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Astronomy 103, Fall, 2006

Star Hopping

Goals of the Lab

Requirements: The telescope, your logbook, and print-outs of the finding charts for objects you will observe (available below).

Note: This is an advanced lab activity which requires familiarity with the telescope and careful observing. You will want to complete at least the Telescope Basics and Stellar Observation labs to build your telescope experience before attempting this lab.

Contents

How To Starhop

Learning how to star-hop can be difficult and frusturating— but with as any difficult task, it can be very rewarding when you master it. Prof. Knop, in his guise as an amateur astronomer (as opposed to his daytime identiy as a professional astronomer), seeks out astronomical objects by star-hopping for fun.

Expect this lab to take more than one lab session to complete. You may spend most of the first session you work on this lab just figuring out star-hopping technique.

  1. Check the alignment of your finderscope.

    Find a bright star or planet, center it on the crosshairs, and make sure it is in the dead center of the 25mm eyepiece. It will be impossible to star-hop succesfully without a well-aligned finderscope. If it is out of alignment, get one of the TA's to align it for you.

    Also, make sure you know the field of view of your finder scope. You have measured this before— although be careful! The Meade and Celestron telescope finders have different fields of view. Make sure you know the field of view of the finder scope you are using.

    Example: Let's assume that we're using a finder scope with a 5° field of view. NOTE: This may not be the field of view of the actual finder scope you will be using!

  2. Choose the object you wish to observe. From the Right Ascension (RA) and Declination (Dec) of the object, locate its position on your starmap (SC001 or SC002). Find the nearest bright star to that object. Make sure that the object you've chosen is overhead! For fainter objects (nebulae, globular clusters, and galaxies), it is best to choose objects in "dark" areas of the sky. Generally, the higher in the sky, the better. If sporting field lights are on and blanching out one quadrant of the sky, it will be harder to find faint objects in that general direction.

    Example: you decide to observe the double star 61 Cyg. You look up its RA (21h 07m) and Dec (38° 44'). Looking at your SC001 star chart (see right), you figure out that this double star is in the constellation of Cygnus (unsurprising, given its name), and that it is near the bright star ε Cygni.

    		 [Map]

  3. Locate the finding chart for the object you're looking for. Finding charts are available in PDF format in the table of objects below. You should have printed the chart out before lab and brought it with you, as mentioned in the "Requirements" above!

    Example: Here is the finding chart for 61 Cygni.

  4. Center the finder on the bright, naked-eye star near the object. Knowing the field of view of your finder scope, match the stars on the finding chart with the stars you see in the finder scope.

    NOTE— make sure you orient the chart correctly! All the finding charts are oriented so that north is up. If you very gently nudging the telescope to the south, all the stars in the finder scope will appear to "lean" slightly to the north. (Your "window" on the sky is moving south, so the north edge of that window moves closer to any stars visible through it.) You can use this to figure out which direction is north in the finder scope. Rotate your star chart for easy comparison with what you see there.

    Look for other stars in the finder field of view, and match them to what you see on the finding chart. Bigger dots on the finding chart represent brighter stars. Depending on how dark the sky is, you will probably not be able to see the dimmer stars plotted on the finding chart! Look for the brightest stars (biggest dots) first.

    Example: You center the finder on ε Cygni. On the star chart, you use the declination scale to gague how much is 5° (or whatever the field of view of your finder is!), and imagine a circle around the star this size (shown in pink in the image below). You see another star a little dimmer than ε Cyg just to the northeast, and pair of stars towards the north of the field of view that form an isocolese triangle with ε Cyg. There is also a star to the southwest. If the sky is dark enough, you may see some more of the stars that are shown on the finding chart.

    [StarHop Image 1]

  5. While looking through the finder scope, move the telescope so that the finder field of view moves in the direction of the object you want, but keeping some stars in the field of view so that you always know where you are. You will probably want to move only one axis at a time. You will need to move far enough that the fine-adjustment knobs won't be good enough; you'll have to unclamp the telescope and carefully move it by hand. (Move carefully so that you don't accidentally move too far and get lost.) If you know where you are, the patterns you see through the finder scope and the patterns on the star chart will match. If you manage to get lost, you will have to start your star-hop over. (Don't feel bad if this happens; Dr. Knop even gets lost sometimes when starhopping.)

