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What makes this year leap?

This February has 29 days since 2012 is a leap year. We have these to keep our calendars and natural cycles such as the seasons in step.

By the 16th century the two were out of step by about 10 days and in 1582, Pope Gregory implemented what is now known as the Gregorian calendar. This corrected the errors of Julian calendar which added one day every four years. This was too much however, and the Gregorian corrected this by making all century years, that is those such as 1500 and 1900, not leap years, but if the year was divisible by 400 it would be a leap year. So 2000 was a leap year.

It's easy to keep track of important dates with apps and electronic devices. Credit: sxc.hu

Simply put, years divisible by 4 are leap years, those divisible by 100 are not but those divisible by 400 are and finally those divisible by 4 000 are not. This should keep everything working nicely for at least another 20 000 years, by which time it will be someone else’s problem!

It is interesting to note that Omar Khayyam’s calendar of the early 12th century was more accurate that our current one. Furthermore, the Mayan calendar was not the most accurate, and it did not predict that the world will end on December 21 this year.

The month starts with a waxing gibbous moon that becomes full on the 7th with the new moon following on the 22nd, with the first crescent becoming visible the following evening just after sunset. After this the moon once again becomes an excellent marker for identifying planets, stars and clusters. After sunset on the 24th the waxing crescent moon is between the planet Mercury, low in the western sky, and the evening star Venus. On the following night the brightening crescent moon is close to Venus, passes by Jupiter on the 26th and 27th, and by the 28th is close to the small cluster of isiLimela. Finally on the 29th, a near quarter moon will be between isiLimela and the small open cluster of the Hyades, with the bright orange giant star Aldebaran at the top.

At the beginning of the month, a bright waxing gibbous moon is very close to isiLimela and the following night it is just below the Hyades and from then on moves eastwards below Orion the Hunter, which is now getting lower in the western sky but still dominates the evening sky high up in the northwest. Venus and Jupiter are shining unmistakably brightly in the western sky and it is interesting to note how, during the course of the month, they get closer and closer together. Mars rose a little before 23h00 on the 1st, but by the end of the month will be well up in the northeast with the ringed planet Saturn rising about an hour later.

To the southeast the Southern Cross and the Pointers are clearly visible and, high up to the upper right, the Large and Small Magellanic Clouds can be seen if you are away from city lights. These are the two nearest galaxies to our own: a little smaller than our Milky Way. The former is about 160 000 light years away and the latter 180 000 light years away.

A pair of binoculars should help you find the small Magellanic Cloud and on the lower right hand edge is the globular cluster 47 Tucanae, looking rather like a “fuzzy tennis ball”, being one of the biggest and brightest. It consists of about a million of some of the oldest known stars.

There are many of these globular clusters and they are found in what is called the ‘halo’ surrounding our Milky Way galaxy and many of the biggest and best of these globular clusters are visible in the southern skies. - Weekend Argus

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