The Planets, January 2012

This page was last amended 31st December, 2011

Note: All times quoted on this web site are in Universal Time (UT) unless specifically stated otherwise. They are only "best estimates" and no responsibility can be accepted for errors. To convert to British Summer Time (when appropriate), add one hour.

The above diagram shows the times during  which the five "naked eye" planets are above the horizon at both the beginning and the end of the month.

To determine how to interpret this diagram, read on; otherwise, for additional information about the individual planets, click here.

The diagram represents a 24-hour period, time running from left to right from noon until noon the next day. This unconventional way of representing a 24-hour day is used so that the hours of darkness (which, generally, are of the greatest interest to astronomers) appear at the centre of the diagram.

The time from Sunset until Sunrise ("hours of darkness") are represented by two blocks of slightly differently coloured purple. They include the dusk and dawn twilight periods, although no attempt has been made to differentiate between these and full darkness. 

The times that the five naked-eye planets are above the horizon are shown for the beginning and end of the month, and are represented by the khaki-coloured blocks. The "tick"-marks pointing upwards from the "Beginning" and downwards from the "End" lines represent the planet's culmination.

The purple dot-and-dash lines extending downwards from the ends of the hours of darkness blocks in the two shades of purple help  you to determine when, if at all, each of the planets are visible.

Generally speaking, times of rising, setting and culmination for other times of the month can be roughly determined by interpolating between the times shown.

The above diagram was generated by the computer program PlanetRise (© 2007, M R Humphries), written in BBC BASIC for Windows.

More information on the planets in January 2012

The bright planet Mercury (magnitude -0.4/-0.7), the closest planet to the Sun, rises at about 07:00 UT at the beginning of the month, but becomes lost in the Sunrise by about 08:00.  As the month progresses, Mercury becomes lower in the sky, disappearing altogether at about the middle of the month.

The current brightest planet in the sky, Venus (magnitude -4.0), can be seen low in the SSW sky soon after Sunset.

The orange/pink planet Mars (magnitude +0.3/-0.6) is about to start a very interesting phenomenon.  All the planets appear to move from E to W against the background stars during the course of time, and if you look at Mars every 3 or 4 days, it can be seen to have moved against the background stars during that time.  But occasionally Mars appears to stop moving against the background stars and even to start moving “backwards” from W to E.  This is known as “retrograde motion”, and it starts on 25th January and finishes on 15th April, lasting about 82 days, until the retrograde motion ends and the planet restarts its usual E to W movement.

Jupiter continues to be a very bright planet in the night sky (magnitude -2.6).  Look about 40° above the SW horizon at 22:00 and you can’t fail to see it.  Finally, the planet Venus can be seen low in the SSW sky soon after Sunset!

Saturn rises in the early hours (magnitude +0.6) and its rings can be seen through a telescope as they (the rings!) have opened again.