December 2018 The Monthly Newsletter of the Bays Mountain Astronomy Club

More on Edited by Adam Thanz this image. See FN1 Chapter 1 Cosmic Reflections

William Troxel - BMAC Chair

More on this image. See FN2 William Troxel

More on Cosmic Reflections this image. See FN3

December is here. It is hard to believe that this is the last December’s constellation winner is Sagitta. This month's of 2018. It seems like yesterday you voted for me as your new constellation is a new one for me. Jason was telling me about it. chairman. We have had a good six . The annual picnic, My interest was peaked so I had to research this new StarFest and StarWatch events all have been wonderful. The constellation for myself. Of course, you know it is not a new weather has been much better for us, then it was in the spring constellation at all. It was first catalogued in the 2nd century by session, so we have seen a lot more of the public and that is a the greek Ptolemy. good thing. There are 3 different myths associated with this very small November’s program showcased our own Jason Dorfman as the constellation. The story is told that this is the arrow that was speaker. Jason always does a wonderful job when he shares his used by Heracles to kill the eagle Zeus sent to gnaw at knowledge, this time was no exception. Jason used the ’ liver. Prometheus was a sculptor that moulded men planetarium to explain how coordinates are used to help and women out of clay in the likeness of Gods and gave them catalogue stars. During his presentation, he set in motion the fire that he had stolen from the Gods. Zeus decided that he had advancement of the sky while the grids were up showing to be punished for this act and chained him to Mt. Caucasus how the stars changed position during the night. It was very where the eagle Aquila would perpetually gnaw his liver, however interesting to see how all the tools work together. The really his liver grows back every night. unusual thing for me personally was how the early Here is where Heracles comes into the picture. Heracles, on one were able to map the stars, and come up with this mapping of his journeys, came across Prometheus and killed the eagle system that still works to this day. After the presentation Jason with the arrow freeing him. took questions from the members. I want to thank Jason again for his wonderful presentation.

Bays Mountain Astronomy Club Newsletter December 2018 3 Sagitta the Arrow. Image from Stellarium, annotations by Adam Thanz

4 Bays Mountain Astronomy Club Newsletter December 2018 In another myth, Sagitta is identified as the arrow used to Astronomical Unit - noun, abv: AU; A unit of length, equal to the kill the Cyclopes because they made the thunderbolts of Zeus mean difference of the from the : approximately 93 that killed Apollo’s son, Asclepius the famous healer, who is million miles (150 million km). It is used when referring to the represented in the constellation Ophiuchus. distance to objects within the . Example of correct use of this term would be: The estimated distance to the The last myth I found has Sagitta associated with the arrow of Jupiter would be between 4.2 to 6.2 AU (astronomical units) Eros which made Zeus fall in with Ganymede. This story tells depending on Jupiter's location in the Solar System. that Aquila guards the arrow in the night sky. Blueshift - noun; 1) a shift in the lines of an objects’ spectrum The Greeks knew this constellation as Oistos, it was the Romans toward the blue end. Blueshift indicates that an object is moving that changed the name to Sagitta as we call it today. toward the observer. The larger the blueshift, the faster the object All three of these myths refer to this constellation as an arrow. is moving. 2) the displacement of the spectrum to shorter Many stories told in different cultures sometimes refer to different wavelengths in the light coming from a distant celestial object characters or items however this one seems to hold the same moving toward the observer. item in all of the myths. Continue to research and see if you can I wanted to remind everyone about the December meeting. Our find other myths around other cultures and maybe on one of your speaker for that meeting will be our own Greg Love. Greg will star gazing sessions you will add this to your observing program. doing a presentation on binoculars in astronomy. Greg has invited I encourage you to read Jason's article as he talks about the you to bring your close-focus binoculars to the meeting as we will astronomical details of this constellation as we know it today. be in the Planetarium again and we will be able to use them to find objects on the dome. This would be a great meeting to invite I will be sharing each month a couple of astronomy terms for us your friends because he will also talk about how to pick a pair to to help build our vocabulary. The goal is to show the definition of start observing for those of you that are just starting out. Just as a the word or words as it is used in astronomy and in the culture reminder, the meeting will be on December 7, 2018 at 7 pm. I should there be a difference. This will also help when you are hope to see everyone at the meeting. explaining our hobby to people who are not familiar with our field of interest. This month I will start with the words "Astronomical Lastly, I wanted to share some upcoming events for the club. The Unit" and "blueshift." club dinner is coming up in January 2019. I will have all the details

5 Bays Mountain Astronomy Club Newsletter December 2018 at the next meeting. I will also be asking you for a rough count for those of you that think you will be interested in being part of the Messier Marathon that is set for March of 2019. This is only a rough count to see if enough members are interested in this “Club Members Only” event.

