WHAT'S UP THIS MONTH - APRIL 2023
(Link to What's Up March 2023)
Click here for Lyrid Meteor Shower
THESE PAGES ARE INTENDED TO HELP YOU FIND YOUR WAY AROUND THE SKY
The chart above shows the whole night sky as it appears on 15th April at 21:00 (9 o'clock) 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 8 o'clock BST at the beginning of the month and at 10 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 quite easy to find. This month it is directly 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 in the evening sky: Mars, Venus Uranus and Mercury (in the early evening).
OBSERVING THE SOUTHERN NIGHT SKY THIS MONTH
The night sky looking south at about 22:00 BST on 15th April
The chart above shows the night sky looking south at about 21:00 BST on 15th April. 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 (in red) at the upper 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 Aries (the Ram), Taurus (the Bull), Gemini (the Twins), Cancer (the Crab), Leo (the Lion), Virgo (the Virgin) and Libra (the Scales).
Moving over the south western horizon is the winter constellation of Orion (the Hunter). Orion is still easy to find by looking for his very obvious three stars of his belt. Orion has his Hunting Dogs Sirius (the big dog) and Procyon (the little dog) to the east (left) and following him.
Above Orion is the constellation of Taurus (the Bull). The most obvious star in Taurus is the lovely Red Giant Star called Aldebaran. It appears slightly orange to the ‘naked eye' but it is very obviously orange when seen using binoculars or a telescope. Aldebaran is located at the centre of the ‘flattened' X shape formed by the brightest stars in Taurus. It appears to be in a cluster of stars known as the Hyades but it is not a true member and is much closer to us than the rest of the cluster.
The brightest planet, Venus, is looking very bright in Taurus this month as it moves towards us. At the end of the top right (upper west) arm of the ‘X' shape of Taurus is the beautiful ‘naked eye' Open Star Cluster Messier 45 (M45) known as the Pleiades (or the Seven Sisters). It is one of the closest open clusters to us and really does look magnificent using binoculars or a small telescope with a low magnification eyepiece.
To the east (right) of Taurus is the rather indistinct constellation of Cancer (the Crab). The stars of Cancer are quite faint and can be difficult to discern especially in a light polluted sky. It is really worth searching out Cancer using binoculars or a telescope to see the Open Cluster M44 (the Beehive Cluster). M44 is older and further away than M45 (the Seven Sisters) so is fainter than M45 but still looks lovely. It has a group of stars that resemble an old straw Beehive with bees around it.
Following Taurus is the constellation of Gemini (the Twins). The two brightest stars in Gemini are Castor and Pollux that are named after mythological twins. To the north of Taurus is the odd pentagon shape of Auriga (the Charioteer). Dominating Auriga is the brilliant white star Capella. For those with a telescope there is a line of lovely open clusters in Taurus and Auriga. These are M35 in Taurus and M36, M37 and M38 in Auriga .
The constellation of Leo (the Lion) follows Cancer along the Ecliptic and was the constellation of the month last month. It does actually look a little like a lion or the Sphinx in Egypt. Around and between Leo and the neighboring constellation of Virgo is a cluster of galaxies. Our Milky Way galaxy and our local group of galaxies are members of this larger group of galaxies called the Virgo Cluster. A medium sized telescope (150mm to 200mm) and a dark sky is required to see these faint objects.
To the north of Virgo is the constellation of Boötes with its bright orange coloured star called Arcturus. The stars in Boötes form the shape of an old fashioned diamond shaped kite with Arcturus located where the string of the tail would be attached. Arcturus is one of just a few stars that do actually appear to be coloured and is noticeably orange to the ‘naked eye'. It is actually a star with a mass similar to our Sun but is older at 7 billion years (our Sun is 4.3 billion years old). Arcturus is a Red Giant approaching the end of its life.
WHERE TO FIND THE PLANETS THIS MONTH
Mercury will be at its very best on 11th April this year.
Venus will be visible in the early evening sky as soon as possible after sunset. It will appear at a rather small diameter (for Venus) and will be and just over half illuminated.
