Just after 2am on the morning of March 20th, asteroid Erigone will block the light from Regulus, the brightest star in the constellation Leo. Stargazers located in the path of asteroid Erigone’s shadow (see map) will see Regulus ‘disappear’ for several seconds. This type of event is called an occultation, from the Latin word ‘hide’.
The asteroid is about 50 miles in diameter and over 100 million miles from Earth. Regulus is three times larger than our Sun and 80 light years distant. It is amazing that a small asteroid can block the light from a star that is over 2 million miles in diameter. It demonstrates just how far stars are from us that their light can be blocked by an object half the size of Connecticut.
Regulus will be in the southwest sky halfway between the horizon and zenith at the time of the occultation. Regulus is a bright star, so a telescope is not needed to witness this event. Just locate Regulus in the constellation Leo (see sky chart) BEFORE 2:06am on March 20th. That is the predicted time Regulus will disappear for this area. To be sure you will not miss it, start watching at 2am sharp to allow for any prediction errors, and then wait for Regulus to ‘wink out’.
Regulus will disappear for about 11 seconds and then reappear. While not visually stunning, much can be learned from an occultation. For example, asteroid Erigone could have a smaller companion asteroid. It is thought 15% of asteroids have companions, and if we see Regulus disappear twice, then Erigone would join a growing list of asteroids that do.
You will not be able to see asteroid Erigone directly because it is too faint. But if the sky is clear, you will see a celestial version of David and Goliath as feeble Erigone briefly blocks the light from mighty Regulus.
Starry Nights!