Until next time… Clear Skies.

References:

Users.skynet.be.com www.oxfordreference.com http://www.seasky.org/astronomy/astronomy-glossary.html#B

6 Bays Mountain Astronomy Club Newsletter December 2018 Chapter 2 BMAC Notes

More on this image. See FN4 More on BMAC News this image. See FN3

BoBfest 2019 Make plans for the Regional Gathering of Amateur Astronomers 2019, aka BoBfest on February 2, 2019! That’s right, BoBfest 2019 will be on Groundhog Day.

See you all at the Catawba Science Center in Hickory, NC!

Bays Mountain Astronomy Club Newsletter December 2018 8 Jason Dorfman using the planetarium instrument to illustrate celestial motions! Image from Robin Byrne.

9 Bays Mountain Astronomy Club Newsletter December 2018 Chapter 3 Celestial Happenings

Jason Dorfman

More on this image. See FN5 Jason Dorfman

More on Celestial Happenings this image. See FN3

It's hard to believe that it's already the end of the year. The Sun locating it. Through a scope you'll see a 9" diameter disk looking is setting early and the colder temperatures are already 86% illuminated. Its appearance will not change much over the beginning to set in. This is great for astronomy enthusiasts - month. will dim by about a half magnitude as its diameter longer and clearer skies create the perfect conditions for decreases slightly to about 7.5". observing the night sky. Mars will make a with the ice giant Neptune this month. Though much larger than Mars, Neptune's great distance As the twilight glow of the setting Sun begins to fade, look low in from the Sun makes it unobservable without a or the southwest for the beautiful ringed world, . On the 1st, binoculars. On the 1st, look about 3.6° to the ENE of Mars to find 45 minutes after sunset, it will be about 10° above the horizon. At this icy, blue world shining at magnitude +7.9. You won't see any magnitude +0.5, you'll be able to easily find it. However, due to features with Neptune as it's disk spans just 2.3". Both planets its proximity to the horizon, observations of Saturn will not be are moving eastward against the background stars but Mars is spectacular. As the month continues, Saturn will appear lower moving much more swiftly, lessening the gap between the two and lower each night at the same time, disappearing into the by 0.6° everyday. On the 6th, Neptune will be just 23' to the ENE bright light of the setting Sun by mid-month. of Mars. The true conjunction occurs at 9:08 a.m. on the 7th when Mars will be just 2.2' north of Neptune. Of course, at that Mars, on the other hand, is still positioned for some good hour both will be well below the horizon for our location (and the observations against the background stars of Aquarius. Look Sun will be up)! By the time the Sun goes down, Mars will have due south an hour after sunset and about 45° up from the moved to 16' to the NE of Neptune. horizon to find the "Red Planet" at the start of the month. At magnitude 0.0, it'll be the brightest point of light in that part of For those willing to stay up late or are early risers, the pre-dawn the sky and, with its orange hue, you should have no problem hours hold some wonderful planetary views this month. Rising in

