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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 change in brightness? 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 star 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 2360 is an open cluster visible with binoculars in the constellation of Canis Major. It was the first deep sky discovery made by Caroline Herschel - the younger sister of William Herschel - on February 26, 1783. She described it as "a beautiful cluster of pretty compressed stars near 1/2 degree in diameter." It's also known as Caroline's Cluster, Caldwell 58 and Melotte 64.
William Herschel included the cluster in his 1786 catalogue of 1,000 clusters, crediting his sister as the discoverer. At magnitude +7.2, NGC 2360 is not visible to the naked eye but is an easy binocular object and a fine sight through small telescopes. The cluster is positioned 8 degrees east-northeast of the brightest star in the night sky Sirius (α CMa - mag. -1.47) and lies 3.5 degrees directly east of gamma CMa (γ CMa - mag. +4.1). At the western edge of NGC 2360 is an unrelated star, HD 56405 (mag. +5.5).
NGC 2261 is a curious reflection nebula in Monoceros that's known as Hubble's Variable Nebula. It was discovered by William Herschel in 1783 and is illuminated by variable star R Monocerotis (R Mon). The nebula is unusual in that it changes shape over a period of just days and can vary by up to 2 magnitudes in brightness. The variations are believed to be due to periodic changes in the amount of dust surrounding R Mon, thus affecting the amount of light that reaches us. With an apparent magnitude of +9.0, it can be spotted with binoculars under dark skies.
The variability of R Mon (between magnitudes +10 and +12) was discovered at the Athens Observatory in 1861, but it wasn't until 1916 when Edwin Hubble realised that the nebula also changes in brightness. The variations are such that even on images taken only days apart, structural changes can be seen.
NGC 2261 was chosen as the "first light" photograph on January 26, 1949 for the 200-inch (5.1 m) Hale reflecting telescope under the direction of American astronomer Edwin Powell Hubble. At the time, the newly constructed Hale telescope was the largest telescope in the world and remained so until 1976. NGC 2261 is number 46 in the Caldwell catalogue.
NGC 1097, mag. +9.5, is a face-on barred spiral galaxy located in the southern constellation of Fornax. It's one of the finest barred spirals in the night sky and a nice object for backyard scopes. Through a small refractor, its nucleus appears bright and is surrounded by a faint haze. With larger scopes, it's possible to make out the centre bar structure and subtle details in the spiral arms.
NGC 1097 is also classified as a Seyfert galaxy and contains an Active Galactic Nucleus (AGN). At the centre of this galaxy is a huge supermassive black hole of about 140 million times the mass of the Sun. Surrounding the black hole are gases, dust and a prominent ring of hundreds of star-forming regions. New stars are being created in the ring, due to material flowing inwards towards the galaxy centre.
The galaxy is best seen from southern locations during the months of November, December and January. It was discovered by William Herschel on October 9, 1790 and is number 67 in the Caldwell catalogue.
NGC 1851 is a globular cluster in the southern constellation of Columba that's easily visible with binoculars. It's an unusual cluster since it was probably a former member of the Canis Major Dwarf galaxy. This dwarf galaxy and Local Group member was discovered in 2003.
James Dunlop, a Scottish astronomer based in Australia, discovered NGC 1851 on May 29, 1826. It shines at mag. +7.3 and spans 11 arc minutes of sky, making it the brightest and largest deep sky object in Columba.
This globular is best seen during the months of December, January and February. From northern temperate locations it appears low down, apart from latitudes above 50N where it's not even visible at all. The object is number 73 in the Caldwell catalogue.
NGC 1275, also known as Perseus A, is a Seyfert galaxy in the constellation Perseus. It's lies at the centre of the Perseus cluster of galaxies (Abell 426) and is the group's dominant member. At 230 million light-years distant, it's way beyond the Local Group but can be spotted in medium size backyard scopes under dark skies and good seeing conditions. This galaxy shines at apparent mag. +11.7.
NGC 1275 is a strong radio and X-ray source that produces peculiar emission lines in its nucleus. It's listed as entry 3C 84 in the 3rd Cambridge Catalogue of Radio Sources and Carl Seyfert include it in his original list of active galaxies. NGC 1275 is actually a complex system consisting of a main galaxy and a high velocity system (HVS). Tidal interactions between the two objects result in large amounts of dust disruption, gas stripping and star formation. In addition, tidal forces send existing gas and dust swirling into the supermassive black hole at centre of the main galaxy, resulting in the powerful X-ray and radio wave emissions.
NGC 1275 was discovered by William Herschel on October 17, 1786.
Almach (γ And) is one of the finest double stars in the sky. To the naked eye, it appears as a single bright star of magnitude +2.10, but small scopes reveal an outstanding double, made up of a bright yellow or slightly orange primary and a fainter deep blue secondary. It's widely regarded as the second best colour contrast double in the sky, surpassed only by Albireo in Cygnus.
NGC 891 is a tenth magnitude unbarred spiral galaxy located in Andromeda. Also known as the Silver Sliver, it's one of the best examples of an edge-on galaxy in the sky although a challenging object for small scopes. Due to its attractiveness and scientific appeal, NGC 891 was selected on October 12, 2005 to be the first light image of the Large Binocular Telescope at Mount Graham International Observatory in Arizona. In 2012, it was again selected as first light image, this time for the Discovery Channel Telescope (DCT) Large Monolithic Imager at the Lowell Observatory in Happy Jack, Arizona.
The Silver Sliver was discovered by William Herschel on October 6, 1784 and is best seen from the Northern Hemisphere during October, November and December. Astronomers think our Milky Way galaxy would look remarkably similar, if viewed edge-on.
NGC 752 is a large sprawling open cluster in the constellation of Andromeda. With an apparent magnitude of +5.7 it's visible to the naked eye from a dark site, appearing as a large unresolved fuzzy patch of light. The cluster is one of the finest large open clusters in the sky and contains over 70 stars spread across a huge 1.25 degrees of apparent sky. Due to its size, NGC 752 is best observed with binoculars or wide field telescopes at low powers.
NGC 752 is located 5 degrees south and slightly west of outstanding double star Almach (γ And - mag. +2.1), the third brightest star in Andromeda. This cluster was discovered by Caroline Herschel on September 29, 1783 although it was probably observed sometime before 1654 by Italian astronomer Giovanni Battista Hodierna. Caroline's brother, William Herschel, subsequently added it to his catalogue a couple of years later.
NGC 752 is best seen from northern latitudes during the months of October, November and December. It's number 28 in the Caldwell catalogue.