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The Night Sky April 2016

Compiled by Ian Morison


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.



Cambridge University Press has recently published two books by the author. An Amateurs Guide to Observing and Imaging the Heavens is a handbook aimed to bridge the gap between the beginner's books on amateur astronomy and the books which cover a single topic in great detail.   Stephen James O'Meara and Damian Peach have both given it excellent reviews. 'A Journey through the Universe' aims to cover our current understanding of the Universe in a accessible way.   Martin Rees has written a very nice review of it.


Image of the Month

Pluto

Northern Pluto

Image:NASA,John Hopkins Univ./APL,Southwest Research Institute,

This is a contrast enhanced colour scene of the northern part of Pluto captured last July by the New Horizons spacecraft.   Currently known as Lowell Regio and informally named after Percival Lowell who started the search that ultimately led to Pluto's discovery by Clyde Tombaugh at the Lowell Observatory.   The North Pole is above and to the left of the centre of the frame.   The pale bluish floor of the broad canyon on the left and running south is about 45 miles wide.   The higher regions have a yellowish hue.   New Horizons has found that both Nitrogen and methane ice are abundent in Lowell Regio.


Highlights of the Month

April - still a great month to view Jupiter.

Jupiter
Jupiter imaged by Damian Peach

This is still a great month to observe Jupiter.   It lies in the southern part of Leo, but still reaches an elevations of ~48 degrees when crossing the meridian during the evening.   An interesting observation is that the Great Red Spot appears to be diminishing in size.   At the beginning of the last century it spanned 40,000 km across but now appears to be only ~16,500 Km across - less than half the size.   It used to be said that 3 Earths could fit within it, but now it is only one.   The shrinking rate appears to be accelerating and observations indicate that it is now reducing in size by ~580 miles per year.   Will it eventually disappear?

  The features seen in the Jovian atmosphere have been changing quite significantly over the last few years - for a while the South Equatorial Belt vanished completely (as seen in Damian's image) but has now returned to its normal wide state.   The diagram on right shows the main Jovian features as imaged by the author at the beginning of December 2012.

The image by Damian Peach was taken with a 14 inch telescope in Barbados where the seeing can be particularly good.   This image won the "Astronomy Photographer of the Year" competition in 2011.

See more of Damian Peach's images: Damian Peaches Website"





Jovian Features
Features in Jupiter's atmosphere - December 2013.





April: Look for the Great Red Spot on Jupiter

Great Red Spot
Observe the Great Red Spot
Image: NASA

This list gives some of the best evening times during April to observe the Great Red Spot which should then lie on the central meridian of the planet.

1st   23.47         18th 22:49

4th   21:16         20th 21:03

6th   22:54         21st 20:18

9th   20:24         23rd 21:57

11th 22:02         25th 23:25

13th 23:41         30th 22:44

16th 21:10


April 3rd - 22:00 BST: Ganymede emerges from Jupiter's shadow

Ganymede
Ganymede emerges from Jupiter's shadow.
Image: Stellarium/IM

During the early evening, Jupiter will apear to have just 3 Gallilean satellites: Io and Callisto to its right and Europa to its left.   Ganymede is hiding in Jupiter's shadow but will emerge just after 22:00 BST later in the evening.  

April 6th: just before dawn - the Moon occults Venus

Venus occultation
A thin crescent Moon occults Venus
Image: Stellarium/IM

On the 6th of the month, the Moon and Venus will lie close together low in the eastern sky before dawn.   At 08:28 BST, as observed from the centre of the UK, Venus will disappear behind the disk of the very thin crescent Moon whose phase will be just 2%.   This will be quite an observing challenge and will need binoculars or a small telesocpe to observe along with a good low eastern horizon.   BUT BEWARE: NOT TO OBSERVE CLOSE TO THE SUN!   If possible stand in the shadow of a wall to the left of your position.   Ideally, using an equatorial mount, locate the Moon when it rises at 06:20 BST and continue tracking as it approaches and then occults Venus.   As seen from the centre of the UK, it will emerge around 20 minutes later as it briefly passes behind the Moon's northern dark limb.   The occultation will not be visible from Scotland and, in the northern part of the UK, Venus will be seen to graze along the Moon's rough northern edge.   Venus will take ~60 seconds to disappear and ~70 seconds to emerge.   NOTE: to show the occultation graphically, I have had to remove the Sun's glare - this will be a very difficult observation.

April 8th: 45 minutes after sunset - Mercury and a thin crescent Moon

Mercury
Mercury 6 degrees from a 2% lit waxing crescent Moon.
Image: Stellarium/IM

Looking west after sunset and as darkness falls, Mercury will be seen just 6 degrees to the right and slightly up from the a very thin waxing crescent Moon.

April 16th - mid evening: A waxing Moon nears Jupiter

Jupiter

Image: Stellarium/IM

During the evening the Moon will be seen gradually nearing Jupiter, closing in to a separation of just over 4 degrees at 22:00 UT.

April 21st all night: The Moon at apogee

Moon

Image: IM

On the 21st the Moon, one day from full, reaches apogee, that is at its furthest distance from the Earth.   So, on the following day, it will not appear as big - or as bright - as when the full Moon is at perigee, its closest approach to the Earth.   Perhaps surprisingly, its angular diameter at apogee is 12% smaller that at perigee and, should a solar eclipse occur near apogee, the Moon's full shadow may not reach the Earth giving rise to what is called an annular eclipse.

April 16th and 29th: Two Great Lunar Craters

10thJuly
Tycho and Copernicus: IM.

