How to Observe Variable Stars: A Beginner's Guide to Stellar Science

Variable stars change brightness over hours, days, or months — and your amateur telescope can detect those changes. Better yet, the data you collect can contribute to real scientific research. Here's how to start variable star observing.

What Are Variable Stars?

A variable star is any star whose brightness (magnitude) changes measurably. There are over 2 million known variable stars in our galaxy. The changes are caused by:

You don't need a large telescope to observe variable stars. Many are bright enough to observe with naked eye or binoculars — a 70mm+ telescope simply gives you more targets and better precision.

Why This Is One of the Most Rewarding Activities in Amateur Astronomy

Unlike observing galaxies (which look like fuzzy smudges), variable star observing has a scientific purpose. The American Association of Variable Star Observers (AAVSO) accepts observations from amateurs worldwide. Your observations fill gaps in professional research data.

Professional telescopes don't have the time to monitor 2 million stars nightly — but thousands of amateurs can. This is one of the few areas where amateur astronomers are directly advancing science.

Equipment You Need

The Comparison Star Method

You can't measure a star's exact brightness by eye, but you can compare it to nearby stars of known brightness. This is the visual observation technique used by AAVSO:

1. Download the variable star chart from AAVSO.org for your target star
2. Identify comparison stars — nearby stars with known, stable magnitudes (labeled on the chart)
3. Estimate where your variable falls between two comparison stars: "It looks like it's between A (mag 8.2) and B (mag 8.6), closer to B" → estimate 8.5
4. Record your estimate with date, time, and any notes
5. Submit to AAVSO WebObs — free registration required

Best Variable Stars to Start With

Start with Algol

Algol is the easiest variable to start with. Its brightness change is large enough to notice without comparing to charts — just look at it twice, 6 hours apart. When it's at minimum (every 2.87 days), it's noticeably dimmer than comparison star Gamma Persei.

Use the Heavens-Above Algol predictor to find the next minimum.

Recording and Submitting Observations

The AAVSO accepts observations in this format:

• Target star: Algol
• Date/time (JD): Julian Date (universal time standard)
• Magnitude estimate: 2.7
• Method: Vis (visual)
• Comparison stars used: Delta Per (3.0), Epsilon Per (2.9)
• Notes: Clear night, excellent seeing

Convert dates to Julian Date using AAVSO's JD Calculator.

What You Can Discover

Long-term variable star observing lets you:

• Build light curves — graphs of brightness vs. time that show the star's behavior
• Detect period changes — many variables slowly change their period over decades
• Catch unexpected outbursts — cataclysmic variables can brighten by 5+ magnitudes in hours
• Contribute to published research — AAVSO data is cited in peer-reviewed papers

Variable Star Observing Programs

All programs are free to join. Observations are free to submit. Your data is publicly accessible to researchers worldwide.

Getting Started Tonight

1. Create a free account at AAVSO.org
2. Download the chart for Algol (Beta Persei)
3. Check when the next Algol minimum occurs
4. Set up your Koolpte telescope and spend 30 minutes estimating Algol's brightness before and after minimum
5. Submit your first observation to AAVSO WebObs

You'll be part of one of the oldest and most scientifically productive traditions in amateur astronomy — and you'll have real data to show for it.