The March night sky

The Sun crosses northwards over the equator at our vernal or spring equinox on the 20th, when days and nights are similar in length around the Earth. As our days lengthen in March, the stars at nightfall shift almost 50° westwards, with Orion toppling from due S into the SW and Leo climbing from the E to the meridian where its leading star, Regulus, stands close to the Moon on the 9th.

Plunging westwards, too, is Venus which sweeps within 42m km of the Earth and passes 8° N of the Sun’s near side on the 25th, giving our best chance in eight years to follow its transition from an evening to a morning star. For a few days, it might be glimpsed both after sunset and before sunrise, but only if our horizons are clear.

The planet is unmissable as it blazes at mag –4.6 in the W this evening, being 53m km away and to the right of the young earthlit Moon on the 1st. Sinking lower with each day, its altitude in the W 30 minutes after sunset falls from 25° on the 1st to 6° on the 20th. By then, it is already rising in the ENE more than 40 minutes before sunrise. Telescopes and binoculars show Venus’ crescent swelling from 47 to 59 arcsec in diameter between the 1st and 25th, while the sunlit portion shrinks from 16% to only 1%.

Mars, above-left of Venus and 5° above the Moon on the 1st, is much fainter (mag 1.3 to 1.5) as it slides from Pisces to Aries. It meets the Moon again on the 30th and sets at our chart time on the 31st.

The Moon is nearing first quarter when it again hides several stars in the Hyades star cluster in Taurus on the night of the 4th-5th. It sets for Britain as it approaches Aldebaran, but the latter is occulted (hidden) for watchers in the USA.

As Mercury begins its best spell as an evening star this year, it lies 10° to the left of Venus on the 20th. It improves to stand 12° high in the W 30 minutes after sunset by the month’s end, lying 8° right of the slender earthlit Moon on the 29th and dimming from mag –1.2 to –0.1 during the period.

Jupiter, conspicuous at mag –2.3 to –2.5 to the N of Spica in Virgo, rises in the E 90 minutes before our map times and passes due S in the early hours. Catch it alongside the Moon on the 14th-15th when it lies 680m km away and its cloud-belted disc is 43 arcsec wide.

Saturn, low in the SE for some three hours before dawn, shines at mag 0.5 in Sagittarius. It stands below-left of the Moon on the 20th when telescopes show its rotation-flattened globe to be 17 arcsec wide, enclosed within impressive rings that measure 38 by 17 arcsec and have their N face tipped 27° towards us.

March diary