Bays Mountain Astronomy Club Newsletter December 2018 11 the ESE about 4 a.m. is our sister world, . Venus begins the In the evening, a very thin will glide past Saturn on month at its brightest, magnitude -4.9. It will dim slightly to mag the 8th and 9th. On the 8th, the two day old Moon will be about -4.6 by month's end. It will appear about 25% lit on the 1st with a 3° to the lower right of Saturn. You might have more luck 40" disk. By the end of the year, its phase will have grown to glimpsing the young Moon on the 9th when it will then be about almost half, but the disk diameter will have shrunk to 26" as it 7° to the upper left of Saturn. On the 14th, a first quarter Moon makes its way towards the far side of the Sun. Venus begins the will appear 4° south of Mars. occurs on the 22nd. month in Virgo, about 5° to the lower left of Spica, and will move eastward throughout the month crossing into Libra on the 13th. Constellation of the Month For the next couple of months, William and I decided to focus on As we reach the second of the month, look about 10° above some of the smaller constellations in the sky which may be the horizon in the ESE as the sky begins to lighten, about 45 somewhat lesser known. Our first is Sagitta, the arrow. This 3rd minutes before sunrise, for . This small, rocky world smallest constellation lies within the lower part of the Summer reaches its greatest western elongation on the 15th when it will Triangle, just above Aquila. It is a slightly more difficult be 21° to the west of the Sun and shining at magnitude -0.4. constellation to locate as all the stars are dimmer than magnitude 3. I'm sure that William will get into some of the mythology After the 15th, Mercury will begin to move eastward back towards associated with Sagitta, but many of the stories represent it as an the Sun and will meet up with Jupiter on the 21st. Jupiter will arrow used by other mythological characters to kill something; begin emerging from the pre-dawn glow of the rising Sun as we Hercules used it to kill an eagle, Aquila, sent by Zeus and in approach mid-month. On the 21st, Mercury and Jupiter will be another it was used by Apollo to kill the Cyclops. just under a degree apart. Look about 8° above the southeastern horizon 45 minutes before sunup. At magnitude -1.8, Jupiter Though Sagitta lies along the band of the Milky Way, its small size outshines Mercury. A telescope will reveal Jupiter's great size as limits the number of observable targets found within it. One of the disk will span about 31" compared to Mercury's 6" disk. note is M71, an 8th-magnitude globular cluster, located about midway between the delta and gamma Sagitta stars. Luna Look to the morning skies on the 3rd for a thin waning crescent Geminids Meteor Shower just 5° above Venus. The pair will form a small triangle with Spica The Geminids peak the night of the 13th when we have a waxing about 7° to the right. occurs on the 7th. crescent Moon. The Moon will set by 11 p.m., providing darker 12 Bays Mountain Astronomy Club Newsletter December 2018 skies for the peak viewing period around 2 a.m. This is one of the richer showers of the year with a maximum predicted zenithal rate of about 120 meteors per hour. Find a good spot with a clear view of a large part of the sky and be sure to bundle up to keep warm.

Clear Skies and Happy Observing!

13 Bays Mountain Astronomy Club Newsletter December 2018 Chapter 4 The Queen Speaks Robin Byrne Robin Byrne

More on Happy Birthday Johannes this image. See FN3

This month I get to honor the person responsible for my interest Kepler had originally planned to become a Lutheran minister and in astronomy. Johannes Kepler showed the world (and me) the was planning to continue studying theology. However, a position orderly and beautiful way the planets behave in their orbits. at a nearby school for a math teacher opened up. Kepler’s colleagues convinced him to take the position. Johannes Kepler was born prematurely on December 27, 1571 in Weil der Stadt, Germany. His premature birth led to a lifetime of Kepler’s mathematical interests were to lead to his first health problems. His family was poor. Under those recognition. In 1595, he tried to relate the orbits of the planets circumstances, it was rare for a child to receive much education. around the Sun to the five geometric solids (pyramid, cube, Kepler was fortunate enough to take advantage of a government octahedron, dodecahedron, and icosahedron). He thought he scholarship allowing intelligent, yet poor, children to go to could represent each orbit by having a different solid placed college. between orbits. He published his work in 1596 in a book titled Cosmographic Mystery. Kepler sent copies to various people, In 1587, Kepler began attending the University of Tubingen to including Brahe. Brahe was so impressed, he invited study astronomy. He was fortunate to have as his instructor one Kepler to join his research staff. When Brahe died a year later, of the few astronomers who believed in the Copernican system Kepler took over his position as imperial mathematician. (all planets orbit the Sun and the Earth rotates on its axis) instead of the Ptolemaic system (everything orbits the Earth and the Kepler was in charge of making sense of Brahe’s observations of Earth is stationary). This early influence led to Kepler’s later Mars. But before he began working on this data, he wanted to discoveries. In 1588, he received his Bachelor of Arts degree first explore how light is refracted (bent) through Earth’s and, in 1591, his Master of Arts degree. atmosphere. This slight bending would change where an object is observed. By correcting for this bending, Kepler could state exactly where the planet was at any given time. In his

Bays Mountain Astronomy Club Newsletter December 2018 15 Portrait of Johannes Kepler (1571-1630). Copy of a lost original from 1610 in the Benedictine monastery in Kremsmünster. Image from Wikipedia

