NASA/courtesy of
NASA/courtesy of

What's Up in Space

This Weekend’s Night Sky (31 January – 1 February 2015)

Mars and Venus remain low on the western horizon after dark, with bright golden Jupiter rising in the north east just as the Sun sets. As we’re heading towards a full moon on the 4th of February, the Moon will already be bright in our sky at the beginning of darkness this weekend, so it’s a good time to concentrate on some of the brighter constellations in the sky.

By far the most impressive at this time of year is the wonderful Orion, currently at its highest in the north in our evening skies. The three bright stars across the middle, Alnitak, Alnilam and Mintaka, form Orion’s belt, although here in New Zealand we often see this as part of “the pot” with the three fainter stars above forming the handle. To Māori they are known as Tautoru, part of Te Manu Rore, the Bird Snare. Each of these three stars is tens or even hundreds of thousands of times more luminous than our own Sun. Mintaka is actually a complex multiple star system.

Although designated as Beta Orionis, the brightest star in the constellation is Rigel, to the top left of the belt as seen from New Zealand. Rigel is in fact a triple star system. The primary, Rigel A, is a massive blue-white supergiant 120000 times as luminous as the Sun. From Earth we see it at magnitude 0.13, making it normally the sixth brightest star in our night sky. The secondary component Rigel B is a spectroscopic binary and should be resolvable from Rigel A even in a small telescope.

In the opposite corner, to the bottom right of the constellation, is Betelgeuse, the second brightest star in Orion. Designated as Alpha Orionis, Betelgeuse is a semi-regular variable red supergiant star that is so large that if it were placed at the centre of the Solar System it would reach out almost as far as the orbit of Jupiter.

Betelgeuse is a star that’s coming to the end of its life and has bloated out and cooled down as it runs out of fuel to burn. One day soon it is likely to end its life in a massive explosion called a supernova, which may be so bright we see it in the day time. Of course soon to astronomers could be a million years, so don’t hold your breath, but with any luck it might go bang within our lifetimes.

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