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« March 2018


The Night Sky April 2018


Compiled by Ian Morison



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This page, updated monthly, will let you know some of the things that you can look out for in the night sky.  It lists the phases of the Moon, where you will see the naked-eye planets and describes some of the prominent constellations in the night sky during the month.


New

The author's: Astronomy Digest

which, over time, will provide useful and, I hope, interesting articles for all amateur astronomers.   A further aim is to update and add new material to link with the books recently published by Cambridge University Press and which are described on the home page of the digest.  It now includes over 40 illustrated articles.




Image of the Month

M35

The clusters M35 and NGC 2158
Image Ian Morison

This image, taken by the author using a 127 mm refractor and DSLR camera, shows two clusters in Gemini.   The larger cluster, including many blue giant stars is Messier 35 and is relatively young at 150 million years old and contains around 2,500 stars spread over a volume 30 light across.   It lies at a distance of 2,800 light years.   Down to its right lies a far older open cluster, NGC 2158 some 1,500 years old, which lies at a distance of about 11,000 light years.   By this age, blue giant stars will have come to the end of their lives and so the cluster is dominated by yellow stars, hence its colour.

The above image shows what can done with simple equipment from a light polluted location.   How the data was talken and processed can be found on the author's Astronomy Digest website.   Perhaps the best image ever taken of these two clusters can be found on the APOD website of January 3rd 2013. This image was taken using a 20 inch f/3 Cassegrain telescope and CCD camera from one of the world's darkest locations in Namibia by Dieter Willasch.


Highlights of the Month


April 2nd - before dawn: Saturn and Mars together in Sagittarius.

Saturn
Saturn and Mars together in Sagittarius.
Before dawn close to the 2nd of April and given a clear sky and a low western horizon, you should be able to spot Saturn and Mars low down above the horizon.   Their closest is on the 2nd when they are just 1.3 degrees apart.   Binoculars might be needed to penetrate the sky's pre-dawn brightness, but please do not use them after the Sun has risen.


April 7th before dawn: Saturn, Mars and a third-quarter Moon.

Mars
Saturn amd Mars below a waning Moon.
If clear before dawn on the 7th, looking just east of south, one should see a waning third-quater Moon lying to the upper left of Saturn and Mars.


April 18th after sunset: Venus and a very thin crescent Moon

Moon
Venus, Mercury and a very thin crescent Moon.
Image:Stellarium/IM

Looking west after sunset on the 19th and given a very low western horizon, one might be able to spot Venus lying below a very thin crescent Moon, just two days after new.   Binoculars may well be needed, but please do not use them before the Sun has set.   A tough observing challenge!   [Note: the sky brightness has been reduced in the chart.]



22nd April - early morning: The peak of the Lyrid Meteors.

Lyrids
The Lyrid Meteor Shower.
Image: Stellarium/IM

After the Moon has set,and so with no moonlight to hinder our view and from a dark rural location one, if clear, would have a chance of observing the peak of the Lyrid meteor shower with up to 10 meteors visible each hour.   As one might expect, the shower's radient is close to Vega in Lyra.   One might also spot them on the 21st and 23rd.


April - latter half: Jupiter in the south

Jupiter

Jupiter can be seen towards the meridian around midnight in the latter part of the month.   But, sadly, it will not lie far above the horizon.










April - Evenings of the 8/9th and 23rd: The Straight Wall

Moon
Location of the Straight Wall: IM.

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!"

The Straight Wall
The Straight Wall at Sunrise and Sunset.















Observe the International Space Station

The International Space Station
The International Space Station and Jules Verne passing behind the Lovell Telescope on April 1st 2008.
Image by Andrew Greenwood

Use the link below to find when the space station will be visible in the next few days. In general, the space station can be seen either in the hour or so before dawn or the hour or so after sunset - this is because it is dark and yet the Sun is not too far below the horizon so that it can light up the space station. As the orbit only just gets up the the latitude of the UK it will usually be seen to the south, and is only visible for a minute or so at each sighting. Note that as it is in low-earth orbit the sighting details vary quite considerably across the UK. The NASA website linked to below gives details for several cities in the UK. (Across the world too for foreign visitors to this web page.)

Note: I observed the ISS three times recently and was amazed as to how bright it has become.