Mars can be seen almost directly overhead and has moved from Taurus into Gemini. It is starting to look small at about 7" (arc-seconds) as it moves further away from us. So Mars is past its best and is now starting to fall behind Earth and will appear to be getting smaller and fainter as it moves away from us.
Jupiter is in conjunction with the Sun this month and is not observable.
Saturn has moved out from its conjunction with the Sun last month and has moved into the early morning sky but will be too close to the Sun for observing.
Uranus will be low in the bright evening south west sky and sets at about 22:00.
Neptune will not be visible this month as it was in conjunction with the Sun on 11th March and is now starting to reappear in the early morning sky before sunrise.
The Lyrid Meteor shower this month.
URSA MAJOR and BOÖTES
The constellations of Ursa Major and Boötes
One of the Constellations of this Month is one of the best known of all the constellations and is certainly the most recognisable . It is Ursa Major (the Great Bear) also known as the ‘Plough' or ‘the Big Dipper' in the USA. It has very little resemblance to a bear and looks much more like a ‘Saucepan'.
Ursa Major is almost overhead at this time of the year as can be seen by the chart at the top of this page. The point in the sky directly overhead of the observer is called the ‘ZENITH' and is shown in red on the chart. The chart shows the sky as it will appear at 22:00 on 15th April.
Ursa Major is a circumpolar constellation, this means it never disappears below the horizon from the UK and so is always visible somewhere in the night sky throughout the year. All the stars in the night sky appear to rotate around a point in the sky that we call the ‘North Celestial Pole'. This point is located very close to the star Polaris in the constellation of Ursa Minor (the Little Bear) and called the Little Dipper in the USA.
The sky rotates around Polaris once a year due to Earth's orbit around the Sun. Polaris can always be found by first finding Ursa Major. Then by following the two stars opposite the handle of the ‘saucepan shape', up and out of the pan and looking about five times the distance between the Pointer Stars. See the chart at the top of this page.
Ursa Major also rotates around the Polaris (the pole star) so it completes one revolution around Polaris every day. It also rotates around Polaris once every year due to Earth's orbit around the Sun. This means that if it is observed at the same time of the night throughout the year it will have moved all around the sky. In spring (now) Ursa Major appears close to Polaris (and directly overhead). In the summer it will be to the east of Polaris and in the winter it will be low over the northern horizon. So it will move around but will always be visible.
The centre star of the three stars forming the handle of the ‘saucepan' is a famous naked eye double star Mizar and its companion Alcor. Anyone with good eyesight or wearing their glasses will be able to see Alcor as a smaller and fainter star close to Miser. In ancient times seeing this pair of stars was used as a measure for good eyesight. So if men were being recruited for an army and they could see Alcor their eyesight was good enough.
Viewed through powerful binoculars or a telescope, Mizar itself can be seen to be a double star. These two stars are quite far apart and orbit around their common centre of gravity. This means Mizar is a double star with Alcor close by so appears as a three star system.
However, this is not the end of the story! When the light from the two component stars of Mizar is examined using a spectroscope each star is found to be double itself. This means the Mizar - Alcor pair is a five star system but the Mizar double / double stars are too close together to be separated and seen using any amateur telescope.
Mizar and Alcol enlarged
INTERESTING OBJECTS IN URSA MAJOR and BOÖTES
There are six Messier objects in Ursa Major although one M40 is disputed and is in fact just a pair of bright stars. M97 is the famous Owl Planetary Nebula. M81, M82, M101 and M108 are all galaxies. The brightest galaxy M81 is a beautiful spiral and is bright enough to be seen using binoculars. Just off the end of the ‘handle' in Canes Venatici is M51 the Whirlpool Galaxy
At this time of the year (April) the constellation of Ursa Major is located in the light sky directly overhead. The chart above shows Ursa Major very close to the point in the sky that we call the ‘Zenith'. This is the point in the sky directly overhead. This is not a fixed point amongst the stars it is simply the point in the sky directly over head of the observer. In six months time Ursa Major will be located above the northern horizon. This is due the sky appearing to rotate as our Earth has moved halfway round its yearly orbit around the Sun.
