Astronomy for all
Wednesday January 26th 2011

Your guide to finding Mars

Picture 16

January 2010 is a great time of year to find Mars in the night sky. Each evening it rises about 7.30 and it is easily identified with a very red glow in the sky. The main thing is where to look. Over the next few weeks it gets closer and closer and makes for easy viewing.

Viewing Mars

Viewing Mars

January and Feburary are the best months to observe Mars for a couple of years as the Earth passes between Mars and the Sun on January 29th(called opposition. Mars will be due south around midnight so highest in the sky. Oppositions of Mars occur at intervals of approximatly 780 days but, because Mars has an eccentirc orbit (as has the Earth to a lesser extent) the distance of Mars at opposition varies widely. If Mars is at its closest point to the Sun (at perihelion) and the Earth at its most distant point from the Sun, the distance between the two will be at its smallest and so Mars will have its greatest angular size. This happened two apparitions ago when Mars was at its closest for ~ 60,000 years and had an angular size of 25 arc seconds. At the opposite extreme when Mars is at aphelion, the angular size only reaches ~14 arc seconds and, sadly, this is the case this year. Closest approach is on 27th Jan at a distance of nearly 100 million kilometres when its magnitude will be -1.3. Very nicely, it then lies in the constellation of Cancer just above the Beehive Cluster. The Moon, near full will be in attendance to as shown in the chart which shows its motion westwards across the sky over the next few weeks. The fact that its angular size is not as big as it can sometimes be is partly compensated for by the fact that it reaches an elevation of around 60 degrees, so the atmosphere will not impede our view as much as when it is lower in elevation.

Why Earth and Mars are so close

Why Earth and Mars are so close

To see significant detail on the surface requires a telescope of 4 inches or more. As the north pole is tilted towards us, we should be able to easily spot the, brilliant white, north polar cap. A slight pity for those with small telescopes is that the most prominent dark feature, Syrtis Major, passes behind the limb in the early evening, so will not be best seen. As Mars’s day is similar in length to ours, we will see a similar face at a given time over quite a long period. The free Planetarium program “Stellarium” will show you what could be seen at any given time of the night during the apparition.

Jan 1, 2010
Mars shines at mag -0.77 in constellation Leo with an apparent diameter of 12.67″. Distance from Earth is 0.73885 AU (111 million km).
Jan 9, 2010
Mars leaves constellation Leo and enters Cancer again, during retrograde opposition loop.
Jan 11, 2010
Apparent brightness of Mars exceeds -1.0 mag.
Jan 27, 2010
Closest approach of Mars and Earth (0.664 AU = 99.33 million km). Apparent diameter of Mars is 14.105″.
Jan 29, 2010
Mars opposition on Earth, Earth in inferior conjunction on Mars. Apparent brightness of Mars reaches -1.28 mag in constellation Cancer.

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2 Responses to “Your guide to finding Mars”

  1. John Flannery says:

    Hi Paul,

    Great site and very informative. I came across it while looking at the news articles about the fireball last night (which I saw driving from Clonskeagh to Ranelagh.) If it was ok, could I ask for a mention of my annual sky guide that is a free 40-page pdf download from (and also — previous years are archived on mediafire too but it is somewhat an ad driven site.) Sky Guide 2010 is geared for observers in Ireland and has information on a wide range of astronomical phenomena for the year ahead as well as a month-by-month calendar. Many thanks! John

  2. paul says:

    Hi John, no problem I’ll post a link and a comment to the giude. It looks very impressive and quite extensive…

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