How much of the earth's surface area is covered by light rays at one time?

Sounds like you already understand most of what you need to do so... what is your question???

Yes, the sun is not a point source of light and, no, the earth is not a perfect sphere.

And, yes, earth's orbit is elliptical so the distance from the sun varies.

You do not seem to account for rays of sun light that reflect off the moon back onto the earth, nor the refraction of visible light but the atmosphere (the long wavelengths refract more than the short wavelength so sun rise and sunset look red. You also do not account for the "transit" of Mercury or Venus (which happened last week).

How precisely do you need your answer to be? Saying it is about half is going to be a good answer.

you does no longer stay to tell the story the dying of the solar. The Earth's ecosystem would be stripped away, and the oceans will boil away. this might take place in some 5 billion years (no longer a million.5-2 billion or 800 billion as has been stated in this thread). The Earth won't fly into interstellar area the two, because of the fact the mass of the solar in its white dwarf point will nonetheless save the Earth gravitationally guaranteed to it. we've different subject concerns to "complication" approximately previously the solar starts off to die, such because of the fact the impeding collision with the Andromeda galaxy...and the undeniable fact that we are dropping our Moon.