Two great Lunar Craters: Tycho and Copernicus
These are two good nights to observe two of the greatest craters on the Moon, Tycho and Copernicus, as the terminator is nearby.   Tycho is towards the bottom of Moon in a densely cratered area called the Southern Lunar Highlands.   It is a relatively young crater which is about 108 million years old.  It is interesting in that it is thought to have been formed by the impact of one of the remnents of an asteroid that gave rise to the asteroid Baptistina.   Another asteroid originating from the same breakup may well have caused the Chicxulub crater 65 million years ago.   It has a diameter of 85 km and is nearly 5 km deep.   At full Moon - seen in the image below - the rays of material that were ejected when it was formed can be see arcing across the surface.   Copernicus is about 800 million years old and lies in the eastern Oceanus Procellarum beyond the end of the Apennine Mountains.   It is 93 km wide and nearly 4 km deep and is a clasic "terraced" crater.   Both can be seen with binoculars.

The Alpine Valley
Full Moon showing Tycho's rays: IM

A Messier Object imaged with the Faulkes Telescope: Messier 27 - The Dumbell Nebula

M27 - The Dumbell Nebula
The Dumbell Nebula
Image:Nik Szymanik
Faulkes Telescope North.

The Dumbell Nebula, imaged by Nik Szymanek.
This image was taken using the Faulkes Telescope North by Nik Szymanek - one of the UK's leading astro-photograpers.   M27 is a planetary nebula, the result of a "nova" expolsion at the end of the life of a star like our Sun.   The core at the centre of the star collapes under gravity until it is about the size of the Earth when "electron degeneracy pressure", resulting from the fact that electrons do not like being squashed too close together, prevents further collapse.   This is called a "white dwarf".   As the dying ember of a nuclear fusion reactor, they are exceedingly hot, but will gradually cool over time.   The outer parts of the star are expelled at high speed into space resulting in the (in this case) spherical nebula surrounding the white dwarf.   The field of the view of the CCD array on the Faulkes Telesocpe is a little too small to encompass the whole nebula.   Once, with a 16 inch telescope under perfect conditions, I visually observed M27 and its central part appeared a vivid iridescent green - the only time I have ever seen colour in a deep sky object!

Learn more about the Faulkes Telescopes and how schools can use them: Faulkes Telescope"

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 7th April 13th April 22nd April 29th

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 9550 pixels. This 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.



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 reached opposition on March 8th but this is still an excellent month to observe it - high in the southern sky during the evening.   It crosses the meridian at around 23:00 (UT) at the beginning of the month and around 21:00 by month's end.   Its brightness falls slightly from magnitude -2.4 to -2.3 whilst its angular size drops from 44 to 41 arc seconds.   Jupiter spends the month in south-eastern Leo, moving slowly westwards in retrograde motion.   With a small telescope one should be easily able to see the equatorial bands in the atmosphere, sometimes the Great Red Spot (see the highlight above) and up to four of the Gallilean moons as they weave their way around it.


See highlight above.


Saturn

Saturn
The planet Saturn. Cassini - Nasa

Saturn rises at ~02:00 (UT) as April begins and a little earlier each night so that by month's end it rises at about 23:00 (UT).   Shining at magnitude +0.3 and brightening to +0.2 during the month it lies in the southern part of Ophiuchus some 5.5 degrees up and to the left of Antares in Scorpius.   Its diameter increases from 17.4 to 18.1 arc seconds as April progresses.   It will be due south in the early hours of the morning at an elevation of ~19 degrees.   The beautiful ring system has now opened out to ~26 degrees - virtually as open as they ever become - and measures 40 arc seconds across.   It will be best observed near the meridian during the hour before dawn.   If only it were higher in the ecliptic; its elevation never gets above ~19 degrees and so the atmosphere will hinder our view of this most beautiful planet.   Sadly, as seen from our northern climes, on each successive apparition it will get lower in the sky, so now is the time to emigrate to the southern hemisphere!


Mercury

Mercury.
Messenger image of Mercury Nasa

Mercury. This month, Mercury has its best apparition of the year for those of us in the northern hemisphere, shining in the west-northwest during the evening twilight.   As April begins, it is low above the horizon, but shining brightly at magnitude -1.5.   It reaches greatest elongation (east) on the 18th of April, so is higher in the sky, but its brightness will have dropped to a still bright magnitude 0.   Then, its highest altitude at sunset will be ~19 degrees, but Mercury will still be at an elevation of ~10 degrees 45 minutes after sunset.   At greatest elongation, its disk will be 7.5 arc seconds across with 38% of the disk illuminated.   During the latter part of the month, it fades rapidly down to magnitude +1.5 and disappears into the Sun's glare around the 28th of the month as it moves towards inferior conjunction on the 9th of May - when we will observe a transit of Mercury - one of two major highlights for next month!



See highlight above.




Mars

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

Mars. At the beginning of April, Mars rises around midnight (UT). As the month progresses it rises earlier each night so at about 10pm (UT) by month's end.   It starts the month in Scorpius, moves into Ophiuchus on the 4th and, as it begins its retrograde motion westwards on April 18th, moves back towards Scorpius which it re-enters on the first of May.   Its brightness increases dramatically this month, increasing from magnitude -0.6 to -1.4.   At the same time its angular size increases from 12 to 16 arc seconds - the largest it has appeared for some ten years!   But as it reaches opposition on the 22nd of May it will subtend over 18 arc seconds.   So now is the time to start seriously observing Mars when details such as the polar caps and dark regions such as Syrtis Major should be easily visible in a small telescope on nights of good seeing.






Venus

Venus
Venus showing some cloud structure

Venus,rises less than half an hour before sunrise at the start of April and could be seen given a low eastern horizon, but it will be unobservable after the 9th or so.   However, it will be worth attempring to observe it on the morning of the 6th when it is occulted by a thin crescent Moon as detailed in the highlight above.



See highlight above.



Radar Image of Venus
Radar image showing surface features



Find more planetary images and details about the Solar System: The Solar System



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