Find details of sighting possibilities from your location from: Location Index

See where the space station is now: Current Position


The Moon

3rd Quarter Moon
The Moon at 3rd Quarter. Image, by Ian Morison, taken with a 150mm Maksutov-Newtonian and Canon G7.
Just below the crator Plato seen near the top of the image is the mountain "Mons Piton".   It casts a long shadow across the maria from which one can calculate its height - about 6800ft or 2250m.
`
new moon first quarter full moon last quarter
April 16th April 22nd April 30th April 8th

Some Lunar Images by Ian Morison, Jodrell Bank Observatory: Lunar Images

A World Record Lunar Image

World record Lunar Image
The 9 day old Moon.

To mark International Year of Astronomy, a team of British astronomers have made the largest lunar image in history and gained a place in the Guinness Book of Records!   The whole image comprises 87.4 megapixels with a Moon diameter of 9,550 pixels.  The resolution of ~0.4 arc seconds allows details as small as 1km across to be discerned!   The superb quality of the image is shown by the detail below of Plato and the Alpine Valley.  Craterlets are seen on the floor of Plato and the rille along the centre of the Alpine valley is clearly visible.  The image quality is staggering! The team of Damian Peach, Pete lawrence, Dave Tyler, Bruce Kingsley, Nick Smith, Nick Howes, Trevor Little, David Mason, Mark and Lee Irvine with technical support from Ninian Boyle captured the video sequences from which 288 individual mozaic panes were produced.   These were then stitched together to form the lunar image.

Plato and the Alpine valley
Plato and the Alpine Valley.

Please follow the link to the Lunar World Record website and it would be really great if you could donate to Sir Patrick Moore's chosen charity to either download a full resolution image or purchase a print.









A Single Imager's Lunar Image

Lunar Image
The 8 day old Moon imaged by Ian Morison.

This image was taken by the author on a night in March 2018 when the Moon was at an elevation of ~52 degrees and the seeing was excellent.   This enabled the resolution of the image to be largely determined by the resolution of the 200 mm aperture telescope and the 3.75 micron pixel size of the Point Grey Chameleon 1.3 megapixel video camera.   The use of a near infrared filter allowed imaging to take place before it was dark and also reduced the effects of atmospheric turbulence.   The 'Drizzle' technique developed by the Hubble Space Telescope Institute (HSTI) was used to reduce the effective size of the camera's pixels to allow the image to be well sampled.   Around 70 gigabytes of data, acquired over a 2 hour period, was processed to produce images of 35 overlapping areas of the Moon which were then combined to give the full lunar disk in the free 'stitching' program Microsoft ICE.   A further HSTI development called 'deconvolution sharpening' was then applied to the image.   The Moon's disk is ~6,900 pixels in height and has a resolution of ~0.6 arc seconds.   Interestingly, as seen in the inset image, the rille lying along the centre of the Alpine Valley is just discernable and this is only ~0.5 km wide!   Due to the time taken to acquire the video sequences, it is unlikely that a single imager (as opposed to the 10 who acquired the World Lunar Record image) could obtain a significantly higher resolution full disk image in a single night.   [Due to size limitations the large image is 2/3 full size.]









The Planets

 A montage of the Solar System
A montage of the Solar System. JPL / Nasa

Jupiter

Jupiter
A Cassini image of Jupiter . Nasa

Jupiter rises in the east-southeast about three hours after sunset at the beginning of the month and about two hour earlier by month's end.   Initially it has a 42.6 arc second disk, shining at a magnitude of -2.4 but, as the month progresses, its apparent diameter increases to 44.6 arc seconds and it brightens to magnitude -2.5.   Jupiter will transit before around 3:30 BST in early April and by around 1:30 BST at its end and so will enable the giant planet to be well seen with the equatorial bands, sometimes the Great (but reducing in size) Red Spot and up to four of its Gallilean moons visible in a small telescope.   Jupiter will reach opposition on the night of May 8-9th.   Sadly, lying in Libra during the month, Jupiter is heading towards the southern part of the ecliptic and will only have an elevation of ~20 degrees when crossing the meridian.   Atmospheric dispersion will thus hinder our view and it might be worth considering purchasing the ZWO Atmospheric Dispersion Corrector to counteract its effects.



Saturn

Saturn
The planet Saturn. Cassini - Nasa

Saturn, now well into its new apparition, rises at around 2:15 am at the start of the month and just after 1 am at its end.   With an angular size of ~16.7 arc seconds (increasing to 17.5 during the month) it climbs higher before dawn and so becomes easier to spot as the month progresses.  Its brightness increases from +0.5 to +0.4 magnitudes during the month.   The rings were at their widest a few months ago and are still, at 26 degrees to the line of sight, well open and spanning ~2.5 times the size of Saturn's globe.   Saturn, lying in Sagittarius, is close to the topmost star of the 'teapot'.   Sadly, even when at opposition later in the year it will only reach an elevation of just over 15 degrees above the horizon when crossing the meridian.   Atmospheric dispersion will thus greatly hinder our view and, as for Jupiter, it might be worth considering purchasing the ZWO Atmospheric Dispersion Corrector to counteract its effects.




