Mars – get ready for opposition
Posted: 03 February 2012
AN's night sky expert Mark Armstrong whets the appetite for Mars as the red planet heads for opposition next month.
Mars is a fascinating body that never fails to thrill when spotted with the naked eye, sporting its customary ruddy hue. There are many factors that make Mars the attraction that it undoubtedly is – perhaps it’s the unanswered question as to whether life has ever existed there, a debate stirred up by Lowell’s canals and numerous Sci-fi films. Furthermore, getting a good view of the red planet at its best is not an annual event like the oppositions of Jupiter and Saturn. So when it does come round there is an elevated feeling of anticipation and excitement. Whatever your reason for getting excited about Mars, now is the time to give it your full attention.
Follow Mars’ progress in Leo through opposition until its second stationary point in mid April. Graphic made using Megastar version 5.
At the start of February Mars is moving retrograde (west to east) against the background of stars beneath the hindquarters of Leo. It is an unmistakeable object by about 10.30pm, shining at magnitude -0.6 in the east-south-east sky about 20 degrees up. It culminates (transits the southern meridian) at 3am at a healthy 45 degrees and remains above the crucial 20 degrees altitude mark until 7am when the morning twilight takes over. By the end of the month Mars has brightened to mag. -1.2 and can be observed shortly after 8pm, culminating just before 1am and remaining above 20 degrees until around 5am.
Mars can be observed with a small telescope – an 80-mm aperture will show the bright north polar cap and the major dark surface markings such as the Syrtis Major. But to really study the planet visually then a 100-mm refractor or a 150-mm-200-mm reflector (the latter in the case of a SCT) realistically is the minimum requirement. Many seasoned observers will not be happy with anything less than a 300-mm for this aphelic opposition.
This is the view of Mars through the eyepiece on 21 February at 10pm. The ‘wedge’ shaped Syrtis Major is prominent. Graphic made using Guide 8.
How much one can see through the eyepiece depends on how high your telescope’s magnification can go; local seeing conditions and the planet’s altitude at the time of the observation are the crucial factors. Perhaps often overlooked is to ensure your telescope optics are well collimated and clean, the detection of fine detail when the seeing is excellent depends on that to a very large degree. Try to aim for a magnification of x35 per inch (25mm) of aperture, with x150 the goal. If the seeing permits then ramp up the magnification as far as possible. Try to observe for a long as possible each night – it will be difficult to see much in the way of detail if you only give the planet a cursory glance, even through a large telescope. Coloured filters are very useful to enhance the dark surface features, with orange/red Wratten 23A and 25 handy in this respect. Blue filters such as W80A and W38A are good for picking out clouds and haze in the Martian atmosphere.
Mars grows in size from 11.9 to 13.8 arcseconds during February and if you are looking out for the famous ‘V’ of the Syrtis Major then it’s not until the third week of February that it’s visible, near the preceding limb. By the time Mars climbs to a respectable altitude at 10pm Mars’ rotation has taken it past the central meridian (CM) and by 2am it’s gone. Right at the end of the month the Syrtis Major transits the CM at 11pm.
High-resolution planetary imaging has come a long way in a few short years with great image almost routine now. Utilising as many clear nights for webcam imaging in February will help sharpen up your techniques (no pun intended), ready for opposition. Increasing your 'scope's focal length to f/30 to f/50 will give the necessary image scale and Mars’ slow rotation will allow ample time to secure many frames before any blurring.
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