Tangra 1.4


Guide to Light Curve Reduction in Tangra

(Including Step-by-Step Reduction Examples)

Doing light curve reduction in Tangra should be intuitive. However there are some special cases that may be challenging if you don't know the various reduction settings. The step-by-step examples below cover those special cases.

General recommendations for Light Curve Reduction

First of all if you are a new user of Tangra and you have used LiMove before you should know that Tangra is a lot different than LiMovie in a number of ways and there are important parts of setting up the measurement objects that do not exist in LiMovie. You should learn about those differences and use them in your advantage. It is fairly important to choose the correct Light Curve Reduction settings for your video for the success of your measurement. As of version 1.4 Tangra supports two types of measurement - Tracked Asteroidal Occultation and Untracked Measurement. Please note that Tracked Mutual Satellite Event is not supported at the moment but support will be added in future as we approach the next season of mutual events involving the satellites of Jupiter.

All light curve reductions in Tangra start with the "Light Curve Reduction" screen where you can choose the type of measurement and other settings. When you measure occultations you will want in 99% of the cases to use Tracked Asteroidal Occultation measurement. This type of measurement is suited for objects that do not have considerable motion relative to the stars but undergo small to considerable brightness variation.

On the Light Curve Reduction screen you should also provide any additional information using the check boxes under the measurement type radio buttons. Here "Field rotation" happens to Alt-Azimuth mounted telescopes. It is a good idea to try and memorize the flags so you can immediately tell whether one of them applies to your next video measurement. For example if you know that there is "Wind, shaking or movement" flag and you do notice wind in your video you would immediately correlate to Tangra this and would not forget to use the flag.

Once you have got the reduction flags to correctly indicate the situation in your video the next important step is to provide sufficient number of good quality guiding stars. As a general rule you should always try to use 2 or 3 guiding stars whenever possible. If you need to measure one comparison star that is fainter then you can use 2 guiding stars and 1 comparison star. If you don't need a comparison star (in many cases you don't) or if all guiding stars are not particularly bright then use 3 guiding stars. Remember that guiding stars are also measured and can be used for comparison. Comparison stars on the other hand cannot be used to improve the tracking.

Setting up the measurement objects and doing the measurement should be intuitive if you know these facts: