As one of the AAVSO’s four primary observational programs, exoplanet photometry involves recording photometric time series of host stars as their exoplanets transit across their surface. The resulting light curves reveal information about the exoplanets’ orbital and physical parameters.
Exoplanets are difficult to observe, but this means that observations of them are especially valuable to researchers. Transits last for hours, and their timing is often considerably uncertain, which makes it difficult for professional astronomers to obtain enough telescope time to follow up on discoveries without help from citizen scientists. AAVSO observers use their telescopes to watch for transits, fueling the field of exoplanet science with critical data.
Exoplanet photometry is one of the most direct ways that you can use your telescope to contribute to science. If you are interested in becoming an exoplanet observer, read on.
Guidelines
You can contribute to exoplanet science with the AAVSO by producing light curves of exoplanet transits and submitting those to the AAVSO Exoplanet Database (AED). There are several ways to obtain data for these light curves—you might use your own equipment, remote telescopes, or even archival imagery—but no matter how you collect the data, the final product will be a transit light curve uploaded to the AED.
The level of precision required to detect most exoplanets is greater than that required to observe variable stars. For this reason, exoplanet photometry has a steeper learning curve than stellar photometry. If you are unfamiliar with photometry in general, we recommend that you practice observing stars before attempting to observe exoplanets.
Equipment
Exoplanet photometry is a precise form of astrophotography which requires equipment similar to that used for deep-sky imaging. Two factors are especially important when choosing equipment:
- Aperture. Most transiting exoplanets have transit depths of only a few millimagnitudes, and transit in a matter of hours, which means that you won’t be able to use especially long integration times to overcome a poor signal to noise ratio. For this reason, large apertures are preferred, with most exoplanet observers using telescopes of 8” aperture or larger.
- Autoguiding. You can increase your photometric precision by freezing the position of the target on the sensor, so that its light always falls on the same few pixels. This optimization is necessary to observe exoplanets, and requires autoguiding.
If you don’t have access to this kind of equipment, you can still contribute by volunteering to analyze data provided by the Exoplanet Watch project. (See the section “Exoplanet Watch” below for details.) You may also want to consider becoming an AAVSO member. AAVSO members can also submit proposals to observe exoplanet transits using our global remote telescope network, AAVSOnet, which is optimized to provide high-quality photometric data in a variety of filters.
Data quality
When observing exoplanets, minimizing systematics is of critical importance. The idea is to eliminate every outside factor which might conceivably influence the photometric magnitude of a star, leaving only the signal from the exoplanet (and the stellar variability, if present).
The subject of how to do this is complex, but we can present a few guiding principles. Ideally, each star should remain completely stationary on the sensor throughout the entire observation. The telescope should be well tuned with regards to polar alignment, tracking, autoguiding, and collimation. Images should be carefully calibrated with flat frames, dark frames, and bias frames.
In addition to following standard best practices for differential photometry in general, we request that all exoplanet observers strive to:
- Start your observation at least 30 minutes before the transit begins, and continue for as long after the transit ends. Transit timings are often uncertain, so the longer you observe the more likely you are to capture the entire transit.
- Take a new set of flat frames for every observation.
- Use a monochrome camera and standard photometric filters.
- Aim for a FWHM of 3–5 pixels.
For more detailed guidelines, please refer to the manual A Practical Guide to Exoplanet Observing.
Major collaborations
To increase the scientific impact of our exoplanet photometry, the AAVSO maintains partnerships with multiple research collaborations.
Exoplanet Watch
In 2021, the AAVSO partnered with NASA on itsto launch the Exoplanet Watch program. Exoplanet Watch offers a way for anyone to contribute to the study of exoplanets by observing and analyzing transit light curves.
We encourage you to contribute by producing transit light curves and uploading them to the AAVSO Exoplanet Database (AED), where they are automatically shared with the Exoplanet Watch scientists. You can record the data for your transit light curves yourself, or you can use remote telescopes; Exoplanet Watch can help you get access. We also need volunteers to analyze archival data, which you can do by ‘checking out’ images from the project’s website.
