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Constellations of the month

 

 
CURRENT MOON

Saturn

Saturn, shining with a magnitude of +0.6, rises two and a half hours before the Sun at the start of the month some 2 hours after Jupiter. Its disk is ~16 arc seconds across and its rings - which are still 24 degrees from the line of sight - spanning 35 arc seconds across. Sadly, Saturn now to the left of the 'teapot' in Sagittarius is now at the lowest point on the ecliptic and so will only have an elevation of ~10 degrees when due south before dawn in a month's time. So, like Jupiter an astospheric dispersion corrector could help.

Jupiter

Jupiter starts the month rising around 2 a.m. and brightens from magnitude -2.0 to -2.3 as the month progresses whilst its angular size increases slightly from 36.2 to 39.7 arc seconds. By month's end it rises by ~1 am BST so will be higher in the sky before dawn. Sadly it is heading towards the southern part of the ecliptic and currently lies in the southern part of Ophiuchus just above Scorpius. By the end of March, it will lie almost due south as the Sun rises but will only have an elevation of ~14 degrees so atmospheric dispersion will blur its image somewhat. The use of an atmospheric dispersion corrector will help to give sharper images.

Mars

Mars, though fading from +1.2 to +1.4 magnitudes during the month, remains prominent in the south western sky after sunset at an elevation of ~37 degrees. Mars is moving north-eastwards through Aries and passes into Taurus on the 23rd/24th of the month. (If only it could have been at this elevation when at closest approach last year!) Its angular size falls from 5.3 arc seconds to 4.7 arc seconds during the month so one will not be able to spot any details on its salmon-pink surface.

Venus

Venus begins March at a magnitude of -4.1. with its angular size reducing from 16 to 13 arc seconds during the month as it moves away from the Earth. However, at the same time, the percentage illuminated disk (its phase) increases from 72% to 81% - which is why the brightness only reduces from -4.1 to -3.9 magnitudes. Venus rises abour 2 hours before the Sun at the beginning of the month with an elevation of ~7 degrees before dawn, but both reduce as the month progresses. We have nearly come to the end of its morning apparition as it moves towards superior conjunction (behind the Sun) in August. It will not then be visible, low in our south-western sky, until late November.

Mercury

Mercury , with an angular size of 7.7 arc seconds at the start of March, reached its greatest elongation east on the 26th of February, then 18 degrees away from the Sun. On the first of March, it sets some one and a half hours after the Sun shining at magnitude +0.1. During the month, its angular size increases to 10.9 arc seconds but its brightness rapidly reduces and and by March 6th, at magnitude 2, will become very difficult to spot in the twilight. Binoculars could well be needed to reduce the background glare, but please do not use them until after the Sun has set. Mercury passes between us and the Sun (inferior conjunction) on the 15th.

The Night Sky In and Around Swindon March 2019

Slide Presentation

The following presentation was given at our last meeting on the 15 February 2019 by Rob Slack

March - Evenings of the 14th and 28th: The Straight Wall



The Straight Wall, or Rupes Recta, is best observed either 1 or 2 days after First Quarter or a day or so before Third Quarter. To honest, it is not really a wall but a gentle scarp - as Sir Patrick has said "Neither is it a wall nor is it straight!"
Compiled by Prof. Ian Morison
The planets this month
The constellation of Ursa Major

The stars of the Plough, shown linked by the thicker lines in the chart above, form one of the most recognised star patterns in the sky. Also called the Big Dipper, after the soup ladles used by farmer's wives in America to serve soup to the farm workers at lunchtime, it forms part of the Great Bear constellation - not quite so easy to make out! The stars Merak and Dubhe form the pointers which will lead you to the Pole Star, and hence find North. The stars Alcor and Mizar form a naked eye double which repays observation in a small telescope as Mizar is then shown to be an easily resolved double star. A fainter reddish star forms a triangle with Alcor and Mizar.

Ursa Major contains many interesting "deep sky" objects. The brightest, listed in Messier's Catalogue, are shown on the chart, but there are many fainter galaxies in the region too. In the upper right of the constellation are a pair of interacting galaxies M81 and M82 shown in the image below. M82 is undergoing a major burst of star formation and hence called a "starburst galaxy". They can be seen together using a low power eyepiece on a small telescope.


M81 and M82

Another, and very beautiful, galaxy is M101 which looks rather like a pinwheel firework, hence its other name the Pinwheel Galaxy. It was discovered in1781 and was a late entry to Messier's calalogue of nebulous objects. It is a type Sc spiral galaxy seen face on which is at a distance of about 24 million light years. Type Sc galaxies have a relativly small nucleus and open spiral arms. With an overall diameter of 170,000 light it is one of the largest spirals known (the Milky Way has a diameter of ~ 130,000 light years).


M101 - The Ursa Major Pinwheel Galaxy
Though just outside the constellation boundary, M51 lies close to Alkaid, the leftmost star of the Plough. Also called the Whirlpool Galaxy it is being deformed by the passage of the smaller galaxy on the left. This is now gravitationally captured by M51 and the two will eventually merge. M51 lies at a distance of about 37 million light years and was the first galaxy in which spiral arms were seen. It was discovered by Charles Messier in 1773 and the spiral structure was observed by Lord Rosse in 1845 using the 72" reflector at Birr Castle in Ireland - for many years the largest telescope in the world.

