The Night Sky This Week

by Mark Armstrong

16 - 31 March

What's up this week? Our weekly guide to the night sky will point you to all the planetary goings on, as well as pick out some deep sky objects for your viewing pleasure. Let's get started with a round-up of the Solar System, or follow the links above to jump to your favourite section.

Solar System Round-Up

Let's hope for clear skies for the last two weeks of March, as there is so much Solar System action with Saturn's opposition taking centre stage and Mars still in the frame for visual and digital observers alike. Don't forget that British Summer Time (BST) starts at 1am local time on 28 March, with the clocks advancing by one hour to 2am BST.

Saturn
Saturn comes to opposition on 22 March and shines moderately brightly at magnitude +0.5 with a distinctly creamy hue. It nestles in the 'bowl of Virgo', just below the main concentration of galaxies on the Virgo/Coma border. By the time the sky is dark at around 7.30pm the ringed planet is about 15 degrees up, still climbing away from the house and treetops and all the murk hugging the eastern horizon. By 9pm most observers, including city-dwellers, should be able to get a 'scope on it and it culminates just after midnight in the south at a respectable 40 degrees altitude. Saturn is a splendid sight even through a small telescope; don't let the narrow angle of the rings put you off observing it. The rings have been steadily 'closing up' from our perspective in 2010 and at opposition they are tilted by just over three degrees. This process continues until May but then the rings open out again to a full ten degrees by the end of the year. Titan is Saturn's largest moon and can be seen in 10x50 binoculars but easier in a small 'scope. In the last fortnight of March it reaches greatest western elongation on 18 March can be seen mere arcseconds north of its parent on opposition night.

At dusk on 31 March, with the Sun six degrees below the horizon, Venus and Mercury make a splendid early-evening pairing. AN graphic by Greg Smye-Rumsby.

Mercury and Venus
Mercury rapidly reappears in the evening sky following superior conjunction on 14 March. In fact this is the best evening apparition of the year for the UK, with the elusive innermost planet reaching greatest elongation east (19.2 degrees) early next month. Mercury is brighter before greatest elongation and by 31 March at around 30 minutes after sunset it will be eight degrees above the western horizon shining at mag. -0.9 and telescopically sports a gibbous phase of 71 percent. This apparition has a real bonus as Venus joins in the fun, passing just over three degrees east of Mercury as it makes its serene progress away from the western horizon. Venus' presence really will help track down Mercury and given clear skies, it is worth making a special effort to secure a flat horizon, especially if you have never seen the planet. Furthermore, this conjunction should make for a really nice photo opportunity!

Mars
Once the inferior planets have been observed, swing your 'scope eastwards to Mars. Although well past opposition, the red planet still has much to offer and besides, March is probably the last good month to observe it. On 16 March as darkness falls around 7.30pm Mars is about an hour from culmination and is 60 degrees up in western Cancer. It is still a great sight, outshining everything bar Sirius and Venus at mag.-0.2. Through a telescope it is still above 10 arcseconds apparent diameter and given good seeing the dusky V-shaped wedge of the Syrtis Major, slap bang on the Martian central meridian, should be well seen. The red planet finally shrinks to under ten arcseconds on 23 March and by then you will need to stay up to 11.30pm to see the Syrtis Major at its best, with Mare Cimmerium in Mars' southern hemisphere favoured early evening. By the month's end Mars will have faded to mag. +0.16 and the great volcano Olympus Mons lies close to the central meridian.

The lunar graze of the star HIP 31696 (top) and the profile of the lunar limb that will be grazed on 23 March. AN graphics by Greg Smye-Rumsby.

Lunar occultation
There is a good lunar occultation on the early morning of 27 March. The wide double star omicron Leonis with components of mag. +3.5 and +9.5 separated by 85 arcseconds, will disappear at the dark limb of a waxing gibbous moon at 1.51am for observers in Edinburgh and at 1.59am for those in London. There is a grazing lunar occultation too on the evening of 23 March, which is well worth checking out if you are lucky enough to be able to live on or travel to the narrow track. HIP 31696 (ZC 1017, mag. +6.8) appears to scrape along the dark edge of the gibbous moon with the graze track running across south-west Ireland from Clifden in County Galway to Waterford, crosses St George's channel and heads across south-west England from Bude in Cornwall (10.15pm) to Slapton on the coast of Devon (10.17pm).

