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The Dumbbell Nebula or M27 is a showpiece object that's a popular visual and imaging target for amateur astronomers. It's arguably the finest planetary nebula in the night sky and was the first of its type to be discovered. The name derives from its resemblance to a dumbbell shape, but it has also been compared to an apple core and an hourglass figure. With a mag. of +7.4, M27 is the second brightest planetary nebula in the sky. Only the Helix Nebula (NGC 7293) in Aquarius is brighter. However, the Dumbbell Nebula has a higher surface brightness and therefore the easier of the two targets to spot.

M27 The Dumbbell Nebula (credit:- ESO)

M57, the Ring Nebula, is a showpiece planetary nebula located in the constellation of Lyra. It's probably the most well-known, studied and photographed object of its kind and a perennial favourite with amateur astronomers. The nebula is relatively bright at magnitude +8.8 and easy to locate. It can be found about 40% the way along an imaginary line connecting stars, Sheliak (β Lyr - mag. +3.5) and Sulafat (γ Lyr - mag. +3.2). For Northern Hemisphere observers, it appears high in the sky during the warm summer months although from southern latitudes it appears much lower down.

M57 was discovered by Antoine Darquier de Pellepoix in January 1779.

M57 The Ring Nebula (NASA, ESA, and The Hubble Heritage Team (credit:- STScI/AURA))

Algol (β Per) is a bright eclipsing binary system located in the northern constellation of Perseus and one of the best-known variable stars in the sky. Often referred to as the "Demon Star", most of the time it shines at mag. +2.1 but every two days, 20 hours and 49 minutes it suddenly dips in brightness to mag. +3.4, remaining dim for about 10 hours before returning to its original state.

Why the brightness change. The Algol system consists of at least three-stars (β Per A, β Per B and β Per C) with the orbital plane of Algol A and B directly in line with the Earth. The regular dips in brightness occur when the dimmer B star moves in front of and eclipses the brighter A star. There is also an extra dimension in that a secondary eclipse occurs when the brighter star occults the fainter secondary, resulting in a very small dip in brightness that can be detected with photo-electrical equipment.

Algol System (credit:- Dept. of Physics and Astronomy - Univ. of Tennessee at Knoxville)

Algol is located in Perseus among the stars of the northern Milky Way. It's positioned west of mag. +0.1 Capella (α Aur) and southeast of the well known "W" of Cassiopeia. The finder chart below shows the position of Algol along with magnitude data of some surrounding stars for comparative purposes.

Finder Chart for Algol (credit:- freestarcharts)

Finder Chart for Algol - pdf format (credit:- freestarcharts)

M87 is a supergiant elliptical galaxy that's a prominent member of the Virgo cluster of galaxies. It's one of the largest and most luminous galaxies known and a strong source of electromagnetic radiation, particularly radio and X-ray emissions. At the centre of M87 is a supermassive black hole from which a jet of extremely energetic plasma extends outwards for at least 5,000 light-years. The galaxy is therefore an interesting object for both professional and amateur astronomers alike.

With an apparent magnitude of +8.6, M87 is the second brightest of the Virgo cluster galaxies. Only M49, at mag. +8.4, is marginally brighter. On dark moonless nights, M87 is visible with 7x50 or 10x50 binoculars, appearing as a faint hazy patch of light. This galaxy was one of eight discovered by Charles Messier on March 18, 1781. He also re-discovered fine globular cluster, M92, on the same day.

M87 lies at the heart of the Virgo cluster. It can be found by imagining a line connecting Denebola (β Leo - mag. +2.1) with Vindemiatrix (ε Vir - mag. +2.8). Just over half way along this line is M87. Faint elliptical galaxy M89 is positioned just over a degree east of M87 with the galaxy pair M84/M86 located 1.5 degrees to the northwest.

The Virgo galaxies are best seen during the months of March, April and May. On April 10, 2019, Astronomers released the first ever image of a black hole, which is at the centre of M87. It measures 40 billion km across - three million times the size of the Earth - and has been described by scientists as "a monster".

M87 Elliptical galaxy by the Hubble Space Telescope (credit:- NASA, ESA, and The Hubble Heritage Team (STScI/AURA))

The first ever picture of a black hole at the centre of M87. It's surrounded by a halo of bright gas (credit:- Event Horizon Telescope Array)

NGC 869 and NGC 884 are two bright open clusters in the constellation of Perseus, that are separated by only half a degree of apparent sky. Together they are commonly known as the "Double Cluster" and form a famous showpiece object, that's easily visible to the naked eye and a wonderful sight in binoculars and telescopes. Both clusters have been known since antiquity and probably pre-historically. Greek astronomer Hipparchus first catalogued them around 130 B.C, with early celestial cartographers naming them as "h Persei" (NGC 869) and "χ Persei" (NGC 884).

The Double Cluster is located in the far northwestern part of Perseus, close to the border with Cassiopeia. With a declination of 57N, it's circumpolar from many northern locations and therefore never sets. To locate the object, draw an imaginary line from Mirfak (α Per - mag +1.8) in a northwesterly direction towards the centre of the "W" of Cassiopeia. The Double Cluster lies just over halfway along this line.

It's listed as number 14 in the Caldwell catalogue.

