wing of Aquila the eagle, it is about five degrees due south of Zeta Aquilae, that marks the wing tip. R Aquilae is a red giant star. It has about the same mass as our Sun, but it has expended as it aged. If it were located at the place of our Sun, Earth would be orbiting just inside its outer atmosphere. At its brightest, R Aquilae is visible to the naked eye as a dim, red star at magnitude five. When it dims to magnitude 12, it is just visible in binoculars. Its period from one dimming to the next is about 270 days. Oddly, this period has been decreasing at an average rate of 0.4 days per year since first determined in 1915. The reason for this decrease is not understood at this time. For more than 100 years, the American Association of Variable Star Observers (AAVSO) has encouraged the observation and study of variable stars, maintaining databases of all submitted observations. Observing techniques include both visual and photometric (CCD/CMOS, DSLR and photoelectric) and now even spectroscopic. For more information on AAVSO and how you can contribute to astronomical science through variable stars, visit their website at www.aavso.org September: Delta Cephei This finder chart for R Aquilae will help you estimate One variable that you can see this month is Delta Cephei,

GEMINI • www.mnastro.org 12 Minnesota Astronomical Society 2021 Star Party Schedule Twilight Completely dark Moon % ELO Public Cherry LLCC Friday Date Sunset ends: from: to: Illuminated Night (Saturday) Grove Weekend Notes August 6 08:31 PM 10:26 PM 10:26 PM 04:08 AM 3% X X August 13 08:21 PM 10:21 PM 11:09 PM 04:21 AM 29% X CWTS: 8/13, 14, 15 August 28 07:57 PM 09:39 PM 09:39 PM 10:54 PM 66% X Saturday: Jupiter opposition September 1 - 7 X This is the proposed time, LLCC has not totally signed off on the date yet. NNSF at LLCC September 3 07:46 PM 09:26 PM 09:26 PM 03:31 AM 11% X X September 10 07:33 PM 09:11 PM 09:38 PM 05:06 AM 17% X X September 11 07:31 PM 09:08 PM 10:09 PM 05:08 AM 26% x X Saturday: Neptune opposition September 25 07:05 PM 08:40 PM 08:40 PM 09:21 PM 80% x Saturday October 1 06:54 PM 08:28 PM 08:28 PM 02:19 AM 23% X X October 8 06:41 PM 08:15 PM 08:15 PM 05:43 AM 7% X X MAS Mini-Messier Marathon (4M) CALLED ON/OFF October 9 06:40 PM 08:13 PM 08:43 PM 05:44 AM 14% X X Saturday: Fall Astronomy Day October 23 06:16 PM 07:51 PM 07:51 PM 07:51 PM 92% X Saturday October 29 06:07 PM 07:42 PM 07:42 PM 01:09 AM 40% X November 5 05:58 PM 07:34 PM 07:34 PM 06:16 AM 1% X X November 6 05:57 PM 07:33 PM 07:33 PM 05:18 AM 5% X X Saturday: Uranus opposition November 26 04:39 PM 06:19 PM 06:19 PM 11:02 PM 57% X X Directions to the Star Party Locations

For maps and further details about the sites, please go to our website at www.mnastro.org/facilities. Eagle Lake Observatory at Baylor Regional Park 10775 County Road 33, Norwood-Young America, MN Cherry Grove Observatory 18781-18861 520th St, Kenyon, MN 55946 Joseph J Casby Observatory at the Belwin Conservancy 1553 Stagecoach Trail S, Afton, MN 55001 Metcalf Field - aka: Metcalf Nature Center Latitude: 44.93734, Longitude: -92.82157 Long Lake Conservation Center 28952 438th Ln, Palisade, MN 56469 normally the fourth-brightest star in the constellation Cepheus, its cyclic dimming by comparing it to the nearby stars Zeta the king. Delta Cephei is the prototype of a whole class of Cephei (magnitude 3.4) and Epsilon Cephei (magnitude 4.2). variable stars known as “Cepheids.” This finder chart for Delta Cephei will help you estimate Astronomer John Goodricke first noted the variability of its brightness. The image is not inverted, so it is suitable for Delta Cephei in 1784. In 1912, Henrietta Swan Leavitt studied binoculars. Delta Cephei is the highlighted circle. Magnitudes Cepheid variables at Harvard College Observatory. These stars are in tenths with the decimal point omitted so as not to be vary in brightness with a regular period, and Leavitt discovered confused with a star; so, 42 = 4.2. Chart is courtesy of AAVSO. that the period of variation of individual Cepheids is related to the intrinsic brightness of the star. Knowing that light dims according to an inverse square law with distance from the source, measuring the apparent brightness and period of variation of a Cepheid lets us determine the star’s distance. In 1914, Harlow Shapley showed that Cepheids pulsate, alternately expanding and contracting in size. The star dims as it expands and brightens as it contracts. By measuring the periods of a dozen Cepheid variables in the Andromeda Nebula, M31, in 1933, Edwin Hubble determined that it was two-million light-years distant and that the so-called “nebula” was another galaxy outside our own Milky Way. Cepheid variables have become one of several “standard candles” allowing us to determine vast distances in the universe. Delta Cephei is much closer, being only 865 light years from us within the Milky Way. It varies from magnitude 3.5 to magnitude 4.4 once every 5.4 days. You can watch it go through

