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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 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 (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)

The Messier Catalogue is a famous catalogue in Astronomy. It consists of 110 deep sky objects, including open and globular star clusters, galaxies, nebulae, an asterism, a double star and even a supernova remnant. It was compiled in the 18th century by Charles Messier.

Messier was a comet hunter who was born in Badonviller, France on June 26, 1730. When searching for comets he was frustrated by fixed objects that looked like comets in the night sky but actually weren't. These fuzzy "comet" like objects hindered his searches so he catalogued them in order to avoid them in future.

The first version of his catalogue contained 45 objects and was published in 1774 in the journal of the French Academy of Sciences in Paris. Over the next 7 years he updated the catalogue and published the final version in 1781, containing 103 objects. Many of these objects he actually discovered himself.

On several different occasions between 1921 and 1966, astronomers and historians discovered evidence of another 7 deep-sky objects that were observed either by Messier or his friend and assistant, Pierre Mechain, shortly after the final version was published. These objects, numbered M104 to M110, are now accepted by astronomers as "official" Messier objects.

M44, also known as the Praesepe or Beehive cluster, is a sprawling open cluster. It's the brightest and most prominent deep sky object in the constellation of Cancer. Visible to the naked eye under dark skies, the cluster appears like a large misty cloud covering over 1.5 degrees of sky. The brightness and size of M44 results from its close proximity to Earth; it lies a mere 577 light-years distant. Only the Hyades (at 153 light-years), Coma cluster (280 light-years), the Pleiades (M45) (425 light-years), Southern Pleiades (480 light-years) and IC 2391 (500 light-years) are nearer. Consequently, M44 is one of the brightest and largest objects of its type in the night sky.

The constellation of Cancer is a faint zodiac constellation that's bordered by much brighter Leo to the east and Gemini to the west. To the north is faint Lynx, with Canis Minor and Hydra located on the southern side. At the heart of Cancer is a grouping of four faint stars. They are Asellus Australis (δ Cnc - mag. +3.9), Asellus Borealis (γ Cnc - mag. +4.7), η Cnc (mag. +5.3) and θ Cnc (mag. +5.3). Of these, the brighter two are relatively easy naked eye objects, the fainter ones more difficult. Positioned at the centre of this grouping is M44. An alternative method of locating M44 is to imagine a line extending in a southeastern direction from Pollux (β Gem - mag. +1.1) for 37 degrees to Regulus (α Leo - mag. +1.4). M44 is positioned approximately at the mid-point of this line.

M48 is a large conspicuous open cluster covering almost a degree of sky in the constellation of Hydra. It's located close to the border with Monoceros. At magnitude +5.5, the cluster is visible to the naked eye under reasonably dark skies, and a superb binocular or small telescope object. It's best seen during the months of December, January and February.

Charles Messier discovered and cataloged M48 on February 19, 1771. However, he made a positioning mistake and hence the object was missing for over 150 years, until it was identified by Oswald Thomas in 1934, and independently by T.F. Morris in 1959. Since M48 was lost, two subsequent independent re-discoveries occurred. The first was by Johann Elert Bode who found it before 1782 and then Caroline Herschel located it on March 8, 1783.

Hydra is the largest constellation in the sky, but finding M48 is relatively easy as it's positioned just 14 degrees southeast of Procyon (α CMi) in Canis Minor. At magnitude +0.34, Procyon is the seventh brightest star in the night sky. Also visible to the naked eye, but better seen with binoculars is a triangle of 4th and 5th magnitude stars located about 5 degrees northwest of M48. The stars in question are Zeta Mon (ζ Mon - mag. +4.4), 28 Mon (mag. + 4.7) and 27 Mon (mag. +4.9).

M48 Open Cluster (credit:- NOAO/AURA/NSF)

M65 is a magnitude +9.6 edge-on spiral galaxy located 35 million light-years distant. It was discovered by Charles Messier on March 1, 1780, the night he also discovered M66. Messier described the galaxy as "a very faint nebula without stars." Apart from M81 and M82 in Ursa Major, M65 and M66 are probably the most sought after galaxy pair for amateur astronomers. With a third galaxy, NGC 3628, lying nearby the trio forms the heart of a small celebrated group, known as the Leo Triplet or M66 group. All can be observed or photographed in the same field of view and are a popular target for observers and astrophotographers alike.

M65 is located in the eastern section of the relatively large and bright zodiac constellation of Leo, the Lion. In western skylore, the Lion's heart is marked by the constellation's brightest and only first magnitude star, Regulus (α Leo - mag +1.4). Positioned approximately 16 degrees northeast of Regulus is Chertan (θ Leo - mag. +3.3). Along with the Zosma (δ Leo - mag. +2.6) and Denebola (β Leo - mag. +2.1), Chertan forms a prominent right-angled triangle. Located 2 degrees south of Chertan is 73 Leonis (mag. +5.3). M65 lies 0.75 degrees east of this star, with M66 a further 0.33 degrees to the southeast of M65. Positioned 0.5 degrees north of the Messier pair is the third member of the triplet, NGC 3628.