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Mercury

Mercury.
Messenger image of Mercury Nasa

Mercury passes in front of the Sun (inferior conjunction) on April 1st and, rising out of the Sun's glare, reaches greatest western elongation of 27 degrees on April 29th.   But, due to the fact that the ecliptic makes a shallow angle to the horizon at this time of the year, it never gets more than 10 degrees above the horizon even when furthest in angle from the Sun.   Not one of its better apparitions.





Mars

Mars showing Syrtis major.
A Hubble Space Telescope image of Mars.
Jim Bell et al. AURA / STScI / Nasa

Mars starts the month in Sagittarius close to the topmost star of the 'teapot' close to Saturn.   Now a morning object, it rises at around 2 am BST at the start of the month.   During the month, Mars has a magnitude which increases from +0.3 to -0.3 and an angular size of 8.4 increasing to 11 arc seconds so, by month's end it should be possible to spot details on its salmon-pink surface.   It will only reach an elevation of ~12 degrees before dawn at the start of the month and just 11 degrees by month's end.   Sadly, the atmosphere will hinder our view.   Another reason for purchasing a ZWO Atmospheric Dispersion corrector?




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Venus

Venus
Venus showing some cloud structure

Venus, seen low in the west after sunset, shines at magnitude -3.9 all month with an angular size of ~10.6 increasing to 11.5 arc seconds.   Venus rises a little higher in the sky as April progresses, initially setting around one hour and a half after the Sun but increasing to two hours by month's end as its elevation at sunset increases from 18 to 25 degrees - so by month's end it will become quite prominent in the evening sky.   Venus starts the month in Aries but, moving higher in declination, passes into Taurus on the 20th before passing between the Hyades and Pleiades Clusters on the 27th.

Radar Image of Venus
Radar image showing surface features


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The Stars

The mid evening April Sky

FebruarySky
The April Sky in the south - mid evening.

This map shows the constellations seen in the south in mid-evening.

The constellation Gemini is now setting towards the south-west and Leo holds pride (sic) of place in the south with its bright star Regulus.  Between Gemini and Leo lies Cancer.   It is well worth observing with binoculars to see the Beehive Cluster at its heart. Below Gemini is the tiny constellation of Canis Minor whose only bright star is Procyon.  Rising in the south-east is the constellation Virgo whose brightest star is Spica.   Though Virgo has few bright stars it is in the direction of of a great cluster of galaxies - the Virgo Cluster - which lies at the centre of the supercluster of which our local group of galaxies is an outlying member.   The constellation Ursa Major is high in the northern sky during the evening this month and contains many interesting objects.

The constellation Gemini

Gemini
Gemini - click on image to enlarge

Gemini - The Twins - lies up and to the left of Orion and is in the south-west during early evenings this month. It contains two bright stars Castor and Pollux of 1.9 and 1.1 magnitudes respectivly. Castor is a close double having a separation of ~ 3.6 arc seconds making it a fine test of the quality of a small telescope - providing the atmospheric seeing is good! In fact the Castor system has 6 stars - each of the two seen in the telescope is a double star, and there is a third, 9th magnitude, companion star 73 arcseconds away which is alos a double star! Pollux is a red giant star of spectral class K0. The planet Pluto was discovered close to delta Geminorum by Clyde Tombaugh in 1930. The variable star shown to the lower right of delta Geminorum is a Cepheid variable, changing its brightness from 3.6 to 4.2 magnitudes with a period of 10.15 days

Gemini
M35 and NGC 2158
This wonderful image was taken by Fritz Benedict and David Chappell using a 30" telescope at McDonal Observatory. Randy Whited combined the three colour CCD images to make the picture

M35 is an open star cluster comprising several hundred stars around a hundred of which are brighter than magnitude 13 and so will be seen under dark skies with a relativly small telescope. It is easily spotted with binoculars close to the "foot" of the upper right twin. A small telescope at low power using a wide field eyepiece will show it at its best. Those using larger telescopes - say 8 to 10 inches - will spot a smaller compact cluster NGC 2158 close by. NGC 2158 is four times more distant that M35 and ten times older, so the hotter blue stars will have reached the end of their lives leaving only the longer-lived yellow stars like our Sun to dominate its light.

