In last month’s constellation post, we talked about bears and the dragon.
In this month’s edition we will talk about ideal constellations to observe warm weather.
“Bow to Arcturus and Spike to Spica”
If you use the drawing below to find the Big Dipper (above right), you will see that the handle of the Big Dipper is curved or arched.
We can follow the arc of the handle of the Big Dipper down and to the left, towards the star Arcturus. Once there, we can “descend” to the star Spica. Arcturus is the brightest star of Boötes the Herdsman and Spica is the brightest star of Virgo the Maiden.
Let’s talk about each of these constellations, followed by the constellation Libra.
Boötes the shepherd
The original stories of this constellation originated in ancient Persia about 3,200 years ago and were passed down to the Greeks through the Egyptians.
About 2,200 years ago, a now famous work known as Ptolemy’s Almagest recorded 48 fairly well-known constellations. However, it was only about 1,100 years ago that the noted astronomer Al Sufi, working in Persia, published a book on the known fixed stars that has become the standard for many scientific naming conventions ever since.
The stories that formed the backdrop to the constellations are often varied, and even the names of the stars don’t always perfectly match the patterns we know today (they may have matched better in ancient times).
Boötes is an example of a constellation that has somewhat mixed ancestry. In some cases he is identified as Arcas, Callisto’s son (we learned this in April Eyes in the Sky).
In fact, the star Arcturus is often interpreted to mean “bear guardian” or “bear guardian.” The name “Boötes” is believed to come from the sound that Greek shepherds made when gathering their animals.
If today we wanted to reinterpret these star shapes into a new constellation, it would be easy to imagine Boötes as an ice cream cone. Arcturus forms the bottom of the cone with a star on each side to complete the mass. The remaining stars form the ice cream itself.
Arcturus is a beautiful reddish star that is located about 37 light years from us. A light year is the distance that light can travel in one year, just under 10 trillion kilometers. Therefore, Arcturus is 370 billion kilometers away (and is one of the closest stars to us!).
Arcturus is a red giant star, a star near the end of its life that has used up most of its hydrogen. Scientists believe that our sun will become a red giant as it nears the end of its life (billions of years from now). Arcturus has about the same mass as our sun, but because red giant stars have puffier atmospheres, it is about 25 times the diameter of our star.
Virgo the maiden
Spica is the brightest star of Virgo the Maiden. Like Boötes, there are several stories to explain to Virgo.
In a story of classical tradition, Virgo represents Persephone, daughter of Demeter. Demeter was the goddess of fertility responsible for the growth of all crops. Persephone was captured by her uncle, Hades, and forced to stay with him.
Demeter searched the land in vain for her missing daughter. Saddened, she neglected the crops, which withered and failed. Finally, upon discovering the whereabouts of his daughter, he demanded Persephone’s return. Hades, however, confirmed that he could not leave because he had drunk from the underworld. By agreement between them, it was agreed that Persephone would live half the year with her mother and half the year with Hades.
During the half with her daughter, Demeter is happy, the weather is good and the crops are growing. However, during the second half, Demeter misses his daughter, so the weather is bad and the crops are ruined.
Spica means “ear of corn” and the star represents the crops that Demeter looked at. It is eight times farther away than Arcturus (almost 250 light years). It is 10 times more massive than our sun and seven times its diameter.
Pound the scales
The constellation Libra represents the scales of law or justice, an interpretation that originated in the time of ancient Greece.
In reality, Libra was considered part of its neighbor to the east: Scorpio the Scorpion. As such, the stars in Libra are actually named after the “claws” of Scorpio. The northern claw is “Zubeneschamali” and the southern claw star is “Zubenelgenubi”. The middle star is “Zubenelakrab”.
For more on this month’s astronomy, visit our May Eyes on the Skies post.