WHAT'S UP THIS MONTH - MAY 2019
(Link to What's Up April 2019)
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THESE PAGES ARE INTENDED TO HELP YOU FIND YOUR WAY AROUND THE SKY
The chart above shows the night sky as it appears on 15th May at 22:00 (10 o'clock) in the evening British Summer Time (BST). As the Earth orbits the Sun and we look out into space each night the stars will appear to have moved across the sky by a small amount. Every month Earth moves one twelfth of its circuit around the Sun, this amounts to 30 degrees each month. There are about 30 days in each month so each night the stars appear to move about 1 degree. The sky will therefore appear the same as shown on the chart above at 23:00 (11 o'clock BST) at the beginning of the month and at 21:00 (9 o'clock BST) at the end of the month. The stars also appear to move 15º (360º divided by 24) each hour from east to west, due to the Earth rotating once every 24 hours.
The centre of the chart will be the position in the sky directly overhead, called the Zenith. First we need to find some familiar objects so we can get our bearings. The Pole Star Polaris can be easily found by first finding the familiar shape of the Great Bear ‘Ursa Major' that is also sometimes called the Plough or even the Big Dipper by the Americans. Ursa Major is visible throughout the year from Britain and is always easy to find. This month it is almost overhead. Look for the distinctive saucepan shape, four stars forming the bowl and three stars forming the handle. Follow an imaginary line, up from the two stars in the bowl furthest from the handle. These will point the way to Polaris which will be to the north of overhead at about 50º above the northern horizon. Polaris is the only moderately bright star in a fairly empty patch of sky. When you have found Polaris turn completely around and you will be facing south. To use this chart, position yourself looking south and hold the chart above your eyes.
Planets observable: Mars and Jupiter. Venus and Saturn are just observable in the early morning.
EXPLORING THE NIGHT SKY THIS MONTH
The Southern Night Sky during May 2019 at 22:00 BST
The chart above shows the night sky looking south at about 22:00 BST on 15th May. West is to the right and east to the left. The point in the sky directly overhead is known as the Zenith and is shown, marked in red' at the top and centre of the chart. The curved brown line across the sky at the bottom is the Ecliptic or Zodiac. This is the imaginary line along which the Sun, Moon and planets appear to move across the sky. The brightest stars often appear to form a group or recognisable pattern; we call these ‘Constellations'.
Constellations through which the ecliptic passes this month are Gemini (the Twins), Cancer (the Crab), Leo (the Lion), Virgo (the Virgin) and Libra (the Scales) rising over the eastern horizon. The constellation of Sagittarius will rise in the east later in the evening.
Mars is still just about visible in the bright sky, just above the western horizon, at sunset but is looking small now. Earth overtook Mars a few months ago as it moved faster along its smaller orbit inside the orbit of Mars. Mars in now being left behind Earth and appears smaller as it moves further away. Although it is looking smaller it is still quite bright.
Jupiter will be rising over the eastern horizon at about 23:00 in the constellation of Sagittarius. It will be midnight before Jupiter is high enough to observe. The view will not be good because Jupiter will be in the dirty and turbulent air close to the horizon.
In the west and sitting astride of the Ecliptic is the constellation of Gemini (the Twins). The twin stars Castor and Pollux are easy to identify. For those that have a telescope, Castor can be seen as a double star. By increasing the magnification, Castor itself will be seen as a pair of stars. It will push a small telescope to its limits to see but this lovely triple star system it is worth the effort.
To the east of Gemini is the constellation of Cancer with its lovely Open Cluster Messier 44 (M44) also known as Praesepe or the Beehive Cluster. This is a lovely Cluster that is best seen using binoculars or a small telescope using a low power eyepiece. The cluster is about twice the diameter of the Full Moon and contains about 200 stars. It is located about 577 light years away and its stars are estimated to be around 400 million years old.
Further to the east (left) of Gemini is the constellation of Leo (the Lion). Leo is quite distinctive with the ‘Sickle' shaped pattern of stars looking much like the head of the lion that Leo represents. In fact the traditional ‘stick figure' shape of Leo as shown on the chart above does look rather like the lion's body or the Sphinx in Egypt. The ‘Sickle' shape is also described as looking like a backwards question mark (?).
Following Leo is the less obvious constellation of Virgo but it does have one fairly bright star called Spica. Virgo gives its name to a large cluster of Galaxies that is also spread over into the neighbouring constellations of Coma Berenices (Berenices' Hair) and into Leo.
To the north of Virgo is the bright orange coloured star called Arcturus in the constellation of Boötes (see the next page). Arctaurus is a Red Giant star that is nearing the end of its ‘life' as a normal star. It has used almost all of its Hydrogen fuel and has expanded to a diameter of around 25 times the diameter of our Sun. At the moment it shines 115 times brighter than our Sun but it is destined to collapse to become a White Dwarf. (See Boötes in the constellation of this month - Hercules)
Higher in the south east is the constellation of Hercules (the Strong Man). Hercules has a rather distinctive distorted square shape, at its centre, called the ‘Keystone' due to its resemblance to the centre stone of an arch or bridge.