Mercury

Mercury reaches greatest elongation west (GEW) on April 11th when it will be situated 27 degrees from the Sun in the morning sky. From northern temperate latitudes, the planet is not well placed for observation, and even at GEW it hugs the east-southeastern horizon just before sunrise, shining at magnitude +0.4. Much brighter Venus (mag. -3.9) lies a few degrees from Mercury. Both planets battle against the bright twilight sky.

From southern and equatorial latitudes, early morning observers are rewarded with great opportunities to spot Mercury as it shares the view with Venus. Much fainter Neptune, mag. +8.0, is also in same region of sky. On April 2nd, Neptune appears only 0.4 degrees south of Mercury (mag. +0.8) with the thin crescent Moon 4 degrees to the south. Mercury and Venus are at their closest on April 16th, when just over 4 degrees apart, with both planets visible throughout the month.

MESSENGER spacecraft image of Mercury (credit:- NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)

Venus

Venus shines at magnitude -3.9 throughout April. As the month progresses its angular size reduces from 13.1 to 11.6 arc seconds with its illuminated disk increasing from 81% to 86%. From northern locations, Venus hugs the horizon just before sunrise and by months end will be difficult to spot.

As previously mentioned, from southern and equatorial latitudes, Venus and Mercury are well placed in the morning sky this month with much fainter Neptune also nearby.

Mars

Mars remains visible after sunset throughout April. The red planet is now towards the lower end of its brightness scale and fades from magnitude +1.5 to +1.6 this month. From northern temperate locations, it still sets over 3 hours after the Sun by months end. However, those located further south don't have it quite so good with a visibility period of up to 2 hours less.

Mars is currently moving through Taurus and is between the Pleaides (M45) and Hyades open clusters during the first week of the month. On April 9th, the thin waxing crescent passes 5 degrees south of Mars. A week later Mars passes 7 degrees north of first magnitude star, Aldebaran (mag. +0.9).

M97, also known as the Owl Nebula, is a famous planetary nebula located in the constellation of Ursa Major. It was discovered by Pierre Mechain on February 16, 1781 and is one of only four planetary nebulae listed in the Messier catalogue. Although not particularly bright at magnitude +9.9, it's a superb object and regarded as one of the most complex examples of its type. The name Owl Nebula was first coined in 1848 by William Parsons the 3rd Earl of Rosse, who noticed owl-like "eyes".

Locating M97 is easy as it's positioned only 2.5 degrees southeast of bright star Merak (β UMa - mag. +2.3). This is the southwest corner star of the bowl of the famous Plough or Big Dipper asterism of Ursa Major. In the same wide field telescope field of view, 50 arc minutes northwest of M97, is barred spiral galaxy M108 (mag. +10.2).

The Owl Nebula is best seen from Northern Hemisphere latitudes during the months of March, April and May. From latitudes north of 35N, it's circumpolar and therefore never sets.

M97 the Owl Nebula (credit:- Adam Block/NOAO/AURA/NSF)

Algol (β Per) is a bright eclipsing binary system located in the northern constellation of Perseus and one of the best-known variable stars in the sky. Often referred to as the "Demon Star", most of the time it shines at mag. +2.1 but every two days, 20 hours and 49 minutes it suddenly dips in brightness to mag. +3.4, remaining dim for about 10 hours before returning to its original state.

Why the brightness change. The Algol system consists of at least three-stars (β Per A, β Per B and β Per C) with the orbital plane of Algol A and B directly in line with the Earth. The regular dips in brightness occur when the dimmer B star moves in front of and eclipses the brighter A star. There is also an extra dimension in that a secondary eclipse occurs when the brighter star occults the fainter secondary, resulting in a very small dip in brightness that can be detected with photo-electrical equipment.

Algol System (credit:- Dept. of Physics and Astronomy - Univ. of Tennessee at Knoxville)

M82 is a superb irregular galaxy located in the constellation of Ursa Major. It has an apparent magnitude of +8.4 and is visible with binoculars. Separated by only 38 arc minutes from M82 is an even brighter and equally stunning galaxy, M81. However, they are very different objects. M81 (mag. +6.9) appears almost face-on, is of a grand spiral deign and therefore exhibits prominent near perfect and well defined spiral arms. On the other hand, M82 (mag. +8.4) is edge on, appears long and thin and is known as the Cigar galaxy. It's classified as the prototype starburst galaxy in which stars are forming at exceptionally high rates.

These two objects are the largest members of the Ursa Major or M81 group of galaxies, which at a distance of 11.7 million light-years is one of the closest groups of galaxies beyond the Local Group. Spatially, M81 and M82 are close and are physically separated by only about 150,000 light-years. When seen through binoculars and telescopes at low powers they form a striking pair.

Both M81 and M82 were discovered by Johann Elert Bode on December 31, 1774. Pierre Mechain then independently rediscovered them in August 1779. He reported his observations to Charles Messier, who added both galaxies to his catalogue on February 9, 1781. Finding M82 is not particularly difficult as the Plough asterism of Ursa Major can be used as a starting point. First focus on Dubhe (α UMa - mag. +1.8) the northwest corner star of the bowl. The M81 / M82 pair is located 10 degrees northwest of this star, with M82 positioned directly north of M81.

The galaxies are best seen from the Northern Hemisphere during the months of March, April and May. From locations north of +21 degrees they are circumpolar and always visible.