M81 a beautiful bright spiral galaxy in Ursa Major
Messier 81 (M81) is a beautiful and almost face on spiral galaxy that is the brightest of the Messier galaxies to be found in Ursa Major. A dark sky and a medium sized telescope will be required to see M81 and the other galaxies in this beautiful and interesting constellation.
One of the best deep sky objects associated with Ursa Major is Messier 51 (M51) the Whirlpool Galaxy that actually resides in the neighbouring constellation of Canes Venatici. It is fairly easy to find just off the end of the handle of the saucepan shape of Ursa Major. A medium sized telescope will reveal the centres of the galaxies but a larger telescope can just show the spiral arms.
Messier 51 (M51) the Whirlpool Galaxy
Messier 51 (M51) is actually a pair of Galaxies that are in the process of colliding. They have already swept past each other and the smaller one is now pulling a trail of stars off the larger one as it moves away. It is likely that pair will be drawn back together for another collision over the next few million years. Our galaxy called the Milky Way will have a similar encounter with M31 the Andromeda Galaxy in about five billion years time.
When giant spiral galaxies collide they may pass through each other a number of times before they combine into a larger single galaxy. One would imagine that events like this would be catastrophic with many of the billions of stars being destroyed in the collisions. However the stars are incredibly far apart compared to their physical size so very few stars will actually collide. The two galaxies will pass through each other like ghosts in the night.
The effect of the combined gravity of the galaxies will however cause great changes to the pair. Gas and the movement of stars within their galaxies will be affected and changed enormously. The final outcome of the merging of the galaxies is they will reform as a single merged larger galaxy. Large spiral galaxies may combine to become an Elliptical Galaxy which is the largest of all types of galaxies.
Gas in the arms of spiral galaxies will be violently disturbed by the gravitational forces that will promote enormous amounts of new star formation. Huge areas of star formation will occur in the spiral arms after each pass as the galaxies are inevitably drawn together and eventually combine into one larger galaxy.
If we follow the arc of the handle of the saucepan shape of Ursa Major we come to a bright orange coloured star called Arcturus in the constellation of Boötes the Herdsman. Arcturus is the only bright star in Boötes, the other stars are fainter and form the shape of an old fashioned diamond shaped kite with Arcturus located where the string of the tail would be attached.
Arcturus is a Red Giant star that is slightly larger than our Sun and older at 7 billion years. It has used almost all of its Hydrogen fuel and has expanded in diameter to around 25x that 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 and a Planetary Nebula.
The beautiful Red Giant Star Arcturus in Boötes
By looking at the star Arcturus we can see the future of our own star. Our Sun is currently 4.3 billion years old but in about 4 billion years time it too will become a Red Giant as it begins its death as a normal star.
THE SOLAR SYSTEM – APRIL 2023
The location of all the planets at midday on 15th April
The chart above shows the location of the planets along the Ecliptic. Saturn and Neptune are now in the early morning sky before sunrise. Jupiter is in conjunction and will not be observable. Mercury, Venus, Mars and Uranus are visible in the evening sky.
MERCURY will be at its very best on 11th April this year so is well worth seeking it out if there is a clear night around this date. A small to medium sized telescope will be required and a high magnification 100x to 200x to see the crescent shape of Mercury. A clear view to the western horizon will be required for observing Mercury as it will be low in the west.
Mercury in the west at sunset on 11th April 2023
Mercury will appear at its apparent furthest point from the Sun from our point of view. This is called ‘Greatest Easterly Elongation'. This is because it appears to be at its furthest point to the east from the Sun on its orbit. Its position is shown on the chart below.
The inner most of the planets is also the smallest planet in the Solar System and always appear close to the Sun in the early morning sunrise in the east or at sunset in the west. It may be small but it receives a lot of light from the Sun so will appear quite bright.
