for Research and Education



The Thacher Observatory is a small telescope observatory located on the campus of The Thacher School in Ventura County, California, with a legacy of astronomy research that dates back to the late 1950’s. In 2016, the observatory was renovated and converted into a fully automated, research-grade facility. The low-elevation site is bordered by the Los Padres National Forest and therefore affords dark to very dark skies allowing for accurate and precise photometric observations. The education and research goals of the Thacher Observatory go hand in hand as our mission is to engage in meaningful and relevant astronomical research as a means for learning physics, astronomy, and programming while also providing a motivating force that encourages students to strive for excellence, build practical skills, engage in equitable collaboration, and hone our ability to communicate in a professional setting.



  • Location: 34° 28' 0.5'' W119° 10' 38.5''

  • Elevation: 1623' (494.7 m)

  • Telescope primary mirror diameter: 0.7m

  • Filter set: g, r, i, z, Johnson-V, [SII], [OIII], H-alpha

  • Camera: Andor iKON-L 936 BV

  • CCD: e2v back-illuminated 2048 x 2048, 13.5µm pixels

  • FOV: 20.8' x 20.8'

  • Plate Scale: 0.608''/pixel

  • Median seeing: ~2.8''

  • Sky brightness: ≤ 22 mags/sq. arcsec in V

  • Zeropoint magnitudes: 22.0 (g), 21.7 (V), 21.9 (r), 21.3 (I), 20.0 (z)



The Thacher Observatory specializes in accurate and precise photometry in the visible (470nm to 1µm) part of the spectrum. We have in-house expertise in the fields of exoplanets, low-mass stars, and planet and star formation. However, our facility is a powerful tool for all transient astronomical phenomena, and with the help of our collaborators, we have been able to make significant contributions to fields as wide-ranging as gravitational wave sources and supernovae.


Low-mass stars—often referred to as "red dwarfs" or "M-dwarfs"—comprise 75% of all stars in our Galaxy. However, not one red-dwarf is visible to the unaided eye. It is now known that low-mass stars harbor on average at least 2 planets per star, amounting to a staggering number of planets, many of which are likely habitable! Since an accurate characterization of an exoplanet depends on an accurate characterization of the host star, a large motivating factor for the study of low-mass stars is to understand the planet populations around them. Thacher Observatory measures the light variations in low-mass eclipsing stellar systems as a means of measuring the basic properties of stars. 

Image credit: Artist’s impression of Earth-sized planets orbiting a red dwarf star. Image credit: NASA, ESA, and G.Bacon (STScI).



With facilities like PanSTARRS, the Zwicky Transient Facility, and ASAS-SN, tens of thousands of supernovae are discovered every year. This places a large burden on follow-up facilities to track, characterize, and draw scientifically meaningful conclusions about these cosmic explosions. Our facility is nicely poised to respond quickly to transient events and provide long term monitoring of interesting objects.

Image credit: The brightness of Type Ia supernova SN2020hvf over the course of a few months. Unpublished data produced by Thacher's Astronomy Researchers.



Having complete control of a research-grade observatory offers the flexibility to do long-term monitoring of astronomical sources that vary in brightness over time. This program began with our work on Boyajian's Star—which continues today—and has now expanded to include other variable stars and active galactic nuclei. Our typical cadence is nightly. However, we have the capability to monitor astronomical sources on various time scales as the scientific objectives require.

Image credit: Artist's impression of one possible explanation for the chaotic changes in brightness seen toward Boyajian's Star: a swarm of comets [NASA/JPL-Caltech]



Expanding upon the Kepler and K2 missions, NASA's Transiting Exoplanet Survey Satellite (TESS) aims to create a catalog of thousands of exoplanets using the transit method, which looks for periodic dips in star brightness, suggesting the potential presence of an exoplanet. The Thacher Observatory is one of many facilities that contribute ground-based follow-up observations of specified targets to confirm true exoplanets and rule out false positives. An example of our data is shown to the right, which can be used with other information to measure the radius, mass and composition of the distant worlds.

Image credit: Brightness of the star XO-2 as a function of time in two photometric bands showing the signature dipping indicative of an exoplanet eclipsing its host star. Unpublished data produced by Thacher's Astronomy Researchers.



Studies of distance Type Ia supernova have shown that the expansion rate of the universe is accelerating. These intriguing explosions are useful standard candles as they are extraordinarily bright, relatively common, and occur in galaxies for which a recessional velocity can be observed. However, most Type Ia supernovae discovered are very far away where they are hard to characterize and understand. Thacher hopes to add scientifically valuable Type Ia supernovae to the present sample by monitoring 1300 nearby galaxies waiting for one of these explosions to occur. Catching these explosions early is key to understanding how to calibrate their intrinsic luminosities. While we have not yet been the first to discover a nearby supernova, we have detected multiple supernovae allowing us to confirm the viability of this ongoing program. Currently, the Thacher Observatory Supernova Search (TOSS) has obtained more than 14,000 images of 500 different galaxies, and we are currently working on a home-grown image recognition machine-learning algorithm to autonomously identify candidate supernovae in our data.

Image credit: One example of the automated supernova searching algorithms used by the Thacher Observatory which subtract a template image from a new image to look for residual point sources. This example shows the real detection of a new supernova.

thacher observatory logo_final_star.png


This is a complete, chronological list of refereed publications associated with the Thacher Observatory.



  • Astronomy Club Sky Viewing with Unistellar eVscope.
    Astronomy Club Sky Viewing with Unistellar eVscope.
    Thu, Mar 04
    5025 Thacher Rd
    Mar 04, 6:30 PM – 7:30 PM
    5025 Thacher Rd, 5025 Thacher Rd, Ojai, CA 93023, USA
    Meet us on the Upper Field to learn about our new eVscope, look at some deep sky objects and talk about becoming an Astronomy Ambassador, getting involved in the Astronomy Program, summer opportunities in astronomy, and more. Bring layers for warmth, and bring a headlamp that has a red light setting
  • Research Proposal Presentations
    Research Proposal Presentations
    Mon, Nov 23
    Nov 23, 2020, 1:20 PM
    The Astronomy Research students put together professional style research proposal presentations that will be used to guide the research they conduct for the rest of the year. Presentations can be viewed at these links: https://tinyurl.com/y6chks5x and https://tinyurl.com/y455oxhy
  • Sky Viewing and Astrophotography Party
    Sky Viewing and Astrophotography Party
    Fri, Oct 30
    5025 Thacher Rd
    Oct 30, 2020, 8:30 PM – 9:30 PM
    5025 Thacher Rd, 5025 Thacher Rd, Ojai, CA 93023, USA
    Explore the sky with the Observatory Heads and Dr. Swift. Activities will include sky viewing through our telescope, orienting ourselves in the cosmos, and an astrophotography workshop. Unfortunately, due to COVID, this event is only open to the Thacher community.


5025 Thacher Rd. Ojai, CA 93023