Andromeda Galaxy  


Project by:

Leila Tarina Ribeiro

Pedro Miguel Veigas

Tiago Jorge Pena Gil

Maria da Conceição César Caeiro Loureiro Santos

Escola Secundária Morgado de Mateus

Vila Real – Portugal

2002

The Constelation of Andromeda

Names

Andromeda Galaxy

Messier

M 31

NGC Nº

NGC 224

Type

Sb Spiral Galaxy

Magnitude

4.1

Distance

2.37 Million Light Yeares

Diameter

160000 Lihgt Yeares

Angular Diameter

03 d 12’ 15’ by 00 d 57’ 16”

Constellation

Andromeda

Locotion

Northern Hemisphere

Best Visibility

2 nd October

R.A.

004252

Declination

+ 411721

Andromeda is the nearest major galaxy to our own Milky Way Galaxy. Our Galaxy is thought to look much like Andromeda. Together these two galaxies dominate the Local Group of galaxies. The diffuse light from Andromeda is caused by the hundreds of billions of stars that compose it. The several distinct stars that surround Andromeda's image are actually stars in our Galaxy that are well in front of the background object .
Andromeda is a "V" shaped constellation best viewed in the fall if you live in the Northern Hemisphere. Andromeda lies close to the North Pole, so only a few in the Southern Hemisphere can see this strangely shaped constellation in the spring .

M31: The Andromeda Galaxy

One myth about Andromeda is found in Greek mythology. Andromeda's mother, Queen Cassiopeia, bragged that she was prettier than the sea nymphs. The nymphs complained to Poseidon, who in turn sent a monster to destroy her land. The queen and her husband, King Cepheus, were told to sacrifice their daughter to save the country .

Andromeda was chained to a cliff for the monster, called Cetus. Just as the monster was ready to bite down on the maiden, Perseus rescued her. Perseus and Andromeda were put in the sky along with Cepheus, Cassiopeia and Cetus.

"Perseus and Andromeda" by Vasari. Painting (1570).

Andromeda is right next to Pegasus, which leads some to believe that at one time, some of these stars used to be part of the winged horse. The image shows Andromeda upside-down, which is often her position in the sky. The Princess' head is the star Alpheratz, which is also the last star in Pegasus.

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There is plenty to see in this fall constellation. The Great Andromeda Galaxy is the most distant object visible to the naked eye. You can find this famous galaxy on the right side of Andromeda, about half-way up the constellation. There are also many other galaxies and some open clusters around this constellation, but many are too faint to see .

The Andromeda Galaxy (also known as M31 and NGC 224) is the nearest spiral galaxy to our own Milky Way galaxy. Its relatively early Hubble type (Sb) and bright absolute magnitude (-20) make it an important and unique source of information on galaxies of this nature. M31 forms an important testing ground for ideas about massive galaxies and about galaxy evolution, and is ripe for detailed astrophysical exploration .

Visible to the naked eye even under moderate conditions, this object was known as the "little cloud" to the Persian astronomer Al-Sufi, who described it 964 AD in his Book of Fixed Stars ; it must have been observed by Persian astronomers as early as 905 AD, or earlier. R. H. Allen (1899/1963) reports that it was also appeared on a Dutch starmap of 1500. Charles Messier was obviously unaware of this early reports, and ascribed its discovery to Simon Marius, who was the first to give a telescopic description in 1612, but (according to R.H. Allen) didn't claim its discovery. Unaware of both Al Sufi's and Marius' discovery, Giovanni Batista Hodierna independently rediscovered this object before 1654. Edmond Halley, however, in his 1716 treat of "Nebulae" , accounts the discovery of this "nebula" to the French astronomer Bullialdus (Ismail Bouillaud), who observed it in 1661; but Bullialdus mentions that it had been seen 150 years earlier (in the early 1500s) by some anonymous astronomer ( R.H. Allen, 1899/1963 ).

It was longly believed that the "Great Andromeda Nebula" was one of the closest nebulae. William Herschel believed, wrongly of course, that its distance would "not exceed 2000 times the distance of Sirius" (17,000 light years); nevertheless, he viewed it at the nearest "island universe" like our Milky Way which he assumed to be a disk of 850 times the distance of Sirius in diameter, and of a thickness of 155 times that distance.

It was William Huggins, the pioneer of spectroscopy, who noted the difference between gaseous nebula with their line spectra and those "nebulae" with continuous spectra, which we now know as galaxies.

In 1912, V.M. Slipher of Lowell Observatory measured the radial velocity of the Andromeda "nebula" and found it the highest velocity ever measured, about 300 km/sec in approach (a better value value is about 266 km/sec, according to Burnham). This already pointed to the extra-galactic nature of this object.

In 1923, Edwin Hubble found the first Cepheid variable in the Andromeda galaxy and thus established the intergalactic distance and the true nature of M31 as a galaxy. Because he was not aware of the two Cepheid classes, his distance was incorrect by a factor of more than two, though. This error was not discovered until 1953, when the 200-inch Palomar telescope was completed and had started observing.

At modern times, the Andromeda galaxy is certainly the most studied "external" galaxy. It is of particular interest because it allows studies of all the features of a galaxy from outside which we also find in Milky Way, but cannot observe as the greatest part of our Galaxy is hidden by interstellar dust.

The Hubble Space Telescope has revealed that the Andromeda galaxy M31 has a double nucleus . This suggests that either it has actually two bright nuclei, probably because it has "eaten" a smaller galaxy which once intruded its core, or parts of its only one core are obscured by dark material, probably dust. In the first case, this second nucleus may be a remainder of a possibly violent dynamical encountering event in the earlier history of the Local Group . In the second case, the duplicity of Andromeda's nucleus would be an illusion causes by a dark dust cloud obstructing parts of a single nucleus in the center of M31 .

Collision Scenario for the Milky Way and Andromeda Galaxies

The Milky Way and the Andromeda galaxy are approaching each other with a speed of 300,000 miles per hour. It would take about 2 billion years, but it is possible that the two galaxies could collide or merge into each other.

It's not certain yet whether we're in store for a head-on collision or a simple sideswiping by the massive galaxy, which is a near twin to the Milky Way. Astronomers will first need to use powerful new telescopes to precisely measure Andromeda's tangential motion across the sky. (Just as a baseball outfielder estimates whether a ball is heading directly toward him or is going to miss him by determining whether the ball is moving sideways.)

A direct collision would lead to a grand merger between the two behemoths, and the Milky Way would no longer be the pinwheel spiral we are familiar with, but would evolve into a huge elliptical galaxy.

Bibliography

Wood, Robert W. Science for the kids: 39 Easy Astronomy Experiments . Blue Ridge Summit, PA: TAB Books, 1991

Hawking, Stephen. The Universe in a Nutsbell . The Book Laboratory, Inc. 2001

Ferreira, Máximo. O meu pequeno livro de astronomia. Bizâncio. Portugal. 2001

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