WHAT'S UP THIS MONTH - APRIL 2022

(Link to What's Up May 2022)

(Link to What's Up March 2022)

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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 located almost 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.

Mercury and Uranus are visible in the early evening sky this month.

THE SOUTHERN NIGHT SKY THIS MONTH

The night sky looking south at about 21:00 BST on 15th April

The chart above shows the night sky looking south at about 22:00 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: Pisces (the Fishes) just off the right of the chart, Aries (the Ram), Taurus (the Bull), Gemini (the Twins), Cancer (the Crab), Leo (the Lion), Virgo (the Virgin) and Libra (the Scales) just coming into view.

In the early evening southern sky 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. At the end of the top right (upper west) arm of the ‘X' is the beautiful ‘naked eye' Open Star Cluster called Messier 45 (M45) also known as the Pleiades (or the Seven Sisters). It really does look magnificent using binoculars.

Following Taurus is the constellation of Gemini (the Twins). The two brightest stars in Gemini are Castor and Pollux and they 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 which is almost directly overhead. For those with a telescope there is a line of lovely open clusters to search out in Taurus and Auriga. These are M35 in Taurus and M36, M37 and M38 in Auriga.

To the south of Taurus is the winter constellation of Orion (the Hunter) that dominates the southern night sky. Orion is easily found by looking for the very obvious three stars of his belt. As he is so easy to find it is a good place to start exploring the sky. Orion has his Hunting Dogs Sirius (the big dog) and Procyon (the little dog) to the east (left) and following him. Orion was featured as constellation of the month in the January magazine.

To the east (left) 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.

The constellation of Leo (the Lion) follows Cancer along the Ecliptic and will be the constellation of the month next month. It does actually look a little like a lion or the Sphinx in Egypt. Around and between Leo and the neighboring constellations of Coma Berenices and 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, see pages 3 to 7. A medium sized telescope (150mm to 200mm) and a dark sky is required to see these faint objects.

The constellation of Virgo (the Virgin) can be seen at the lower east (left) of the chart above. To the north (above) and between Virgo and Leo is the fainter constellation of Coma Berenices (the hair of Berenices).

Where to find the planets this month

All the planets, except Uranus and Mercury are in the early morning eastern sky.

Mercury will be low in the eastern morning sky and reach its greatest elongation on 29th April .

Venus is very bright in the eastern sky before sunrise and was at its greatest westerly elongation (furthest from the Sun) on 20th March so is now moving back towards the Sun.

Mars is still close to the Sun and appears very small as it is on the other side of the Sun.

Jupiter was in conjunction on 5th March so is now in the eastern sky before sunrise.

Saturn was in conjunction on 4th February and is now in the eastern sky before sunrise.

Uranus can be found in the south east in the early evening but really needs a telescope.

Neptune was in conjunction on 15th March so is now in the eastern sky before sunrise.

 

CONSTELLATIONS OF THE MONTH – URSA MAJOR & URSA MINOR

Ursa Major and Ursa Minor

The Constellations of this Month are among the best known of all the constellations and one is certainly the most recognisable . It is Ursa Major (the Great Bear) also known as the ‘Plough' or ‘the Big Dipper' in the USA. The familiar pattern, formed by the brightest stars, has very little resemblance to a bear and looks much more like a ‘Saucepan'. It is the third largest (by area) of the 88 internationally recognised constellations.

Ursa Major is directly overhead at this time of the year as can be seen on the chart above. The point in the sky directly overhead of the observer is called the ‘ZENITH' and is shown in red on the chart above. The chart shows the sky as it will appear at 21:00 on 15th April.

Ursa Major is a circumpolar constellation this means it never disappears below the horizon from the UK so it 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) also called the Little Dipper in the USA.

The sky also 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 (Dubhe and Merak) opposite the handle of the ‘saucepan shape', up and out of the pan and looking about five times the distance between the pointer stars we can find Polaris. See the chart above.