    Find another star that is generally in the right direction, and "hop" over to that star in the finder scope.

    Example: You move the telescope to the north and to the east, so that εCyg is now near the southwest edge of the field of view. The two stars that make the isocoles traingle with εCyg are on the west edge. Another brightish star has come into the field of view north of those two, as has another over towards the east side of the field of view.

    [Starhop Image 2]

  6. Repeat the previous step until you get the finder scope centered on the object you are looking for. Note: particularly with nebulae and galaxies, you may not be able to see the object you're looking for in the finder scope! If this is the case, then you must center the crosshairs of the finderscope on the right spot so that the pattern of stars you see around the crosshairs in the finder scope match the pattern of stars you see on the finding chart.

    Example: Recenter the telescope so that the brightish star on the east side of the finder scope field of view moves down toward the south edge (see below). Now 61 Cyg is in the finder field of view! This is an object you should be able to see in the finder. Center the crosshairs on it.

    [StarHop Image 3]

  7. Look in the telescope for the object. Start with the 25mm eyepiece. Focus the telescope as best you can. If you're looking for something fuzzy, you will have better luck by focusing on other stars in the field of view. If it's a double star you're looking for, you should be able to see it. If the star doesn't look double, star at it for a little bit; it may be that it's a very close double that you're having a hard time splitting! Or, you ended up on the wrong object....

    If you're looking for a faint fuzzy object, like a galaxy or nebula, if you can't see it at first spend a couple of minutes looking through the telescope. Move your eye around; you may not be perfectly centered on it!

    You often get a better view of dim objects by using averted vision. The receptors that are most sensitive to dim light (the rods) are concentrated more away from the center of your field of vision. By looking a little off to the side of a dim object, the light from that dim object then falls on those dimmer receptors. Try this, to see if you can get a better view of a nebula, cluster, or galaxy.



Part I: Uranus

Uranus is the 7th planet in the Solar System. Because it is too dim to be spotted with the naked eye, it wasn't discovered until William Herschel spotted it in his telescope in 1781. It is, however, easily observable with the lab telescopes.

If you are sharing the telescope with the lab partner, each partner should independently find Uranus. Of course you can help each other, but each person should be able to accomplish the work.

Procedure

  1. Print out and bring to lab the Uranus Finding Chart.

  2. Star-hop to locate Uranus in the telescope. Because Uranus is a planet, its position relative to the "fixed" stars will change over the course of the semester. It will be somewhere along the line on the finding chart. At magnitude about 5.8, it should be about as bright as the other brightest stars that will be in the same finder scope field of view with it.

  3. Draw faint or dotted lines on the finding chart to indicate the stars you hopped past in order to find Uranus. (Be sure to turn in the finding chart when you turn in the lab.)

  4. When you have located Uranus and confirmed it through the telescope, make a sketch of the field of view of the finder scope. Use a generic observation template (either the small version or the large version). Be sure to indicate north and east on your drawing, and the scale of your drawing. Use bigger dots to indicate brighter stars. Clearly label which object is Uranus.

  5. Observe Uranus with both the 25mm and 10mm eyepieces. Make some notes about its appearance. Can you see anything about it's color? Does anything else about it strike you? Make sure that the telescope is in as good focus as possible.

  6. Using the finder scope, center the telescope on the brightest star that is within a few degrees of Uranus. Look at this star through the telescope using both eyepieces (focusing as well as you can). Then return to Uranus. Can you see the difference between the star and Uranus? That is, can you tell the difference in color, and can you see that Uranus is a ball rather than an unresolved point?



Part II: Double Stars

  1. Choose two double star systems from the appropriate table of objects below.

  2. Star-hop to locate the first double star in the telescope.

  3. Use a generic observation template to sketch the double star as it appears through the 25mm eyepeice. As always, remember to indicate the sale and orientation of your sketch. Draw not only the double star, but any other stars that are visible in the field of view. Spend a little time looking; as you observe it, you may be able to spot fainter stars.

  4. Make some notes about the double star. How easy is it to "split" the two stars? Is one brighter than the other, and if so, how many times brighter does it appear to you? Is there any detectable color difference?

  5. Repeat steps 2-4 with your second chosen star. If you are sharing the telescope with a partner, then the person primarily "driving" the star-hop for the second double star should be different from the first double star. Naturally, each of you should make your own observations and notes on each star.



