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M40 is one of three curiosities in the Messier catalogue (along with M73 and M102). It's a faint double star in the constellation of Ursa Major that was discovered by Charles Messier on October 24, 1764. Messier was searching for a nebula reported in the area by Johann Hevelius. Although he didn't see any nebula, Messier catalogued this double star instead. However, despite no nebulosity existing, the double star remained on the list.
American astronomer Robert Burnham called M40, "one of the few real mistakes in the Messier catalogue". He faulted Messier for including it, when he found no trace of a nebula and all he saw was a double star. In 1863, it was rediscovered by Friedrich August Theodor Winnecke and hence is sometimes referred to as Winnecke 4 or WNC 4. M40 is best seen from the Northern Hemisphere during the months of February, March and April.
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.
Arcturus, mag. -0.04, is an orange giant that's usually regarded as the fourth brightest star in the night sky. However, it does have justifiable claims for third position since it's marginally brighter than both main components of the Alpha Centauri system. Arcturus is the brightest star in the northern section of the celestial hemisphere.
Arcturus is the stand out star in the large constellation of Boötes, the Herdsman or Plowman. A vague legend has it that the herdsman was placed in the heavens for successfully inventing the plough. The constellation's next brightest star, Izar (ε Boo), shines at magnitude +2.35 and is much fainter than Arcturus. As a bright night time star, Arcturus has been significant to observers since antiquity. It was mentioned in the Bible and featured on old Chinese maps with the name Dajido. In India, it was sometimes referred to as Nishtya or the Outcast, presumably because of its position in the sky far away from the zodiac and Milky Way band.
The name Arcturus derives from Arktouros, which means in ancient Greek the "Bear's Tail" or the "Keeper of the Bear". The name in Greek literature goes back to at least the time of Hesiod, who wrote about this star in his book "Works and Days." Despite being a beautiful star, Arcturus has not always been held in high regard. For example, seamen of ancient times regarded it as an unlucky omen.
More recently, Ptolemy called it "golden red" and curiously, in 1852, some well-respected astronomers observed a change in the star's colour, before it reverted back to normal a few years later. It's difficult to believe anything intrinsically had changed as Arcturus is not that type of star and it's more likely the "colour changes" were simply due to atmospheric effects.
M110 is a dwarf elliptical galaxy located in the constellation of Andromeda. It's one of many satellite galaxies orbiting M31, the famous and spectacular Andromeda galaxy. Of these, at least 14 are dwarf galaxies with M110 being the second brightest (after M32). The galaxy is classified as Hubble type E5 and designated as peculiar, due to unusual dark structures that are probably caused by dust clouds.
At magnitude +8.7, M110 is a challenging binocular object. It covers 22 x 11 arc minutes but suffers from low surface brightness and therefore even a small amount of light pollution can render it invisible. Surprisingly, Charles Messier never included it in his famous list. However he depicted it, together with M32, on a drawing of the Andromeda galaxy that he made on August 10, 1773. Caroline Herschel independently rediscovered the galaxy on August 27, 1783. Much later in 1967, Kenneth Glyn Jones suggested assigning a Messier number. Although now commonly known as M110, it's still often referred to in many texts and charts by its New General Catalogue designation, NGC 205.
To find M110, first locate the Andromeda Galaxy, which is positioned northeast of the Great Square of Pegasus. Of the four stars of the square only three of them actually belong to Pegasus. The northeast corner star, Alpheratz (α And - mag. +2.1), is part of neighbouring Andromeda. Located 7 degrees northeast of Alpheratz is δ Andromedae (mag. +3.3) and a further 8 degrees to the northeast is Mirach (β And - mag. +2.1). The Andromeda galaxy is another 8 degrees northwest of Mirach at the end of a line connecting μ Andromedae with ν Andromedae. M110 is positioned 36 arc minutes northwest of the centre of M31.
The galaxies are best seen from the Northern Hemisphere locations during the months of September, October and November.
