Category: Sky Events
Sky events
The Moon and Mars
This evening will see the Moon pass by Mars. The two will be about 12° apart tonight and about the same tomorrow night. As the red planet passed through opposition on the 3rd it is still quite bright at -1.2 magnitude, a nice match for a nearly full Moon.
Venus and Jupiter
The two brightest planets in the sky will join up for a dance spanning several days starting this evening. Looking up tonight you will see the pair about 5° apart, with the dimmer Jupiter above Venus. Over the next few days they will slide closer, arriving at their closest approach on March 13th, with about 3° separation. The pair will remain close for several evenings, on the 14th the distance will have widened to just over 3° and on the 15th the separation will be 3.5°. This is the last dance of the February-March planetary alignment, after this the dancers will go their separate ways.
Neptune Appears in the Dawn
This week will find Neptune emerging from the Sun’s glare to reappear in the dawn. The planet will arrive at opposition on August 24th.
Mars Close Approach
Mars was at opposition two days ago, but not at its closest. Close approach of the two planets is not necessarily on the same day as opposition, but can vary up to two weeks. This year sees the two planets approaching to 99,331,411 km (61,721,554 miles) at 07:01HST. At this distance the red planet will show a disk 13.89″ arc-seconds across in the eyepiece.
All month Mars will be visible throughout the night, high in the sky at midnight. This is the time to enjoy observing our closest neighboring planet while it is nearby and high in the night sky.
Mercury at Maximum Elongation
Today Mercury reaches maximum elongation, the furthest point it will reach from the Sun in the sky and the highest it will be above the sunset this apparition. The planet is easily visible as a bright, starlike object about 15° above the setting Sun as the sky grows dark. Over the next couple weeks Mercury will slide back into the sunset, heading for inferior conjunction on Mar 21.
Mars Opposition
Closest approach of the two planets is not necessarily on the same day as opposition, but can vary up to two weeks. This year closest approach will occur March 5th with the two planets approaching to 99,331,411 km (61,721,554 miles) at 07:01HST. At this distance the red planet will show a disk 13.89″ arc-seconds across in the eyepiece.
All month Mars will be visible throughout the night, high in the sky at midnight. This is the time to enjoy observing our closest neighboring planet while it is nearby and high in the night sky.
Venus and Jupiter
Tonight the two brightest planets in the sky will be almost exactly 3° apart. Jupiter will be shining at a brilliant -2.1 magnitude, even that will be outshone by Venus at an even more brilliant -4.3 magnitude. At 3° separation the pair will fit together in the field of a pair of binoculars or a rich-field telescope. If you miss tonight the pair will remain close for several nights, only 3°11′ apart tomorrow night, and 3°34′ apart on March 15th.
Take a look, it will be hard to miss these two brilliant planets high in the evening sky.
A Leap Day
Today is February 29th, that odd date that only occurs every four years.
The reason for a leap day inserted into the calendar, the existence of February 29th, is ultimately astronomical. Perhaps a little explanation is in order…
We originally defined days as the time it takes the Earth to rotate. While we define years as the time it takes the Earth to orbit once around the Sun. The problem is that these values do not divide evenly into one another.
It is that bunch of decimals, the 0.24219 etc., that is the problem, every four years the count drifts out of sync by roughly one day. The insertion of an extra day every four years helps bring the calendar back into synchronization with the orbit of the Earth and with the seasons.
Even leap years do not quite fix the problem as 0.24219 is close, but not quite 0.25 or one quarter of a day. Thus additional corrections are needed… Enter leap centuries.
Our current calendar was instituted by Pope Gregory XIII in 1582, setting up a standard set of corrections for the fractional difference between the length of a year and the length of a day. Scholars knew that errors had been accumulating in the calendar for centuries, resulting in a drift of several days. Religious authorities were concerned that this drift had displaced important celebration in the church calendar, in particular the celebration of Easter. After much argument it was decided to reform the calendar. The current solution was devised by a number of astronomers, including Aloysius Lilius, the primary author of the new system.
The Gregorian Calendar uses an extra day in February every four years, unless the year is divisible by 100, then there is no leap leap day that year. However, if the year is divisible by 400, then it is a leap year. While this may sound odd, it does create a correction much closer to the ideal value of 365.24219 days per year.
Even this is not perfectly precise. The correction is close but will drift given enough time. The length of a tropical year also changes slowly over time. We will eventually have to add another correction to keep the calendar and the seasons in sync. But not for a few millennia, good enough, for now.
As 2012 is divisible by four, there will be a leap day added to the end of this February… Today.
The Moon and Pleiades
Tonight a bright half Moon will be just under 4° from the Pleiades star cluster. The Moon will be 43% illuminated, bright, but the cluster is bright enough to be seen even against a bright Moon. As the Pleiades move to the west over coming months there will be a few more lunar conjunctions, with increasingly smaller crescents.