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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.
The annual Orionids meteor shower peaks this year on October 21st and the prospects are favourable as the three-day-old Moon will not interfere. Generally regarded as a strong shower, the Orionids is active between October 2nd and November 7th, with most meteors visible a few days before, during and after peak day. In the past rates of up to 70 meteors per hour have been observed, but currently the shower is not so active. A figure between 20 and 25 is now the norm.
Gemini is a northern zodiac constellation and one of the 48 constellations described by second century astronomer Ptolemy. Its name is Latin for the twins and it's one of the few constellations in the sky that actually looks like what it suppose to represent. This bright grouping contains two-standout stars, Castor (α Gem) and Pollux (β Gem). At mag. +1.16, Pollux is the brighter while multiple system Castor shines at mag. +1.58. Surprisingly, Pollux was assigned beta Geminorum by Johann Bayer - the German astronomer who labelled the stars with Greek letters in 1603 - even though it easily outshines Castor. Some astronomers have suggested that maybe Pollux has since brightened or Castor faded, but both possibilities seem extremely improbable. The likelihood is that Bayer simply made a mistake and didn't carefully distinguish which was the brighter star.
In Greek mythology, Castor and Pollux were twin brothers whose mother was Queen Leda although Castor was the mortal son of King Tyndareus and Pollux the divine son of Zeus. Together the twins were known as the Dioscuri, which means the sons of Zeus. However, in most versions of the myth only Pollux was Zeus's child. The twins were the patron saints of mariners, appearing in ships rigging as the St Elmo's fire phenomena. When Castor died, Pollux begged Zeus to give Castor immortality, which he did, thereby reuniting the twins together in the heavens forever.
Uranus, the seventh planet from the Sun, reaches opposition on October 19th. The distant "Ice Giant" shines at mag. +5.7 and is located in the constellation of Pisces. It's marginally bright enough to seen with the naked eye and easy to spot with binoculars and small scopes.
Uranus is positioned close to the Aries constellation border. It's about 15 degrees south and 30 degrees east of the centre of the Great Square of Pegasus and a couple of degrees west and slightly north of omicron Piscium (ο Psc - mag. +4.3). Further to the northeast is Taurus, which contains first magnitude orange star Aldebaran and naked eye open clusters, the Pleiades and Hyades.
Betelgeuse is a red supergiant in Orion that's one of the most famous stars in the sky. It's an irregular variable that usually fluctuates between magnitudes +0.3 and +0.8, though on rare occasions it has been known to peak at magnitude 0.0 and dim down to magnitude +1.2. The star currently hovers around magnitude +0.42. It marks the upper left-hand corner of the ancient hunter figure.
Although lettered alpha (α) Orionis, Betelgeuse is usually fainter than Rigel (β Orionis - mag. +0.13) and is therefore the constellations second brightest star. Sir John Herschel, in 1836, was the first person to record brightness variations and on two occasions, in October 1837 and November 1839, he observed it to be brighter than Rigel. At best, Betelgeuse is comparable in brightness to Rigel and Capella (α Aur - mag. +0.08) but when towards the lower end of its range, appears more like Aldebaran (α Tau - mag(v). +0.75 -> +0.85).
The Hyades is a very large loose naked eye open cluster located in the constellation of Taurus. It spans 5.5 degrees of sky, which is equivalent to 11 times the diameter of the full Moon. At a distance of 153 light-years this is the nearest open cluster - the Ursa Major Moving Group is closer, but's extremely scattered and more of a cluster like object than a true cluster. Consequently, the Hyades is one of the top studied open clusters of all.
The Hyades is easily found as it circles the brightest star in Taurus, first magnitude orange giant star Aldebaran (α Tau - mag. +0.87). It's not unreasonable to assume that Aldebaran is also a member of the Hyades. However, it's purely a foreground star, an interloper located only 65 light-years distant that happens to be in the same line of sight. As a naked-eye object, the Hyades have been known since prehistoric times.
The cluster is best seen from northern latitudes during the months of November, December and January.
M45, commonly known as the Pleiades or Seven Sisters, is the finest open cluster in the sky. It's a breathtaking site, known since antiquity and easily visible to the naked eye. Located in the large and prominent zodiac constellation of Taurus, this showpiece object is best seen during the Northern Hemisphere Winter and the Southern Hemisphere Summer months.
Finding M45 is easy. The cluster is positioned about 14 degrees northwest of orange giant star Aldebaran (mag. +0.9), the brightest star in Taurus. At first glance with the naked eye, it's obvious that something is special about this small section of sky. On closer inspection, M45 reveals itself to be a beautiful cluster of about half a dozen white stars, covering an area much greater than that of the full Moon. At the heart of the cluster is a set of stars that form a small dipper shape, similar to the brightest stars of Ursa Major. Even under light polluted skies the dipper shape is readily visible. From dark sites, the Pleiades is an outstanding naked eye object. The main stars appear bright and striking, with up to 10 or more visible under ideal conditions.
IC 59 and IC 63 are faint reflection and emission nebula located in the northern constellation of Cassiopeia. They are challenging objects to spot with telescopes for a number of reasons. Both nebulae are faint at apparent mag. +10, they have extremely low surface brightness and surround bright variable star gamma Cas (γ Cas). This remarkable star is partly unstable and is known as a "shell star". It currently shines at mag. +2.15, making it the brightest star in Cassiopeia.
IC 59 and IC 63 are 610 light-years distant. From our perspective, IC 59 is located on the northern side of gamma Cas and IC 63 to the northeast. Spatially the nebulae are roughly 3 light-years from gamma Cas, although IC 63 is slightly closer to the star. As a result, it's appears mostly red due to a dominance of H-alpha emission, whereas IC 59 exhibits much less H-alpha emission and appears mostly blue due to dust reflected starlight.
Orion is a prominent constellation that's one of the brightest and most familiar sights in the night sky. Straddling the celestial equator it can be seen from all locations on Earth. Named after a great hunter in Greek mythology, it contains two first magnitude stars, many other bright stars, a famous belt, spectacular nebulae, some impressive multiple stars and fine open clusters. Its most famous inhabitant, the Orion Nebula, is one of the most spectacular deep sky objects in the sky.
The distinctive pattern of Orion has been used historically and in the modern World extensively. The earliest linking is an ivory carving found in a cave in the Ach valley in Germany, which is estimated to be at least 32,000 years old. In Greek mythology, Orion was a handsome strong hunter, born to Euryale the daughter of King Minos of Crete and Poseidon, the god of the sea. Many myths surround the character particularly involving his death. Various versions exist, but generally Orion brought the wrath of goddess Artemis who sent the scorpion to kill him. The resulting outcome is that the hunter and the scorpion are placed on opposite sides of the sky. When Scorpius rises in the east, Orion is setting in the west.
In medieval Muslim astronomy, Orion was known as al-jabbar, the giant. In old Hungarian tradition, Orion was a magic Archer or Reaper and in China the constellation was one of the 28 lunar mansions that reflect the movement of the Moon. The Egyptians associated Orion with Osiris, the god of death, afterlife, resurrection, regeneration and rebirth. They also aligned part of the Great Pyramid of Giza with Alnitak, one of the stars of the belt. For the Aztecs, Orion rising in the east signaled the time to perform the "New Fire" ceremony, a ritual designed to postpone the end of the World. More recently, the film company Orion Pictures used the constellation's main shape as its logo.
Orion is best seen during the months of December, January and February.