Horizon Winter Solstice 2006.Pdf
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Winter Solstice, 2006/2007 Beginner's Corner: Star Hopping - Navigating Your Way through the Celestial Wilderness BY DINOSAUR DAVE GILL, THE OLD STAR HOPPER for stones that look sturdy and are close enough together for you to hop between them with sin- When Editor Phil wanted to have an article gle steps. Similarly, in star hopping, you choose dealing with the art of star hopping, he wisely landmarks you want to use as stepping-stones yielded the keyboard to someone who still thinks based on how big a field of view you are using that GOTO is two words. As the proud owner of and how recognizable these fields will be. two Dobs, I've had to become reasonably profi- cient at finding things in the sky without benefit SKILLS and TOOLS of setting circles or computer-driven scopes. There are several things that are required for Now, don't get me wrong - I am not denigrating star hopping: the GOTO technology… it is a great break- Pattern recognition: It helps if you have a through that allows us to spend more time look- good eye for pattern. The stars don't come ing AT things rather than looking FOR them. labeled in the sky like they are on the charts. But, star hopping is still a skill that it is helpful to (Even with really high "Wal-Mart powered" tele- have in your toolbox along with the extra Telrad scopes you can't see those little Greek letters next batteries and your Geek Light. to the stars…) Rather you need to recognize pat- Star hopping is the process of getting from terns - chains of stars, skinny triangles, close something you know in the sky - like a visible pairs, etc. that you will see both on your charts star - to someplace else that you don't know. We and in the sky. do it in discrete steps - like crossing a stream by Orientation flexibility: Things are not stepping on stones that are sticking out. You look always oriented the same way in the sky that they are in the charts. You may need to do mental rotations or flips of the charts to match the sky. Inside Horizon Sometimes you can just flip the chart. Sometimes it is easier to stand on your head - Dark Times . .page.7 unless there is two feet of snow on the ground. Good charts: Good star charts are essential. Orion the Hunted . .page.9 And you need to learn to pick the right chart for the right job. This will depend on what you are And More! looking for and what you are looking with. The key variables are scale - how many inches of HORIZON 2 chart represent a degree of arc in the sky, and magnitude - how faint does the chart go. The HORIZON is the quarterly newsletter of two are closely related. A chart with relative The Wilderness Center Astronomy Club. broad scale - showing entire constellations - Editor: . Phil Hoyle becomes quite cluttered when too many faint stars are plotted. Commercial charts like Contributors: . .Phill Creed, Dave Gill Norton's Star Atlas, SkyAtlas 2000.0 or the Layout . John Waechter Millennium Star Atlas are carefully designed with this in mind. WCAC Officers: One of the revolutions of modern amateur President: . Bill Castro astronomy is the ability to plot your own custom Vice President: . Matt Hawrysko charts. Programs such as The Sky, Starry Night, Secretary: . John Waechter Guide, MegaStar, and Cartes du Ceil enable you Treasurer: . Brian Gray to make your own custom finder charts. You do Planetarium Coordinator: . Dave Ross need to be cognizant of the magnitude-clutter Observatory Coordinator: . .Brian Gray rule mentioned above. But you now have it in Inreach: . Dave Gill your power to make custom charts for nearly Education Outreach: . John Waechter anything, and not fear marking it up to your WebMaster: . Bill Castro heart's content. WCAC Address: Familiar Field Sizes - When you are plot- ting that path across the stream it is important to P.O. Box 202 know how big your steps are. Similarly, if you Wilmot, Ohio 44689-0202 are star hopping you need to know how big your Web Site: http://www.twcac.org eyepiece fields are. In some cases, like binocu- lars, the fields are written on the instrument, like takes for a star to drift across the field, divide by "4.5 degrees" or "3.5 degrees" or whatever. You 4 and you get the number of degrees in your can also calculate the field knowing the eyepiece field. Getting a full diameter is probably the specs and design. But the most accurate means hardest part. I'd suggest doing it several times is to measure it directly using the instrument and and averaging your results - statistics are your the sky. friends. CALCULATING FIELD SIZE I would suggest doing this for your finder and This exercise is useful, and it is an excuse to several of your favorite eyepieces - the ones you get the scope out on a moony night instead of like to use for finding things. Note that the same watching Desperate Housewives. The principle eyepieces will give different results with different is to use the Earth's rotation as your guide. You telescopes! Alternatively, for the finder, you can pick a star relatively near the celestial equator eyeball patterns in the sky - like the bowl of the and time it as it drifts across the diameter of your dipper or other patterns to find a pair of stars that eyepiece field. You know that the Earth rotates span the diameter of the field. This will be quick- once in 23 hours 56 minutes with respect to the er, since a 4-degree finder will take more than 15 stars. 24 hours is accurate enough for this exer- minutes for a drift measurement. cise. That is 15 degrees in an hour, or one degree In transferring this newfound information to in 4 minutes. So, measure the time in minutes it your star atlas, you will have to have a degree HORIZON 3 scale for your atlas. Use the DECLINATION Similarly, when we were looking for 5391 scale. Declination is like latitude on earth - the Emmons (a 16th magnitude asteroid), we had to circles of declination are all of the same length make a set of custom charts and star hop through from pole to pole. the eyepiece. This was made more complicated MAKING A TEMPLATE because we looked for it through several instru- ments - my 14" Newtonian, the Keller 16" Cass Once you know your field sizes, you are with a right angle viewer, and using Dick ready to make a tool for hopping among the Emmons's image intensifying eyepiece which stars. A common tool that is shown in many electronically erected the image. These all pres- books is a loop of wire with the loop diameter at ent the image oriented differently. The mental the size you have determined for your field. My gymnastics there were challenging. But the basic personal favorite has been circles drawn on star hopping skills are the same: gauge the field transparencies. If you have multiple instruments, size, recognize the patterns, jump, recognize the eyepieces and atlases, the combinations get over- next pattern, jump…. and so forth. It just whelming for wires. With PCs and printers, you requires more Excedrin. can use a graphic program or a CAD program to Even if you use a GOTO telescope to get you draw the circles and label them for the telescope, close, when you are looking for something faint, atlas and eyepiece you are using. you still will need a good chart to assure you that Another option that is open to you is to make you have found what you are looking for - espe- your own charts with chart software. Most pack- cially if it is not an extended object. Again, vari- ages allow you to define a circle size for the field able stars, asteroids, and Pluto are good exam- of your eyepiece. This is really a flexible way to ples of such objects. Use your GOTO to get you go. In fact, a few years ago, I made finder charts into the general field, then star hop to your goal. for the Messier Marathon - custom charts for all If you use your GOTO regularly, you will know the objects with star hopping fields defined for how accurate your pointing is. Maybe it gets you each based on where I wanted to start and which dead on - in which case you still need to ID the eyepiece I wanted to use. object. The pattern recognition skill still applies. FINDING STUFF Even if you don't make circular templates for For most of the brighter objects, you will find your eyepieces, it is extremely helpful to know the finder field will get you close enough, espe- your eyepiece field size for judging fields in pub- cially if you use a wide field eyepiece first. But lished maps. For example, both Sky and in looking for fainter objects, you will probably Telescope and The Observers Handbook publish need some combination of finder and eyepiece finder charts for Pluto each year. If you want to fields. For instance, in looking for faint variable find it, you will need to know how to translate stars, you typically use a progression of higher between the map scale and your telescope. In and higher resolution charts from AAVSO, des- this case, it boils down to knowing your field ignated a, b, c, d and e, which have generally sizes as part of knowing your equipment.