13 August 2021 MN ASTRONOMICAL SOCIETY P.O. Box 14931 Minneapolis, MN 55414 a publication of the Minnesota Astronomical Society

How to pay your dues August 2021 Volume 47 Number 4

Your MAS membership expires at the beginning of the month shown on your membership card. You will be notified of your renewal by e-mail two months prior to expiration and by USPS mail the month of your expiration. You may renew by mail or online using PayPal. By mail: Send your payment to the MAS membership coordinator at: Minnesota Astronomical Society, Attn. Membership coordinator, P.O. Box 14931, Minneapolis, MN 55414. Make checks payable to MAS. Current annual membership rates when paying by check are: $26 regular, $13 student, and $65 for patron memberships. You may renew for one year or for two years at a time. Online using PayPal: PayPal charges a fee, so MAS includes a voluntary contribution in the PayPal membership rates to offset that fee. Membership rates using PayPal are $27.50 regular, $13.75 student and $67.25 patron. The membership form and the procedure for joining or renewing using PayPal may be found at www.mnastro.org/members/join/. Sky and Telescope and Astronomy Magazine Subscriptions

MAS members are offered subscriptions to these magazines at an astronomy club discount. Regular Sky & Telescope subscriptions are $54.95 annually. S&T offers astronomy club discount print + digital subscriptions for $43.95 annually. To renew your subscription, go to www.skyandtelescope.org/clubrenew and fill out the web form, paying online using your credit card. For new subscriptions go to www.skyandtelescope.org/clubspecial If you wish to call instead, call S&T customer service at 800-253-0245 and tell them you are a member of MAS. If you wish to pay by check instead of by credit card, you can ask the customer service rep to send you an invoice in the mail. Astronomy magazine regular print subscriptions are $44.95 annually. The Astronomy magazine club discount print or digital subscription is $34 for one year, $60 for two years, or $83 for three years. To subscribe or to renew your current subscription at the astronomy club discount rate, go to www.astronomy.com/clubmember and fill out the web form, paying online using your credit card. You have the choice of a print-only subscription or a digital-only subscription at the above prices, or you can choose a print + digital subscription for $46.00 (one year), $84.00 (two years), or $119.00 (three years). You can also call the Astronomy magazine customer service toll-free number at 1-877-246-4835 to subscribe.

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Loaner Scopes & Astronomy DVDs Available to Astronomy DVDs from The Great Courses All MAS Members • The Life and Death of Stars Go to mnastro.org/loaner scopes • Skywatching: Seeing and Understanding Cosmic • Celestron NexStar 102SLT Refractor Wonders • Orion SkyQuest XT-8 • Our Night Sky • Orion SkyQuest XT-10 • The Remarkable Science of Ancient Astronomy • Celestron C6 SCT on Voyager Mount • Experiencing Hubble: Understanding the Greatest • Celestron NexStar 8SE SCT Images of the Universe • Sky-Watcher 4″ Refractor • Understanding the Universe: An Introduction to • Celestron NexStar 5 SE SCT Astronomy • Coronado Solar Scope • What’s New in Astronomy • Meade LightSwitch 8 SCT GO-TO • Earth at the Crossroads: Understanding the Ecology of • Hardin 10 inch Dob a Changing Planet • Celestron CPC 800 SCT • Earth’s Changing Climate • The Inexplicable Universe: Unsolved Mysteries • A Visual Guide to the Universe • A Field Guide to the Planets • New Frontiers: Modern Perspectives on our Solar System • Dark Matter, Dark Energy: The Dark Side of the Universe • Cosmology: The History and Nature of our Universe • The Search for Exoplanets: What Astronomers Know 14