CONSTELLATION OF THE MONTH - HERCULES (the Strong Man)
The constellation of Hercules with Lyra and Boötes
The chart above shows the constellation of Hercules and its location to the west (right) of Lyra and the Summer Triangle and has Boötes to the west (right). Hercules is the great strongman from Greek mythology. He is illustrated in the picture below (up-side-down), as he appears in the sky, with a club held above his head. The ‘Keystone' asterism (shape) can be a little difficult to identify in a light polluted sky but easy to find again.
An illustration of the constellation of Hercules
The jewel of Hercules is without doubt is the Great Globular Cluster, Messier 13 (M13). M13 can be found in the western (right) vertical imaginary line of the ‘Keystone'. It is just visible using a good pair of 9 x 50 binoculars. The cluster, of about a million stars, can be seen using a 90mm f 10 telescope but will look even more impressive when using a larger telescope.
The Great Globular Cluster Messier 13 (M13) in Hercules
Globular clusters are thought to be the cores of small galaxies that have ventured too close to Giant Spiral Galaxies like our Milky Way. The outer stars of these smaller galaxies have been stripped away, by the gravity of the giant spiral. This process has left the dense core clusters of between 100,000 and a million stars. There are about 100 Globular Clusters in a halo around the Milky Way.
There is another Globular Cluster in Hercules Messier 92 (M92) but it is further away and needs a telescope to see. It is much further away than M13 and consequently it appears much smaller and fainter. When observed using a larger telescope M92 appears as a really neat and compact ball of stars and very beautiful to look at.
Messier 92 (M92) imaged using a large telescope
THE SOLAR SYSTEM MAY 2019
MERCURY will be very low over the eastern horizon before sunrise at the beginning of the month and will be very difficult to see. It will move into Superior Conjunction (pass behind the Sun) on 21st May.
VENUS rises over the eastern horizon at about 04:30 and will be very difficult to see as it draws closer to the Sun. Although Venus is very bright at magnitude -3.8 its light will be drowned out by the Sun rising just half an hour later. Venus will be moving into Superior Conjunction (pass behind the Sun) on 14th August. See the chart below.
Mercury, Venus and Uranus in the early morning sky
MARS is still observable in the early evening but is much lower now and getting close to the southern western horizon in turbulent and smoggy air. The Red Planet is looking smaller at 4.0 arc-seconds in diameter but still quite bright at magnitude +1.7.
JUPITER is now a late evening object rising over the eastern horizon around 23:50 at the beginning of the month and 22:00 at the end of the month. So it will have risen high enough for observing at midnight at the end of the month. See the chart below.
Saturn and Jupiter at 02:00
SATURN will rise at midnight at the end of the month so will be observable at about 01:30 but will be low over the horizon. It will of course be worth staying up for if it is a clear night.
URANUS will not be observable this month as it will be too close to the Sun. See the Venus chart above.
NEPTUNE will not be observable this month as it will be very low and too close to the Sun
The Sun rises at 05:20 at the beginning of the month and at 04:45 by the end of the month. It will be setting at 20:35 at the beginning and 21:10 at the end of the month.
There was a lovely sunspot from 8th April until 20th April the best seen so far this year.
The sunspot imaged by Steve Harris on 11th April 2019
The image above was taken on 11th April 2019 using a DSLR camera mounted to the focuser in place of the eyepiece. The telescope used was the 120mm aperture 1000mm focal length Skywatcher refracting telescope. The exposure was 1/3000 second. There has been no processing of the image.
Sunspots are caused by the magnetic force lines on the Sun. These lines of magnetic force emanate from the poles and loop around the Sun from pole to pole. Being composed of gas, the mass of the Sun is fluid and the equatorial region rotates faster than the poles. This stretches and distorts the lines of magnetic force around the equator.
After about four years the lines of magnetic force become so stretched they begin to break up and loop in and out of the surface of the Sun. As the surface is broken the indentations allow a slightly cooler lower layer to become visible as a darker Sunspot.
Sunspots may be active on the Sun for about four of five years then will become less common or even disappear completely for four of five years. This sequence is known as the Solar Activity Cycle and repeats approximately every eleven years. So we will see a ‘quiet' period for about 3 years then the activity will begin to increase into an active period of about four years until the activity again diminishes. There may be other longer cycles where the overall activity may decrease until no significant activity will be seen for a few decades. Some astronomers think we might be entering one of these ‘quiet' periods now but we will need to wait and see.
A very impressive group of sunspots imaged August 2015
THE MOON PHASES IN MAY
New Moon will be on the 4th May
First Quarter will be on 12th May
Full Moon will be on 18th May
Last Quarter will be on 26th May
The First Quarter imaged on 13th April
The Full Moon imaged on 19th April
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