A triple junction in the Sky

D'oh! I started this entry two weeks ago, since it's such a fabulous image, of Regulus and Leo I, but never finished the entry and of course APOD covers it today.



I called the entry "A Triple Junction in the Sky" because of three distance scales that converge at this place in the sky. Leo I, being a (barely) extragalactic source, is that of all things outside of our own galaxy. It's not the farthest thing in the image; there are many angularly small galaxies that are quite a distance aways. The second scale is stellar: Regulus shines at 75 light-years away. One of the four Royal Stars of Persia, it quarters the sky with Aldebaran, Antares, and Fomalhaut.
The third scale, not visible in the image, is the the planetary scale. Regulus lies nearly on the ecliptic, the plane of the solar system, and the moon frequently occults Regulus. In fact other planetary objects can occult Regulus: the asteroid Rhodope covered it for a few seconds in Europe in 2005. Astronomers can use these occultations to measure the sizes of asteroids.

Be sure to see the large-sized image.
Image copyright: © 2005 Russell Croman, www.rc-astro.com