The Constellation Libra

For the reputation that Libra has amongst astrologists, witch doctors and fortune tellers as a fire sign, Libra is actually very faint in the night sky with no first magnitude stars.

Libra, Latin for “weighing scales” has been known since ancient times. In Mesopotamia, the Sun God of the people Shamash was the patron of truth and justice and held the scales as sacred.

In actual terms, the Sun is actually in the boundaries of Libra from the 30th of October until the 22nd of November. Please note that astrology doesn’t give an accurate dating of when the sun passes through a particular constellation. They are all varying shapes and sizes and will stay within the boundaries of some constellations longer than others.

When the sun travels along the plain of the plain of the ecliptic at the autumnal equinox, the day and night are more equal hence belief that the scales show an equality between night and day.

In real terms Libra isn’t so bright or big. It is ranked 29/88 for size and is reasonably faint. Even with my own high powered telescope it’s quite hard to look at given it’s brighter neighbours in the celestial sphere.

Alpha Librae also known as Zubenelgenubi, is a multiple star system when viewed through a telescope. The main star Alpha2 Librae, is a blue-white star of magnitude 2.7 and the secondary Alpha 1 Librae is white. Its traditional name means “the southern claw”. Beta Librae is the corresponding “northern claw” to Zubenelgenubi. The brightest star in Libra, it is a green-tinged star of magnitude 2.6, 160 light-years from Earth.

Gamma Librae is called Zubenelakrab, which means “the scorpion’s claw”, completing the suite of names referring to Libra’s archaic status. It is an orange giant 152 light-years from Earth. Given the names of the stars and their English translations, it is possible that the bordering constellation Scorpio and Libra were hard to distinguish without proper observation tools.

The most exciting thing about Libra for me are the Gliese planets. They are orbiting the star Gliese 581 and are listed as among the most likely to harbour life! So how can we tell this by looking from here? When a planet passes in front of the star we see the black dot. With the star’s colour and size we work out it’s distance. How much of the star is covered by the black dot tells us the size of the planet and how far away from the star it is.

Around Gliese 581, the planet 581d lies within its habitable zone. This means that it is at a similar distance from the star as we are from the sun meaning it could support liquid water on its surface. There is potentially one tidally locked planet around the star. That means that one side faces the star all the time in the same way our moon only has one side visible. Some believe tidally locked planets can support life although without a rotation or day and night cycles I’m not so sure personally.

There’s an open cluster within the boundaries of Libra. A globular cluster is a tightly bound collection of stars although when up close and personal the stars will actually be hundreds of billions of kilometres from one another.

Next stop Scorpio.

Jude Morrow

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