With shortened nights there is only a short window for observing the night sky and the constellations you will see are more subdued. However there is still plenty to observe and enjoy. Vernon from the Callander and West Perthshire U3A Astronomy group shares what to look out for this month. 

It is always helpful to have a star chart to follow when navigating and observing the heavens.  A free star chart which also contains lots of additional observational notes is published monthly by Skymaps. Simply go to skymaps.com and scroll down to ‘Download the latest issue’. From here you will can download the northern hemisphere version and save it.  This is then best printed double sided to an A4 sheet. It is worth noting that planets do not appear on skymaps. In this note of astronomical events I have only included items that can be seen either with the naked eye or with a pair of binoculars.

Should you venture outside you will need a torch. Use a red light head torch if you have one, or put red plastic over a torch to illuminate the skymap and preserve your night vision which improves greatly over time. Wrap up warm and with a little perseverance, about 20 minutes, you will feast your eyes on the universe that you live within. Enjoy and indulge!

May features

With shortened nights there is only a short window for observing the night sky and the constellations you will see are more subdued.  Hercules and Virgo can be seen, but if you can find a pair of binoculars the constellation of Coma Berenices, not bright to the naked eye, makes a wonderful target.  The magnitude 2.7 open cluster Melotte 111 (also known as the Coma Star Cluster) as well as the interesting galaxy M64 or the “Black Eye” Galaxy lay inside the constellation and make excellent sites to explore. Two other binocular sites of interest are the Whirlpool Galaxy, or M51, in Canes Venatici and secondly the Spiral Galaxy, M101, which sits towards the end of the Plough’s handle. Then there is the Eta Aquarid meteor shower which peaks this month. Because the radiant of this shower is near the celestial equator the viewing is poor from our northerly latitudes.

Looking South

Early in the evening is the bright star Spica which sits in the constellation of Virgo. Virgo, the second largest constellation in our skies, contains over 200 galaxies and many of the brighter ones can be seen using amateur telescopes. The Virgo Cluster, Messier 87, is a giant elliptical galaxy and the closest of its kind to the solar system. Although it looks like a globular cluster, a fuzzy blob in smaller telescopes, it is one of the largest known galaxies containing over a million, million stars in a region of just 160,000 Light Years in diameter. Meanwhile, many more orbit the cluster in a halo that continues outwards to 250,000 Light years. Radio signals indicate that the nucleus of M87 has a supermassive Black Hole which feeds on material from its surroundings which probably comes from a galaxy within the cluster.

This is the time of year that the Spring Triangle asterism becomes useful. The asterism is huge taking up much of the south and south eastern sky. It is denoted by the three brightest stars in the spring sky, Arcturus, Regulus and Spica. To find the Spring Triangle first of all using your skymaps.com chart find the Plough which is virtually overhead and the seven brightest stars in the constellation of Ursa Major, the Great Bear. In US publications this is called the Big dipper, not after a roller coaster but a saucepan shaped pan for dispensing water. Now follow the handle of the dipper which is rounded forming part of an arc. Follow that arc downwards to the bright star Arcturus which forms the tail of the kite shaped Constellation of Bootes, the Bear Driver. Then head to your right and slightly upwards, a full 60 degrees, or six clenched fists, towards the next bright star Regulus which is also known as the King Star because it is the heart of the king of beasts, Leo the Lion. From here follow to the left until you find the third bright star to form the triangle, Spica, which is the hand at the waist of Vigo. With this asterism it is fairly easy to navigate your way to all of the stars and constellations in this huge sector of the sky for several months to come.

Image showing the Plough asterism and the Spring Triangle

Looking North

The constellations of Lyra, the Harp, Cephus, representing the king of Ethiopia and husband of Cassiopeia, Ursa Minor, the Little Bear which carries the weight of the of Polaris on the tip of its tail and Draco are all well placed in the sky. We will concentrate on the Plough asterism within the constellation of Ursa Major, Ursa Minor and Cassiopeia so we can locate true north and dispel a myth. Starting with Plough we have two bright stars to the side of the pan without the handle. They are called Merak at the base and Dubhe at the lid of the pan and known as the Pointers. Follow the line of the two Pointers until you reach a moderately bright star often further from the Plough than many think.