The orbits of Venus and Mercury in the west at sunset on 11April 2023
VENUS is the brightest of all the planets, Venus, will be visible in the early evening sky as soon as possible after sunset. It will appear at a rather small diameter (for Venus) and will be and just over half illuminated. It is still beyond the Sun from our point of view but will be approaching the point on its orbit where it will appear to be half illuminated on 4 th June. This is when Venus will appear at its apparent furthest point from the Sun from our point of view. This is called ‘Greatest Easterly Elongation'. This is because it appears to be at its furthest to the east from the Sun. Venus is still beyond the Sun from our point of view but will be approaching the point on its orbit where it will appear to be half illuminated on 4 th June. It is brightest of all the planets but it will appear with a rather small diameter (for Venus) and will be and just over half illuminated (Gibbous).
MARS can be seen high in the evening sky as soon as the Sun has set and the sky darkens. It is looking small at about 6" (arc-seconds). Mars is past its best and is now starting to fall behind Earth and will appear to be getting smaller as it moves further away from us.
JUPITER is in conjunction with the Sun this month and is not observable, see the chart below.
Jupiter Saturn and Neptune after Sunrise 15th April
SATURN has now moved into the bright morning sky just before sunrise but will be very difficult to observe as it is very low in the brightening eastern dawn sky.
URANUS will be more difficult to find and will really need a telescope. This month it will be in the south west and sets at about 22:00 but will be very difficult to see in the bright dusk sky.
NEPTUNE will not be visible this month as it was in conjunction with the Sun on 11th March and is now reappearing in the early morning sky before sunrise.
THE SUN
The Sun rises at about 06:27 at the beginning of the month and 05:35 at the end. It sets at 19:40 at the beginning of the month and 20:25 at the end. There have been some very nice Sunspots recently and an aurora seen from the UK on 26th & 27th February. There has been some nice Sunspot activity over the last few months.
Anyone can follow the activity progress even without a telescope. The Sun activity can still be observed by downloading the spectacular daily images online from the NASA orbiting Solar and Heliospheric Observatory (SOHO) at: http://sohowww.nascom.nasa.gov/ .
Sunspots imaged by SOHO on 25th March 2023
THE MOON PHASES DURING APRIL
Last Quarter will be on 6th April
New Moon will be on 13th April
First Quarter will be on 20th April
Full Moon will be on 27th April
LYRID METEOR SHOWER
There will be a meteor shower during the night of 22nd and 23rd April with a peak of activity around 1 o'clock BST (00:00 GMT). This is a minor shower (with just 10 meteors per hour) but does sometimes produce the occasional bright meteor known as a fireball. To observe the shower, look high towards the South East to North East. The Radiant point of the Lyrid meteor shower is always located to the west (right) of the familiar shape of Lyra and its very bright star Vega. Although Lyra does not appear over the eastern horizon until 10 o'clock BST in the evening of 22nd April, meteors may be seen rising up over the horizon before the constellation appears. The number of meteors is usually at its highest after midnight because at this time Earth is crashing headlong into the particle stream.
SOME ADVICE FOR OBSERVING METEORS
Before rushing out into the garden to look for meteors, there are a few things to consider for your own comfort, the first and most important is clothing. The nights, even in summer, can be cold so it is essential to dress in warm clothes. A number of layers of clothes are often better than one overcoat. A vest or tee shirt, a long sleeved shirt and a jumper, perhaps a body warmer and then an outer jacket should be considered. Two layers on the legs are also necessary. Long leg thermal pants are excellent for men or women but track suit bottoms are also good as an under garment. Then jeans or a thick pair of trousers should be worn over the top. Water proof trousers and jackets are also good for keeping the damp and wind out. Two pairs of socks are a good idea and warm shoes. Most trainers these days are padded and are quite warm. A woolly or padded hat is essential because a lot of the body heat is lost from the head but peaked hats should be avoided. Finally a pair of gloves must be worn. It is always best to start warm and stay warm because once the cold has set in it is very difficult to get warm again.
