I have a homework problem that I am having troubles with. There are 2 parts(adsbygoogle = window.adsbygoogle || []).push({});

A transiting exoplanet with a diameter twice that of the Earth orbits a sun-like star in a circular orbit of radius 1.5 AU

a) How much reduction in the flux of the star occurs during the transit?

Earth's diameter=Planet's radius (R_{p}) =8.5175×10^{-5}AU

And because it says a "sun-like" star, I used the same values as the sun for radius

Star's radius (R_{s}) =4.649×10^{-3}AU

And I can use the formula [itex]\frac{ΔF}{F}[/itex]=[itex]\frac{R^{2}_{p}}{R^{2}_{s}}[/itex]

By plugging in the values, i got 0.03% reduction in flux

b) How long do you expect the transit to last?

I am stuck on this one. I was not told the impact parameter b so do I assume that the transit happens through the centre?

or do I use the formula τ=[itex]\frac{2(Rp+Rs)}{V}[/itex]

where τ= transit duration, Rp=diameter of planet, Rs=diameter of star, V=velocity

Any help is appreciated, thanks in advance!

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# How long do you expect transit to last?

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