Boötes - the Herdsman

Boötes - the Herdsman
Boötes and Corona Borealis

Boötes (pronounced boh-oh-teez) is one of the oldest constellations in the sky. When Homer mentioned it in The Odyssey three thousand years ago, its stars already formed a Babylonian constellation. Babylon, a Middle Eastern civilization with a well-developed astronomical tradition, flourished from about 1800 BCE for over a thousand years.

How to find Boötes and Corona Borealis
The constellation is easy to find. First look for the Big Dipper (known as the Plough in the UK), which is one of the best known star patterns in the sky. Then follow the curved handle of the dipper around to the next bright star, which is Arcturus. The skywatcher's memory aid is “arc to Arcturus”.

Arcturus (alpha Boötis) is the 4th brightest star in the sky, a red giant with a diameter 25 times that of the Sun. It's a yellowish color like spring flowers, and when Arcturus appears, spring isn't far behind. At 37 light years distance, it's a near neighbor in galactic terms.

Once you've found Arcturus, in a fairly dark sky you should be able to see the rest of Boötes. In the past, Boötes may have been envisaged as a person, but as you can see in the header image, it looks very much like a kite to modern eyes. Arcturus is right where the kite is attached to the tail.

You may also be able to spot a horseshoe of stars alongside Boötes. That's the attractive little constellation called Corona Borealis (Northern Crown). One of its ancient names, Ariadne's Crown, is part of the myth of of Theseus, Ariadne and the Minotaur. Their story is related in The Starry Crowns – Corona Borealis to which there's a link at the bottom of this article.

The Herdsman
Ancient constellations collect many stories over their long lives. One of the earliest descriptions of Boötes simply has him as a herdsman driving a bear around the sky. The bear, of course, is Ursa Major (Great Bear) which the constellation Boötes follows around the North Pole. In the seventeenth century, astronomer Johannes Hevelius gave the herdsman two dogs, represented by the constellation Canes Venatici, as shown in his star atlas.

One of the later tales is of Zeus and his seduction of the nymph Callisto, which produced a son named Arcas. Poor Callisto ended up being turned into a bear, in some versions by Zeus's jealous wife Hera, in others by Zeus to hide Callisto from Hera, and in yet another version by the goddess Artemis to whom Callisto had sworn chastity. In later life Arcas met Callisto the bear in the forest and, of course, not realizing it was his mother was ready to slay her. Zeus rushed in to prevent this tragedy by flinging them both into the sky where Callisto became Ursa Major and Arcas became Boötes.

Quadrantid shower
Soon after New Year's Day, the section of the sky where we see Boötes is the radiant (the apparent source) of the annual Quadrantid meteor shower.

Since meteor showers are named for the radiant of the shower, this one ought to be called the Boötids. However, when the shower was first observed early in the nineteenth century, the radiant was in the constellation of the Mural Quadrant, named for an old astronomical instrument. The radiant hasn't moved, but the Mural Quadrant wasn't included in the 88 constellations officially agreed by the International Astronomical Union (IAU) in 1922.

Boötes does have several meteor showers of its own, but they tend to be minor ones, only producing a good show at rare intervals.

Stars and exoplanets
As of March 2019, ten stars in Boötes are known to have exoplanets.

One of them, Tau Boötis, is somewhat larger and hotter than the Sun. A hot Jupiter orbits it every 3 days 7.5 hours. (A hot Jupiter is a gas giant that orbits close to its star.) It was one of the first exoplanets ever discovered, and represents a type of planet not present in the Solar System. In 2014 a team of astronomers were able to detect the presence of water in the planet's atmosphere which will aid in understanding how these planets evolve.

All of the other ten known planets are also as massive as – or more massive than – Jupiter. In fact, WASP-14b is one of the most massive transiting exoplanets observed to date. But one of these gas giants, HD 136418 b, orbits in the habitable zone of its star. The habitable zone is the area around a star in which liquid water could exist. Although we wouldn't expect a gas giant to harbor life, it could have a habitable rocky moon.

Galaxies, black holes, and the Void
Boötes contains a large region full of galaxies so far away that light takes from 6-11 billion years to get here. This means we're looking back in time when we see these thousand galaxies with their supermassive black holes, some with the mass of billions of Suns. Since there's evidence that most galaxies have a supermassive black hole at the center – including ours – these galaxies have been a great help in understanding how galaxies form and evolve.

Yet perhaps the most surprising thing found in Boötes wasn't a thousand galaxies and their black holes. The really amazing find was nothing. The Boötes Void was discovered in 1981 – an area 350 million light years across, apparently containing no galaxies. Since the original observation, some galaxies have been discovered. However the region is greatly underpopulated compared to other areas of space. There are theories, but its emptiness remains a mystery.

You Should Also Read:
Arcturus - the Bear Guardian
Absolute Beginners - Spring Skies
The Starry Crowns - Corona Borealis

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