Star Hopping

This is an advanced lab activity which requires familiarity with the telescope, precise focusing, and careful observing.

Summary: Star hopping is a method used to locate objects in the night sky. To star hop, the observer uses well known or well charted bright objects to find his/her way to a target object. This is a good way to find objects in parts of the sky that are unfamiliar or to find faint objects.

Star hopping is the technique used to find countless faint objects in the sky such as star clusters, nebulae, galaxies, and planetary nebulae. Some of these are truly beautiful. Keep in mind that most of these are faint and are adversely affected by the light pollution from the city lights.

You would be quite surprised to see some of these objects from a dark sky....

Goal: In this lab, you will star hop to as many different stars and celestial objects as you can. By doing so, you will quickly improve your skills with the telescope as well as become much more familiar with the stars and constellations in the sky. You also get to look at several types of objects discussed in class that are beyond the solar system. These are known as "deep sky" objects. This lab will probably take more than one lab period.

To complete this lab, you need to observe:

6-8 bright stars (list #1)
6 double stars (list #2)
4 deep sky objects (list #3)
At least 2 stars known to have planets (list #4)

Where to Start: Choose objects that are visible on that particular night (consult your star charts), preferably those that are closer to the meridian. This is the line that goes from the North cardinal point, through the zenith (overhead) and to the South cardinal point. Avoid searching for objects anywhere close to the horizon, except for bright, naked eye stars.

Procedure

Successful star hoping depends on your knowledge of constellation and your ability to use star charts and the finderscope. It requires patience and perseverance. It is essential to have the finderscope well aligned with the main telescope. You need star charts that show the your target and nearby stars. For some objects, such as bright stars, bright double stars, and a few "deep sky" objects located near bright stars (such as M57, M35, M44, M42) you can use the SC001 or SC003 charts. For the fainter objects, you need more detailed star charts that will be provided by the TAs (to be returned at the end of the lab). Make sure you get the chart appropriate for the objects you are looking for.

Check the alignment of the finderscope and start with the 25mm eyepiece.
Locate your target on the star chart and identify naked eye stars surrounding it (on the chart and in the sky).
Design a path on the star chart that connects one nearby (within 10^oor so) naked eye star to you target. This will be your "star hop"
At this point, it is very useful to know the field of view of the finderscope. Using the declination scale on the star chart, to get a sense of scale for the chart, you will know the size of the field of view on the star chart, an additional aid in finding your way.
Center the naked eye star (your starting point) in the finderscope and follow your "star hop" through the finderscope to the target location, jumping from star to star, using the particular patterns of stars and star brightnesses that surround your target. Be careful at all times to identify distinctive patterns. While you may see more of fewer stars than are shown on the chart, the patterns you see through the finderscope and on the chart must be identical. Note that the target may not be visible in the finderscope. In that case set the cross hair to the target location using surrounding stars as reference points. REMEMBER: The view in the finderscope in inverted (upside down). Don't forget this or you will get lost in space! You can turn the chart upside down to match the view. Another hint: Stars appear brighter through the finderscope (and the main scope) than to the naked eye.
Have a look in the main telescope. Depending on how careful you have been, your object may or may not be in the field of view. Keep in mind what you are looking for.
- A double star is usually easy to recognize if the components are far enough apart. You may have to switch to the 10mm eyepiece to be certain.
- Nebulae can be VERY faint (and, if it is a bad night, not visible at all). Double and triple check your position before declaring that you can't see it.
- Planetary nebulae can be very small in the 25mm eyepiece. You will need to inspect each stellar image carefully (focus well!) to tell the nebula apart from stars. You can verify that you found the right object by switching to the 10mm eyepiece.
- Globular clusters are round, fuzzy aggregation of faint stars. Depending on the conditions, they will show well or be barely visible at all.
- Open star clusters are concentrations of stars that usually stand out well from the background.
Keep in mind that anything that doesn't look like a single star in the field is probably what you are looking for. Double check with your TA if in doubt.
If there's nothing in the field of view but background stars, then you missed. You need to scan the surrounding area in search of your target, keeping in mind that it may be just outside the field of view. Scan using the two slow-motion controls (RA & Dec), ONE AT A TIME. The idea is to scan E-W (2-3 fields of view), then move in declination by about 1/2 the field of view and repeat. Check regularly in the finderscope to ensure that you are still in the correct area and that you have not gotten lost.
If this fails, go back to your starting star and star hop again. You may have gotten confused in your star identifications.

