A shepherd to the herdsman

With new moon occurring on June 10, the early part of the night will be dark, making it the perfect time to stargaze, writes Ian Griffin.

Ian Griffin
Ian Griffin
This week, we will explore a region of the sky often overlooked by local stargazers, simply because it never rises very far above the horizon.

The fourth-brightest star in the sky and the brightest star in the northern celestial hemisphere is Arcturus. This time of year, Arcturus is due north at 10pm, as seen from Dunedin.

Look for a bright orange star approximately 25 degrees above the horizon. Astronomers have measured the distance to Arcturus as a little over 36 light-years. The light you see when viewing the star began its journey to your eyes in 1985!

Arcturus is located in the constellation Bootes. Traditionally, this upside-down kite-shaped constellation is said to represent a herdsman, driving bears away from his flock. He is assisted by his dogs, depicted by the nearby constellation of Canes Venatici.

Unfortunately, most of Canes Venatici can not be seen from our latitude. However, if you do have an unrestricted view of the northern horizon you can at least see Cor Caroli, the constellation’s brightest star. It is roughly four degrees above the horizon at 10pm.

Incidentally, Cor Caroli got its name from King Charles II’s court physician. He said the star shone with remarkable brilliancy on the eve of the King’s return to London on May 29, 1660.

Once you have found Arcturus, scan down and to the right. You should be able to spot a very distinct downwards-pointing semicircle of stars.

This is the constellation Corona Borealis, the northern crown. It is one of the 48 constellations listed by the Greek-Egyptian astronomer Ptolemy in his second-century treatise, Almagest. It represents the coronet worn by Ariadne at her wedding to Dionysus, the god of wine.

Coma Berenices is a very indistinct constellation to the left of Arcturus. It is relatively devoid of stars because Coma Berenices is far from the plane of the milky way, but astronomers have found thousands of galaxies within its boundaries.

 

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