WHAT'S UP THIS MONTH - MARCH 2016
(Link to What's up - April 2016)
(Link to What's up - February 2016)
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The chart above shows the night sky as it appears on 15th March at 21:00 (9 o'clock) in the evening Greenwich Mean 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 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 night sky: Jupiter, Mars and Saturn.
Remember British Summer Time begins on 27th March.
EXPLORING THE NIGHT SKY THIS MONTH
The night sky looking south on 15th March
The chart above shows the night sky looking south at about 21:00 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 or Nadir and is shown on the chart at the upper centre of the chart. The curved brown line across the sky is the Ecliptic or Zodiac. This is the imaginary line along which the Sun, Moon and planets appear to move across the sky. The constellations through which the ecliptic passes are known as the constellations of the ‘Zodiac'.
Constellations through which the ecliptic passes are (west to east): Aries (the Ram), Taurus (the Bull), Gemini (the Twins), Cancer (the Crab), Leo (the Lion) and Virgo (the virgin) on the eastern horizon.
The Milky Way can be seen reaching up from the bottom of the chart and passing through Puppis (on the southern horizon), Orion, Taurus Auriga and Cassiopeia. This is the galaxy in which we live and our Sun is just one of the 200 billion stars that reside in this large spiral galaxy.
The beautiful constellation of Orion is still dominating the southern sky at this time of the year. Orion (with a little imagination) does look like the hunter after who it is named. The most obvious feature is the line of three stars that make up Orion's belt. Below his belt we can see two bright stars called Saiph and Rigel that define the bottom of his ‘skirt like' tunic. Above the belt are two stars Betelgeuse and Bellatrix that denote the position of his shoulders. Above and between his shoulders is a little group of stars that mark out the head. From his right shoulder (Bellatrix) he holds out a shield. From his left shoulder (Betelgeuse) a club is held above his head.
In mythology Orion the hunter has two hunting dogs and his representation in the sky also has two dogs . By following the line of his belt down to the south east the bright star Sirius in the constellation of Canis Major (the Large Dog). Following an imaginary line through Bellatrix and Betelgeuse to the east the star Procyon in the constellation of Canis Minor (the Little Dog) can be found.
Above Orion's head is Taurus with the bright red star Aldebaran located at the centre of a cross shape of stars that defines Taurus. Up to the right is the beautiful Open Cluster M45 known as the Pleiades or the Seven Sisters. The cluster looks like a fuzzy patch of light at first glance with the ‘naked eye' but after a good hard look, up to seven stars can be made out.
To the east (left) of Taurus is Gemini with the stars Pollux and Castor as the Twins. At the end of the line of stars leading from Castor is a lovely Open Cluster M35. It can be seen using binoculars as a small ‘fuzzy' patch but a telescope will show it as a ball of stars.
There are another three open clusters known as M36, M37 and M38 in the neighbouring constellation of Auriga that appear to be almost in a line with M35.
To the east of Cancer is the magnificent constellation of Leo the Lion. It is one of the few constellations that do look like what it is supposed to represent. Leo was the constellation of the month last month. Leo heralds spring and the ‘Season of the Galaxies'. Leo is on the edge of a large group of galaxies. The main group is located in the neighbouring constellations of Virgo and Coma Berenices to the east (left) of Leo. However Leo does have five bright galaxies of its own, these are known as: M65, M66, M95, M96 and NGC 3628 and are marked in yellow on the chart above, below Leo . A medium sized telescope and a dark sky will be required to see even the brightest of the galaxies. See the February issue of this magazine.
The planets Saturn, Mars and Jupiter in the morning before sunrise
For those early rising observers most of the planets can be found in the southern sky before sunrise . Mercury is in conjunction with the Sun and will not be visible. Venus is just visible but is very close to the Sun. Uranus and Neptune are close to the Sun and not observable. Jupiter is visible all night and Saturn is visible from midnight until dawn.
THE MOTIONS OF THE SKY
The night sky looking to the south at about 21:00 on 15th March
The chart above shows the night sky looking to the south at about 21:00 (9 o'clock in the evening) on 15 th March (around the middle of the month). The sky will appear very much the same an hour later at the beginning of the month and an hour earlier at the end of the month. This is due to the movement of Earth along its orbital path around the Sun. The Sun takes 1 year to complete its orbit around the Sun therefore it will move 1/12 th of its orbit every month. Put another way it will have moved 360º ¸ 12 = 30º each month. This is to say, in another way, it moves about 1º every day. As a result of our Earth moving around the Sun the sky appears to move about 1º every day or 30º every month.
Earth also rotates once a day (24 hours). This means the sky appears to move 360º ¸ 24 = 15º every hour due to Earth's rotation about its axis. Therefore if the sky has moved 30º every month due to the Earth moving along its orbit and Earth rotates 30º every 2 hours (2 x 15º) the sky will appear the same two hours earlier each succeeding month. To put that another way, the sky will appear the same on the 1 st day of the month as it does an hour later in the middle of the month and two hours later at the end of the month.
