Instructor: William Fenton, Science Department, The Hotchkiss School

Visually Observing the Variable Star Delta Cep

Each student in the class will observe Delta Cepheus, a bright, long period variable star near the north celestial pole as often as weather allows. Below are the steps necessary for making visual magnitude estimates:
  1. Find the correct sky region

    In our case we'll be observing delta cepheus, a star located in the north, not far from the North Star. Any star chart can help you find the constellation Cepheus. Use google or your book or any other of many sources to find a map. The website for Orion Telescopes has a good, printable monthly star chart here. I recommend the "printer friendly" chart if you plan on printing it out. Once you familiarize yourself with the stars nearby, try to go outside and find Cepheus. I usually just use the Big Dipper to find the North Star, then keep on going to Cepheus.

  2. Find &delta Cep

    Once you've found the constellation Cepheus you must find the star &delta (delta) Cepheus. The &delta means that it is the fourth brightest star in the constellation, so it should not be hard to find. On the Orion star map &delta Cepheus is marked as an open circle (signifying that it is a variable star) and labeled with a &delta. Now find the star with your binoculars.

  3. Find comparison stars

    Now grab the finder chart which will give a you a zoomed in (15° X 15°) view of the stars and will also give you magnitudes of comparison stars. The comparison stars are marked with a two-digit number which indicates the magnitude of that star. Using decimal points would be problematic since they could easily get mixed up with stars so a 3.4 mag star is simply labeled 34.

  4. Estimate Brightness

    To estimate the magnitude of &delta Cep, find a comparison star(s) that is similar in brightness. &delta Cep will probably not match a comparison star exactly so you will have to interpolate its magnitude from two or more comparison stars. Luckily, &delta Cep has two comparison stars right near it that approximately equal its brightest and dimmest.

  5. Record your observation

    You should immediately enter the following information in a log book:

    • name of the variable star
    • UT of observation
    • estimated magnitude of the variable
    • magnitudes of comparison stars used
    • location of observation
    • notes on weather/conditions/moonlight/etc

  6. Upload your data!

    This is a class collaboration so we need to be able to share data efficiently. This form will allow you to simply enter a night's magnitude and be done. (Bookmark it!) All the data will be compiled automatically into a spreadsheet that we can review in class. Note: you must have a google apps for education account and be signed in. If you don't have one go get one. It uses your Hotchkiss email address to connect you with other Hotchkiss people (like your teacher). You'll notice the form requires the time of observation in heliocentric julian day format. This converter will convert from UT to HJD but you'll have to do the conversion to UT for Eastern Standard or Eastern Daylight on your own.