A monthly look at astronomical events in the sky and on Earth
Well, were you able to take advantage of that wonderful run of clear, moonless nights during the second half of April? I hope so, because from about May 3rd right through to the end of July, it doesn’t get astronomically dark at all. And this prevents observation of all but the brightest deep sky objects, and even those can only be seen between midnight and 0200 BST.
This is the time therefore to concentrate on the Moon and planets (where possible), star clusters, double stars, maybe the Sun, and of course maintaining your telescope(s) and observatory if you have one.
By the way, comet ATLAS which was hoped would put on a good show has broken up and its remnants are only visible in large telescopes. Pity.
The solar system
We are still in solar minimum but it’s worth keeping an eye on https://www.spaceweather.com and the EU aurora service for news of sunspots and potential aurora. There was a small sunspot visible on April 26th so you never know.
And just in case you’re new to astronomy, do recognise that you will blind yourself if you look at the sun using binoculars of a telescope. To observe safely, use the eyepiece projection method or make yourself a full aperture solar filter using the correct filter material from a reputable source.
Best seen in a waxing gibbous phase between the 1st and 4th of the month then as a wafer-thin crescent low in the NNW at about 2150BST on the 24th (see Mercury and Venus below) and as a waxing crescent from then until first quarter on the 30th.
Elusive Mercury may be glimpsed very low in the WNW – NW sky from the 21st. It is 1½° below brilliant Venus on the 21st, and 1½° to Venus’ left on the 22nd, both at about 2145. Mercury and Venus are joined by the Moon on the 24th, with Mercury being half way between the Moon and Venus and above an imaginary line between them. From then on, Mercury continues to rise and move to the left each day, reaching its maximum altitude of just over 11° on the 31st. It will remain visible through until about June 10th.
Venus continues to dominate the western sky for most of the month, but gradually moves lower and to the right and into the sunset glow as month-end approaches. It’s “coming up on the inside lane” as it heads towards inferior conjunction (directly between us and the Sun*) on June 3rd. Its appearance is as a narrowing crescent, growing from 40 to a whopping 57 arc seconds, and by the middle of the month this shape can even be seen in any decent pair of binoculars if they’re held steady, perhaps by resting them on the roof of a car if you haven’t got a tripod and binocular clamp.
* Not absolutely directly between us and the Sun, as if this happened there would be a transit of Venus. In this conjunction, Venus passes about ¼° north of the Sun.
Mars can only be glimpsed low in the SE around 4:00 to 4:30 in the morning. It’s 3° above the crescent moon on the 15th. It’s a long way away, only 8½ arc seconds in diameter and at magnitude 0.2 so hardly worth observing. Wait until much nearer to its opposition in October.
Jupiter and Saturn
These planets are close together, unrewardingly low in the SSE in the morning sky and can only really be observed around 4 a.m. They are joined by the crescent moon on the 12th. I wouldn’t bother with them this month unless you’re a real night hawk. Wait until July.
Uranus and Neptune
Both these planets are too close to the Sun to observe this month.
Three Star Clusters: M3, M5 and M13
The three globular clusters: M3, M5 and M13 are well worth your attention.
The star map below shows the locations of these three objects. Compass direction is shown along the horizon. For the best views, wait until way past 10:30 pm if possible.
For an insight into these mysterious objects, read the Wikipedia entry.
M3 is a truly fine globular about 18 arc minutes in diameter and of magnitude 6.2. It lies north of Arcturus and about half way between it and the 3rd magnitude star Cor Caroli in Canes Venatici. As with all globulars, whack up the magnification for a chance to see individual stars (of which there are 500,000!).
M5 is another stunning globular, magnitude 6.0 and 23 arc minutes in diameter. Find it by following the line of 4th magnitude stars running along the top edge of Virgo.
M13 is the daddy of all globulars and deserves the name “The Great Globular Cluster”. Its magnitude is 5.8, 2/3rds the apparent diameter of the moon and easy to find on the edge of the central “square” of Hercules. A small telescope will see it as a fuzzy patch but 6-inch telescope is needed to resolve its stars. Do give it a go.
Mizar and Alcor
This famous naked eye double star one away from the tail end of the Great Bear is directly overhead in May and offers a quick opportunity to check your eyesight. The separation is about 12 arc minutes. Mizar itself is a double with a separation of 14 arc seconds and is easily seen with even a small telescope. This Sky and Telescope article describes them in more detail.
Cor Caroli (Alpha Canum Venaticorum)
Cor Caroli (Alpha Canum Venaticorum) which we mentioned above is also a beautiful double star, in fact one of the finest in the sky for small telescopes. The components are of magnitude 2.9 and 5.4 with a separation of 19.6 arc seconds. The brighter star has a spectral type of A0 and looks white; its companion has a spectral type of F2 (not unlike the Sun) and looks yellow. There’s quite an interesting Wikipedia entry about Cor Caroli.
Passes of the International Space Station (ISS)
The ISS is visible nearly every night in May, and on some nights three times! See the Heavens-Above web site for more details. Here is a link with all fields relevant to York selected.
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 28/04/2020