The AAVSO Winter Observing Challenge—to track the brightness of δ Cephei or ℓ Carinae—is suitable for newbies and seasoned skywatchers alike. | By Kalée Tock
Depending on your location, you may choose to observe Delta Cephei (δ Cep) in the Northern Hemisphere, or ℓ Carinae (L Car) in the Southern Hemisphere.
Open Stellarium or your favorite planetarium app. Check that it shows your correct location. Determine when your target will be visible in your night sky. At that time, go outside and search for the target (circled in red) and comparison stars (circled in blue). If you bring your device outside to help locate the star, be sure to dim the screen or put it into “night mode” to help your eyes stay dark-adapted.
For magnitudes in astronomy, higher means dimmer. For example, zeta Cep (ζ), with magnitude 3.6, is brighter than epsilon Cep (ε), with magnitude 4.2. Using the blue circled comparison star brightnesses as reference points, assign a magnitude to your target. Be sure to write down the date and time.
Upload your Observations to AAVSO WebObs
If you do not yet have an AAVSO Observer code, follow the steps below:
- Create an AAVSO account at aavso.org
- Login with your username (which is not your email address)
- Go to View → Profile → Account
- Under “Personal Information,” click “Request an obscode”
Now go to the home page, scroll down to the Resources section, and click “Submit and Access Data” → Upload Photometry → Individual Observations. Alternatively, go to AAVSO WebObs. Notice your observer code on the form!
Fill in the form fields The Observation Type is “Visual.” You must convert the date to the UTC time zone. If you have trouble with formatting, use this Julian Date Converter to convert the UTC date to a number and copy-paste the number.
Enter the magnitudes of the comparison star or stars that you used, multiplied by 10.
If you observed Delta Cep:
- Enter 36 (not 3.6!) for Zeta Cep (ζ) as the magnitude of the first comp star
- If you were able to see Epsilon Cep (ζ), enter 42 (not 4.2!) as the magnitude of the second comp star
- Enter the Chart ID: X38937H1
If you observed L Car:
- Enter 30 (not 3.0!) Nu Car (𝝂) as the magnitude of the first comp star
- If you were able to see the unlettered blue-circled star, enter 38 (not 3.8!) as the magnitude of the second comp star
- Enter the ChartID: X38937IG
Click any relevant Comment codes, and add any notes about your observation to the Comments field. For example, you might want to include some notes about the weather that night.
Check your Observation online!
Go to the Light Curve Generator and enter your target (“delta Cep” or “L Car”) into the search. Select “bands” and enter the checkbox for “vis.” By default, this will show all visual observations of this star that have been contributed in the last two years. Yours will be among them, and your name will be in the list below the plot! If you click on the box next to your name, your observations will be highlighted on the plot with a brown cloverleaf.
Optional: Generate a Light Curve!
The observations above appear jumbled because they are taken at random points during the pulsation period of the star. To pull a lightcurve out of the jumble, follow the steps below:
- From the AAVSO home page, click “Submit and Access Data” → “Download Photometry.” Fill in the information on the form. For “Discrepant Data” and “Diff / Step” data, click “No.” Format should be “comma-delimited.” Download the file to your computer.
- Run the first cell of this Colab. At the prompt, upload the file you downloaded in the previous step (or use this file).
- Run the second cell to generate a lightcurve of Delta Cep from AAVSO Visual Observations.
- (Optional) Change the Observer Code on the second to last line of the second cell to your AAVSO Observer Code. This will plot your observations with red stars!
Need additional help? Reach out to the author!
Learn more about Delta Cep and L Car!
Learn more about period folding, which describes the way in which a light curve is made out of your observations!
Kalée Tock is a science instructor at the Stanford Online High School and a member of the AAVSO Marketing Committee.