Earth's rotation about its axis means that the sky appears to rise over the eastern horizon as our view from Earth moves to the left when we are looking south. This is rather like when we look out of a train window as the train starts to move out of a station. As we look out the window the station will appear to move to the right as the train starts to move to our left. Stars rise over the eastern horizon (to our left). They move to the right and set over the western horizon (right). We on Earth are moving to the left as Earth rotates.
The stars appear to be fixed in their location in the sky in relation to all the other stars. So the whole sky appears to rotate around the axis of rotation of Earth. This gives us a rather odd perspective of the sky due to the axis of Earth being tilted at 23.4º to the plain of the solar system. It means in simple terms our equator on Earth is tilted 23.4º to the equator of the Sun and the solar system. It also means the axis of rotation of Earth (our North and South Poles) is also tilted at 23.4º.
Diagram showing Earth's tilt during one orbit
When the axis of rotation of Earth is projected up into the night sky it points towards the star Polaris in the constellation of Ursa Minor, the Little Bear. Polaris is also known as the Pole Star or the North Star. To the naked eye Polaris is stationary and all the other stars appear to rotate around it once every day as the Earth rotates. Polaris is called the North Star because it is always positioned 38.6º north of overhead (the Zenith) when seen from Newbury in southern England .
THE PLANETS THIS MONTH
The planets looking to the south during March at 06:00
he planets are not fixed in the sky because they are orbiting the Sun and therefore can be seen to move. The inner planets Mercury and Venus appear to move quite quickly and move in relation to the stars noticeably, certainly over the period of a week. Mercury has an orbit that takes just over 87 Earth days. Venus takes 226 days. The outer planets take a lot longer: Mars 1.88 years, Jupiter 11.86 years, Saturn 29.46 years, Uranus 84.01 years and Neptune 164.79 years. The Moon moves a lot quicker as it orbits Earth taking a month for each orbit. This means it moves approximately 360º ¸ 30 days = 12º per day. It therefore moves noticeably from night to night.
OBSERVING THE PLANETS THIS MONTH
MERCURY is located on the far side of the Sun and is not observable this month. It will be in conjunction with the Sun on 23rd March.
VENUS is just 25º west of the Sun and will be very close to the eastern horizon as the Sun rises. It will be very difficult to see even though it is very bright at magnitude -3.8.
MARS rises over the eastern horizon at about midnight and will be observable until the sky begins to brighten at dawn. It appears small at just 10 arc-seconds in diameter. A medium sized telescope will show the darker areas and one of the polar ice caps.
JUPITER is now at its best and will be at opposition on 8 th March. That means it will be due south and at its highest point in the sky at midnight. It rises in the east at 17:50 in the beginning of the month and at 16:20 by the end of the month. It will be in a good position for observing a couple of hours later and will still be around as the Sun rises. The ‘King of the Planets' will appear quite large at 44 arc-seconds in diameter and bright at magnitude -2.5
SATURN rises at 02:00 at the beginning of the month and at 00:40 by the end of the month. It will be in its best position for observing just before the Sun begins to brighten the sky at about 05:30. Unfortunately it will only rise to about 17º above the horizon so will be low and in quite turbulent air. It is 17 arc-seconds in diameter and the rings are starting to close up now.
Saturn and its moons on 12th March 05:30
URANUS is too close to the Sun to be observed. It is moving towards conjunction with the Sun on 6th April.
NEPTUNE was in conjunction with the Sun last month. It is still too close to the Sun to observe .
The Sun rises at 06:30 at the beginning of the month and at 05:45 by the end of the month. It will be setting at 17:50 at the beginning and 18:25 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 MOON PHASES IN MARCH
Last Quarter will be on 1st March
New Moon will be on the 9th March
First Quarter will be on 15th March
Full Moon will be on 23rd March
Last Quarter will be on 31st March
The Moon is the easiest astronomical object to image and would normally the first target for anyone wanting to use a camera with a telescope. A standard DSLR camera can be used to take some spectacular pictures especially of the Moon. The image below was taken on 28 th September 2015 just before the Moon was eclipsed by Earth's shadow for the Lunar Eclipse.
The image was taken using a Sony DSLR with the lens removed and replaced with and adaptor for mounting it to a 120mm (5”) refracting telescope. The adaptor replaced the camera lens enabling it to be fitted to the focuser in place of the eyepiece. The camera was focused using the focuser of the telescope because it is not possible to use the camera focusing system with the lens removed. This was the first attempt by the author to image a night sky object using a DSLR camera. So anyone can do it.
The Moon imaged on 28th September 2015