Shows the shape of plough asterism pointing to the north star, includes the silhouette of a person. looking up.

Where the North Star appears in the sky depends on your latitude. At the North Pole, the North Star appears directly overhead, but at the equator, it would appear on the horizon – both corresponding to the latitudes of the location. By using the “fist” method you can count how many “fists” the North Star appears above the horizon That will give you your latitude. Remember that a “fist” counts as approximately 10 degrees for latitude. Callander sits at latitude 56degrees 24minutes.

Now to dispel the myth, many people think Polaris is the sky’s brightest star. In fact, Polaris ranks only 50th in brightness. In addition, Polaris will not remain the North Star forever. Every 26,000 years the North Celestial Pole describes a 47 degree arc through our sky. Because of this Polaris gradually changes position by 1 degree every 73 years and by 2102 it will be its closest to the Celestial North Pole, a separation distance of just 27 minutes of 0ne degree. After 2102 it will slowly move away and within 2000 years will be close to Errai, a star in the constellation of Cephus. Observational Celestial Navigation will be more difficult by this time as Errai is three times dimmer than Polaris.

Meteors

We are fortunate to have two different meteor showers this month, the Eta Aquarid shower peaks on the 5th and the Eta Lyrid meteor shower on the 9th and the Eta Aquarid meteor shower on the 5th/6th.

The Planets

This month provides us with a good opportunity to see Mercury, Venus, Mars, Saturn and Jupiter. Dates, Locations and best times are in the ‘Nights of particular interest’ section.
Mercury is at its greatest elongation on May 17th. Easiest opportunity for sighting is on 15th.
Venus will become visible for a brief period towards the end of the month in the evening sky, magnitude -3.9.
Mars can be observed crossing Gemini, magnitude 1.6/1.7.
Jupiter can be observed in Aquarius, magnitude 2.2/2.4.
Saturn can be observed on Capricornus, magnitude 0.7/0.6.

Nights of particular interest

Some of the objects described below are expressed in degrees from the Moon. This is far less complicated to measure than you might think. To measure 10 degrees, hold your hand up towards the sky at arm’s length and turn your hand up so that it obscures part of your view. The width of your hand is 10 degrees and holding just one finger is two degrees.

03rd –  20.51 Last Quarter Moon
04th –  05.30 Jupiter and Saturn are moving slowly away from the Sun with the Moon positioned between them on the South East horizon.
06th –  04.00 Eta Aquarid shower peaks with around 40 shooting stars per hour in the East at about 30 degrees, or three clenched fists, above the horizon. The shower begins at 02.30, peaks at 04.00.
11th –  20.01 New Moon
11th –  21.53 Moon at apogee, 406,512 km, greatest of the year.
15th –  22.45 The Moon is now a 4 day old crescent and will be sitting just below to the right of Mars. By imagining a straight line between the Moon and Mars extending to the horizon and looking down that line you will encounter Mercury which will look like a pinkish-white star.
17th –  05.54 Mercury at its greatest elongation from the Sun, magnitude 0.3
19th –  20.13 First Quarter Moon. Look for bright star Regulus just below the Moon this evening.
23rd –  The bright star under the Moon this evening is Spica in the constellation of Virgo.
26th – 12.15 Full Moon
26th – Total Lunar eclipse, Americas, Pacific, Australia and Asia.
28th – 22.45 Mercury is past its best but can still be seen just to the left of Venus by using a pair of binoculars.
31st –  04.35 The Moon is two days from first quarter. This morning it will be directly below Saturn in the morning twilight and closer to Jupiter tomorrow morning.