Stellar Observations
Goals of the Lab
To observe a number of bright single and double stars.
To study through observations the relationship between a star's color and its spectral type.
Requirements: several (at least 4 pages of) observation templates generic observation template and a protractor
Part I: Bright Star Observations
Table of Stars
The word "type" in the table below means the spectral classification of the star. The first letter is the broad classification (O, B, A, F, G, K, or M). The number following it is a subclass within the broad classification, and may be ignored for this lab. The Roman numeral represents the luminosity class (I and II = supergiant; III = giant; IV = subgiant ; V = main sequence). "Mag." is the visual magnitude.
(All data on this table comes from SIMBAD.)
| Common Name |
Name | RA | Dec | Mag. | Type |
|---|---|---|---|---|---|
| Megrez | δ Canis Majoris | 12h 15m 25.6s | +57° 01' 57" | 3.3 | A3V |
| Spica | α Virgins | 13h 25m 11.6s | -11° 09' 41" | 1.0 | B1III |
| Arcturus | α Bootis | 14h 15m 39.7s | +19° 10' 57" | 0.0 | K1III |
| Nusakan | β Coronae Borealis | 15h 27m 49.7s | +29° 06' 20.5" | 3.7 | F0p |
| Antares | α Scorpii | 16h 29m 24.5s | -26° 25' 55" | 1.1 | M1I |
| – | β Herculis | 16h 30m 13.2s | +21° 29' 23" | 2.8 | G7III |
| Rastaban | β Draconis | 17h 30m 26.0s | +52° 18' 05" | 2.8 | G2Iab |
| Vega | α Lyrae | 18h 36m 56.3s | +38° 47' 01" | 0.0 | A0V |
| – | γ Cygni | 20h 22m 13.7s | +40° 15' 24" | 2.2 | F8I |
| Deneb | α Cygni | 20h 41m 25.9s | +45° 16' 49" | 1.3 | A2I |
| – | ε Cygni | 20h 46m 12.7s | +33° 58' 13" | 2.5 | K0III |
| Sadalmelik | α Aquarii | 22h 05m 47.03s | -00°19' 11" | 3.0 | G2I |
| Fomalhaut | α Piscis Austrini | 22h 57m 39.0s | -29° 37' 20" | 1.2 | A3V |
| Markab | α Pegasi | 23h 04m 45.7 s | +15° 12' 19" | 2.5 | B9III |
| Alpheratz | α Andromedae | 00h 08m 23.3s | +29° 05' 26" | 2.0 | B8IV |
| Caph | β Cassiopeiae | 00h 09m 10.7s | +59° 08' 59" | 2.3 | F2IV |
| Mirach | β Andromedae | 01h 09m 43.9s | +35° 37' 14" | 2.0 | M0III |
| Hamal | α Arietis | 02h 07m 10.4s | +23° 27' 45" | 2.0 | K2III |
| Menkar | α Ceti | 03h 02m 16.8s | +04° 05' 23" | 2.6 | M1III |
| Capella | α Aurigae | 05h 16m 41.4s | +45° 59' 53" | 0.1 | G5III |
Note:All observations should include N/S and E/W, the time, date, and weather conditions.
Choose at least eight stars on the Table of Stars above to observe. Use your star wheel to determine which stars are up or will be up during lab. Note that, some of these stars will not rise until later at night and/or later in the semester. Similarly, some will set later in the night and later in the semester.
Of the eight stars you choose, you need at least one of each type: B, A, F, G, K, and M.
Perform the following steps in this section on each star you've chosen.
Center the star in the 25mm eyepiece.
If you are sharing the telescope with a lab partner, each partner needs to find at least four of the stars you're observing; don't depend on one partner to find all of the stars. Each person needs to make a sketch of every star observed. Even if the person you are sharing the telescope with found the star, you cannot copy his/her drawing!
Indicate who found each star on your drawing.
