TRIANGULAM GALAXY

                                                                                            TRIANGULAM GALAXY                                                                                                                                                                                                                                                                            The Triangulum Galaxy is a spiral galaxy approximately 3 million light-years (ly) from Earth in the constellation Triangulum. It is catalogued as Messier 33 or NGC 598, and is sometimes informally referred to as the Pinwheel Galaxy, a nickname it shares with Messier 101. The Triangulum Galaxy is the third-largest member of the Local Group of galaxies, which includes the Milky Way, the Andromeda Galaxy and about 44 other smaller galaxies. It is one of the most distant permanent objects that can be viewed with the naked eye.

The Triangulum Galaxy is sometimes informally referred to as the "Pinwheel Galaxy" by some amateur astronomy references and in some public outreach websites. However, the SIMBAD Astronomical Database, a professional astronomy database that contains formal designations for astronomical objects, indicates that the name Pinwheel Galaxy is used to refer to Messier 101, and several other amateur astronomy resources and other public outreach websites also identify Messier 101 by that name.

Under exceptionally good viewing conditions with no light pollution, the Triangulum Galaxy can be seen with the naked eye. It is one of the most distant permanent objects that can be viewed without the aid of a telescope. Being a diffuse object, its visibility is strongly affected by small amounts of light pollution. It ranges from easily visible by direct vision in dark skies to a difficult averted vision object in rural or suburban skies.For this reason, Triangulum is one of the critical sky marks of the Bortle Dark-Sky Scale.

The Triangulum Galaxy was probably discovered by the Italian astronomer Giovanni Battista Hodierna before 1654. In his work De systemate orbis cometici; deque admirandis coeli caracteribus ("About the systematics of the cometary orbit, and about the admirable objects of the sky"), he listed it as a cloud-like nebulosity or obscuration and gave the cryptic description, "near the Triangle hinc inde". This is in reference to the constellation of Triangulum as a pair of triangles. The magnitude of the object matches M33, so it is most likely a reference to the Triangulum galaxy.

The galaxy was independently discovered by Charles Messier on the night of August 25–26, 1764. It was published in his Catalog of Nebulae and Star Clusters (1771) as object number 33; hence the name M33. When William Herschel compiled his extensive catalogue of nebulae, he was careful not to include most of the objects identified by Messier. However, M33 was an exception and he catalogued this object on September 11, 1784 as H V-17.




NGC 604 in the Triangulum Galaxy

Herschel also catalogued the Triangulum Galaxy's brightest and largest H II region (diffuse emission nebula containing ionized hydrogen) as H III.150 separately from the galaxy itself, which eventually obtained NGC number 604. As seen from Earth, NGC 604 is located northeast of the galaxy's central core. It is one of the largest H II regions known, with a diameter of nearly 1500 light-years and a spectrum similar to that of the Orion Nebula. Herschel also noted 3 other smaller H II regions (NGC 588, 592 and 595).

It was among the first "spiral nebulae" identified as such by Lord Rosse in 1850. In 1922–23, John Charles Duncan and Max Wolf discovered variable stars in the nebulae. Edwin Hubble showed in 1926 that 35 of these stars were classical Cepheids, thereby allowing him to estimate their distances. The results were consistent with the concept of spiral nebulae being independent galactic systems of gas and dust, rather than just nebulae in the Milky Way.

ANDROMEDA GALAXY

                                                                                                                                                                       ANDROMEDA GALAXY                                                                                                                                                                                       Andromeda I is a dwarf spheroidal galaxy(dSph) about 2.40 million light-years away in the constellation Andromeda. Andromeda I is part of the Local group of galaxies and a satellite galaxy of the Andromeda Galaxy (M31). It is roughly 3.5 degrees south and slightly east of M31. As of 2005, it is the closest known dSph companion to M31 at an estimated projected distance of ~40 kpc or ~150,000[6] light-years.

Andromeda I was discovered by Sidney van den Bergh in 1970 with the Mount Palomar Observatory 48-inch telescope. Further study of Andromeda I was done by the WFPC2 camera of the Hubble Space Telescope. This found that the horizontal branch stars, like other dwarf spheroidal galaxies were predominantly red. From this, and the abundance of blue horizontal branch stars, along with 99 RR Lyrae stars detected in 2005,lead to the conclusion there was an extended epoch of star formation. The estimated age is approximately 10 Gyr. The Hubble telescope also found a globular cluster in Andromeda I, being the least luminous galaxy where such a cluster was found.

The Persian astronomer Abd al-Rahman al-Sufi wrote a line about the chained constellation in his Book of Fixed Stars around 964, describing it as a "small cloud". Star charts of that period have it labeled as the Little Cloud. The first description of the object based on telescopic observation was given by German astronomer Simon Marius on December 15, 1612.Charles Messier catalogued it as object M31 in 1764 and incorrectly credited Marius as the discoverer, unaware of Al Sufi's earlier work. In 1785, the astronomer William Herschel noted a faint reddish hue in the core region of M31. He believed it to be the nearest of all the "great nebulae" and based on the color and magnitude of the nebula, he incorrectly guessed that it was no more than 2,000 times the distance of Sirius.