Our planet Earth rotates around the North Celestial Pole once a day (24 hours). If we look straight up to the Zenith we can see that as Earth rotates the sky appears to rotate clockwise around Polaris above us. As the sky appears to rotate, Ursa Major and the other constellations will appear to move around the North Celestial Pole in an east to west direction. Ursa Major will appear to move clockwise around Polaris as shown on the chart above (saucepan handle behind). The movement is slow and not perceivable in real time.

So Ursa Major will move around Polaris once a year but will also move about half way around Polaris during the night due to the 24 hour rotation of Earth on its axis (½ day). However a long exposure using a camera will show the stars as trails as they rotate around the Pole Star as shown in the image below.

Star trails imaged by Gregory Ballos

The axis of rotation of our Earth is tilted over at 23.4º to the axis of rotation of our Solar System. So we see our axis of rotation 23.4º to the north of our Zenith (the point directly overhead). We do not normally notice that we have a slightly odd view of the sky due to this tilt of Earth. Astronomers are acutely aware of this strange perspective we have of the sky as we need to take account of it when we are observing the moving sky.

So the two bears in our sky are quite important constellations. Ursa Minor because it hosts the North Celestial Pole and Ursa Major because it is used to help us to find Polaris with the North Celestial Pole close by. As Ursa Major is always somewhere in the night sky we can always use it as our starting point for finding our way around the sky.

The image below shows the stars that make up the familiar constellation of Ursa Major but the most striking feature of the constellation is the obvious ‘saucepan shape' formed by the seven brightest stars. Although there are many open clusters in our galaxy, one of the most commonly known by name is seldom mentioned. This is the Ursa Major Cluster.

The seven brightest stars in Ursa Major

In 1869, it was discovered that most of the stars in the Constellation Ursa Major (Big Dipper) are moving in roughly the same direction at roughly the same velocity toward Sagittarius. They also contain the same mixture of ‘metals' in their atmospheres and are about the same age hence they have a common origin. It is believed that they were formerly as an Open Cluster that was created about a half billion years ago therefore they were much closer together then.

The Ursa Major Moving Group is now scattered over a region of about 18 by 30 light-years with an average distance of about 80 light-years from Earth.

 

INTERESTING OBJECTS IN URSA MAJOR

Chart showing the interesting objects in Ursa Major

Before looking at the interesting Deep Sky objects we really must mention the star Mizar that is located in the middle of the handle of the ‘saucepan'. This is a rare ‘naked eye' double star. Taking a close look at Mizar a fainter star can be seen close to the bright star Mizar. This is a true associated pair of stars with the smaller star Alcor in orbit around the larger star Mizar. Using binoculars the pair can be seen easily.

Mizar and Alcor as they appear using binoculars

To be able to see the double star is quite interesting but there is a further interesting feature to the pair. Mizar is in fact a double star itself and can be seen as a double using a modest telescope with Alcor orbiting the pair. It does not stop there the two stars that make Mizar a double star are both double stars themselves so this makes Mizar and Alcor a five star system.

The two stars that comprise the Mizar pair are very close double stars themselves that are so close together that they cannot be separated using normal telescopes. However when their spectra are examined they show that each star has two separate and different spectra. This reveals they are in fact both very close double stars orbiting a common centre of gravity.

MESSIER OBJECTS TO SEE IN URSA MAJOR USING A TELESCOPE

Messier objects are deep sky object listed by Charles Messier in the 1700's as being fuzzy comet like objects that looked like comets but were not comets. Now those objects that Charles listed to help him ovoid him mistaking them for the new comets that he sought are the things we like to seek out using our telescopes. These objects are prefixed with a letter ‘M' for example M81 and include Star Clusters, Galaxies and Nebulae (gas clouds in space). Most of these objects do need a clear dark sky and a telescope to see them.

There are seven Messier objects within the boundaries of Ursa Major these are:

Messier 40 (Winnecke 4) This is thought to be a mistake by Messier it may be a double star.