Gemini
The Eskimo Nebula, NGC2392, Hubble Space Telescope

To the lower right of the constellation lies the Planetary Nebula NGC2392. As the Hubble Space Telescope image shows, it resembles a head surrounded by the fur collar of a parka hood - hence its other name The Eskimo Nebula. The white dwarf remnant is seen at the centre of the "head". The Nebula was discovered by William Herschel in 1787. It lies about 5000 light years away from us.

The constellation Leo

Leo
Leo - click on image to enlarge

The constellation Leo is now in the south-eastern sky in the evening. One of the few constellations that genuinely resembles its name, it looks likes one of the Lions in Trafalger Square, with its main and head forming an arc (called the Sickle) to the upper right, with Regulus in the position of its right knee. Regulus is a blue-white star, five times bigger than the sun at a distance of 90 light years. It shines at magnitude 1.4. Algieba, which forms the base of the neck, is the second brightest star in Leo at magnitude 1.9. With a telescope it resolves into one of the most magnificent double stars in the sky - a pair of golden yellow stars! They orbit their common centre of gravity every 600 years. This lovely pair of orange giants are 170 light years away.

Leo also hosts two pairs of Messier galaxies which lie beneath its belly. The first pair lie about 9 degrees to the west of Regulus and comprise M95 (to the east) and M96. They are almost exactly at the same declination as Regulus so, using an equatorial mount, centre on Regulus, lock the declination axis and sweep towards the west 9 degrees. They are both close to 9th magnitude and may bee seen together with a telescope at low power or individually at higher powers. M65 is a type Sa spiral lying at a distance of 35 millin klight years and M66, considerably bigger than M65, is of type Sb. Type Sa spirals have large nuclei and very tightly wound spiral arms whilst as one moves through type Sb to Sc, the nucleus becomes smaller and the arms more open.

M65 and M66
The galaxies M65 and M66
M65 M66
M65 - Type Sa spiral, 9.3 magnitude M66 - Type Sb spiral, 8.9 magnitude

The second pair of galaxies, M95 and M96, lie a further 7 degrees to the west between the stars Upsilon and Iota Leonis. M95 is a barred spiral of type SBb. It lies at a distance of 38 million light years and is magnitude 9.7. M96, a type Sa galaxy, is slightly further away at 41 million light years, but a little brighter with a magnitude of 9.2. Both are members of the Leo I group of galaxies and are visible together with a telescope at low power.

M95 and M96
The galaxies M95 and M96
M95 M96
M95 - Type SBb spiral, 9.7 magnitude M96 - Type Sa spiral, 9.2 magnitude

There is a further ~9th magnitude galaxy in Leo which, surprisingly, is in neither the Messier or Caldwell catalogues. It lies a little below lambda Leonis and was discovered by William Herschel. No 2903 in the New General Catalogue, it is a beautiful type Sb galaxy which is seen at somewhat of an oblique angle. It lies at a distance of 20.5 million light years.

NGC2903
The 8.9th magnitude, type Sb, Galaxy NGC2903

The constellation Virgo

Virgo
Virgo

Virgo, rising in the east in late evening this month, is not one of the most prominent constellations, containing only one bright star, Spica, but is one of the largest and is very rewarding for those with "rich field" telescopes capable of seeing the many galaxies that lie within its boundaries. Spica is, in fact, an exceedingly close double star with the two B type stars orbiting each other every 4 days. Their total luminosity is 2000 times that of our Sun. In the upper right hand quadrant of Virgo lies the centre of the Virgo Cluster of galaxies. There are 13 galaxies in the Messier catalogue in this region, all of which can be seen with a small telescope. The brightest is the giant elliptical galaxy, M87, with a jet extending from its centre where there is almost certainly a massive black hole into which dust and gas are falling. This releases great amounts of energy which powers particles to reach speeds close to the speed of light forming the jet we see. M87 is also called VIRGO A as it is a very strong radio source.

M87 MERLIN images
The Giant Elliptical Galaxy M87 HST image showing the jet

Below Porrima and to the right of Spica lies M104, an 8th magnitude spiral galaxy about 30 million light years away from us. Its spiral arms are edge on to us so in a small telescope it appears as an elliptical galaxy. It is also known as the Sombrero Galaxy as it looks like a wide brimmed hat in long exposure photographs.

The Sombrero Galaxy
M104 - The Sombrero Galaxy

The constellation Ursa Major

Ursa Major
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
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
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
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.

Owl Nebula Owl Nebula
M97 - The Owl Planetary Nebula Lord Rosse's 1848 drawing of the Owl Nebula