A garden ‘lounger' chair is an excellent piece of equipment especially the type that can be reclined into a near horizontal position. This will help avoid neck and back ache when looking up. When sitting in a garden chair a blanket or old quilt can also be used for additional warmth. A sky chart, like the one at the end of this magazine , will be useful to locate the part of the sky where the meteor radiant will be located. To read the star chart in a dark garden will require a torch but a bright white light should be avoided. A red lamp such as a rear cycle lamp is better, to avoid ruining the dark adaptation of the eyes. Even this may prove too bright so a piece of card can be used to shutter off some of the light. The card can be secured over the lamp with tape or an elastic band. A 10mm hole cut in the card should provide enough light to read the chart and not ruin the night vision . Turn off any light that you can and set up a screen to hide street lights to stop them dazzling you.
You may wish to take notes of what you have seen or even mark the positions of the meteors on your star chart so a pencil should be taken out to the observing spot. If you intend to have a long observing session, especially for a meteor watch, then a hot drink in a flask would prevent missing some of the show and avoid losing dark adaptation by going indoors to make a hot drink.
Most importantly ensure that you are comfortable before you start observing and have everything you need to hand. It is very irritating to have to keep getting up to try to find something you have forgotten especially if you need to go indoors to get it. Once you are comfortable and settled, with everything you need, then you are ready to start the meteor watch session.
Now on to where to position yourself. For the Lyrids a clear view towards the south east is required so set up your lounger seat with your feet facing east to south east. Use the patio or path if possible, they are more comfortable and less prone to dampness from dew. Obviously try to set up away from trees or buildings but this may not be possible so set up in the best place to view your intended target, you can always move to another position later. Make sure you have everything to hand, a small table or box by your side will provide a convenient place to put your chart, torch, spectacles or even a hot drink and will save fumbling around on the ground for things in the dark.
To start viewing allow about five minutes for your eyes to become adapted to the dark. This period can be used to familiarise yourself with the sky and work out where everything is. Try to turn off all lights around you. If there is a street light bothering you, it may be possible to erect a screen around yourself using garden canes, step ladders, washing poles, string and old sheets, curtains, towels or even newspapers. Even lights which appeared dim when you first began your session seem to get very bright when your eyes are fully adjusted to the dark.
It is useful if you can observe from your own back garden because you can quickly get used to the positions of stars from one night to the next. It is not always possible to use your own garden due to the dazzling effect of street lights or perhaps trees or buildings blocking the view. It may be necessary therefore to go to a darker area away from lights. If this is the case it is much better to go with a friend, if possible, as it will be safer and more enjoyable. A remote observing site also has the disadvantage of having to transport any equipment. If it is decided to try a remote site, always check the weather forecast first - this might save a lot of travelling and anguish when the sky clouds over shortly after all has been set up.
After making yourself warm and comfortable and allowing enough time for your eyes to become adapted to the dark it is time to start observing. The first thing to do is to look around the sky to find familiar objects. The most common thing used is the constellation of Ursa Major also called the Plough. Use the instructions on the front page to align the chart. Now position your star chart just above your eyes ensuring that the south position on the map is at the bottom. What you see represented on the chart should be what you see in the sky. Once the orientation is complete the chart can be lowered into a convenient reading position.
Observing can start before midnight but there will most likely be fewer meteors at this time. There are two reasons for this, first the radiant of the Lyrid shower will be below the eastern horizon until just before midnight so fewer meteors will appear rising up above the horizon . Secondly, after midnight Earth will be ploughing head on into the main meteor stream. It is normally best to look up at an angle of around 45° above the horizon and 30° to 90° right or left from the radiant point. It will also be useful to familiarise yourself with the positions of the constellations in the direction you are looking while you are waiting for the meteors.
If you feel quite enthusiastic about observing the meteors, you may wish to make a log of every one you see - this can be done in two ways: Notes can be made on a pad detailing the time, direction and brightness. It will be necessary to note which constellations the meteor passes through or at least where it ended. These notes can then be plotted on to the chart later. You could alternatively draw the path on your chart and note the time and brightness on the line. The latter should be more fun because if the shower is good you will soon see a pattern developing where the lines trace back to a common point which is the radiant. There may also be some sporadic meteors which are not members of the shower and do not originate from the same place. These are also interesting when marked on the chart, it may be possible to establish if they came from another old sparse shower.