The Night Sky in February
On Feb 12, early risers get to see Mars close to its celestial rival, the red supergiant star Antares, the star marking the heart of Scorpius the Scorpion. The name Antares derives from ancient Greek meaning “equal to Mars”, attributed because, like Mars, it shines with an orange hue. On Feb 12 both objects will also have similar brightness making this an ideal time to compare them. The apparent proximity of Mars and Antares is a line-of-sight effect, of course. In reality Antares will be slightly over 22 million times more distant than Mars on this date.
This month the Moon is new and lined up with the Sun on Feb 15. The early months of the year favour views of the evening, waxing crescent Moon, which appear just after the new phase. This is because the Moon’s path in the sky tilts steeply against the western horizon after sunset during the spring. There is a theoretical threshold known as the Danjon Limit, which states that the centre of the Moon’s disc needs to be more than 7degrees from the centre of the Sun for the emerging thin lunar crescent to be seen. The Moon’s surface is rugged, covered in craters, valleys and mountains, and the Danjon limit takes this into account.
The challenge of seeing a very thin lunar crescent can become addictive but it’s important to wait for the Sun to have set properly before looking. Failure to do so could lead to eye damage. In order to spot a thin Moon, you need to know where to look and to make sure that the horizon in that direction is unobstructed. The weather also needs to be kind.
On Feb 16, a 21.5-hour old, 0.8per cent illuminated crescent may be seen close to the brilliant planet Venus. Both objects will be low in the west, best seen approximately 20-30 minutes after sunset. The centre of the Moon will appear 0.75degrees to the left and slightly below Venus at this time. One degree is equal to the width of your little finger at arm’s length. This thin crescent will be extremely challenging to see against the bright twilight sky. However, such opportunities aren’t common and with Venus guiding the way, this is a great time to try.
The sky around midnight marks a transition from winter. The bold constellations surrounding Orion now appear west of south, chased from the east by more subtle patterns of spring. Distinctive Leo the Lion dominates the view east of south, easily identified thanks to its backward question mark pattern known as the Sickle. The brightest star in Leo is Regulus, located at the base of the Sickle. The lion faces west towards Gemini the Twins, highlighted by the twin stars Castor and Pollux. Lying midway between Regulus and the twin stars is the inverted Y-shaped constellation of Cancer the Crab.
Cancer isn’t particularly bright. A small pattern of four stars in its centre frame a lovely open cluster known as M44, the Beehive Cluster or Prasepe meaning “manger”. The ancient Chinese describe the cluster as the “exhalation of piled-up corpses”, a reference to the belief that the cluster marked a gateway for departing souls transitioning from this world to the next. The Beehive appears as a misty patch from a dark sky location and looks wonderful through binoculars.
A fainter open cluster known as M67 sits west of Cancer’s alpha star, Acubens. This cluster requires binoculars or a telescope to see and is believed to have formed at the same time as the Sun.