16 Bays Mountain Astronomy Club Newsletter December 2018 Birthplace of Johannes Kepler in Weil der Stadt. Image from MarkusHagenlocher, Wikipedia

17 Bays Mountain Astronomy Club Newsletter December 2018 Kepler's Platonic solid model of the Solar system. Image from Johannes Kepler: Mysterium Cosmographicum, Tübingen 1596, Tabula III: Orbium planetarum dimensiones, et distantias per quinque regularia corpora geometrica exhibens. Wikipedia

18 Bays Mountain Astronomy Club Newsletter December 2018 publication, Kepler not only did this, but also explained how the witch. Thanks to Kepler’s defense, his mother was acquitted. human eye works and how telescope optics work. Even after death, Kepler could get no peace. His grave was completely destroyed during the 30 Years’ War. Once these corrections were made, Kepler began work on the orbit of Mars. Up to this point everyone believed that the planets Johannes Kepler brought astronomy into a new era by showing were perfect and moved in perfect circles. Try as he might, Kepler the orderly way planets behave. Meanwhile, I owe my career to could not get the orbit of Mars to match a circle perfectly. Not Kepler for showing me how beautiful nature can be, and the even by using circles on circles. Instead, what he found was that amazing fact that we can describe it all with simple equations and the orbit was an ellipse with the Sun at one focus. This statement, ideas. Thank you Johannes Kepler. which applies to all planets, is known as Kepler’s First Law. It was Reference: The New Encyclopaedia Britannica also thought that the planets would move at constant speeds. There is a constancy to how the planets move, but it is not their speeds. It turns out that if you connect the planet and the Sun with a line, as the planet orbits, the area swept out by the line sweeps out equal areas in equal times. This means that as the planet gets closer to the Sun, it moves faster, and as it gets farther, it moves slower. This is Kepler’s Second Law and the astronomical idea that got me hooked. This was the first time I realized that objects behave in an orderly manner that can be described simply. These two discoveries were published in 1609 in a book titled New Astronomy. In 1619, Kepler published his Third Law relating a planet’s distance and period of orbit: the square of the period is proportional to the cube of the distance.

Kepler’s personal life was not nearly as orderly or well defined. He married three times. His first wife had died. Little mention is made of his second wife. Also, his mother was accused of being a

19 Bays Mountain Astronomy Club Newsletter December 2018 Chapter 5 Space Place

More on this image. See FN6 David Prosper

Observe ’s Lunar Milestones More on this image. See FN3

NASA Night Sky Notes: you imagine what phase Earth would appear as if you were December marks the 50th anniversary of NASA’s Apollo 8 standing on the Moon, looking back? The three brave astronauts mission, when humans first orbited the Moon in a triumph spent 20 sleepless hours in orbit around the Moon, starting on of human engineering. The mission may be most famous for Dec 24, 1968. During those ten orbits they became the first “Earthrise,” the iconic photograph of Earth suspended over the humans to see with their own eyes both the rugged lunar surface. “Earthrise” inspired the imaginations of and an Earthrise! The crew telecast a holiday message on people around the world and remains one of the most famous December 25 to a record number of Earthbound viewers as they photos ever taken. This month also brings a great potential orbited over the lifeless lunar terrain; "Good night, good luck, a display of the Geminids and a close approach by Comet 46P/ merry Christmas and God bless all of you - all of you on the Wirtanen. good Earth." 50 years later, spot the Moon on these holiday evenings as it travels through Cancer and Leo. Just two days You can take note of Apollo 8’s mission milestones while later the astronauts splashed down into the Pacific Ocean after observing the Moon this month. Watch the nearly full Moon rise achieving all the mission’s test objectives, paving the way for just before sunset on December 21, exactly 50 years after Apollo another giant leap in the following year. 8 launched; it will be near the bright orange star Aldebaran in Taurus. The following evenings watch it pass over the top of The Geminids, an excellent annual meteor shower, peaks the Orion and on through Gemini; on those days five decades earlier, evening of December 13 through the morning of the 14th. They astronauts Frank , Jim , and Bill sped get their chance to truly shine after a waxing crescent Moon sets towards the Moon in their fully crewed command module. Notice around 10:30 p.m. on the 13th. Expert Geminid observers can how the Moon rises later each evening, and how its phase wanes spot around 100 meteors per hour under ideal conditions. You’ll from full on Dec 22 to gibbous through the rest of the week. Can spot quite a few meteors by avoiding bad weather and light

Bays Mountain Astronomy Club Newsletter December 2018 21 More on this image. See FN8

22 Bays Mountain Astronomy Club Newsletter December 2018 pollution if you can, and of course make sure to bundle up and take frequent warming breaks. The Geminids have an unusual origin compared to most meteor showers, which generally spring from icy comets. The tiny particles Earth passes through these evenings come from a strange “rock comet” named asteroid 3200 Phaethon. This dusty asteroid experiences faint outbursts of fine particles of rock instead of ice.

