Orion and Mars dominate February's evening sky

FEBRUARY is always a splendid, if chilly, month for stargazing and it is just a pity that it is the shortest of the year. Our southern evening sky is peppered with bright stars and interesting sights while Mars is at its brightest and best.

Indeed, the Red Planet is alongside the full Moon and directly opposite the Sun in the sky tonight, so that it stands low in the east-north-east at nightfall and crosses the high southern sky overnight to lie low in the west-north-west before dawn. By our star map times it stands high in the south-east, roughly halfway between the stars Castor and Pollux in Gemini, and Regulus, the leading star of Leo. As it tracks westwards against the background stars of Cancer, it passes 3 north of the Praesepe star cluster on the 7th and meets up with the Moon again on the 25th.

As I mentioned last month, this is not a particularly favourable opposition of Mars, since our encounter occurs with the planet further from the Sun and the Earth than usual. Even so, it shines at magnitude -1.3 at present, which is only a little fainter than the -1.5 of Sirius, the brightest star in our night sky.

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Whereas Sirius twinkles vividly low in the south at our map times, Mars has a distinctive reddish, or some would say salmon-pink, hue, and shines with a steady light. Viewed through a telescope, its disk appears only 14 arcseconds across so we need good "seeing", perhaps when Mars is highest during the midnight hours, to glimpse surface features such as its white northern polar cap.

Over the coming month, Mars recedes from 99 million km to 116 million km, shrinks to 12 arcseconds and halves in brilliance to magnitude -0.6.

Nasa's Spirit and Opportunity rovers have just celebrated the sixth anniver- sary of their arrival at Mars and, although Opportunity is performing well, Spirit has been wallowing in soft sand on the lip of a small crater since last May. With two of its six wheels faulty, attempts to extricate it have failed and its controllers back on Earth must now focus on placing it in the best attitude to survive the coming southern-hemisphere winter.

Meanwhile, the Phoenix lander has been silent since 2008, when frost and ice descended on its landing site in the Martian arctic. There are hopes, albeit slim ones, that it might awake again in the Martian spring, but not a peep has been heard (so far) by listening orbiting craft passing overhead.

The Sun climbs 9.5 northwards and our days grow two hours longer during February as sunrise/sunset times for Edinburgh change from 08:08/16:46 on the 1st to 07:07/17:45 on the 28th. Nautical twilight lasts for a little more than 80 minutes. Tomorrow's full moon is followed by last quarter on the 5th, new moon on the 14th, first quarter on the 22nd and full moon again on the 28th.

The starting point for any exploration of our southern evening sky at present has to be Orion, which, since it straddles the celestial equator, is visible in its entirety everywhere on Earth outside the polar regions. The line of three stars forming Orion's Belt is probably its most distinctive feature and I have often mentioned that this slants upwards to Aldebaran and the Pleiades in Taurus, and in the opposite direction to Sirius.

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The Belt lies just south of the celestial equator, so it passes overhead as viewed from the Earth's equator. For us, though, it is Capella in Auriga that sails overhead as Orion marches from the south-east at nightfall to the south-west by midnight. A line upwards at right angles to the Belt passes the red supergiant Betelgeuse in Orion's shoulder and extends into Gemini and the stars Castor and Pollux. Below Gemini is Procyon in Canis Minor which, with Betelgeuse and Sirius, completes an equilateral triangle which we call the Winter Triangle.

As Orion sinks westwards after midnight, and Gemini and Mars follow, it is replaced in the south by Leo while the Plough looms overhead. Virgo, following Leo, contains the bright planet Saturn which rises in the east a few minutes before our map times and stands due south six hours later.

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Saturn is magnitude 0.7 and appears 19 arcseconds across if viewed through a telescope. The rings extend for 42 arcseconds and have their north face tipped 5 towards us, though the tilt decreases a little during February. Look for Saturn above-left of the Moon next Tuesday night.

Jupiter is still conspicuous at magnitude -2.0 low in the west-south-west at nightfall but will soon sink into the twilight as it heads for the Sun's far side on the 26th. Before it disappears, though, it meets and passes the brilliant (magnitude -3.9) Venus as the latter begins to emerge as an evening star. To glimpse them, though, we will need a perfectly clear west-south-western horizon and binoculars to scan the bright twilight in the minutes just after the Sun has safely disappeared. Venus climbs from 1.5 below Jupiter on the evening of the 15th, to 0.6 below on the 16th and 0.9 left of Jupiter on the 17th.

Watch also for the brightly earthlit and very slender crescent Moon as it climbs steeply away from the Sun on those evenings. On the evening of the 21st the near-first-quarter Moon slides just to the south of the Pleiades, occulting a few of the cluster's outlying stars in the process.

Even by the month's end, Venus stands only 8 high at sunset and sets itself just one hour later. The sole remaining bright planet, Mercury, might be sighted near the south-eastern horizon just before dawn over the next week or two.