The Night Sky in March
The centre of the Sun crosses the celestial equator at 21:58 GMT on March 20, marking an instant in time known as the Northern Hemisphere’s spring equinox. There are two equinoxes during the year, the one in March marking the moment the Sun moves from the southern into the northern half of the sky. The second occurs during late September and marks the point when the Sun moves south across the celestial equator.
An equinox is often described as the time when day and night have equal length for all locations on Earth, but this isn’t strictly true.
The true date this happens is called an equilux and occurs a few days earlier than the March equinox, and, the Northern Hemisphere’s autumn equilux occurs a few days after the September equinox. The precise date depends where you are on the planet. It is noticeable how quickly the lengths of day and night change at the equinoxes – the rate of change is at its greatest value for the year. This is most evident with Orion. Viewed at the same time of night, the stars gradually move a small amount further west over consecutive nights. As Orion follows suit, the expanding period of daylight envelops him with surprising rapidity and by the end of the month, his altitude is becoming low in the south-west.
Appearing high in the south as Orion approaches the south-west horizon are the constellations of spring. Of these, the most noticeable is Leo the Lion. Its brightest star, Regulus, sits at the base of a backward-facing question mark pattern known as the Sickle. This represents the front of the lion. The body then extends to the east (or left as seen from the UK). Leo’s back legs dangle south, with the tail marked by the middle-bright star Denebola further to the east.
Leo marks a direction in the sky away from the Milky Way. Using binoculars or a telescope it’s possible to see other galaxies beyond the confines of the Milky Way in Leo’s direction. Three prominent examples are M65, M66 and NGC 3628, which lie slightly east of the midpoint of the upper part of Leo’s rearmost leg. Together these form the Leo Triplet.
Binoculars should show the brighter pair of M65 and M66 but a telescope or larger binoculars are likely necessary to see NGC 3628. M65 is around 35million light years away, a distance shared by the other two galaxies in the group.
M66 is larger than M65 and the brightest of the three. NGC 3628 appears faintest and is hardest to see. A thin, dark dust lane runs horizontally across its core, giving an overall appearance reminiscent of a celestial hamburger.
Lying north of Leo is a faint pattern of stars, which looks like a squashed diamond with a tail. It represents Leo Minor, the Little Lion. The constellation contains numerous objects of interest including NGC 3432, the Knitting Needle galaxy, which looks like a thin sliver of light seen through a telescope.
In 2007, a Dutch schoolteacher, Hanny van Arkel, discovered an odd feature which has consequently become known as Hanny’s Voorwerp (Hanny’s Object). The best description is that it appears like a blob with a hole in it, close to the spiral galaxy IC 2497.
The Voorwerp is galactic in size, its hole measuring 16,000 light years. It’s believed to be the remnant of an interaction between IC 2497 and another galaxy, and is a very rare phenomenon called a quasar ionisation echo.