Why do we see stars? (Intermediate)

If the sun seems so small at only 8 minutes of light speed away, how is it that we are able to see stars at all that are light-years away? It seems to me that their visible size should be infinitesimally small and therefore they should be invisible.

Whether we are able to see an object or not just depends only on the amount of light that is reaching us and is independent of its size. If you cannot see an object, it just means that the amount of light coming is not enough for your eye to discern it.

It is true that the angular size of stars is extremely small and that is the reason why no telescope has ever taken a well resolved picture of a star. For us at the Earth, the atmosphere causes an angular blurring by scintillation (which is why stars twinkle) and smears their size to about 1 arcsecond (which is 1/3600 of a degree).

Even for telescopes like Hubble which is above the Earth's atmosphere, the star's angular size is too small to be resolved. But remember that each star produces a lot of light which is more than enough for the eye to discern them. Hence we see stars; However they are too small; so we see them as points and not disks (as you would with planets).

 

This page was last updated July 18, 2015.

About the Author

Jagadheep D. Pandian

Jagadheep D. Pandian

Jagadheep built a new receiver for the Arecibo radio telescope that works between 6 and 8 GHz. He studies 6.7 GHz methanol masers in our Galaxy. These masers occur at sites where massive stars are being born. He got his Ph.D from Cornell in January 2007 and was a postdoctoral fellow at the Max Planck Insitute for Radio Astronomy in Germany. After that, he worked at the Institute for Astronomy at the University of Hawaii as the Submillimeter Postdoctoral Fellow. Jagadheep is currently at the Indian Institute of Space Scence and Technology.

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