The night sky in March

Want to know what's up in the sky tonight? Our night sky chart will provide you with the information you need to locate the brightest planets, stars and deep-sky objects ...

March is a wonderful month to observe the heavens! The constellations on view contain many of the brightest stars in the northern sky (Taurus, Orion, Gemini and Canis Major).

march This month’s chart shows the night sky looking South in mid March at 2300. (click on image for larger view)

Auriga – this month’s sky highlight

Auriga was named after the mythological inventor of the chariot. Auriga contains the sixth brightest star in the sky, Capella, a binary star system whose components are thought to be red giant stars.

Look due West at 2100 and at an elevation of 60 degrees and you will see Capella a beautiful yellow-orange star. About five degrees below in a seven o’clock position, you will find an arrow shaped arrangement of stars pointing towards the position of two o’clock . This asterism is affectionately known as ‘The Kids’.

Using a star atlas try to locate the three famous Messier objects within this constellation: M36, M37 and M38.

M36 is a nice open cluster embedded in the faint radiance of the Milky Way. It contains a dozen or so bright members against a hazy background of fainter stars. Because it lies against the Milky Way, it’s hard to discern the edges of this loosely packed cluster. In binoculars, M36 along with M38 and M37 can be seen in the same field of view. M36 is a young cluster (only 30 million years old), so it contains no red giant stars.

Under very dark skies M37 is a naked eye cluster. It is a joy to observe and undoubtedly the best open cluster in Auriga and a favourite amongst observers. Dozens of bright stars can be resolved. Fainter white stars surround a red 9th magnitude star near the centre of this cluster, adding to its aesthetic beauty. A telescope and careful observation reveals several dark voids within the cluster, which are dust lanes of the Milky Way.

M38 is a large open cluster with many bright and fainter members. This populous cluster is easily seen in binoculars along with nearby NGC 1907, a smaller 8th magnitude open cluster. A combination of brighter stars, double stars and dark lanes make it a delightful site. M38 is relatively old for an open cluster, having formed 220 million years ago.

A variable star project

Throughout the month of March, Algol is nearly overhead at sunset and visible the entire evening. This star is easy to overlook because it’s not nearly as bright as some stars in the night sky but it is Algol’s brightness that makes it so unusual and fascinating. Algol’s brightness changes making it a so called ‘variable star’. There are many different reasons for a star to change its brightness, this one does so because it is regularly eclipsed by a darker companion orbiting around it. Algol is an eclipsing variable.

During eclipse Algol dims from a magnitude of 2.1 to 3.4. It takes the eclipsing binary star exactly 2 days, 20 hours, 48 minutes and 56 seconds to complete its orbit. Each eclipse lasts about 10 hours but it’s during the middle 2 hours that the maximum eclipsing occurs.

This is a fascinating event to watch but, of course, the first thing you have to do is find Algol. These directions will help you (use our monthly sky map above).

Imagine a line from the very bright star Capella to the not too bright stars of Almaak, Mirach and Alpheratz. There is a star on either side of the line between Almaak and Capella, about midway between them. The one to the north is Mirphak but the one to the south is our target – Algol (don’t confuse it with the brighter star Hamal and don’t confuse any of these with Saturn and Jupiter which would be visible farther south than these stars!

Now that you know where it is, you’ll want to know when to watch for Algol dimming. It the best way is to watch over consecutive nights and compare Algol to the brightness of the stars around it. Use Almaak, which always has a magnitude of 2.1 (Algol’s normal magnitude), as a reference. At minima, Algol will be as faint as either of the two stars flanking it.

Good luck! we would love to hear from you if you are successful at observing Algol’s minima.

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© Macclesfield Astronomical Society 2017