Understanding Star Charts Star Charts are pages in an astronomical atlas much as state and city maps are pages in a road atlas. The primary objects in a star chart are the constellations and the stars contained within them. The constellations have boundaries as well as unique names, much like counties on a road map. In addition, a grid is normally superimposed on the constellations that shows the equatorial coordinate system (RA and Dec). The RA will be marked of in hours from 0 to 24 mostly along the bottom and top of the graph and the Dec will be marked off in degrees from -90 to +90 mostly along the left and right edges of the graph. Most of the objects placed on the chart will be stars of different sizes representing different brightnesses. Other objects such as nebulae and galaxies will have their own symbols. There might also be a few additional lines showing the apparent path of the sun over the year (the ecliptic) and the plane of the Milky Way galaxy. A few of the objects will have numbers and letters that serve as identifiers for those objects. The brightest stars will have Greek letters that represent Bayer catalog identifiers. They are placed such that an earlier letter represents a brighter star. For example, the second brightest star in the constellation Lyra is Beta Lyrae. Numbers next to a star are from the Flamsteed catalog. They represent an ordering of the stars within a constellation by increasing RA. Thus the bright star with the lowest numerical value of RA in the constellation Orion will be denoted 1 Orionis. The Flamsteed catalog includes fainter (and consequently more) stars, but there are still many more even fainter stars with neither identifier. Some of these will have other identifiers based on other catalogs. Non-stellar objects have two major catalogs to represent them. The first is the Messier catalog, denoted by a capital M follow by a number. For example, the Great Nebula in Orion happens to be M42. This catalog has 110 entries, which are usually the brightest and more easily seen. A much more complete catalog is the New General Catalog with about 7800 entries. They are denoted by a capital NGC followed by a number. Some charts leave out the letters "NGC " to minimize clutter. So if you see and object that is not a star but has just a number next to it, it is almost always an NGC identifier. A particularly bright or interesting object may be included in many catalogs and thus have many identifiers, but, in general, the oldest identifier is the one that is most often displayed on the chart.

Star Hopping and Star Charts: Here are some more tips for painless star hopping. Each "hop" should move you in the general direction of the final object and should be relatively short in angular size. Hops should be done in the finder scope since it provides a wider field and can thus allow a greater grasp of the orientation of objects. In some cases, your target will be due North (or East, etc) of a star, something you can see by inspecting the star chart. In that case, all you need to do is to center the star in the telescope (25mm eyepiece) and move the telescope in the required direction. Do this using the slow motion controls while looking through the eyepiece. You should see your target enter the field.

Orientation of the field of view: Another way to orient yourself if there are not enough stars in the scope to do so, is to remember your coordinate system. If you lock the RA wheel and nudge the scope in Declination, you will be moving either North toward Polaris or South. The stars, since they are fixed, will of course move in the opposite direction. So a nudge in the direction of Polaris will make the stars appear to move toward the South. To determine East and West you could turn of the tracking motor and watch stars drifting toward the West. Then it becomes easy to compare the view from the scope with the star chart.