You can also look for comet 46P/Wirtanen while you’re out meteor watching. Its closest approach to Earth brings it within 7.1 million miles of us on December 16. That’s 30 times the average Earth-Moon distance! While passing near enough to rank as the 10th closest cometary approach in modern times, there is no danger of this object striking our planet. Cometary brightness is hard to predict, and while there is a chance comet 46P/Wirtanen may flare up to naked eye visibility, it will likely remain visible only via binoculars or . You’ll be able to see for yourself how much 46P/Wirtanen actually brightens. Some of the best nights to hunt for it will be December 15 and 16 as it passes between two prominent star clusters in Taurus: the Pleiades and the V-shaped Hyades. Happy hunting!

Catch up on all of NASA’s past, current, and future missions at .gov. This article is distributed by NASA Night Sky Network. The Night Sky Network program supports astronomy clubs across the USA dedicated to astronomy outreach. Visit nightsky.jpl.nasa.org to find local clubs, events, and more!

23 Bays Mountain Astronomy Club Newsletter December 2018 Chapter 6 BMAC Calendar and more

More on this image. See FN7 More on BMAC Calendar and more this image. See FN3

Date Time Location Notes

BMAC Meetings

Program: “Binoculars for Astronomy.” Dr. Greg Love, ETSU Physics and Chemistry Instructor and BMAC Nature Center member, will speak about how to use common, everyday binoculars to enjoy the night sky. Bring your binoculars Friday, December 7, 2018 7 p.m. Planetarium in the planetarium theater and look at a number of deep sky objects as projected by our Carl Zeiss ZKP4 star Theater projector!.; Free.

Nature Center Friday, February 1, 2019 7 p.m. Program: Program TBA; Free. Discovery Theater

Nature Center Friday, March 1, 2019 7 p.m. Program: Program TBA; Free. Discovery Theater

SunWatch

Every Saturday & Sunday 3-3:30 p.m. At the dam View the Sun safely with a -light view if clear.; Free. March - October if clear

StarWatch

Mar. 2, 9, 2019 7 p.m. View the night sky with large telescopes. If poor weather, an alternate live tour of the night sky will be held in the Mar. 16, 23, 30, 2019 8 p.m. Observatory planetarium theater.; Free. Apr. 6, 13, 20, 27, 2019 8:30 p.m.

Special Events

January ?, 2019 6:30 p.m. ? Annual BMAC Dinner. The Saturday a week later is the snow date.

Bays Mountain Astronomy Club Newsletter December 2018 25 Bays Mountain Astronomy Club Regular Contributors:

853 Bays Mountain Park Road William Troxel

Kingsport, TN 37650 William is the current chair of the club. He enjoys everything to do with astronomy, 1 (423) 229-9447 including sharing this exciting and interesting hobby with anyone that will www.BaysMountain.com listen! He has been a member since 2010. [email protected] Robin Byrne

Robin has been writing the science history column since 1992 and was chair in 1997. She is an Associate Professor of Annual Dues: Astronomy & Physics at Northeast State Community College (NSCC). Dues are supplemented by the Bays Mountain Park Association and volunteerism by the club. As such, our dues can be kept at a very low cost. Jason Dorfman $16 /person/year Jason works as a planetarium creative and $6 /additional family member technical genius at Bays Mountain Park. He has been a member since 2006. Note: if you are a Park Association member (which incurs an additional fee), then a 50% reduction in BMAC dues are applied. Adam Thanz

The club’s website can be found here: Adam has been the Editor for all but a number of months since 1992. He is the https://www.baysmountain.com/astronomy/astronomy- Planetarium Director at Bays Mountain club/#newsletters Park as well as an astronomy adjunct for NSCC.

