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The Evening Sky in Feburary 2013 - what you can see.


Notes by Alan Gilmore, University of Canterbury's Mt John Observatory, www.canterbury.ac.nz


The Evening Sky in February 2013

Feburary evening
          sky

Chart produced by Guide 8 software; www.projectpluto.com.


Jupiter is the 'evening star', appearing in the northwest soon after sunset. North of the zenith is Sirius, the brightest true star. South of overhead is Canopus, the second brightest star.

Jupiter shines with a steady golden light. A telescope will easily show the four bright moons first seen by Galileo in 1610. Binoculars, steadily held, often show one or two. Jupiter is 720 million km from us now. The planet is 11 times Earth's diameter and 320 times Earth's mass. The moon appears close to Jupiter on the 18th. Jupiter sets in the northwest after midnight.

Sirius, 'the Dog Star', marks the head of Canis Major the big dog. A group of stars above and right of it make the dog's hindquarters and tail. Procyon, in the northeast below Sirius, marks the smaller of the two dogs that follow Orion the hunter across the sky. Sirius is eight light years* away.

Midway between Sirius and Jupiter are Rigel and Betelgeuse, the brightest stars in Orion. Between them is a line of three stars: Orion's belt. To southern hemisphere star watchers, the line of three makes the bottom of 'The Pot'. The handle of "The Pot" is Orion's sword. It has the Orion Nebula at its centre; a glowing gas cloud many light-years across and around 1300 light years away.

Just above Jupiter is a V-shaped pattern of stars making the face of Taurus the bull. The V-shaped group is called the Hyades cluster. It is 130 light years away. Orange Aldebaran, Arabic for 'the eye of the bull', is not a member of the cluster but merely on the line of sight, half the cluster's distance from us.

Below and left of Jupiter is the Pleiades or Matariki star cluster, also known as the Seven Sisters and Subaru. Six stars are seen by most eyes. Dozens are visible in binoculars. The cluster is 400 light years from us. Its stars formed around 100 million years ago. From northern New Zealand the bright star Capella is on the north skyline. It is the sixth brightest star in the sky.

Crux, the Southern Cross, is in the southeast. Below it are Beta and Alpha Centauri, often called 'The Pointers'. Alpha Centauri is the closest naked-eye star, 4.3 light years away. Beta Centauri, like most of the stars in Crux, is a blue-giant star hundreds of light years away. Canopus is also a very luminous distant star; 13 000 times brighter than the sun and 300 light years away.

The Milky Way is brightest in the southeast toward Crux. It can be traced up the sky, fading where it is nearly overhead. It becomes very faint east or right of Orion. The Milky Way is our edgewise view of the galaxy, the pancake of billions of stars of which the sun is just one.

The Clouds of Magellan, LMC and SMC are high in the south sky, easily seen by eye on a dark moonless night. They are two small galaxies about 160 000 and 200 000 light years away.

Mercury might be seen very low in the western sky soon after sunset. It is 150 million km away, mid month, and tiny in a telescope.

Saturn (not shown) rises in the east around before 1 a.m. at the beginning of the month. It is up at 11 pm by the end of February. It is below and right of Spica, a star a little fainter than Saturn. Saturn is 1420 million km away mid month. It is always worth a look in a telescope. The moon is near Saturn on the morning of February 4th.

Venus is low in the dawn twilight, rising less than an hour before the sun. It is on the far side of the sun from us; around 250 million km away. It will be hidden behind the sun from March till around May then begin to appear low in the western evening sky.

*A light year (l.y.)is the distance that light travels in one year: nearly 10 million million km or 1013 km. Sunlight takes eight minutes to get here; moonlight about one second. Sunlight reaches Neptune, the outermost major planet, in four hours. It takes four years to reach the nearest star, Alpha Centauri.