Part III: Star Clusters

  1. Pick an open cluster from the appropriate table of objects below.

  2. Star-hop to locate this open cluster. The open cluster may be visible as a fuzzy patch in the finder, or even as a close-knit group of stars.

  3. Observe the open cluster through the telescope using the 25mm eyepiece. Make some notes describing what you see. How many stars do you observe? Is this star field noticably different from other random starfields you have seen through the telescope? Do the colors of any of the stars stand out?

  4. Pick a globular cluster from the appropriate table of objects below.

  5. Star-hop to locate this globular cluster. If working at the telescope with a partner, the person who didn't do most of the work finding the open cluster should take the lead in finding hte globular cluster. Many of the globular clusters won't be visible in the finder scope, making them callenging objects to zero in on.

  6. Observe the globular cluster through the telescope using the 25mm eyepiece. Make a sketch of it using the generic observation template. Make some notes about its appearance. Can you pick out any individual stars, or is it an undifferentiated fuzz? How dense is it? What looks different about this cluster as compared to the open cluster you observed?



Part IV: Nebulae and Galaxies

These are the most challenging star-hopping objects. Many of these will not be visible at all in the finder scope; you will have to find them by aligning the crosshairs at the right position relative to other stars in the finder field of view. Good finder scope alignment is absolutely crucial.

  1. Find and observe M42, the Orion Nebula. In the fall, the constellation Orion won't come up until late in the semester, and even then it only comes up late at night. In the Spring, Orion is nicely overhead at the beginning of the semester, but is low in the West towards the end of the semester. You can almost point directly at this object without having to go through the whole star-hopping routine. It is one of the most beautiful objects visible under a good sky in an amateur telescope. The darker and clearer your sky and the higher in the sky it is, the better it will look.

  2. Make some notes about the appearance of the M42 through the 25mm eyepiece. What color is it? What is its shape? Is it undifferentiated fuzz, or is there structure? If there is structure, what sort of structure can you see?

  3. Center the telescope on the four stars in a small trapezoid shape near the brightest part of M42, and switch to the 10mm eyepiece. This star system is known as the "trapezium". All of these stars are hot young stars recently formed in the stellar nursery that is the Orion nebula. The biggest of them is responsible for the ultraviolet radiation that ionizes and lights up much of the nebula.

    Make a sketch of what you see through the 10mm eyepiece, using a generic observation template.

  4. Pick two more objects from the table of nebulae and galaxies below, including one additional nebula and one galaxy. Star-hop to find each of these objects. As before, if you are working with a partner, make sure to swap of primary duties in finding the objects.

  5. Observe the object in both the 25mm and 10mm eyepiece. Always start with the 25mm until you have found the object. Many of these will not be visible in the finder scope, so you will still be trying to locate them in the 25mm eyepiece. Depending on sky conditions, they may be impossible to see! Don't give up on an object until you've made a good effort to find it, and are really sure that you have the telescope pointed at the right place. Make some note about the appearance of the object. How hard or easy is it to see? Is it just a faint, barely-visible fuzzpatch, or can you discern any shape?

  6. Make a sketch of each of the two objects using the generic observation template. Make a sketch of the object as it appears through either the 25mm or 10mm eyepiece, whichever gives the better view. Be sure to include in your sketch any other stars in the field of view (as always using bigger dots for brighter stars).



Object Tables

Click on the object's name to get a PDF finding chart for that object. Make sure to bring finding charts for each object you might observe!

Finding charts were created using XEphem

Table 1: Double Stars

Double stars on this list were gleaned from the following two Sky & Telescope articles:

Name RA Dec Position Angle Separation Visual Mag. Comment
1 Ari 01h 50m +22° 17' 165° 2.8" 5.8,6.6 Close pair
ο2 Eri 04h 15m -07° 39' 105 & 347 89" & 8" 4.5, 9.5, 11 Unusual Triple system. Primary is a K1 V star; secondary is a white dwarf; third and faintest companion is a low-mass M5 V star.
12 Lyn 06h 46m +59° 27' 68°,310° 1.7",8.9" 5.4,6,7.3 Triple system; third star may be hard to split!
145 CMa 07h 17m -23° 19' 52° 26.8" 4.8,6
ζ Cnc 08h 12m +17° 39' 80° 6.4" 5.6,6.3 Primary has another 6th mag. companion 0.9" away in the direction of the secondary; this extra companion is very hard to split; can you see it?
24 Com 12h 35m +18° 23' 270° 20.6" 5,6.6
39 Boo 14h 50m +48° 43' 46° 2.7" 6.2,6.8 Close pair!
κ Her 16h 08m +17° 03' 12° 27.1" 5,6.2
41 Dra 18h 00m +80° 00' 233° 19.3" 5.7,6
95 Her 18h 02m +21° 36'  256° 6.3" 5,5.2
12 Aqr 21h 04m -05° 49' 197° 2.5" 5.8,7.3 Close pair!
61 Cyg 21h 07m +38° 45' 150° 30.8" 5.2,6 Famous nearby double, 11LY away. 4th nearest naked eye (under a dark sky) star, first star with measured parallax (by Bessel in 1838). Plotted on SC001.


Table 2: Star Clusters

Name Constellation RA Dec Size (arcmin) Distance Comments
NGC884/869 Perseus 02h 19m +57° 08' 29' / 29' 7,400 LY Famous Double (open) Cluster. Age = 11Myr / 6Myr.
M34 Perseus 02h 42m +42° 46' 30' 1,500 LY Bright open cluster. Age = 100 Myr.
(Look at γ Andromedae while you're in the area!)
M36 Auriga 05h 36m +34° 08' 12' 4,100 LY 25 Myr old open cluster
M35 Gemini 06h 09m +24° 21' 25' 2,200 LY 107Myr old open cluster.
M41 Canis Major 06h 46m -20° 45' 38' 2,400 LY Open cluster 4° south of Sirius. 100 Myr old.
M3 Canes Venatici 13h 42m +28° 23' 18' 34,000 LY Globular Cluster
M5 Serpens Caput 15h 19m +2° 05' 23' 24,000 LY Globular Cluster
M44: The Beehive Cancer 08h 40m +19° 40' 80' 520 LY Very large open cluster. 660 Myr old.
M13 Hercules 16h 42m +36° 28' 10' 22,000 LY Globular cluster framed by 2 stars of 6th mag
M92 Hercules 17h 17m +43° 08' 8' 25,000 LY Globular cluster, compare with M13
M11 Scutum 18h 51m -06° 16' 13' 5,600 LY Very dense open cluster. 224 Myr old.
M15 Pegasus 21h 30m +12° 10' 5' 32,000 LY Globular cluster.
M2 Aquarius 21h 33m -00° 49' 16' 38,000 LY Globular Cluster


Table 3: Nebulae and Galaxies

Name Constellation RA Dec Size (arcmin) Distance Comments
M42: Orion Nebula Orion 05h 35m -05° 23' 10' 1,600 LY Region of Star formation. Surrounds multiple star Theta 1 Ori.
M31: Andromeda Galaxy Andromeda 00h 43m 41° 16' 190' 2.6 MLY Spiral Galaxy. Also look for M32, a small elliptical galaxy, 24" to the north (both are visible in one 25mm field of view).
M81 Ursa Major 09h 56m +69° 04' 21' 12 MLY Spiral Galaxy. Look for M82 nearby!
M82 Ursa Major 09h 56m +69° 41' 9' 12 MLY Near to (and dimmer than) M81. A "starburst" galaxy.
NGC3242 Hydra 10h 25m -18° 39' 20" 1,500 LY Planetary Nebula, 6000 years old
M97 Ursa Major 11h 15m +55° 01' 3' 2,600 LY The "Owl Nebula": Planetary Nebula, 6000 years old.
M101 Ursa Major 14h 03m +54° 21' 22' 27 MLY Spiral Galaxy: "The Pinwheel Galaxy"
M57 Lyra 18h 54m +33° 02' 70'' 2300 LY Famous Planetary Nebula ("Ring nebula"). Neb is 3900 years old
NGC6826 Cygnus 19h 45m +50° 32' 25'' 2300 LY "Blinking " planetary nebula. Look for central star! Neb. is 5200 years old
NGC7331 Pegasus 22h 37m +34° 25' 10' 49 MLY Inclined spiral galaxy. Very challenging!

Last modified: 2005-August-18, by Robert Knop

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