Bays Mountain Astronomy Club Newsletter December 2018 26 More on Footnotes this image. See FN3

miles across) orbits outside the rings on the right of the image. The small moon Atlas (30 Footnotes: kilometers, 19 miles across) orbits inside the thin F ring on the right of the image. The brightnesses of all the , relative to the planet, have been enhanced between 30 and 60 1. The Rite of Spring times to make them more easily visible. Other bright specks are background stars. Spokes -- ghostly radial markings on the B ring -- are visible on the right of the image. Of the countless Saturn has seen since the birth of the solar system, this one, captured here in a mosaic of light and dark, is the first witnessed up close by an emissary from This view looks toward the northern side of the rings from about 20 degrees above the ring plane. Earth … none other than our faithful robotic explorer, Cassini. The images were taken on Aug. 12, 2009, beginning about 1.25 days after exact , using Seen from our planet, the view of Saturn’s rings during equinox is extremely foreshortened and the red, and blue spectral filters of the wide angle camera and were combined to create this limited. But in orbit around Saturn, Cassini had no such problems. From 20 degrees above the natural color view. The images were obtained at a distance of approximately 847,000 kilometers ring plane, Cassini’s wide angle camera shot 75 exposures in succession for this mosaic showing (526,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 74 degrees. Saturn, its rings, and a few of its moons a day and a half after exact Saturn equinox, when the Image scale is 50 kilometers (31 miles) per pixel. sun’s disk was exactly overhead at the planet’s equator. The Cassini-Huygens mission is a cooperative project of NASA, the and The novel illumination geometry that accompanies equinox lowers the sun’s angle to the ring the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of plane, significantly darkens the rings, and causes out-of-plane structures to look anomalously Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, bright and to cast shadows across the rings. These scenes are possible only during the few Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed months before and after Saturn’s equinox which occurs only once in about 15 Earth years. Before and assembled at JPL. The imaging operations center is based at the Space Science Institute in and after equinox, Cassini’s cameras have spotted not only the predictable shadows of some of Boulder, Colo. Saturn’s moons (see PIA11657), but also the shadows of newly revealed vertical structures in the For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov/. The rings themselves (see PIA11665). Cassini imaging team homepage is at http://ciclops.org. Also at equinox, the shadows of the planet’s expansive rings are compressed into a single, Image Credit: NASA/JPL/Space Science Institute narrow band cast onto the planet as seen in this mosaic. (For an earlier view of the rings’ wide shadows draped high on the northern hemisphere, see PIA09793.) 2. Leo Rising The images comprising the mosaic, taken over about eight hours, were extensively processed before being joined together. First, each was re-projected into the same viewing geometry and A sky filled with stars and a thin veil of clouds. then digitally processed to make the image “joints” seamless and to remove lens flares, radially Image by Adam Thanz extended bright artifacts resulting from light being scattered within the camera optics. At this time so close to equinox, illumination of the rings by reflected off the planet vastly 3. The Cat's Eye Nebula, one of the first planetary nebulae discovered, also has one of the most dominates any meager sunlight falling on the rings. Hence, the half of the rings on the left complex forms known to this kind of nebula. Eleven rings, or shells, of gas make up the Cat's illuminated by is, before processing, much brighter than the half of the rings on the Eye. right. On the right, it is only the vertically extended parts of the rings that catch any substantial sunlight. Credit: NASA, ESA, HEIC, and The Hubble Heritage Team (STScI/AURA) With no enhancement, the rings would be essentially invisible in this mosaic. To improve their Acknowledgment: R. Corradi (Isaac Newton Group of Telescopes, Spain) and Z. Tsvetanov visibility, the dark (right) half of the rings has been brightened relative to the brighter (left) half by a (NASA) factor of three, and then the whole ring system has been brightened by a factor of 20 relative to the planet. So the dark half of the rings is 60 times brighter, and the bright half 20 times brighter, 4. Jupiter & Ganymede than they would have appeared if the entire system, planet included, could have been captured in a single image. NASA's Hubble Space Telescope has caught Jupiter's moon Ganymede playing a game of "peek- a-boo." In this crisp Hubble image, Ganymede is shown just before it ducks behind the giant The moon Janus (179 kilometers, 111 miles across) is on the lower left of this image. Epimetheus planet. (113 kilometers, 70 miles across) appears near the middle bottom. (81 kilometers, 50