The galaxies are best seen during the months of March, April and May.

Messier 65 spiral galaxy by the Hubble Space Telescope (credit:- NASA/ESA/The Hubble Heritage Team STScI/AURA)

Cassiopeia
Cassiopeiae
Cas
The Seated Queen

Introduction

Cassiopeia is a prominent northern constellation named after Queen Cassiopeia, the wife of King Cepheus of Ethiopia. In Greek mythology, the Queen was arrogant and extremely boastful about her beauty. Legend has it she claimed both her and her daughter, Andromeda, were more beautiful than all the Nereids the nymph-daughters of the sea god Nereus. This brought the wrath of the ruling god of the sea Poseidon who decided to destroy the kingdom.

After consulting a wise oracle, the only way the King and Queen could stop Poseidon from carrying out his threat was to scarify Andromeda. The princess was left helplessly chained to a rock at the sea edge, awaiting her fate at the hands of Cetus, the sea monster. However, just in time, the hero Perseus arrived to save Andromeda and in the process killed the sea monster. Although Andromeda lived to marry Perseus, Poseidon deemed that Cassiopeia should not escape punishment and banished her to the sky forever, tied to the chair of torture!

The constellation is one of the original 48 plotted by second century astronomer Ptolemy and remains as one of the 88 modern constellations. It's one of the most recognisable constellations due to the distinctive W shape of its five brightest stars. This asterism forms part of the chair and consists of γ Cas (mag.(v) +1.6 -> +3.0), Schedar (α Cas - mag. +2.24), Caph (β Cas - mag. +2.28), Ruchbah (δ Cas - mag. +2.66) and ε Cas (mag. +3.35). Variable star γ Cas can peak at magnitude +1.6 and when it does it's easily the brightest member but currently it hovers around magnitude +2.15.

Since located right bang at the centre of the rich northern Milky Way, Cassiopeia is full of wonderful deep-sky objects. It contains over a dozen bright open clusters visible in small scopes. In addition, there are some beautiful double stars and interesting variable stars. At Cassiopeia's southern end there are three faint galaxies, two of which are dwarfs and members of the M31 Group. For larger scopes there are four faint nebulae within range.

M66 is a superb bright intermediate spiral galaxy located in the constellation of Leo. It's the brightest of a trio of galaxies that forms - along with M65 and NGC 3628 - the well known and popular Leo Triplet or M66 group. All three objects can be observed with small telescopes in the same low power field of view. After the M81/M82 pair in Ursa Major, the Leo Triplet is arguably the next most sought after galaxy grouping for amateur astronomers.

Charles Messier discovered both M66 (mag. +8.9) and M65 (mag. +9.6) on March 1, 1780. The apparent magnitude of the third member of the triplet, NGC 3628, is unclear. Some texts record it as the brightest group member, while others have it as the faintest. For our purposes we estimate NGC 3628 to be brighter than M65 and almost as bright as M66. However, what is clear is that it suffers from a low surface brightness and therefore is the most difficult member of the trio to spot. Messier missed it completely and it was not until April 8, 1784 when it was finally discovered by William Herschel.

To find the triplet, look to the eastern part of Leo. This zodiac constellation is relatively large and bright and somewhat looks like the Lion that it's supposed to represent. The brightest star in Leo and its only first magnitude star is Regulus (α Leo – mag +1.4). Positioned approximately 16 degrees northeast of Regulus is Chertan (θ Leo - mag. +3.3). Along with the Zosma (δ Leo - mag. +2.6) to the north and Denebola (β Leo - mag. +2.1) to the east, Chertan forms a prominent right-angled triangle. Located 2 degrees south of Chertan is 73 Leonis (mag. +5.3). M65 lies 0.75 degrees east of this star with M66 a further 0.33 degrees southeast of M65. NGC 3628 is positioned 0.5 degrees north of the Messier pair.

NGC 3626, mag. +10.9, is a spiral galaxy in Leo that was discovered by William Herschel on March 14, 1784. It's one of many galaxies in the constellation within the range of small scopes.

NGC 3626 is located 70 million light-years away. It covers 2.7 x 1.9 arc minutes of apparent sky, which corresponds to a spatial diameter of 55,000 light-years and is estimated to contain 40 billion stars.

Patrick Moore listed, NGC 3626, as number 40 in his Caldwell catalogue. It belongs to the NGC 3607 group of galaxies.

NGC 3626 (credit:- NASA, Sloan Digitalised Sky Survey)

Finder Chart for NGC 3626 (credit:- freestarcharts)

Finder Chart for NGC 3626 - pdf format (credit:- freestarcharts)

NGC 3626 is positioned 2.5 degrees southeast of Zosma (δ Leo - mag. +2.6). A trio of elliptical galaxies, consisting of NGC 3607, NGC 3608 and NGC 3605, are located 50 arc seconds west-southwest of NGC 3626. Of these, NGC 3607 is the brightest at magnitude +9.9. NGC 3608 is similar in brightness to NGC 3626. At 12th magnitude the third member, NGC 3605, is by far the faintest.