Stellar Observations
Goals of the Lab
To observe a number of bright (naked-eye) stars with the telescope.
To observe how some bright stars are in fact double stars.
To look at stars of a variety of types and to notice any correlation between the observed color of those stars and their stellar types.
Requirements: the telescope, your logbook, protractor
Part I: Bright Star Observations
Table of Stars
The "type" field indicates 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 final Raman number is 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 | Notes |
|---|---|---|---|---|---|---|
| Arcturus | α Bootis | 14h 15m 39.7s | +19° 10' 57" | 0.0 | K1III | |
| 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 | ||
| 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 | (Check for Double) |
| 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 |
Choose at least eight stars on the Table of Stars above to observe. Make sure the stars you're going to look at are up! Some of these stars won't come up until later at night and/or later in the semester. Similarly, some will set later in the night and later in the semester.
Make sure that of the eight stars you choose, you have at least one of each type: B, A, F, G, K, and M.
Perform the rest of the steps in this section on each star you've chosen.
Center the telescope on the star. Use the 25mm eyepiece. Make sure you get the right star! You will probably want to check the alignment of your finder scope before beginning.
If you are sharing the telescope with a lab partner, make sure that each partner finds at least four of the stars you're observing; don't depend on one partner to find all of the stars.
Whether you are working alone or sharing the telescope, indicate in your logbook who found each star.
Sketch the field of view of the 25mm eyepiece. Stare for a couple of minutes; you should be able to see some stars other than just the star you're looking at! Remember to use larger dots in your sketch to represent brighter stars, and to indicate the direction of North and East on your drawing. Use the generic observation template for your sketch. 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.
For each star, make some notes in your logbook about the appearance of the star. How bright does it appear compared to the other stars you looked at? Can you tell anything about its color, and if so, what color is it? How does the color as seen in the telescope compare to your impression of the color looking at the star with your naked eye? (Note that sometimes slightly de-focusing the telescope will help you see 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. Make sure the stars you're going to look at are up!
Center the telescope on the star; make sure you get the right star! You will want to verify that your finder is aligned before beginning this.
Observe the star with the 25mm eyepiece. Make some notes about its appearance. How easy is it to separate the two components? Do you see all of the components if there are more than two stars?
Put in the 10mm eyepeice. Make a sketch of the field of view, using the generic observation template. Use bigger dots to indicate brighter stars. Draw any other stars in the field of view in addition to your target double. Remember to indicate which was is North and which way is East on your drawing!
In your logbook, make some notes on the appearance of the star through the 10mm eyepiece. Can you see any color contrast between the stars? What colors do the stars appear? How extreme is the brightness contrast? How easy is it to separate the stars? Note anything else that comes to mind.
Part III: Analysis and Contemplation
This part is to be completed outside of lab after you have made all of your observations.
For the bright stars, including the double stars, did you notice any correlation between the types of the stars and their colors? Was this what you might have expected from what you know about stellar classificaiton (if that's alredy been covered in lecture)?
What was the closest double star you observed? Based on this, how close do you believe a double star could be while you could still "split" it?
For each double star you observed, use a protractor to measure the position angle of the star on your sketch. 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 these measurements off of your own drawings and tabulate them before talking to anybody else in the lab!
For each double star, find four other people in the lab who looked at the same star. (It can be the same four people if they looked at all of the same stars as you did; but if they didn't, you can compare some with some people, others with other people.)
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.
Based on these measurements, 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?