Using coordinates to find objects: This is an alternative method to star hopping that uses the coordinate dials of the telescope. Instead of going through the sometimes frustrating task of star hopping, you can use the known coordinates of celestial objects to locate them. The location of objects on the celestial sphere is analogous to that on the surface of the Earth. Geographical coordinates are two angles, the latitude and the longitude and uniquely specific a point on the surface of the Earth. In the sky, we use declination and right ascension. Like latitude, declination is the angle between the object and the celestial equator. It runs from -90^o at the south celestial pole through 0^o on the celestial equator and +90^o at the north celestial pole. Right ascension is similar to longitude and is measure from a reference meridian in the sky. Instead of running from 0^o to 360^o, however, it runs from 0 to 24 hours, increasing toward the East. This makes sense since the celestial sphere appears to make one complete turn in 24 hours.

With these telescopes, it is best to use not the absolute coordinates of an object, but the difference in coordinates between the target and some nearby star (say, within 10^o or so). Given your target use the star chart to identify a suitable nearby naked eye star. Acquire the star in the telescope and center it in the 25mm eyepiece. Calculate the difference in declination and right ascension between your target and your star, using star charts (or the table below) to get the coordinates. Using the dials, move the telescope by the required number of degrees in Dec and minutes in RA. Be careful to go in the right direction! This needs to be done with an accuracy of better than 1^o since the field of view of the 25mm eyepiece is only about 0.6^o. Make a 1^oerror and the object won't be in the field of view. In that case, start scanning the area (#6 above) and if you get impatient, start over again.

Object List #1: Bright Stars

Note: There's no need to "star hop" to stars this bright! These are starting points for star hopping! Look at 6 to 8 of these stars,choosing a variety of spectral types. In your observing notes, remember to comment on the color of each star and see if you can relate the color and the spectral types of stars.

Name	Constellation	R.A.	Dec.	Vis. Mag.	When to View (Fall / Spring)	Distance	Sp.Type	Comment
Dubhe	Ursa Major	11h 04m	+61d 45'	1.8	Early / Middle	105 LY	K0 II	34th brightest
Spica	Virgo	13h 25m	-11d 09'	1.0	Early / Late	275 LY	B1 V	16th brightest
Arcturus	Bootes	14h 16m	+19d 11'	0.0	Early / Late	37 LY	K2 III	4th brightest
Rasalhauge	Ophiuchus	17h 35m	+12d 34'	2.1	Middle / ---	60 LY	A5 III	55th brightest
Vega	Lyra	18h 37m	+38d 47'	0.0	Middle / ---	27 LY	A0 V	5th brightest
Altair	Aquila	19h 51m	+08d 52'	0.8	Middle / ---	16.5 LY	A7 IV	12th brightest, 64th closest
Deneb	Cygnus	20h 41m	55d 17'	1.3	Middle / ---	1600 LY	A2 I	19th brightest
Alderamin	Cepheus	21h 18m	+62d 35'	2.4	Middle / Early	52 LY	A7 IV	86th brightest
Fomalhaut	Pisces Austrinis	22h 58m	-29d 37'	1.2	Middle / ---	23 LY	A3 V	18th brightest
Markab	Pegasus	23h 05m	+15d 12'	2.5	Middle / Early	110 LY	A0 III	30th brightest
Alpheratz	Andromeda	00h 08m	+29d 05'	2.1	Middle / Early	120 LY	B9 IV	...
Schedar	Cassiopeia	00h 40m	+56d 32'	2.2	Middle / Early	150 LY	K0 II	65th brightest
Hamal	Aries	02h 07m	+23d 27'	2.0	Middle / Early	75 LY	K2 III	48th brightest
Polaris	Ursa Minor	02h 32m	+89d 15'	2.0	All / All	300 LY	F7 I	49th brightest; "The North Star"
Menkar	Cetus	03h 02m	+04d 05'	2.5	Middle / Early	150 LY	M2 III	91th brightest
Mirfak	Perseus	03h 24m	+49d 52'	1.8	Middle / All	570 LY	F5 I	33rd brightest
Capella	Auriga	05h 17m	+46d 00'	0.1	Late / All	45 LY	G5 III	6th brightest
Aldebaran	Taurus	04h 36m	+16d 31'	0.9	Late / All	68 LY	K5 III	13th brightest
Betelgeuse	Orion	05h 55m	+07d 24'	0.5	Late / All	520 LY	M2 I	10th brightest
Sirius	Canis Major	06h 45m	-16d 43'	-1.5	Late	8.6 LY	A1 V	1st brightest, 8th closest
Castor	Gemini	07h 35m	+31d 54'	1.6	--- / Middle	49 LY	A2 V	23rd brightest. double star, 3" sep.
Procyon	Canis Minor	07h 39m	+5d 14'	0.4	--- / Middle	11 LY	F5 V	8th brightest
Regulus	Leo	10h 08m	+11d 59'	1.5	--- / Late	...	...	...

Object List #2: Double Stars

Notes: Position Angle refers to the location of the secondary (the fainter of the two stars) with respect to the primary (the brighter member of the double). Astronomers measure angles counterclockwise from north (the 12 o'clock position). Separation refers to the angular distance between the pair, in units of seconds of arc. Magnitude is the apparent magnitude of the two members of the binary, fainter stars have larger magnitudes. Take notes about the appearance of the double star: relative brightness of the components, separation, and color contrast if any.

Name of Primary	Constellation	RA	Dec	Position Angle	Separation	Visual Mag.	Comment
Beta	Cepheus	21h 29m	+70 34'	249	13.3"	3.2, 7.9	...
Alpha	Cassiopeia	00h 41m	+56d 32'	282	69.5"	2.2, 8.9	...
Eta	Cassiopeia	00h 49m	+57d 49'	293	12.2"	3.4, 7.5	...
Alpha	Canes Venatici	12h 56m	+38d 19'	228	19.3"	2.9, 5.5	...
Epsilon	Perseus	03h 58m	+40d 01'	10	8.8"	2.9, 8.1	...
Eta	Perseus	02h 51m	55d 54'	300	28.3"	3.3, 8.5	...
Gamma	Aries	1h 53m	+19d 17'	0	7.8"	4.5, 4.5	...
Alpha	Hercules	17h 15m	+14d 23'	110	4.6"	3-4, 5.4	...
Gamma	Leo	10h 20m	+19d 51'	125	4.6"	2.6, 3.5	...
Alpha	Ursa Minor	02h 32m	+89d 16'	218	18.4"	2.0, 9.0	Alpha Ursa Minoris is, of course, Polaris
Theta 1	Orion	05h 35m	-5d 24'	---	13"-16"	5.4, 6.3, 6.7, 6.8	Quadruple system known as "the Trapezium," at center of Orion Nebula.
Zeta	Ursa Major	13h 24m	+54 56'	152	14.4"	2.3, 4.0	Zeta Ursa Majoris is a wide double with the brighter separated into two, i.e. a triple system. It is the closer pair that is given here.
Gamma	Andromeda	02h 04m	+42d 20'	063	9.8"	2.3, 4.8	...
Beta	Cygnus	19h 31m	+27d 58'	054	34.4"	3.1, 5.1	Notice the nice color constrast between the two stars in both Gamma Andromeda and Beta Cygnus. Why?
Epsilon	Lyra	18h 44m	+39d 40'	+173	207.7"	4.7, 5.1	Epsilon Lyrae' stars are both doubles themselves (a double double). The separation is very small (2.5 arc seconds) and is best viewed in the 10mm eyepiece.
Zeta	Lyra	18h 49m	+37d 36'	150	43.7"	4.3, 5.9	...
Nu	Draco	17h 32m	+55d 11'	312	61.9"	4.9, 4.9	Notice the lack of color contrast between the two stars in both Zeta Lyra and Nu Draco. Why?
61	Cygnus	21h 07m	+38d 44'	144	31"	5.3, 5.9	Famous nearby double, 11.1LY away. 4th nearest naked eye star, first star with measured parallax (by Bessel in 1838).
Omicron 2	Eridanus	...	...	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.
Iota	Cassiopeia	2h 29m	+67d 24'	241 & 114	2.2" & 7.3"	4, 7, 8	Triple system.

Object list #3: Clusters and Nebulae

Notes: Most of these objects are challenging when seen from a large city. You may experience difficulty seeing them even if the telescope is pointing in the right spot! They are nevertheless among the most beautiful objects in the night sky and quite interesting to look at. As an aside on light pollution, you should know that while faint, several of these objects are visible to the naked eye under a very dark site. Always start with the 25 mm eyepiece to locate the object. For the smaller ones (planetary nebulae), you may have to switch to the 10mm to clearly distinguish the object from the surrounding stars. In all cases, use both magnifications (eyepieces) when making your observations as one may reveal something the other doesn't. If you have difficulty finding these objects with the star hopping method, you may have more luck using coordinate offsets from a nearby star you can locate easily (such as in the "Bright stars" list above).

Sketch the object in your logbook. Indicate the orientation and scale of your drawing and add notes to complement your sketch.

*** = extra challenging. Good luck!

Name	Constellation	RA	Dec	Size (arcmin)	Distance	Comments
M42: Orion Nebula	Orion	5h 35m	-5d 27'	10'	1600 LY	Region of Star formation. Surrounds multiple star Theta 1 Ori.
M34	Perseus	2h 42m	+42d 47'	30'	1500 LY	Bright galactic cluster. Age = 100 Myr.
NGC884/869	Perseus	2h 20m	+57d 09'	29' / 29'	7400 LY	Famous Double cluster. Age = 11Myr / 6Myr.
M45: The Pleiades	Taurus	3h 47m	+24d 07'	100'	400 LY	Very bright, very large galactic cluster. Age = 70 Myr. You can see the brightest stars naked eye. With a largeish telescope under a dark sky, you can see faint nebulosity around the stars.
M41	Canis Major	6h 47m	-20 44'	38'	2400 LY	Galactic cluster 4d south of Sirius. 100 Myr old.
M44: The Beehive	Cancer	8h 41m	+19d 45'	80'	520 LY	Very large galactic cluster. 660 Myr old.
*** M13	Hercules	16h 40m	+36d 33'	10'	22000 LY	Globular cluster framed by 2 stars of 6th mag
*** M92	Hercules	17h 16m	+43d 11'	8'	25000 LY	Globular cluster, compare with M13
M11	Scutum	18h 48m	-6d 20'	13'	5600 LY	Very dense galactic cluster. 224 Myr old.
M57	Lyra	18h 52m	+32d 58'	70''	2300 LY	Famous Planetary Nebula ("Ring nebula"). Neb is 3900 years old
NGC6826	Cygnus	19h 43m	+50d 24'	25''	2300 LY	"Blinking " planetary nebula. Look for central star! Neb. is 5200 years old
*** M15	Pegasus	21h 30m	+12d 10'	5'	32000 LY	Globular cluster.
*** M36	Auriga	5h 36m	+34d 08'	12'	4100 LY	25 Myr old galactic cluster
*** M35	Gemini	6h 09m	+24d 20'	25'	2200 LY	107Myr old galactic cluster.

Object List #4: Stars Known to Have Planetary Companions

Notes: This is a list of several solar-type stars known to have planets in orbit around them. (Many more planets than the ones on this list are known to exist!) The planets themselves are hopelessly beyond the reach of amateur telescopes (in fact, they have not yet been seen directly, even with the most advanced telescopes used by astronomers), but it is interesting to see what a star like the Sun looks like from afar and think that it has planetary companions, some perhaps similar to those in our solar system. These stars are not visible to the naked eye from campus, but can be glimpsed in the finderscope. They are an easy sight through the telescope. What would the Sun and its family of planets look like to an alien civilization living on a planet orbiting such a star? How hard would it be to identify the stars worth investigating for signs of (perhaps intelligent) life? Take time to make notes and record your impressions.