Utah Skies: Moon Meets Spica

May 25, 2021

Credit Stellarium Software

This past week the moon has moved near the planets Venus, Mercury, and Mars. Wednesday the moon’s phase will be first quarter. By the evening of Saturday and Sunday the waxing gibbous Moon will pass the brightest star in the constellation Virgo the Maiden, called Spica. 

Spica is the 16th brightest star in the sky. Spica lies at a distance of 262 light-years from Earth. That means that when you observe Spica the light from that star began its journey across space 262 years ago, so you see the star as it was 262 years ago.

When we observe Spica with our unaided eyes it appears as one star but in fact, it consists of two stars that orbit each other. The distance between these two stars is only a few million miles, much closer than the separation of the Earth from the Sun.

Both stars in the Spica system are bigger than our Sun. The larger of the two is 11 times the mass of the Sun while the smaller is 7 times the mass of the Sun. 

Because the two stars are so close to each other their gravitational pull on each other distorts their shape so they would look like two eggs.

Because of the larger size of the bigger star, its lifetime will end in a few million years as it will explode as a supernova. The smaller star will end its life by expanding its diameter then it will become a small white dwarf about the size of the Earth

You can use the moon to find Spica. On Saturday evening look south for Spica to the lower left of the waxing moon, on Sunday evening look for Spica to the lower right of the waxing moon.