TrES1 Transit – 2010 July 15, by Paul Rix

One of the benefits of being married to another amateur astronomer is sharing the love of astronomy through various aspects, which in turn, expands our overall enjoyment. Through sharing his images and what he’s researched, it opens up whole new areas of the hobby that I might not have experienced.  Such is the case in his report below. What a fascinating endeavor and quite an accomplishment! ~ E. Rix

TrES1 Transit – 2010 July 15, by Paul Rix

For many years Astronomers theorized that stars other than our own Sun should have their own solar systems (after all, there is nothing particularly unusual about our own star). It wasn’t until the mid 1990’s that advances in technology finally allowed this to be confirmed. Since then over 450 extrasolar planets have been discovered, with more being added to the long list almost on a weekly basis.

One method of detecting an extrasolar planet is to measure the luminosity of a star before, during and after a ‘transit’. This is where the planet crosses the face of the star (when seen from here on Earth). The planet will block out a small amount of the star’s light, causing it to slightly dim. This dip in brightness can be measured. For this to work the planet’s orbit around its star has to be almost exactly edge on to us. As you can imagine, the chances of that happening are rather slim. Despite the odds, over 80 transiting extrasolar planets have been discovered so far.

Over the past few years, the equipment available to Amateur Astronomers has advanced incredibly, especially in the field of astro-photography. Affordable, purpose built CCD camera’s are now standard equipment for many amateurs. These cameras are sensitive enough to detect the slight reduction in brightness of a star as an extrasolar planet crosses in front of it.

A few months ago I set myself the goal of detecting an extrasolar planet by the end of this year. On 14th /15th July (Wednesday night /Thursday morning) I managed to detect a transit of the planet named TrES-1 that orbits a star in the constellation Lyra. TrES-1 is a gas giant similar in size to Jupiter. Unlike Jupiter, TrES-1’s orbit is very close to its star (closer than Mercury orbits the Sun). The planet completes an orbit every 3.03 days.

To find out the timings for known transits, I looked at the Exoplanet Transit Database website. This site is a great resource that gives you all the information you need to know : Timing, Right Ascension and Declination co-ordinates, how much the star is anticipated to dim and even a photo of the star field showing the target star. Once I had everything set up, I let the camera run from 90 minutes before the predicted transit until about 45 minutes after it was due to be complete (I had to cut the session a little shorter than planned).

The hard work came the next day when it was time to process and plot the data as a graph, which is known as a Light Curve. I used a freeware program called Iris to measure the intensity of the target star in each of the 367 frames and compared the values with those of two nearby ‘comparison’ stars. As I worked through the images, it slowly became apparent that the target star had dimmed ever so slightly at the predicted time and then picked back up again. That was exciting to see but the best moment came after transferring the brightness values into a graphing program and seeing my first Light Curve with a noticeable dip in the middle.

TrES1 transit 20100715

Image showing the star involved with the transit.

The equipment I used to detect this transit was a Meade 10inch LX200 Classic SCT, F3.3 Focal Reducer, Meade DSI III Pro CCD camera and a Photometric ‘R’ band filter. For processing I used a program called IRIS (, the Open Office spreadsheet ( and Graph (

In future I will use a program that will automate the processing which will save a lot of time and work.

This has been a fascinating project for me, which marks my first steps in Photometry and doing science with a telescope. There is much for me to learn and I am looking forward to improving my skills and knowledge with this side of amateur astronomy.


~ by Erika Rix on July 23, 2010.

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