Regulus - Observations

Observations

Of the brightest stars in the sky, Regulus is closest to the ecliptic, and is regularly occulted by the Moon. Occultations by the planets Mercury and Venus are also possible but rare, as are occultations by asteroids. The last occultation of Regulus by a planet was on July 7, 1959, by Venus. The next will occur on October 1, 2044, also by Venus. Other planets will not occult Regulus over the next few millennia because of their node positions.

Regulus is expected to be occulted by the asteroid 163 Erigone on March 20, 2014. This event will be visible along a path about 40 miles wide from New York City to Oswego in the United States, and extending approximately northwest into Canada on a track that includes Belleville and North Bay, Ontario.

An occultation of Regulus by the asteroid 166 Rhodope was observed by 12 observers from Portugal, Spain, Italy, and Greece on 2005-10-19. Details are at http://www.euraster.net/results/2005/index.html#1019-166

Although best seen in the evening in northern hemisphere in late winter and spring, Regulus can be found at some time of night throughout the year except for about a month on either side of August 22, when the sun is too near. Regulus passes through SOHO's LASCO C3 every August. For most Earth observers, the heliacal rising of Regulus occurs in the first week of September. Every 8 years, Venus passes Regulus around the time of the star's heliacal rising, most recently in 2006.

The primary of Regulus A has about 3.5 times the Sun’s mass and is a young star of only a few hundred million years. It is spinning extremely rapidly, with a rotation period of only 15.9 hours, which causes it to have a highly oblate shape. This results in so-called gravity darkening: the photosphere at Regulus' poles is considerably hotter, and five times brighter per unit surface area, than its equatorial region. If it were rotating only 16% faster, the star's gravity would provide insufficient centripetal force to hold it together, and it would tear itself apart.