When a planet is transiting across a sun we can calculate the radius of the planet by the change in photon flux. However, I've read that limb darkening (reduced photon flux at the edges of the sun) can affect the calculation of the planet's radius. How can this be? Surely this wouldn't as you would measure the flux before the planet obscures any part of the sun then measure the flux when the planet is mid transit thus negating any effect limb darkening has on the readings. Am I missing something?

When a planet is transiting across a sun we can calculate the radius of the planet by the change in photon flux. However, I've read that limb darkening (reduced photon flux at the edges of the sun) can affect the calculation of the planet's radius. How can this be? Surely this wouldn't as you would measure the flux before the planet obscures any part of the sun then measure the flux when the planet is mid transit thus negating any effect limb darkening has on the readings. Am I missing something?

 

Not all exoplanets will be observed tracking across the centre / longest path (a diameter geometrically) - some will cross a much shorter router than is almost entirely in outskirts (a short chord geometrically).

 

When you have a short transit then limb darkening can have a much more pronounced effect

When you have a short transit then limb darkening can have a much more pronounced effect

Sorry for being silly but what effect does limb darkening have?

Sorry for being silly but what effect does limb darkening have?

 

I finally found the website I read this on when it was first published - I thought it was a deeper treatment than this but it may be some help to you

http://blog.planethunters.org/2013/01/21/what-factors-impact-transit-shape/

 

For your guidance there is a deeper problem with planetary radius estimation due to limb-darkening - but I still cannot find my sources for that and to be honest you might understand it but I couldn't really claim to. This concerns the nexessary assumptions that have to be made to account for the limb-darkening and how the figures being used (from tables) were not satisfactory.

 

By the way - this looks handy

http://astro.unl.edu/naap/esp/animations/transitSimulator.html