Exoplanet TrES-3b, transit observation: 24 June 2025

We recently observed the transit of the extrasolar planet TrES-3b, while fine tuning our telescopes for this kind of observation. The result is below.

Exoplanet TrES-3b: the 24 June 2025 transit.

The light curve above comes from a set of unfiltered images, each exposed for 30 seconds, remotely taken with the Celestron C14+Paramount ME+SBIG ST10-XME robotic unit available as part of the Virtual Telescope Project in Manciano, Italy. Each image was carefully calibrated, then processed to extract the photometric information, eventually plotted to create the graph.

The observed exoplanet is TrES-3b, a hot Jupiter orbiting its host star with breathtaking speed. Its official name is Umbäässa. The resulting light curve is a textbook example of planetary transit: a sharp, symmetric dip in brightness as the planet briefly eclipses a tiny portion of its sun.

TrES-3b is a remarkable world. Located about 1300 light-years from Earth in the constellation Hercules, it’s roughly the size of Jupiter and twice its mass. With a “year” (orbital period) of just 1.3 days, it is one of the shortest-period gas giants known. This extreme proximity to its star gives us frequent chances to observe its transits from Earth.

Thanks to the sensitive instrumentation of the Virtual Telescope and careful data reduction, we were able to trace the full transit event in detail. The ingress and egress phases are clearly defined, with the light curve dropping by about 2.5%, consistent with the planet’s size and orbital parameters. The timing of the event also aligned perfectly with the ephemerides, confirming the planet’s stable orbit.

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