Sketch the field of view of the 25mm eyepiece. Stare for a couple of minutes; you should be able to see some other stars in the field of view. Use larger dots to represent brighter stars. Label the sketch with the name of your target star, and draw a little arrow on your sketch to indicate which is the target star. Determine which way is N/S and E/W using the method you learned in the Telescope Basics lab. Label your sketch with these directions.
For each star, note the appearance of the star. Describe its brightness (relative to other stars) and its color -in the eyepiece and with your naked eye. Note that slightly de-focusing the telescope may help you see a star's color.
Part II: Observations of Bright Double Stars
Table of Bright Double Stars
The RA/Dec given are for the primary star. Magnitudes and Spectral types are given as in the table of Bright Stars above.
| Common Name |
Name | RA | Dec | Mag1/Mag2 | Type1/Type2 | Sep. (") |
Notes |
|---|---|---|---|---|---|---|---|
| Sarin | δ Herculis | 17h 15m 01.9 | +24° 50' 21" | 3.1, 8.3 | A3IV, &mdash | 9 | |
| – | ε Lyrae | 18h 44m 20.4s | +39° 40' 12" | 5.1, 6.0; 5.1, 5.4 |
A4V, F1V; A8V, F0V |
2.4 ;209 ; 1.6 |
Double-double |
| Albireo | β Cygni | 19h 30m 43.3s | +27° 57' 35" | 3.1, 5.1 | K3II, B8V | 35 | |
| Shedir | α Cassiopeiae | 00h 40m 30.4s | +56° 32' 14" | 2.3, 8.8 | K0III, K0 | 70 | |
| Almach | γ Andromedae | 02h 03m 54.0 | +42° 19' 47" | 2.3, 4.8 | K3II, B8V | 10 | |
| Algieba | γ Leonis | 10h 19m 58.4s | +19° 50' 29" | 2.0, 2.6, 3.5 | K0, KIII, G7III | 1.4, 5.7 | Triple |
| Mizar | ζ Ursa Majoris | 13h 23m 55.5s | +54° 55' 31" | 2.3, 4.0 | A2V, A1 | 15 | Alcor 12' away |
Note: you may well not be able to see ε Lyrae with your naked eye. Center your finder scope on Vega; ε Lyrae will be nearby.
Choose at least four star systems from the Table of Bright Double Stars above to observe. Again, use your star wheel to determine which stars are up or will be up during lab.
Observe the star with the 25mm eyepiece. Describe its appearance, i.e. its brightness and color. How easy is it to separate the two components? Do you see all of the components if there are more than two stars?
Observe the star with the 10mm eyepiece. Sketch the field of view. Use bigger dots to indicate brighter stars. Draw other stars in the field of view in addition to your target double. Determine the directions N/S and E/W. Indicate these directions on your sketch.
Describe the brightness and color of each star in the doublet/triplet as viewed in the 10mm eyepiece. Describe any color differences among the doublet/triplet. How extreme is the brightness contrast? How easy is it to separate the stars?
Part III: Analysis and Contemplation
From your observations, do you notice a correlation between the types of the stars and their colors? Given what you've learned about stellar classifications in class, are your observations what you expected?
What was the closest double star you observed, (i.e. closest to each other in the telescope)? Based on this, how close do you believe a double star could be while you could still "split" it?
For each double star observed, use a protractor to measure the position angle of the star. This is defined as the angle (between 0° and 360°) of the line going from the brighter star to the dimmer star; 0° is North, and 90° is East. Make measurements from your drawings and tabulate the values.
Compare the position angle of each double star with four other students. Make a table summarizing your values and those of your peers. This table should include the name of the person who made the measurement, along with their measured value.
For each double star, make a table of the position angles measured by everybody you talk to, including yourself. This table should have the name of the person who made the measurement, and their measurement.
Using your table of data, how well (to within how many degrees) do you think you are able to measure the position angle of a double star using this method? Are you able to do any better with stars that are farther apart, or stars that are closer together?