What’s Up! March 2020

A monthly look at astronomical events in the sky and on Earth

Solar System

The Moon

Best seen from Sunday 1st to Saturday 7th as it waxes from crescent through first quarter on the 2nd to gibbous, high in the sky to the SW and S. It can again be seen as a wafer-thin crescent low in the SW on the 27th through to the end of the month.


Mercury

You just missed it! It was visible in February but not now. There’s another chance in late May.

Venus

Venus dominates the south-west to western sky this month. On 1st March, the planet will be at 37° altitude at sunset and at magnitude -4.3. It reaches greatest eastern elongation (GEE) on the 24th, when it is 46° away from the Sun. On that day, Venus will present as a perfect “first quarter moon” 23.5 arc seconds in diameter and have a magnitude of -4.5. On the 28th, Venus will be joined by the Moon. Venus will get even brighter and larger in April.

Mars, Jupiter and Saturn

These planets are clustered together in the morning sky and on the 18th are joined by the waning crescent Moon. None of these three planets is worth observing for its own sake at the moment, but the group – together with the Moon – is definitely worth a look if you can force yourself out of bed by about 0530. They’re only at 6-8° altitude and in the SE-SSE (azimuth 145°). If you have a camera with a 10° field, you could capture all four, or you could get Jupiter, Mars and the Moon in a 3° field.

Uranus and Neptune

Both these planets are too close to the Sun to observe this month.


Non-Solar System Objects

There follows a shortlist of objects that are roughly in the south this month at 2030 hrs – a convenient time for family viewing.

The southern night sky mid-evening
The image above shows the horizon-to-zenith sky at 20:30, looking roughly south (from SkyViewCafe.com)

Castor and Pollux

The “heavenly twins” and the two brightest stars in the constellation of Gemini.

A 2 or 3-inch telescope will show Castor as a double star (separation 4 arc seconds) but in fact each of those stars is itself a double, discovered spectroscopically as they are too close to be separated optically. Each pair comprises a hot, bright A-class main sequence star orbited by a cool, faint M-type red dwarf. What’s more, this pair of doubles is orbited by another very faint double, making Castor an amazing 6-star system. Its combined magnitude is 1.58.

While your telescope is pointing at Gemini, take a moment to look at Pollux. Its orange colour is clearly very different from that of Castor. Pollux is a giant K-type star nine times the diameter of the Sun but only twice its mass. At 34 light years distant, it’s the nearest giant star to us. It does have a planet at least twice the size of Earth orbiting it called Thestias. Unfortunately, at only 1.6 astronomical units (a.u.) from the star when the habitable zone round Pollux is between  6 and 12 a.u., life on Thestias could be a tad challenging!


The Winter Triangle (Procyon, Sirius and Betelgeuse)

These three interesting stars form a near-equilateral triangle. See star map above.

Sirius
The smaller twin of the double star Sirius is a challenge to see.

Sirius

The brightest star in the sky. Is actually a binary. Sirius A is a main sequence A0 star; Sirius B is a white dwarf hundreds of times fainter than Sirius A. Although their angular separation is currently 10 arc seconds, the difference in brightness (magnitudes -1.44 and 8.5) makes spotting Sirius B a challenge for even large telescopes. The Hubble image on the left illustrates this.

Procyon A-B
Double star Procyon, also a challenge.

Procyon

Another binary star. Procyon A is an F5 star and thus cooler and yellower than Sirius. Procyon B is another white dwarf. Their magnitude difference and closer separation (4.3″) makes spotting the fainter component even more difficult than for Sirius but Giuseppe Donatiello has done it with a home made 127mm f/9 ED refractor!

Betelgeuse
Betelgeuse, a red supergiant. One of the few stars large and near enough for specialist telescopes to see it as a disc.

Betelgeuse

Now Betelgeuse is something quite extraordinary. It’s an M1 red supergiant and one of only a handful of stars that are large and near enough for specialist telescopes to see their surface as a disc. This is a NASA image. Put it where the sun is and it would extend nearly to the orbit of Jupiter. It’s a semiregular variable whose magnitude changes by 1.3; its surface temperature is only 3600K but it’s luminosity is 90,000 to 150,000 times that of the sun.


Three Open Clusters, M44, M41 and M47

All three are on the SkyViewCafe sky view above.

M44, also known as the Beehive Cluster or the Praesepe contains over 1000 stars, is one of the nearest open clusters to Earth, and is about magnitude 3.7. It can be seen with the naked eye as a faint fuzzy patch 1.5° in diameter. It is best seen in binoculars or a telescope with a low power wide field eyepiece. The Moon passes just to the north of it at about 2200 hrs on the evening of the 6th.

M41 and M47. These often neglected clusters are fine targets in modest telescopes and even binoculars. M41 is 5° below Sirius, and M47 is 12° east and 2° north of Sirius. They’re both at magnitude 4.5 and about the apparent diameter of the full moon. Note that M41 contains a mixture of red giants and white dwarfs  but M47 comprises mainly young blue stars and only a few red giants.

M41

Messier 41
This open cluster below Sirius contains a mixture of red giants and white dwarfs

M47

Messier 47
This open cluster north east of Sirius contains mainly young blue stars

Images taken from https://www.messier-objects.com (A great site for exploring all the Messier objects.)


Passes of the International Space Station (ISS)

The ISS is visible every night in March except for the 14th – 18th. See the Heavens-Above web site for more details. Here is a link with all fields relevant to York selected.

Space News

For action in the satellite and spacecraft world and for  up-to-date news, scroll https://www.space.com/32286-space-calendar.html

Clear skies and good viewing.

John Rowland 27/02/2020

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