Messier 81 (Bode's Galaxy)

Messier 82 (The Cigar Galaxy)

Messier 97 (The Owl Nebula)

Messier 101 (The Pinwheel Galaxy)

Messier 108

Messier 109

Messier 81 (M81) and Messier 82 (M82)

Messier 81 (M81) and Messier 82 (M82)

Johann Elert Bode discovered Messier 81 (right, also known as Bode's Galaxy) and its companion Messier 82 (left, also known as the Cigar Galaxy), in 1774. Both are located about 12 million light-years away from Earth in the constellation Ursa Major. M81 is a beautiful face on Giant Spiral Galaxy.

Messier 82 (M82) is also known as NGC 3034 or the Cigar Galaxy and is a starburst galaxy approximately 12 million light-years away in the constellation Ursa Major. M82 is a member of the M81 Group and is about five times more luminous than our Milky Way Galaxy. It has a centre one hundred times more luminous than our Milky Way. We look at it as an edge on view so it is not quite as impressive as M81.

Messier 97 (M97) the Owl Nebula

Messier 97 (M97) the Owl Nebula

Messier 97, also known as the Owl Nebula, or NGC 3587, is a planetary nebula located at around 2,030 light-years away from us. This nebula is around 8,000 years old.

The Owl Nebula has an apparent magnitude of +9.9. A 16 th magnitude star resides in its centre that has reached the turning point of its evolution where it collapsed to become a white dwarf.

This central star has 55-60% of our Sun's mass, 41-148 times its brightness and an effective temperature of around 123,000 K this is 21.2 times hotter than our Sun.

The nebula itself holds around 0.13 solar masses of matter, such as hydrogen, helium, nitrogen, oxygen, and sulphur (all with a density of fewer than 100 particles per cubic centimetre). Its outer radius is around 0.91 light years and it is expanding with velocities in the range of about 27 to 29 km per second into the surrounding interstellar medium.

Messier 101 (M101) the Pinwheel Galaxy

Messier 101 (M101) the Pinwheel Galaxy

Messier 101 (M101) the Pinwheel Galaxy (also known as NGC 5457 ) is a beautiful face-on spiral galaxy 21 million light-years away from Earth in the constellation Ursa Major . It was discovered by Pierre Méchain in 1781 and was communicated that year to Charles Messier , who verified its position for inclusion in the Messier Catalogue as one of its final entries.

Messier 108

Messier 108 (M108) the Surfboard Galaxy

M108, or the Surfboard galaxy, is located in the constellation Ursa Major approximately 46 million light-years away. It is called the Surfboard galaxy because, when viewed with a telescope, it is seen nearly edge-on with no apparent bulge or pronounced core.

M108 is one of the largest and brightest members of the Ursa Major cluster. It has a magnitude of 10 and is located just under the bowl of the Saucepan shape of Ursa Major. M108 can be seen with small telescopes as an elliptical streak of light with a brighter core while telescopes 200mm or larger will reveal more detail. The best time to observe M108 is in April but it can be seen throughout the year for those in the Northern Hemisphere.

Messier 109 (M109)

Messier 109 (M109) a Barred Spiral Galaxy

Messier 109 (M109) is a barred spiral galaxy located in the constellation Ursa Major. The galaxy lies at a distance of 83.5 million light years and has an apparent magnitude of 10.6. It has the designation NGC 3992 in the New General Catalogue.

The galaxy can be seen in large binoculars in exceptionally good conditions. Telescopes of about 100mm will show a hazy streak of light. A 150mm instrument will reveal the galaxy's nucleus surrounded by nebulosity. Only the galaxy's bright central region with the bar can be seen visually. The best time of year to observe M109 is during the spring. Messier 109 is estimated to contain 1 trillion stars that makes it about 5 times the size of our Milky Way.

 

Messier 51 (M51) The Whirlpool Galaxy

There is one more very interesting object that is not actually in Ursa Major but Ursa Major is often used to find it. The Galaxy Messier 51 (M51) is actually a pair of Galaxies that are in the process of colliding. M51 is usually found by following the handle of the familiar saucepan shape of Ursa Major to its end. On a clear night and from a dark location Messier 51 can be found just below the star Alkied which is the star at the end of the 'handle' of the saucepan. See the chart above.