To learn more, please visit the Exoplanet Watch website. You may also be interested in the 2025 Exoplanet Watch webinar, which was presented to the AAVSO community by Rob Zellem, Principle Investigator of Exoplanet Watch.
TESS Follow-up Observing Program
The AAVSO supports the Transiting Exoplanet Survey Satellite (TESS) space telescope by contributing to the TESS Follow-up Observing Program (TFOP), an international collaboration of astronomers working to confirm exoplanets discovered by TESS and determine their physical parameters. TFOP’s Seeing-Limited Photometry subgroup (SG1) specifically relies on photometric time series from ground-based telescopes, including those operated by AAVSO observers.
Similar to Exoplanet Watch, TFOP SG1 collects exoplanet transit light curves, but with more formal coordination and an emphasis on specific targets of scientific interest, making this an ideal program for an experienced exoplanet observer.
To learn more, please review the document “AAVSO Support of the TESS Follow-up Observing Program”. You may also be interested in the 2025 TFOP SG1 webinar, which was presented to the AAVSO community by Karen Collins, Chair of TFOP SG1.
Interested observers are encouraged to join TFOP SG1 through the AAVSO’s working group. Please contact the AAVSO Exoplanet Special Interest Group to apply.
AAVSO Exoplanet Database
We maintain the AAVSO Exoplanet Database (AED), a global repository containing observations of exoplanet transits. Since its launch in 2018, the AED has grown exponentially, with many thousands of new transit light curves uploaded each year.
The AED’s documentation describes the file format and upload process.
Exoplanet Special Interest Group
The AAVSO’s Exoplanet Special Interest Group (SIG) coordinates exoplanet observers across the globe, overseeing contributions to the AED as well as our joint collaborations. Joining the Exoplanet SIG is an excellent way to network with other observers, get answers to your exoplanet-related questions, and learn how to maximize your research impact.
SIGs exist for complimentary areas of interest, as well. To browse the full list of SIGs, see Special Interest Groups.
Learn more
The AAVSO offers a wide range of educational materials to support observers interested in exoplanet photometry.
Further reading
A Practical Guide to Exoplanet Observing, authored by Dennis Conti (leader of the AAVSO Exoplanet SIG), offers a thorough manual for the exoplanet observer. A Practical Guide details all stages of exoplanet observing, including:
- Target selection
- Equipment considerations
- Best practices for data quality
- Tutorials for recording and processing data
The Guide’s usefulness cannot be overstated, and it is highly recommended reading for all exoplanet observers.
Meanwhile, the following press releases provide more information about the AED, the Exoplanet Watch AAVSO–NASA partnership, and the scientific value of exoplanet observations contributed by AAVSO observers:
- (2018) “AAVSO to archive amateur astronomer exoplanet data”
- (2021) “Join Exoplanet Exploration: Citizens Help NASA Observe Other Worlds with Exoplanet Watch!”
- (2023) “AAVSO Exoplanet Database Supports NASA’s Exoplanet Watch Program”
Courses
We periodically host courses on the subject of exoplanet observing as a part of our online CHOICE course program. These online courses are a great way for new observers to increase their understanding of methods in exoplanet photometry.
Visit the CHOICE course page to view the schedule. Each course accepts only a limited number of students, so we recommend registering early.
Webinars
During our interactive webinar series, we often discuss exoplanet photometry. Because each webinar is recorded and uploaded to our YouTube channel, we have over time built up a free library of information-rich lectures.
Exoplanet observers may find the following lectures to be of particular interest:
- Introduction to Exoplanet Observing
- Using AAVSO’s Exoplanet Database for Reporting and Retrieving Exoplanet Observations
Also worth highlighting are a pair of lectures presented by Rob Zellem (Principle Investigator of Exoplanet Watch) and Karen Collins (Chair of TFOP SG1). If you are considering joining Exoplanet Watch or TFOP SG1, we highly recommend watching these related lectures: