WHAT'S UP THIS MONTH - MARCH 2020

(Link to What's Up April 2020)

(Link to What's Up February 2020)

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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 March at 21:00 (9 o'clock) in the evening Greenwich Meantime Time (GMT). 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 10 o'clock GMT at the beginning of the month and at 8 o'clock GMT 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 high in the east 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: Uranus and Venus in the early evening with Mars, Saturn and Jupiter early morning.

REMEMBER British Summer Time (BST) begins on 29th March

 

EXPLORING THE NIGHT SKY THIS MONTH

The Southern Night Sky during March 2020 at 21:00 GMT

The chart above shows the night sky looking south at about 20:00 GMT on 15th March. 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), Aries (the Ram), Taurus (the Bull), Gemini (the Twins), Cancer (the Crab), Leo (the Lion), Virgo (the Virgin) and Libra (the Scales) rising over the eastern horizon.

Just disappearing over the south western horizon is the constellation of Pisces (the Fishes). The planet Uranus is in Pisces and can be found in the early evening using binoculars. Venus is shining very brightly in the constellation of Aries (the Ram).

Still prominent in the south is the constellation of Taurus (the Bull). It sits on the Ecliptic and looks like a squashed cross ‘X'. 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 Messier 45 (M45) known as the Pleiades (or the Seven Sisters). It really does look magnificent using binoculars.

Following Taurus along the Ecliptic is the constellation of Gemini (the Twins). The two brightest stars in Gemini are Castor and Pollux that are named after mythological twins and they are so alike they do look like twins. There are lines of fainter stars linked to Pollux and Castor and extending to the south west (down to the right). There is a lovely Open Cluster called Messier 35 (M35) just off the end and above the upper line of stars emanating from the star Castor. M35 will need a telescope to see well.

Following Taurus along the Ecliptic is the rather faint constellation of Cancer (the Crab). It does need a dark and unpolluted sky to see with the naked eye. In a good sky the faint stars can be seen with a nice Open Cluster of stars at its centre. The cluster is called Messier 44 (M44) or ‘the Beehive Cluster' because of its resemblance to an old straw built beehive with a swarm of stars looking like bees around it. It looks best using binoculars.

Following Cancer along the Ecliptic is the constellation of Leo (the Lion). It does actually look a little like a resting male African lion but perhaps more like the Sphinx in Egypt. Below Leo are some relatively bright galaxies M65, M66, M95 and M96 but they do need a telescope to see them. The sky around Leo and particularly between Leo and Virgo hosts a cluster of nearby galaxies. Our Galaxy (the Milky Way) is actually a member of a small local group of galaxies that forms part of this larger cluster of galaxies.

To the south of Taurus and Gemini is the spectacular constellation of Orion (the Hunter). Orion dominates the southern sky and is one of the best known constellations. It also hosts some of the most interesting objects for us to seek out.

 

WHAT IS HAPPENING TO BETELGEUSE?

 

The constellation of Orion

At this time of the year amateur astronomers are enjoying the magnificent sight of the constellation of Orion (the Hunter) as it dominates the southern sky. This year we have another reason for visiting Orion, something strange is happening to the beautiful Red Giant Star called Betelgeuse.

First a few words about measuring star brightness.

We measure the brightness of a star by magnitudes. Without going into this too deeply, this means a change in Magnitude of 1 represents a change in brightness of a star by about 2½ times. The brighter the star appears the lower the Magnitude number will be. For example a Mag. +6.0 is 5 times (2x(2.5)) fainter than a Mag. +3.0 star, a Mag. +2.0 star is 5 times fainter than a 0.0 star and a Mag. 0.0 star is 5 times fainter than a Mag. -2.0 star.

Betelgeuse is the bright orange looking star located at the Hunter's left shoulder, as we look at him. This star normally has an apparent magnitude of about +0.45 but is naturally variable between 0.0 and +1.6. Interestingly it has faded noticeable over the last few months and is now close to +2.0 and still fading. This is much fainter than its normal minimum of variability at +1.6.

To put this change in brightness into context, the star Bellatrix at Orion's opposite shoulder has a magnitude of +1.62 so it is normally fainter than Betelgeuse even at its faintest (+1.6). At the time of writing this article Betelgeuse appears fainter than Bellatrix to the naked eye. This is not a perfect comparison because of the colour difference but it is noticeable that Betelguese is definitely fainter than Bellatrix. This is despite Bellatrix always being fainter than Betelguese so what we are seeing is unusual to say the least.

Betelgeuse is a Red Giant Star and is in fact the largest (in diameter) of all the stars in our vicinity. Its diameter is equal to the orbit of Jupiter around our Sun. It is a star that is approaching the end of its life and has become inflated and quite unstable.

A photographic image of Betelgeuse (the spikes are an artefact from the telescope)

It always was a giant star, 11.6 times the mass of our Sun. Being so large it used its Hydrogen fuel supply up at a frantic rate and its core filled with the Helium produced in the Fusion process. As a giant star it was then able to fuse the Helium into Carbon and Oxygen. The fusion process was then able to fuse the Carbon into Neon, Magnesium, Sodium Aluminium and eventually Silicon. All these additional fusion processes provided additional energy to the star to push out against its gravity and caused the star to expand in diameter.

Betelgeuse has nearly reached the end of this process and will, at some time, begin to produce Iron in its core. At this point things will start to happen very quickly as the core fills rapidly with Iron. The Iron fusion process consumes energy and does not produce energy during its production. The star will become very unstable and suddenly collapse. The collapse will cause a catastrophic Supernova explosion that will destroy the star.

A Supernova is the ‘death' of a star more than about five times the mass of our Sun. Giant stars consume their Hydrogen fuel at an exponentially faster rate than smaller stars. Consequently bigger stars do not ‘live' as long as smaller stars. As stars begin to exhaust their supply of Hydrogen they develop into a Red Giant like Aldebaran. Very massive stars develop into larger Red Super Giants like Betelgeuse.

A star like our Sun and those up to about twice the mass of our Sun become Red Giants and eventually slowly collapse as their fuel eventually runs out. The outer layers of the Red Giant drift away to form a gas bubble but the core ‘gently' collapses to form a White Dwarf Star.

Stars that are five or more times the mass of our Sun come to a more dramatic end. As the fuel of a larger Red Giant Star finally runs out and Iron accumulates in its core, the star suddenly collapses and all the mass of the star falls inwards under the massive force of its own gravity. The collapse reaches a point where the pressure and heat causes a gigantic thermonuclear explosion. The outer regions of the giant star are blown into space to create a Supernova Remnant like M1. The inner regions are compressed into a super dense Neutron Star about 10km in diameter but with a mass from 1.4 times and up to just over twice the mass of our Sun.

There is some speculation that we may be witnessing the final days of Betelgeuse but this is nowhere near certain. It may be just an extreme minimum in its normal variability cycle. Alternately it may just be suffering a giant star's equivalent of indigestion and could puff off some of its mass into space.

An artist's impression of the Betelgeuse Supernova

Whatever is happening we need to keep a close watch on Betelgeuse just in case we do miss the Supernova.

 

THE SOLAR SYSTEM THIS MONTH

MERCURY will just be observable this month but it will be very close to the horizon in the east before the Sun rises at 06:15. The innermost planet will be at Greatest Western Elongation (furthest position from the Sun) on 24th March, see the chart below. Mercury is small but quite bright although its brightness is rather overwhelmed by the brightness in the sky from the rising Sun. It is best seen using binoculars or telescope but we must make sure the Sun is below the horizon before sweeping the sky using binoculars to find Mercury.

Neptune, Mercury, Saturn, Jupiter and Mars at sunrise

VENUS has been moving out from behind the Sun and will reach Greatest Eastern Elongation (appearing furthest from the Sun on 24th March). See the gray orbit arc on the chart below. The fainter section (closer to the elliptic) shows the section that Venus has moved along and the brighter section is the part of its orbit it will be moving along during the next few months. Venus has looped out from behind the Sun is moving towards us. It will now appear to move back towards the Sun, following the brighter gray orbit arc. At the moment Venus looks ‘half Moon' shaped using a telescope but it will develop into a narrower crescent and will appear to become larger in diameter as it moves closer to us.

Venus how it will appear on 24th March

MARS will be observable (with difficulty) this month, low in the east before sunrise. Mars is still a long way from us on the other side of the Solar System so it looks small at just 5.9” (arc seconds). See the chart above.

JUPITER is moving away from the Sun in the early morning sky in the east. It will be very low in the sky and looking rather large but disappointing in the dirty and turbulent air close to the horizon.

A good pair of 9 x 50 binoculars will just about show the four bright moons known as the Galilean Moons. These four bright moons Io, Europa, Ganymede and Callisto and are known as the ‘Galilean Moons' after Galileo who first recorded seeing them.

Jupiter and the Galilean Moons imaged by Steve Harris

Jupiter always displays an almost full disc but can lose a tiny amount from the edge when it is at greatest elongation (at 90° from the Sun as we view it from Earth). However Jupiter will appear full to the untrained eye. For these reasons Jupiter will be as good as it gets, subject to clear skies, from around midsummer until later in the year.

The Belts and Zones are regions of higher and lower atmospheric pressure. The lighter coloured ‘Zones' are regions of rising gas caused by convection of heat from the core of Jupiter. The darker ‘Belts' are regions of falling gas and are approximately 20 kilometres lower in altitude than the Zones. In the regions where the belts and zones meet, huge storms are created. This is due to the friction as the belts and zones move at different speeds and directions. A larger telescope will allow some detail of the storm patterns to be seen.

The cloud markings on Jupiter

The most famous feature in the cloud system is the ‘Great Red Spot' (GRS). This huge storm has been raging for over 350 years. We know this because it was recorded by astronomers in 1664 using some of the earliest telescopes. The GRS does change its colour, size and shape but it is always there. Its colour may fade from the normal pink to nearly white when it may almost disappear. The colour is thought to be caused by Phosphorus welling up from deep regions in Jupiter's atmosphere. See the Mercury chart above.

SATURN will be low in the south east as the sky brightens before the Sun rises over the eastern horizon. Saturn is very low and in the murky and turbulent air close to the southern horizon. It will be in the bright dawn sky and will require a clear view to the eastern horizon. It may still just be possible to see the ring system although it will appear unstable due to the air movement close to the horizon. See the chart above.

URANUS will be visible in the early evening as a slightly fuzzy blue, star like, object, using a small telescope. A larger telescope with a magnification of 100x or more will show it as a small blue/green disc. See the chart below.

Uranus and Venus at Sunset on 24th March

NEPTUNE will be in conjunction with the Sun on 8th March and will appear to pass behind the Sun. It will still be very close to the Sun after conjunction so will not be observable this month. See the chart Mercury above.

 

THE SUN

The Sun rises at 06:30 GMT at the beginning of the month and at 05:45 GMT by the end of the month. It will be setting at 17:45 GMT at the beginning and 18:25 GMT by the end of the month. 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/ .

The 20th March will be the Spring (Vernal) Equinox. This is the time when the Sun will appear directly overhead on the Equator. We will be half way between midwinter and midsummer and the day and night will be the same length both will be 12 hours long.

The diagram above shows how Earth's tilt causes the seasons

 

THE MOON PHASES IN MARCH

First Quarter will be on 2nd March

Full Moon will be on 9th March (see below)

Last Quarter will be on 16th March

New Moon will be on the 24th March

 

THE ‘SUPER MOON' ON 9th MARCH

 

The Moon at Perigee (closest to Earth) on 9th March

We hear a lot about the ‘Super Moon' these days, mainly from the television news or in the popular news papers. So what does this mean and does it have any significance for astronomers?

The simple answer is no, it is of no real scientific interest to astronomers but it is of general interest. There are two factors that produce the effect we call the Super Moon. One is a physical effect and the other is illusionary.

The first effect is to do with the orbit of the Moon around Earth. Like most orbiting bodies the orbit of the Moon is elliptical and not circular. This means the Moon will be closer to Earth at one point that we call ‘Perigee' and furthest away at the point we call ‘Apogee'. At Apogee the Moon can be up to 406,700 km away from Earth but at Perigee can be as close as only 356,500 km.

Comparison of size Perigee to Apogee

With this change in distance the Moon will actually look larger at Perigee (closest) and smaller at Apogee (furthest away). The difference in apparent diameter is up to 14% and the difference in the Moon's reflective area is about 30% so this does make a difference.

The second Super Moon effect is an optical illusion and is most noticeable during the summer months. It is caused by the Moon appearing low in the summer night sky. The 23.4º tilt in Earth's axis of rotation results in our view of the sky appearing to be tilted by the same amount. So during the summer the Sun appears higher in the daytime sky but the Moon and planets appear low in the night sky as they move along the Ecliptic (the equator of the Solar System).

A full Moon always rises in the east as the Sun is setting in the west. So as the Moon rises over the horizon our eyes try to compare the size of the very distant Moon to the nearer features on the horizon. Our eyes are confused and try to relate the apparent size of the Moon to the features near the horizon and an optical illusion causes the Moon look larger.

The Super Moon Effect

So if a summer Full Moon coincides with the Moon's orbital Perigee then the Moon can look particularly large as it rises over the eastern horizon. This due to it actually appearing larger combined with the optical illusion.

If a Full moon occurs when the Moon is less than 361,885 km from Earth it is regarded as a ‘Super Moon'. The Full Moon on 9th March 2020 will occur when the Moon will be 357,404 km from Earth so will officially be a ‘Super Moon'. However the next Full Moon on 8th April will look even larger as it will be just 357,035 km from Earth which is almost 400 km closer to Earth than on 9th March.

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