Jupiter is the brightest 'star' in the sky, midway down in the northwest. Sirius is the brightest true star, northeast of the zenith. Between them is the bright constellation of Orion the Hunter marked by bluish Rigel and orange Betelgeuse with the well-known 'pot' or 'saucepan' pattern between them. Above Jupiter is the V-shaped pattern of stars making the face of Taurus the Bull. He is upside down in our southern hemisphere view. Orange Aldebaran, just above Jupiter is one of Taurus's eyes. Left of Jupiter and lower is the Pleiades or Matariki star cluster.

Low in the northeast are Castor and Pollux marking the heads of Gemini the Twins. Right of the Twins is the Praesepe star cluster making the shell of Cancer the Crab.

The Hyades cluster, above Jupiter, is 150 light years away. Its brightest stars (not Aldebaran!) are about 70 times brighter than the sun. Aldebaran is not a member of the cluster but simply on the line of sight. It is 65 l.y. away and 150 times brighter than the sun. Aldebaran is a giant star about 25 times bigger than the sun though only five times heavier. Its orange colour is due to its temperature, around 3500o C. The sun is 5500o C. Aldebaran is Arabic for "the eye of the bull".

Orion, in the northern hemisphere view, has a shield raised toward Taurus and a club ready for action. The line of three stars makes Orion's Belt. The line of faint stars above the belt form Orion's Sword in the northern view, hanging from his belt. To most southern hemisphere sky watchers the belt and sword form The Pot, or the Saucepan. Rigel is a blue 'supergiant' star around 40 000 times brighter than the sun and 800 l.y. away. Its surface temperature is around 20 000oC, giving it a bluish colour. Betelgeuse is a red giant star 250 times bigger than the sun -- wider than earth's orbit! -- but only around 20 times heavier. It is mostly very thin gas surrounding a hot dense core. It is 10 000 times brighter than the sun, about 400 l.y. away, and has a surface temperature around 3000oC.

Sirius is the brightest star because it is 22 times brighter than the sun and relatively a close 8.6 l.y. away. Sirius was often called 'the dog star' being the brightest star in Canis Major, one of the two dogs that follow Orion across the sky.

Seen in a dark sky the Praesepe cluster is a pale spot of light the size of the full moon. It is also known as the Beehive. Binoculars show how it got that name: dozens of stars cluster like bees around a hive. The cluster is some 500 light years from us and about 700 million years old.


Interesting Objects in the Southern Sky

Large & Small Clouds of Magellan (LMC & SMC) appear as two luminous patches, easily seen by eye in a dark sky. They are two galaxies like the Milky Way but much smaller. Each is made of billions of stars. The Large Cloud contains many clusters of young luminous stars seen as patches of light in binoculars and telescopes. The Large Cloud is about 160 000 light years away, the Small Cloud 200 000 l.y; away very close by for galaxies. (1 light year is about 10 000 billion km, or 1013 km.)

Canopus is the second brightest star. It is 13 000 times brighter than the sun and 300 light years away. Sirius, north of Canopus on autumn evenings, is the brightest star in the sky.

Alpha Centauri, the brighter Pointer, is the closest naked-eye star, 4.3 light-years away. Alpha Centauri is a binary star: two stars about the same size as the sun orbiting around each other in 80 years. A telescope that magnifies 50x splits the pair. (A very faint and slightly closer star, Proxima Centauri, orbits a quarter of a light-year, or 15 000 Sun-earth distances, from the Alpha pair.)

Coalsack nebula is a cloud of dust and gas about 600 light years away, dimming the more distant stars in the Milky Way. Many similar ‘dark nebulae’ can be seen, appearing as slots and holes in the Milky Way. These clouds of dust and gas eventually coalesce into clusters of stars.

The Jewel Box is a compact cluster of young luminous stars about 7000 light years away. The cluster formed less than 10 million years ago. To the eye it looks like a faint star.

The Southern Pleiades is a newish name for a cluster of stars at one point of the 'Diamond Cross'. It is formally the Theta Carinae cluster, after its brightest star but is also known as the 'Five of Diamonds' cluster, the reason obvious when it is seen in a telescope. It is much fainter and smaller than the real Pleiades in Taurus but a nice sight in binoculars. The cluster is about 500 light years away and is around 10 million years old.

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