Is the sun shrinking 200 miles/year?

Hmmm..lets do some math!

The solar radius is 441,000 miles and it is at a distance of 93 million miles. It subtends an angle of 30 arc minutes at this distance, so 200 miles is an angular change per year of 30minutes x 60 seconds/minute x 200/441,000 = 0.8 arcseconds/year. If this has been going on for the last 50 years, this would have changed the angular diameter of the sun by 40 arcseconds or a little under 3 percent of its apparent size. A change that is 100 times smaller than this (0.4 arcseconds) in that amount of time would have gotten the attention of astronomers a LONG time ago.

There is no evidence that the size of the sun has changed appreciably over the last 100 million years, because the amount of heat the sun produces at the earth depends on the second power of the solar diameter, all other factors being equal, so a little change on the sun would throw the earth into a global heat wave or ice age.


Return to the Ask the Space Scientist main page.

All answers are provided by Dr. Sten Odenwald (Raytheon STX) for the
NASA IMAGE/POETRY project.