The Moon has a giant companion at dawn the next couple of days. Make that two giants. The star Antares is close to the lower left of the Moon tomorrow, and about the same distance to the upper right of the Moon on Monday.
About half way between those appearances, the Moon will pass directly between Earth and Antares. As seen from much of Asia, the scorpion’s brightest star will disappear behind the Moon.
Such a disappearing act is known as an occultation. And over the past couple of centuries, occultations helped astronomers learn a lot about Antares.
During one in 1819, for example, one astronomer saw that the light from Antares faded in steps — one drop, followed a few seconds later by a second one. That showed that Antares consists of two stars.
Precise timing of how long it takes the two stars to vanish and reappear reveals the apparent sizes of both stars. Astronomers combine that with measurements of the system’s distance — about 550 light-years. That allows them to calculate the true sizes of the stars. The smaller star is more than four million miles in diameter — more than 1600 times the diameter of the Moon. And the main star is almost 600 million miles across — roughly 270 thousand times the width of the Moon.
The Moon will occult Antares every month this year. That’ll give astronomers chances to learn even more about this pair of giant stars.
Script by Damond Benningfield