The Night Sky This Month: March 2017

Plato and Lunar Alpine Valley

This year, the Spring Equinox falls on Monday, March 20th, a date which officially marks the beginning of the astronomical spring in the Northern Hemisphere, although meteorologically speaking the season actually starts on March 1st. The month will also provide a good opportunity to see the planets of Venus, Mars and Jupiter, as well as a closer look at the constellations of Gemini, Leo, Virgo, and Ursa Major, the latter of which despite being circumpolar, is best seen during March, April and May when it is highest in the night sky.

The Moon

Northern observers might be inspired to brave the chilly nights in order to observe the Lunar Alpine Valley both on the 6th and on the 19th of March. Look for this spectacular cleft through the Apennine Mountain range that marks the rim in the Mare Imbrium, the Man in the Moon’s right eye, just to the east of the major crater Plato. While large binoculars will reveal the 79-mile-long feature, a small telescope fitted with a suitable lunar filter will provide an almost close-up view.


First Quarter: 5th
Full Moon: 12th
Last Quarter: 20th
New Moon: 28th

Constellations and Deep Sky Objects

PleiadesProminent constellations in the Northern Hemisphere at this time of year include Orion in the south, with Taurus to its upper right (north-west) presenting a wealth of targets for binocular and small telescopes. To the upper rightward of Taurus is the spectacular Pleiades (M45), an open star cluster containing hot blue stars which remains a hauntingly beautiful sight, with or without optical aid.

Nearly overhead is the constellation Auriga, with its brightest star Capella, almost exactly at the zenith. To the upper leftward (north-east) of Orion is Gemini, the Twins, whose heads are marked out by the stars fCastor and Pollux. Also rising in the east is the constellation Leo, the Lion, sporting Regulus as its brightest star. Almost between Gemini and Leo is the constellation Cancer, which is home to M44, or Preasepe, a beautiful star cluster also known as the Beehive Cluster, which is an easy binocular target under reasonably dark skies.

The Planets

– Mercury becomes visible low above the western horizon around the 15th, having passed through a position of superior conjunction on the 7th. Look for the little planet as it passes close by Venus and gains altitude on the 19th, after which its brightness begins to decrease from magnitude -1.4 to only -0.4 as its angular diameter shrinks to around 7.3 seconds of arc. This will make it almost impossible to discern any detail on the planet’s disc.

– Venus starts the month shining at magnitude -4.8, which is about as bright as it gets. In fact, the planet is now visible due south, and so bright that it is easy to spot during the late afternoon without optical aid. In dark locations, it might also be possible to spot delicate shadows cast by the planet. Venus’ angular diameter grows during the month from 48 to about 59 seconds of arc, but because its illumination decreases from 16% to only about 1% over the same period, its brightness will remain fairly constant at around magnitude -4.1. Keen observers should also notice Venus starting to rise before dawn on about the 15th of the month, which means that the planet will be both a predawn and early evening object for some days around the middle of the month. This does not happen very often, but the planet does occasionally reach a position far enough from the Sun to make it possible.

– Mars starts the month in the constellation Pisces, a few degrees to the upper leftward of Venus. As the month wears on, Mars continues its eastward motion to move into the constellation of Aries, which it reaches on the 8th, while Venus descends towards the western horizon. Mars will also dim slightly from magnitude +1.3 to magnitude +1.5 due to its angular diameter shrinking from 4.6 to 4.1 seconds of arc, which makes discerning features on the surface difficult, if not impossible.

Jupiter near Spica in Virgo– Jupiter starts the month in the constellation of Virgo, about four degrees or so to the upper right of its brightest star Spica. The King of the planets rises in the east at about 22:45 UT, but it will rise progressively earlier as the month wears on, until by the end of March it will rise at about 20:45 UT. Look for the planet due south at about 34 degrees or so above the southern horizon at around 02:00 UT at the beginning of the month, and around 00:00 UT at the close of the month. Jupiter’s angular diameter will increase marginally from 42 to 44 seconds of arc, which will increase its brightness from magnitude -2.3 to magnitude -2.5. Small telescopes should easily reveal the equatorial bands, and during good seeing, the Great Red Spot might also be visible.

– Saturn starts the month in the western reaches of the constellation Sagittarius, where it will be highest and brightest in the pre-dawn hours, shining as it does at magnitude +0.5. However, even though the planet might be high enough over the southeastern horizon to observe the ring system in good seeing conditions, the planet never rises above 18 degrees or so during the whole of 2017, which might make it worthwhile for northern observers to invest in an atmospheric dispersion corrector to be able to observe the planet’s beautiful ring system.

Meteor Showers

Although no meteor showers occur during March, this time of year is known as the “fireball” season”, when the incidence of bright meteors known as fireballs increases at around the time of the equinox. In some years, the average bright meteor count can increase by as much as 30 % or more during the weeks on either side of the equinox, but the reason for this phenomenon remains unexplained.

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