William Huggins in 1864 observed the spectrum of M31 and noted that it differed from a gaseous nebula. The spectra of M31 displayed a continuum of frequencies, superimposed with dark absorption lines that help identify the chemical composition of an object. The Andromeda nebula was very similar to the spectra of individual stars, and from this it was deduced that M31 had a stellar nature. In 1885, a supernova (known as S Andromedae) was seen in M31, the first and so far only one observed in that galaxy. At the time M31 was considered to be a nearby object, so the cause was thought to be a much less luminous and unrelated event called a nova, and was named accordingly "Nova 1885".

The first photographs of M31 were taken in 1887 by Isaac Roberts from his private observatory in Sussex, England. The long-duration exposure allowed the spiral structure of the galaxy to be seen for the first time.However, at the time this object was still commonly believed to be a nebula within our galaxy, and Roberts mistakenly believed that M31 and similar spiral nebulae were actually solar systems being formed, with the satellites nascent planets.[citation needed] The radial velocity of this object with respect to our solar system was measured in 1912 by


Vesto Slipher at the Lowell Observatory, using spectroscopy. The result was the largest velocity recorded at that time, at 300 kilometres per second (190 mi/s), moving in the direction of the Sun.

MILKY WAY GALAXY

                                                                                                                                                                    MILKY WAY GALAXY                                                                                                                                                                 The Milky Way is the galaxy that contains our Solar System. Its name "milky" is derived from its appearance as a dim glowing band arching across the night sky in which the naked eye cannot distinguish individual stars. The term "Milky Way" is a translation of the Latin via lactea, from the Greek  (galaxías kýklos, "milky circle") From
Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Up until the early 1920s, most astronomers thought that all of the stars in the universe were contained inside of the Milky Way. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis,observations by Edwin Hubble definitively showed that the Milky Way is just one of many—now known to be billions—of galaxies.

The Milky Way is a barred spiral galaxy some 100,000–120,000 light-years in diameter, which contains 100–400 billion stars. It may contain at least as many planets as well. The Solar System is located within the disk, about 27,000 light-years away from the Galactic Center, on the inner edge of one of the spiral-shaped concentrations of gas and dust called the Orion Arm. The stars in the inner ≈10,000 light-years form a bulge and one or more bars that radiate from the bulge. The very center is marked by an intense radio source, named Sagittarius A*, which is likely to be a supermassive black hole.

Stars and gases at a wide range of distances from the Galactic Center orbit at approximately 220 kilometers per second. The constant rotation speed contradicts the laws of Keplerian dynamics and suggests that much of the mass of the Milky Way does not emit or absorb electromagnetic radiation. This mass has been given the name "dark matter"The rotational period is about 240 million years at the position of the Sun. The Milky Way as a whole is moving at a velocity of approximately 600 km per second with respect to extragalactic frames of reference. The oldest known star in the Milky Way is at least 13.82 [26] billion years old and thus must have formed shortly after the Big Bang.

Surrounded by several smaller satellite galaxies, the Milky Way is part of the Local Group of galaxies, which forms a subcomponent of the Virgo Supercluster, which again forms a subcomponent of the Laniakea Supercluster.

When observing the night sky, the term "Milky Way" is limited to the hazy band of white light some 30 degrees wide arcing across the sky.[29] Although all of the individual stars that can be seen in the entire sky with the naked eye are part of the Milky Way Galaxy,[30] the light in this band originates from the accumulation of un-resolved stars and other material when viewed in the direction of the Galactic plane. Dark regions within the band, such as the Great Rift and the Coalsack, correspond to areas where light from distant stars is blocked by interstellar dust. The region where the Milky Way is self-obscuring is also known as the zone of avoidance.

The Milky Way has a relatively low surface brightness. Its visibility can be greatly reduced by background light such as light pollution or stray light from the Moon. It is readily visible when the limiting magnitude is +5.1 or better and shows a great deal of detail at +6.1. This makes the Milky Way difficult to see from any brightly lit urban or suburban location, but very prominent when viewed from a rural area when the Moon is below the horizon.

As viewed from Earth, the visible region of the Milky Way's Galactic plane occupies an area of the sky that includes 30 constellations. The center of the Milky Way lies in the direction of the constellation Sagittarius; it is here that the Milky Way is brightest. From Sagittarius, the hazy band of white light appears to pass westward to the Galactic anticenter in Auriga. The band then continues westward the rest of the way around the sky, back to Sagittarius. The band divides the night sky into two roughly equal hemispheres.

The Galactic plane is inclined by about 60 degrees to the ecliptic (the plane of Earth's orbit). Relative to the celestial equator, it passes as far north as the constellation of Cassiopeia and as far south as the constellation of Crux, indicating the high inclination of Earth’s equatorial plane and the plane of the ecliptic, relative to the Galactic plane. The north Galactic pole is situated at ri
ght ascension 12h 49m, declination +27.4° (B1950) near β Comae Berenices, and the south Galactic pole is near α Sculptoris. Because of this high inclination, depending on the time of night and year, the arc of Milky Way may appear relatively low or relatively high in the sky. For observers from approximately 65 degrees north to 65 degrees south on Earth's surface, the Milky Way passes directly overhead twice a day.