Course Icon

Astronomy

Lab: Using a telescope

SO Icon

Astronomy Lab Instructions

Astronomy Lab: Basic Telescope Usage

Goal: Align a telescope sighter scope

Materials and Equipment:

Procedure

  1. Preparation: Do some preliminary homework and determine what objects you will observe based on the date and time of your observing session.
    • Select at least 5 stars of magnitudes 1-5. If Cygnus and Lyra are visible, you may find this group useful:
      StarLocation in constellationMagnitude
      DenebTop of the Cross1.25
      SadrCenter of the Cross2.23
      AlbireoBottom of the Cross3.05
      Eta CygniBetween Sadr and Albireo3.89
      Vega (in Lyra)Brightest star0
    • If Cygnus will not be visible during your viewing session, identify a constellation with a range of star magnitudes to observer and construct a similar table so that you can document your seeing and transparency.
    • Identify at least one double star to view (if Cygnus is visible, Albireo is an excellent candidate). Note the angular separation in arcseconds of the two stars you have selected.
    • Identify at least one planet to view, if at all possible: Jupiter or Saturn are good candidates as they have easily identifiable features (bands, moons, or rings).
    • Identify at least one star cluster to view. This can be an open cluster like the Pleiades (Messier 45), or a globular cluster such as the one in Hercules (Messier 13).
    • Identify at least one diffuse object to view, such as the Andromeda Nebula (Messier 31) or the Ring Nebula (Messier 57) in Lyra.

    "Messier" numbers refer to objects in the catalog of diffuse objects compiled by Charles Messier in 1771. He wanted to identify permanent astronomical entities so they wouldn't be confused with possible comets. The 110 objects in his catalog include planetary nebula (spherical or circular nebula from stellar novas), irregular nebula from supernova explosions, galaxies, open clusters and globular clusters. These are some of the most beautiful objects in the sky. Among amateur astronomers, it is a goal to complete the "Messier Marathon" and view all 110 objects in a single night, something that is actually possible from the southern US in late March, with appropriate planning and discipline.

  2. Setting Up for Detailed Observing: Select a dark site away from direct street and landscape lighting, with a clear view of at least 1/4 of the sky down to your horizon.
    1. If your telescope is equipped with a sighting scope (sometimes called a finder scope), you will need to align it. (You can also do this in the daytime with a nearby object, which is sometimes easier than trying to do it at night when you may have limited time. You need to be careful in transporting your telescope to the observing site so that you do not bump your carefully adjusted sighting scope!)
      1. Chose some very bright, easy object, such as the moon or a bright star low in the sky, and point the main telescope at it.
      2. Try to center the object in your eyepiece as carefully as possible.
      3. Now use the set screws on the sighter scope to align the sighter scope so that the object you have chosen shows in the cross hairs.
      4. Verify that you are still looking at your original star through the eyepiece. If you have taken too much time in adjusting your set screws, the object may have moved out of your field of view. If necessary, adjust the direction of the telescope and repeat the steps to align the sighter scope.
      5. Chose another star, but this time, use the sighter scope to align the telescope, then check whether your selected star is now visible in the eyepiece.
    2. If your telescope does not have a sighting scope, view along the body of the telescope as a guide to align it and find the object you wish to view. Start with something large (like the moon!) and practice!
    3. If your telescope has an equatorial mount, you may wish to align the scope to use these features. Check out the websites below for help.
      1. Daylight Polar alignment
      2. Polar Alignment of your Equatorial Mount (McWiki Blog)
  3. Detailed Observing:
    1. Find your visual magnitude stars from your viewing plan and estimating seeing and transparency with your naked eye for objects with magnitudes between 1 and 4 (5 if seeing is really good.) Then find each star with your telescope and record your observations. Are you able to see fainter stars with the telescope? If so, make drawings of the locations of the fainter stars so that you can look them up.
    2. Observe the double star you selected and draw a diagram of the star positions relative to your field of view -- draw the stars in the same positions and scale, using a circle to define your field of view.
    3. Observe the planet you selected, and draw what you see. Include your field of view.
    4. Observe the star cluster you selected. Does it fit in your field of view? Make notes of any particular features you observe.
    5. Observe the diffuse object you selected. Does it fit in your field of view? Make notes of any particular features you observe (shape, dust lanes, brighter areas).
    6. If you have time and a second eyepiece for your telescope, change eyepieces and view the double star again.
  4. Analysis
    1. Look up the faint stars you observed, and record their actual magnitude. How do the magnitudes with and without the telescope compare?
    2. Using the double star, estimate the width of your field of view in terms of arc seconds with your eyepiece(s).
    3. Using your field of view determination, try to estimate the angular size of the planet you observed, the star cluster, and the diffuse object. Check each one (remember than planet size will vary with synodic position!) and determine the error in your estimates.

Report

Write a report of all your observations and post it to the Moodle assignment for this lab. Be sure to include

  1. A list of the materials you actually used.
  2. A brief description of your procedure, with notes on any major changes you made to the suggested procedure above.
  3. A complete report of your observing notes, including your analysis.
  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.