Dwarf planet Makemake
Heading into the frozen depths of the deepest Solar System, dwarf planet Makemake reaches opposition on 16 March, shining at a photon-challenged mag. +16.9. CCD observers using even small telescopes can image Makemake and its slow crawl eastwards against the backdrop of the stars of Coma Berenices will be detectable in a series of images taken a few nights apart. Centre your 'scope at R.A. 12h 35.29m and Decl. +28° 27.7' on opposition night. Moving back in towards the Sun, comet 81P/Wild is at it?s brightest at around mag. +9; it's best to chose the moonless third week of the month to attempt to track it down as it tracks through eastern Virgo, passing a couple of degrees south of iota Virginis.

Details of Comet 81P/Wild 2's path over the coming month.

Comets
Comet 81P/Wild is at its brightest this month at mag. +9 and is well worth tracking down as tracks through Virgo in the early morning skies. It should be picked up in 10x50 binoculars and an ideal time to try for it is mid-month when the Moon is at or close to new and the comet is around two degrees south of iota Virginis.

Happenings down under

There are six planets on show in the later half of March but you will need flat horizons to the east and west and be somewhat of a night owl to see them all. Uranus is the only planet not on show as it is in conjunction with the Sun on 17 March. The equinox occurs on 21 March at 1.25pm (Sydney) and marks the start of autumn.

Saturn
Saturn and Mars are the mainstays for observers with Saturn coming to opposition on 22 March. Saturn rises around 7pm local Sydney time and by 9.30pm has gained sufficient altitude for meaningful observations to begin. It culminates shortly after 1am at a very respectable 54 degrees and can be observed until 5am, after which low altitude may have a detrimental effect on local seeing conditions. The ringed planet is not particularly bright, shining at mag. +0.5; it can be as bright as -0.2. This is because the current low orbital tilt of the planet with respect to us (3.1 degrees) means that the rings are barely open and this has a big bearing on Saturn's apparent brightness, as well as diminishing it's telescopic impact. But this does have one significant advantage as it allows the major satellites to undergo phenomena similar to the Galilean moons of Jupiter, but, with the exception of Titan, are much harder to observe. Unfortunately there are no events involving Titan in March but there will be in April.

Dione is eclipsed on 22 March at 3.34am local Sydney time, some eight hours prior to opposition. It disappears right at the western limb with the ringed planet barely casting a shadow. Graphic made using Guide 8 software www.projectpluto.com

Saturn's moons move east to west across the face of the creamy globe and west to east behind it. So observers with very large 'scopes or digital imagers with moderate apertures can see the larger moons such as Rhea, Dione and Tethys move behind Jupiter (occultation), move in and out of Saturn's shadow (eclipse) and move in front of the globe (transit) and seen silhouetted again the cloud tops together with their dark shadows (shadow transit; much easier to see). After conjunction and before opposition Saturn's shadow falls to the west and eclipse precedes occultation and shadow transit precedes transit; after opposition the order of phenomena is reversed. Below are some of the better events to try and observe (all times are local to Sydney adjusted for daylight saving time).

On 25/26 March at 9.33pm Rhea is occulted at Saturn's western limb. It reappears from eclipse right at the eastern limb at 12.58am with once again very little shadow cast by Saturn. Graphic made using Guide 8 software.

Mars
March represents the last good chance of observing Mars before its apparent diameter shrinks too much. On 23 March its diameter falls below 10 arcseconds and by the end of the month it will have faded to mag. +0.1. Mars lies in western Cancer and moving prograde again (west to east) towards another encounter with the Beehive cluster next month. Jupiter can be seen in the morning sky and by the end of the month it is around 15 degrees above the eastern horizon about 30 minutes before sunrise. Neptune is almost 20 degrees above Jupiter and should be visible in 10x50 binoculars and small scopes four degrees north-east of delta Capricorni (mag. +2.8).

If you have a flat western horizon, Venus and Mercury should be visible about 30 minutes after sunset. Before attempting to sweep for Mercury, ensure that the Sun has set from your observing site. Graphic made using the Sky Version 5 www.bisque.com/sc/pages/thesky6family.aspx

Mercury and Venus
Mercury and Venus are both evening objects but hugging the western horizon. By the end of March Venus is barely five degrees above the horizon 30 minutes after sunset and is a good guide for locating Mercury below it. It?s probably best to sweep with binoculars but wait until the Sun has set. On18 March a young crescent moon is close to Venus. Speaking of the Moon, the full moon of 30 March is a blue moon, the second full moon of the month for Australia, the first having occurred in the small hours of 1 March.

Deep Sky