Bays Mountain Astronomy Club Newsletter December 2018 27 Ganymede completes an orbit around Jupiter every seven days. Because Ganymede's orbit is Hubble couldn't directly view the planets, but instead employed a powerful search technique tilted nearly edge-on to Earth, it routinely can be seen passing in front of and disappearing behind where the telescope measures the slight dimming of a star due to the passage of a planet in front its giant host, only to reemerge later. of it, an event called a transit. The planet would have to be a bit larger than Jupiter to block Composed of rock and ice, Ganymede is the largest moon in our solar system. It is even larger enough light — about one percent — to be measurable by Hubble; Earth-like planets are too small. than the planet Mercury. But Ganymede looks like a dirty snowball next to Jupiter, the largest However, an outside observer would have to watch our Sun for as long as 12 years before ever planet in our solar system. Jupiter is so big that only part of its Southern Hemisphere can be seen having a chance of seeing Jupiter briefly transit the Sun's face. The Hubble observation was in this image. capable of only catching those planetary transits that happen every few days. This would happen if Hubble's view is so sharp that astronomers can see features on Ganymede's surface, most the planet were in an orbit less than 1/20 Earth's distance from the Sun, placing it even closer to notably the white , Tros, and its system of rays, bright streaks of material blasted from the star than the scorched planet Mercury — hence the name "hot Jupiter." the crater. Tros and its are roughly the width of Arizona. Why expect to find such a weird planet in the first place? The image also shows Jupiter's Great Red Spot, the large eye-shaped feature at upper left. A Based on radial-velocity surveys from ground-based telescopes, which measure the slight wobble storm the size of two , the Great Red Spot has been raging for more than 300 years. in a star due to the small tug of an unseen companion, astronomers have found nine hot Jupiters Hubble's sharp view of the gas giant planet also reveals the texture of the clouds in the Jovian in our local stellar neighborhood. Statistically this means one percent of all stars should have such atmosphere as well as various other storms and vortices. planets. It's estimated that the orbits of 10 percent of these planets are tilted edge-on to Earth and Astronomers use these images to study Jupiter's upper atmosphere. As Ganymede passes behind so transit the face of their star. the giant planet, it reflects sunlight, which then passes through Jupiter's atmosphere. Imprinted on In 1999, the first observation of a transiting planet was made by ground-based telescopes. The that light is information about the gas giant's atmosphere, which yields clues about the properties planet, with a 3.5-day period, had previously been detected by radial-velocity surveys, but this was of Jupiter's high-altitude haze above the cloud tops. a unique, independent confirmation. In a separate program to study a planet in these revealing This color image was made from three images taken on April 9, 2007, with the Wide Field Planetary circumstances, Ron Gilliland (STScI) and lead investigator Tim (National Center for Camera 2 in red, green, and blue filters. The image shows Jupiter and Ganymede in close to Atmospheric Research, Boulder, CO) demonstrated Hubble's exquisite ability to do precise natural colors. photometry — the measurement of brightness and brightness changes in a star's light — by also looking at the planet. The Hubble data were so good they could look for evidence of rings or Earth- Credit: NASA, ESA, and E. Karkoschka (University of Arizona) sized moons, if they existed. But to discover new planets by transits, Gilliland had to crowd a lot of stars into Hubble's narrow 5. 47 Tucanae field of view. The ideal target was the magnificent southern globular star cluster 47 Tucanae, one of In the first attempt to systematically search for "extrasolar" planets far beyond our local stellar the closest clusters to Earth. Within a single Hubble picture Gilliland could observe 35,000 stars at neighborhood, astronomers probed the heart of a distant globular star cluster and were surprised once. Like making a time-lapse movie, he had to take sequential snapshots of the cluster, looking to come up with a score of "zero". for a telltale dimming of a star and recording any light curve that would be the true signature of a planet. To the fascination and puzzlement of planet-searching astronomers, the results offer a sobering counterpoint to the flurry of planet discoveries announced over the previous months. Based on statistics from a sampling of planets in our local stellar neighborhood, Gilliland and his co-investigators reasoned that 1 out of 1,000 stars in the globular cluster should have planets that "This could be the first tantalizing evidence that conditions for planet formation and evolution may transit once every few days. They predicted that Hubble should discover 17 hot Jupiter-class be fundamentally different elsewhere in the galaxy," says Mario Livio of the Space Telescope planets. Science Institute (STScI) in Baltimore, MD. To catch a planet in a several-day orbit, Gilliland had Hubble's "eagle eye" trained on the cluster The bold and innovative observation pushed NASA Hubble Space Telescope's capabilities to its for eight consecutive days. The result was the most data-intensive observation ever done by limits, simultaneously scanning for small changes in the light from 35,000 stars in the globular star Hubble. STScI archived over 1,300 exposures during the observation. Gilliland and Brown sifted cluster 47 Tucanae, located 15,000 light-years (4 kiloparsecs) away in the southern constellation through the results and came up with 100 variable stars, some of them eclipsing binaries where the Tucana. companion is a star and not a planet. But none of them had the characteristic light curve that Hubble researchers caution that the finding must be tempered by the fact that some astronomers would be the signature of an extrasolar planet. always considered the ancient globular cluster an unlikely abode for planets for a variety of There are a variety of reasons the globular cluster environment may inhibit planet formation. 47 reasons. Specifically, the cluster has a deficiency of heavier elements that may be needed for Tucanae is old and so is deficient in the heavier elements, which were formed later in the universe building planets. If this is the case, then planets may have formed later in the universe's evolution, through the nucleosynthesis of heavier elements in the cores of first-generation stars. Planet when stars were richer in heavier elements. Correspondingly, life as we know it may have appeared surveys show that within 100 light-years of the Sun, heavy-element-rich stars are far more likely to later rather than sooner in the universe. harbor a hot Jupiter than heavy-element-poor stars. However, this is a chicken and egg puzzle Another caveat is that Hubble searched for a specific type of planet called a "hot Jupiter," which is because some theoreticians say that the heavy-element composition of a star may be enhanced considered an oddball among some planet experts. The results do not rule out the possibility that after if it makes Jupiter-like planets and then swallows them as the planet orbit spirals into the star. 47 Tucanae could contain normal solar systems like ours, which Hubble could not have detected. The stars are so tightly compacted in the core of the cluster – being separated by 1/100th the But even if that's the case, the "null" result implies there is still something fundamentally different distance between our Sun and the next nearest star — that gravitational tidal effects may strip between the way planets are made in our own neighborhood and how they are made in the cluster. nascent planets from their parent stars. Also, the high stellar density could disturb the subsequent migration of the planet inward, which parks the hot Jupiters close to the star. 28 Bays Mountain Astronomy Club Newsletter December 2018 Another possibility is that a torrent of ultraviolet light from the earliest and biggest stars, which formed in the cluster billions of years ago may have boiled away fragile embryonic dust disks out of which planets would have formed. These results will be published in The Astrophysical Journal Letters in December. Follow-up observations are needed to determine whether it is the initial conditions associated with planet birth or subsequent influences on evolution in this heavy-element-poor, crowded environment that led to an absence of planets. Credits for Hubble image: NASA and Ron Gilliland (Space Telescope Science Institute)

