Observing Variable Stars With AAVSO

If you're new to observing variable stars, which are stars that changes brightness over time, the American Association of Variable Star Observers (AAVSO) has a useful on-ramp. Citizen Sky supports collaboration with professional astronomers by helping you to find variable stars, measure their brightness, and submit your observations. Start your pursuit of variable stars with the AAVSO's 10-Star Training Tutorial

Available under the Online Resources in multiple languages, the guide helps beginning observers to use a star chart to find the constellation that houses your target star. Then, with an AAVSO variable star chart you star hop from naked eye stars with fixed brightness to your specific variable star. Measure its brightness against known comparison stars and report your observations online or by mail.

Citizen Sky introduces star hopping and using comparison stars to find and measure naked-eye variable stars.

A feature of the AAVSO is its excellent collection of finder charts, and the 10-Star Training Tutorial continues the tradition with ten star charts for naked-eye variable stars. You don't need a telescope to participate; you just need to look up. Of course, light pollution can lessen the stellar population visible from a site. Find any of these prominent constellations and dig in from there:

• Orion

• Gemini

• Cassiopeia

• Perseus

• Lyra

• Cepheus

• Aquila

• Auriga

AAVSO variable star chart of Lyra and two variable stars compares stars between magnitude= 5.4 and magnitude= 3.2. The decimal points are removed to prevent confusing them with stars. Image: American Association of Variable Star Observers.

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Variable Star Coming Soon: A Recurring Nova

The AAVSO has a prominent role in the evolving story of an imminent stellar outburst. Astronomers predict the star T Coronae Borealis (T CrB) will brighten significantly when an outer layer of material accreted from an adjacent star explodes. Briefly appearing to the naked eye as a "new" star, T CrB is a unique variable star--a recurring nova. Be sure to photograph the constellation Corona Borealis before, during, and after its eruption. Even as the nova fades from view you can capture its decline with a cell phone camera.

As CrB transitions from an evening to a morning constellation, tracking it becomes a morning pursuit.

My only images from the month of December occurred on December 8, 2024, at 6:15 pm. See it in the power lines (below)?

Excerpted from above image, six of seven stars of the u-shaped Northern Crown appear low on the horizon on December 8, 2024. The faint stars, not all visible to the naked eye, appear in the image because the camera takes a long duration photo.

Of course, professional astronomers and enthusiasts alike don't want to miss the peak of the nova before its brightness falls off. In the AAVSO Observing Campaign 875: Monitoring T Coronae Borealis forum, AAVSO Executive Director Brian Kloppenborg revisits the 1946 light curve and writes about the visual brightness (V):

I don’t think you’re at any risk of missing the eruption due to a few hours’ delay. Here’s a closer look at the 1946 event:

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Light curve of 1946 eruption suggests nova is visible to the naked eye for a couple days (green); can be captured by a cell phone camera for over a week (red); and then drops into the realm of telescopic viewing only. Image: adapted from AAVSO.

The first observation at V = 10 was on 1946-02-02, followed by V = 5.1 on 1946-02-04 and a peak at V = 3 on 1946-02-09. The brightening phase, therefore, took a few days—not hours. After the peak, V = 6 was recorded a week later on 1946-02-16, and the system didn’t return to V ≈ 9.6 until a month later on 1946-03-09.

While the event was relatively fast by nova standards, a few hours’ delay won’t ruin the show in my opinion. I’ll still be happy just knowing I saw it happen with my own eyes. In case you’d like to explore this event, here is a direct link to the light curve generator

The graph shows the light curve of T CrB with brightness (in magnitudes) on the y-axis and the date (spaced by 1-week intervals) on the x-axis. The small green box shows the realm of typical naked-eye visibility, ending around 4th magnitude for a moderately dark sky. Visibility of the nova lasts only a few days. The cell phone camera can capture around 7th magnitude, so you can image the nova for over a week if history holds. Then the brightness levels off around 10th magnitude and is in the realm of telescopic views only.

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Other Variable Stars

While CrB consumes attention, there are many other variable stars to observe--far more than can be monitored by the professionals--and each has a story to tell. Per Citizen Sky, large numbers of citizen science observations help astronomers get the precision needed for research. Modest telescopes expand the population of variable stars to observe easily through the seasons and around the earth.

In a feat of citizen science, the AAVSO facilitates one of the oldest citizen science projects in history with thousands of volunteer observers covering half the globe, Participants are especially welcome from the Middle East, Asia, and the Pacific to help close the gap in coverage. Especially as the nova T Coronae Borealis approaches outburst, now is a good time to tap into the resources available from the AAVSO.