Messier 51 (M51) Colliding Galaxies

M51, also known as the Whirlpool Galaxy, is a beautiful 'face on' Spiral Galaxy located in the constellation of Canes Venatici just below Ursa Major. M51 is one of the most famous galaxies in the sky, appearing face-on when viewed from Earth. At a magnitude of +8.4, it is relatively bright and visible in binoculars, especially from dark sites. M51 has a much smaller dwarf companion known as NGC 5195 and together they form the finest and most studied example of an interacting (colliding) galaxy pair in the sky.

 

THE SOLAR SYSTEM - APRIL 2022

The location of the planets at 07:30 BST on 15th April 2022

The chart above shows the location of the planets along the Ecliptic after sunrise in the east. The sky has been darkened to make the planets visible. The planets are: Mercury, Venus, Mars, Jupiter, Saturn and Neptune. They are visible along the Elliptic from the West (right) to East (left). The planets appear low in the bright morning sky before sunrise and are not well positioned for observing.

MERCURY will be in Superior Conjunction with the Sun on 2nd April. It will now be moving into the early evening sky. Mercury will appear low in the western evening sky and reach its Greatest Elongation (apparent distance from the Sun) on 29th April (see the Uranus chart).

VENUS rises about two hours before the Sun climbs over the eastern horizon. It is looking very bright in the east before sunrise. It will show a fairly large diameter but it will be getting smaller and will appear as a widening crescent, see the computer generated images below. Venus is bright often called the ‘Morning Star' at this time.

Venus as it will appear on 1st April

Venus as it will appear on 30th April

MARS is on the other side of the Sun (so appears very small) and still appears close to the Sun so will be difficult to see. Mars has moved out of conjunction with the Sun and into the early morning sky but will not appear in the evening sky again until September 2022.

JUPITER was in conjunction (passed just below the Sun) on 5th March but will actually be on the far side of the Sun from our point of view. After its conjunction with the Sun on 5th March it will now begin to move away from the Sun and to the west (right). Jupiter will then continue to move westward through the daytime sky until it eventually appears in the evening sky before midnight in August.

Planets in the east at sunrise 15th April

SATURN has now moved away from the Sun after its conjunction on 4th February so will be appearing in the morning sky about two hours before sunrise. It will be very low over the eastern horizon in the brightening sky and will be moving into the evening sky later in the year.

URANUS will be observable this month in the early evening sky and will be best seen at about 20:00 when it will be in the south west and at its highest point above the horizon but it is small and faint at +5.7. It sets over the western horizon at about 21:30 BST.

Uranus and Mercury in the early evening sky on 15th April

NEPTUNE was in conjunction with the Sun on 13 th March so will now appear in the early morning sky. It will be small and difficult to see but being close to Jupiter will help to find it.

 

THE SUN

The Sun rises at about 06:30 at the beginning of the month and 05:40 by the end of the month. It sets at 19:45 at the beginning of the month and 20:15 at the end of the month. The Sun was half way to midsummer on 20th March when it was the spring (Vernal) equinox. On this date the day and night were of equal length at exactly 12 hours long.

Midsummer will be on 21st June (Summer Solstice) when it will be the longest day at 16 hours and the shortest night at just 8 hours long. The Sun is starting to climb higher in the sky now. It will be at its highest on 21st June 2022 (Summer Solstice) and at its lowest point (Winter Solstice) on 21st December 2022.

There have been a few nice Sunspots recently as we move into the Sun's more active phase. Sunspots and other activity on the Sun can be followed live and day to day by visiting the SOHO website at: http://sohowww.nascom.nasa.gov/ .

Sunspots imaged by NASA's SOHO Space Observatory on 29th April 2022

Sunspots are caused by the magnetic field of the Sun. Magnetic lines of force cause a depression on the surface that can expose a cooler and darker layer below the very bright visible surface (Photosphere). Most telescopes can be used to observe the buy fitting a special Solar Filter over the end of the telescope. Never look directly at the Sun without using a filter.

THE MOON PHASES DURING APRIL

New Moon will be on 1st April

First Quarter will be on 9th April

Full Moon will be on 16th April

Last Quarter will be on 23rd April

New Moon will be on 30th April

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