6. Space Place is a fantastic source of scientific educational materials for children of all ages. Visit them at: http://spaceplace.nasa.gov

7. NGC 3982 Though the universe is chock full of spiral-shaped galaxies, no two look exactly the same. This face-on spiral galaxy, called NGC 3982, is striking for its rich tapestry of star birth, along with its winding arms. The arms are lined with pink star-forming regions of glowing hydrogen, newborn blue star clusters, and obscuring dust lanes that provide the raw material for future generations of stars. The bright nucleus is home to an older population of stars, which grow ever more densely packed toward the center. NGC 3982 is located about 68 million light-years away in the constellation Ursa Major. The galaxy spans about 30,000 light-years, one-third of the size of our Milky Way galaxy. This color image is composed of exposures taken by the Hubble Space Telescope's Wide Field Planetary Camera 2 (WFPC2), the Advanced Camera for Surveys (ACS), and the Wide Field Camera 3 (WFC3). The observations were taken between March 2000 and December 2009. The rich color range comes from the fact that the galaxy was photographed invisible and near-infrared light. Also used was a filter that isolates hydrogen emission that emanates from bright star-forming regions dotting the spiral arms. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA) Acknowledgment: A. Riess (STScI)

8. Earthrise, 1968. Note the phase of Earth as seen from the Moon. Nearside lunar observers see Earth go through a complete set of phases. However, only orbiting astronauts witness Earthrises; for stationary lunar observers, Earth barely moves at all. Why is that? Credit: Bill Anders/NASA

29 Bays Mountain Astronomy Club Newsletter December 2018