Alpha Centauri is the third brightest star in the night sky. To the naked eye it shines at apparent magnitude -0.27, which is fainter than Canopus (mag. -0.72) but brighter than Arcturus (mag. -0.04). However, Alpha Centauri is not a single star; it's a triple consisting of two bright components and a feeble red dwarf. For most of their orbit, the main stars are easily split with small telescopes. This is also the nearest star system to the Solar System.
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 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.
NGC 457 is the brightest open cluster in Cassiopeia and one of the finest objects of its type in the northern sky. At magnitude +6.4, it's just beyond naked-eye visibility but easily seen with binoculars and a beautiful sight through telescopes. The brightest cluster stars are arranged in prominent lines and curves that resemble an Owl shape, hence the popular name "The Owl Cluster".
NGC 457 was discovered by William Herschel in 1787. Finding the Owl Cluster is easy as it's located two degrees south-southeast of eclipsing binary star system Ruchbah (δ Cas - mag. +2.7). This star is one component of the characteristic "W" asterism of Cassiopeia. The brightest star inside NGC 457 is Phi Cassiopeiae (φ Cas - mag. +5.0). Despite not being a member of the cluster, this foreground star is visible to the naked eye. Together with another non-cluster star, seventh magnitude HD 7902 (HIP 6229), they form the bright eyes of the Owl.
NGC 457 is best seen from Northern Hemisphere latitudes during August, September and October. It appears high in the sky and even overhead from many locations. From latitudes greater than 32N, the Owl is circumpolar and therefore never sets.
The first item in the Messier catalogue is the famous Crab Nebula, a remnant of a supernova explosion observed and recorded by Chinese and Arab astronomers in 1054. The supernova itself was brilliant and with a peak magnitude of –7 was easily visible in daylight. Today, it still rates as one of the brightest natural stellar events ever recorded. Roll on 950+ years and the initial explosive has long since faded but the aftermath - the nebula - remains visible. At mag. +8.4 and with an apparent size of 7x5 arc minutes, it's a relatively easy target under dark skies and can be spotted with a pair of binoculars.
M1 is located in the zodiacal constellation of Taurus. It's not difficult to find as it's positioned just a degree northwest of mag. +3.0 star Zeta Tauri (ζ Tau). The remnant was first observed by John Bevis in 1731. Charles Messier observed it in September 1758 and the appearance of this dying remnant inspired him to begin compiling a list of nebulae that possibly could be mistaken for comets. The list eventually became his famous catalogue. The following century, William Parsons, the Third Earl of Rosse made a drawing of M1 (around 1844) and christened it the Crab Nebula due to its wispy filamentary structure.
M1 is best seen from the Northern Hemisphere during the months of November, December and January.
M100, mag. +9.5, is a spiral galaxy located in the southern part of the constellation of Coma Berenices. It's one of the brightest members of the Virgo cluster of galaxies and appears almost face-on from our perspective. It exhibits prominent well-defined spiral arms and is therefore regarded as a grand design spiral. Other notable galaxies that fall into this category are M51, M74, M81 and M101.
M100 was discovered, along with M98 and M99, by Pierre Méchain on March 15, 1781. Charles Messier subsequently observed all three objects and added them to his catalogue on April 13, 1781. He described the galaxy as faint without stars. It was not until 1850 that its spiral nature was first detected by Ango-Irish astronomer William Parsons, the 3rd Earl of Rosse. He included it in his list of 14 spiral nebulae.
Finding the area of sky where M100 is positioned is not difficult once familiar with the location of the Virgo cluster. The cluster centre is positioned close to supergiant elliptical galaxy M87 and about halfway along a line connecting Denebola (β Leo - mag. +2.1) with Vindemiatrix (ε Vir - mag. +2.8). M100 is towards the northern section of the group, 2 degrees southeast of star 11 Comae Berenices (mag. +4.7).