Astronomy Lab: Basic Observing with Coordinate Systems

Goal: To become familiar with finding objects using the Celestial Coordinate system

Materials and tools

• Star maps
• Paper and pencil/pen to record observations
• "Night light": flashlight with red cellophane or filter
• Telescope or binoculars
• Compass

Preparation

You should try to do this observing session over a three-hour period, so that you can compare positions of planets and the Moon (if visible), as well as key stars, in the sky over time. Plan you observation ahead of time, so that you can compare predicted positions with your actual observations.

1. Review the notes on how to perform labs and write lab reports in the Student Survival Guide.
2. Use the Starry Night Enthusiast, My Sky, or Stellarium Planetarium sites to plan your observing.
3. Print off projections for the east, west, south, and overhead sky views.
4. Using your projections, determine the sidereal time for your observing time, and list five stars that you expect to see directly (or nearly directly) between your south horizon and your zenith. Predict two stars you would see between your north horizon and your zenith.

   For example, if I were to plan an observation session for the night of 15 September, starting at 9pm, from my home in Bellevue, my sidereal time would equal the right ascension of a star on my south horizon, or anywhere on my meridian -- about 19^h40^m. I will see stars like Altair (19^h50^m, magnitude 0.8) above my south horizon.

   My north horizon will have a right ascension offset by 12 hours -- so it will be at 7^h45^m. About the brightest start I will see above my horizon is Muscida, the nose of the great bear (Ursa Major), at 8^h30^m.

   Stars on my east horizon will have right ascensions 6 hours less than my sidereal time (or in this particular case, 13^h45^m; stars on my west horizon should be 6 hours more than my sidereal time, or 1^h45^m.

Observng Session

1. Begin by recording information about your observation session. What is the date and time? Where are you? What are the weather conditions (including temperature if you can determine that)? What is the cloud cover?
2. Estimate your seeing level using the reference stars you established in the previous lab.
3. Look along the meridian, the line running from the north point to your south point. Find a bright star as close to this line as you can, above your southern horizon, identify it and look up its RA and declination. The RA of the stars on this line is your sidereal time. Estimate the star's altitude and azimuth. Record the time of your observation.
4. Identify the major constellation and brightest star for your east, west, and north horizon points. Estimate the altitude and declination of the stars, and record the time of your observations.
5. Find a major planet. Estimate its altitude and azimuth and note the time. Identify its location on a star map, and determine its celestial coordinates. You may want to find a star that it is near, and look up the coordinates for the star.
6. Find the moon. Estimate its altitude, azimuth, RA, and declination (depending on which day you do this lab, your RA and declination may be quite different from that shown on the map, since the moon moves rapidly across the sky). What is the moon's phase? How does it affect viewing the nearby sky?
7. What constellation is nearest your zenith? What star is nearest your zenith?
8. Find the Pole Star (above your north horizon). Estimate its altitude. Compare this with your latitude.
9. Chose 2 stars you identified in steps 3 and 4. Estimate their new altitude and azimuth and note the time.
10. Repeat the observation for #3 and identify the stars now on your meridian. Look up their right ascension. How much time has passed since your first observation in step 3? Compare this with the difference in RA between the two meridian stars you identified.

Report

Write a report of all your observations and post it to the lab assignment at the Moodle.

1. A list of the materials and optical instruments that you actually used.
2. A brief description of your procedure, with notes on any major changes you made to the suggested procedure above. All lab reports should include enough information about your materials and methods to allow a similarly equipped fellow student to repeat your observations under similar conditions.
3. Basic session information, as follows:
   1. Date, time, time zone
   2. Location (city name, park; geographic coordinates -- latitude and longitude -- if you know them).
   3. Temperature and air quality (still, windy)
   4. Cloud cover ("haze in the north, clear to the south")
   5. Moon location and phase; time of rising (check newspaper)
   6. Seeing level
4. Any other observations you think interesting or important.

© 2005 - 2025 This course is offered through Scholars Online, a non-profit organization supporting classical Christian education through online courses. Permission to copy course content (lessons and labs) for personal study is granted to students currently or formerly enrolled in the course through Scholars Online. Reproduction for any other purpose, without the express written consent of the author, is prohibited.