M51 - The Whirlpool Galaxy
Lying close to Merak is the planetary nebula M97 which is usually called the Owl Nebula due to its resemblance to an owl's face with two large eyes. It was first called this by Lord Rosse who drew it in 1848 - as shown in the image below right. Planetary nebulae ar the remnants of stars similar in size to our Sun. When all possible nuclear fusion processes are complete, the central core collpses down into a "white dwarf" star and the the outer parts of the star are blown off to form the surrounding nebula.

M97 - The Owl Planetary Nebula & Lord Rosse's 1848 drawing of the Owl Nebula
March 12th - evening: a waxing Moon approaches the Pleiades and Hyades clusters


A waxing Moon approaches the Pleiades and Hyades clusters in Taurus
Image: Stellarium/IM

Looking high in the southwest during the early evening one will, if clear, spot the Moon lying below the Pleaides and Hyades open clusters in Taurus.

The constellation Taurus
Taurus is one of the most beautiful constellations and you can almost imagine the Bull charging down to the left towards Orion. His face is delineated by the "V" shaped cluster of stars called the Hyades, his eye is the red giant star Aldebaran and the tips of his horns are shown by the stars beta and zeta Tauri. Although alpha Tauri, Aldebaran, appears to lie amongst the stars of the Hyades cluster it is, in fact, less than half their distance lying 68 light years away from us. It is around 40 times the diameter of our Sun and 100 times as bright.

More beautiful images by Alson Wong : Astrophotography by Alson Wong
To the upper right of Taurus lies the open cluster, M45, the Pleiades. Often called the Seven Sisters, it is one of the brightest and closest open clusters. The Pleiades cluster lies at a distance of 400 light years and contains over 3000 stars. The cluster, which is about 13 light years across, is moving towards the star Betelgeuse in Orion. Surrounding the brightest stars are seen blue reflection nebulae caused by reflected light from many small carbon grains. These relfection nebulae look blue as the dust grains scatter blue light more efficiently than red. The grains form part of a molecular cloud through which the cluster is currently passing. (Or, to be more precise, did 400 years ago!)

VLT image of the Crab Nebula
Close to the tip of the left hand horn lies the Crab Nebula, also called M1 as it is the first entry of Charles Messier's catalogue of nebulous objects. Lying 6500 light years from the Sun, it is the remains of a giant star that was seen to explode as a supernova in the year 1056. It may just be glimpsed with binoculars on a very clear dark night and a telescope will show it as a misty blur of light.

Lord Rosse's drawing of M1
Its name "The Crab Nebula" was given to it by the Third Earl of Rosse who observed it with the 72 inch reflector at Birr Castle in County Offaly in central Ireland. As shown in the drawing above, it appeared to him rather lile a spider crab. The 72 inch was the world's largest telelescope for many years. At the heart of the Crab Nebula is a neutron star, the result of the collapse of the original star's core. Although only around 20 km in diameter it weighs more than our Sun and is spinning 30 times a second. Its rotating magnetic field generate beams of light and radio waves which sweep across the sky. As a result, a radio telescope will pick up very regular pulses of radiation and the object is thus also known a Pulsar. Its pulses are monitored each day at Jodrell Bank with a 13m radio telescope.
The constellation Orion
Orion, perhaps the most beautiful of constellations, will be seen in the south at around 11 - 12 pm during January. Orion is the hunter holding up a club and shield against the charge of Taurus, the Bull up and to his right. Alpha Orionis, or Betelgeuse, is a read supergiant star varying in size between three and four hundred times that of our Sun. The result is that its brightness varies somewhat. Beta Orionis, or Rigel, is a blue supergiant which, at around 1000 light years distance is about twice as far away as Betelgeuse. It has a 7th magnitude companion. The three stars of Orion's belt lie at a distance of around 1500 light years. Just below the lower left hand star lies a strip of nebulosity against which can be seen a pillar of dust in the shape of the chess-board knight. It is thus called the Horsehead Nebula. It shows up very well photographically but is exceedingly difficult to see visually - even with relativly large telescope.

The Horsehead Nebula: Anglo Australian Observatory
Beneath the central star of the belt lies Orion's sword containing one of the most beautiful sights in the heavens - The Orion Nebula (M42). It is a region of star formation and the reddish colour seen in photographs comes from Hydrogen excited by ultraviolet emitted from the very hot young stars that make up the Trapesium which is at its heart. The nebula, cradling the trapesium stars, is a beautiful sight in binoculars or, better still, a telescope. To the eye it appears greenish, not red, as the eye is much more sensitive to the green light emitted by ionized oxygen than the reddish glow from the hydrogen atoms.

The Orion Nebula: David Malin
March 26th to 31st - early evening: Mars approaches the Pleiades and Hyades open clusters

Mars near the Pleiades cluster
Image: Stellarium/IM
If clear on these evenings one should be able to see Mars approaching the Pleiades cluster in Taurus. The Hyades cluster lies over to the left.
March 29th - before dawn: Saturn just above the Moon

Saturn and the Moon
Image: Stellarium/IM
If clear before dawn, and given a low horizon towards the south southeast, one should spot Saturn lying close above the Moon just after third quarter. A great photo opportunity!