Tonight – March 31, 2015 – can you find the star that’s shining close to the big and bright waxing gibbous moon? That’s Regulus, the brightest star in the constellation Leo the Lion. In sky lore, Regulus is considered to be the Lion’s Heart. Regulus is also the only first-magnitude star to sit almost exactly on the ecliptic – the Earth’s orbital plane projected outward onto the sphere of stars. We often show the ecliptic on our sky charts, because the moon and planets are always found on it, or near it.
Don’t mistake the planet Jupiter, that much brighter starlike object in the moon’s vicinity, for Regulus. Although Regulus ranks as a first-magnitude star, it pales next to Jupiter, the fourth-brightest celestial object to adorn the heavens, after the sun, moon and Venus. (Venus is seen in the west after sunset.) In fact, Jupiter shines about 30 times more brightly than Regulus does.
Use the moon to find Regulus tonight. Then you can refer to the “pointer stars” of the Big Dipper to locate Regulus on any night. The two outer stars making up the bowl of the Big Dipper point northward to Polaris, the North Star, and southward to the constellation Leo and its brightest star, Regulus. See illustration at left.
Regulus and three other 1st-magnitude stars reside close enough to the ecliptic to be occulted – covered over – by the moon on occasion: Regulus, Spica, Antares, and Aldebaran. In fact, the last lunar occultation of Regulus happened on May 12, 2008, and the next one will be on December 18, 2016.
Lunar occultations of bright stars are not terribly uncommon. A series of monthly occultations of Aldebaran began on January 29, 2015, and will end on September 3, 2018. Then Regulus will present a series of monthly occultations from December 18, 2016 to April 24, 2018, followed by a series of Antares’ occultations from August 25, 2023 to August 27, 2028.
An occultation of a first-magnitude star by a planet is extremely rare. The last time a planet occulted a first-magnitude star was when Venus occulted Regulus on July 7, 1959. The next time will be when Venus occults Regulus on October 1, 2044.
Before 1959, the most recent planet/first-magnitude star occultation took place on November 10, 1783, when Venus occulted Spica. Venus will again occult Spica on September 2, 2197.
Bottom line: Tonight – March 31, 2015 – the moon shines close to Leo’s brightest star, Regulus, the only 1st-magnitude star to sit almost exactly on the ecliptic.