Double Flee A

At a distance of 216 trillion miles, the light of Arcturus is spread out over a sphere with an area of 586,000,000,000,000,000,000,000,000,000 square miles. The Earth has a cross-sectional area of about 50 million square miles. So the fraction of Arcturus' light that falls upon the Earth is about 1 part out of 10 sextillions. That's 1 followed by 22 zeros.

Of the starlight that falls on Earth, an even tinier fraction enters the pupil of my eye to form an image of the star. Another calculation: How does the area of my pupil compare to the cross-sectional area of the Earth? I'll spare you the details. Click, click, click on the calculator. Another factor of 10,000,000,000,000,000,000, more or less.

So the fraction of Arcturus' light that enters my eye is one part out of 100,000,000,000,000,000,000,000,000,000,000,000,000,000.

posted by dale @ 12:32 AM