Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during February 2012.

The constellation of Orion takes centre stage with its bright stars, Betelgeuse and Rigel. Orion's Sword contains M42, the Orion Nebula, visible as a hazy glow through binoculars. Sirius, our brightest night-time star, is down and to the left; atmospheric scintillation makes it twinkle colourfully. Above and right of Orion is Taurus the Bull, containing the red star Aldebaran as its eye and the Hyades Cluster, which forms its head. The Pleiades, or Seven Sisters, are nearby. Up and left of Orion is Gemini, containing the Heavenly Twins, Castor and Pollux, while Auriga is towards the zenith with its bright star Capella. The Milky Way runs through Auriga and hosts several open star clusters. Leo the Lion rises in the east later in the evening, above the planet Mars.

The Planets

• Jupiter is at its highest (about 50°) around sunset, shining at magnitude -2.4 in Aries. With an angular size of 38.7", a small telescope will show its equatorial bands and Great Red Spot.
• Saturn is up from late at night until morning, reaching 31° elevation. It brightens from +0.6 to +0.5 during the month and its rings continue to open to our line of sight, reaching 15° from edge-on and allowing the gaps between sets of rings to be seen.
• Mercury passes behind the Sun (superior conjunction) on the 6th, but reappears near month's end, shining at magnitude -1.1 after sunset in the south-western sky. Its angular size is around 6" and is increasing.
• Mars moves westwards in the sky from night to night, contrary to the usual apparent planetary motion; this is called retrograde motion, and results from the Earth overtaking it on the inside track as the two planets orbit the Sun. Its angular diameter is increasing and, at the end of the month, it is 14" in size, rises by 6pm and reaches 50° elevation. Surface features can be seen using a small telescope, including Syrtis Major and the north polar cap.
• Venus is about 30° above the south-western horizon at sunset at the beginning of the month and 37° above by the end, as it increases its angular separation from the Sun. Its angular size increases over the month from 15 to 18" as its illuminated fraction drops from 74 to 64%, giving it a very bright and constant magnitude of -4.1.

Highlights

• Comet Garradd can be seen in the east before dawn this month. The globular cluster M13 is nearby, above the Keystone, which is the asterism consisting of the four brightest stars in the constellation of Hercules. It is the best-seen globular cluster in the northern hemisphere, and the cluster M92 is not far away, to the left of the Keystone. The two are at magnitudes of +6 and +6.5 respectively, and the magnitude +7 comet makes its closest appearance to M92 on the 3rd, allowing it to be found with binoculars.
• Mars can be seen close to a waning gibbous Moon at around 9pm on the 9th.
• Saturn makes a near-straight line in the sky with a waning Moon and the star Spica before dawn on the 12th.
• Jupiter, Venus, Mercury and a thin crescent Moon are all in close proximity early on the evening of the 25th. You should be able to see Earthshine, otherwise known as 'the old Moon in the new Moon's arms'.
The Hyginus Rille is a nice feature of the Moon to look at around the middle of this month. It appears in the Mare Vaporum as a line with an 11-km crater in the centre, which is probably the result of a volcano during the Moon's early history.

Southern Hemisphere

John Field from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during February 2012.

Three planets are visible in the evening sky: Venus, which sets in the west after sunset, Jupiter, which sets in the north-west around midnight, and Mars, which rises red in the north-east after twilight.

The brightest star in the night sky, Sirius, sits high in the north in the constellation of Canis Major, the Large Dog. Towards the northern horizon is Procyon, the eighth-brightest night-time star, in the constellation of Canis Minor, the Little Dog. The two dogs accompany Orion, the Hunter, while between them is Monoceros, the Unicorn. It contains a number of beautiful stars, including the triple system Beta Monocerotis, which can be separated in a telescope, and the double star Epsilon Monocerotis, with its yellow and blue components. The constellation also offers a number of star clusters as it is on the edge of the Milky Way. Between Sirius and Procyon is M50, also designated NGC 2323, a cluster of about 100 stars that is visible in binoculars. To the north-east of Monoceros is NGC 2232, an irregular open cluster, while the bright, scattered cluster NGC 2244 sits in the centre of the Rosette Nebula. Other interesting clusters include NGC 2261, NGC 2301 and NGC 2264, the last of which is also called the Christmas Tree Cluster due to its shape. It contains the Cone Nebula at its tip, which can be seen through a large telescope. Monoceros is also home to the massive 6th-magnitude binary system Plaskett's Star, which has a mass of around 100 times that of our Sun. The 15th-magnitude star V838 Monocerotis has variable brightness, but is usually very faint. Other well-known variable stars include Beta Persei (Algol), which varies because it is an eclipsing binary system, and Betelgeuse, which swells and cools as it nears the end of its life.

In the south-east is Crux, the Southern Cross, and near to that is Musca, the Fly, with the Coalsack Nebula joining the two. The star Alpha Muscae is a double that can be split with a medium-sized telescope. Theta Muscae is also a double, and the brighter of the two partners is a Wolf-Rayet star, meaning that it ejects a lot of material. Nearby are the globular clusters NGC 4372 and NGC 4833 and the 10th-magnitude planetary nebula NGC 5189, which has an S-shaped appearance.

Highlights

• Two meteor showers, known as the Centaurids, occur in early February, producing 5-25 meteors per hour. The Moon will hamper their observation this year, however.
• The constellations of Orion, Taurus and Gemini are visible this month, but will soon slide away into the twilight sky.
• The Milky Way runs almost from north to the south in the evenings this month, with the constellation of Carina and its bright star Canopus overhead. There are many star clusters and nebulae to be found with binoculars in this region of the sky.