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 frequently referred to as M31 since it is the 31st object on Messier's list of diffuse sky objects.
The Andromeda Galaxy, M31, is located 2.3 million light years away, making it the nearest major galaxy to our own Milky Way.
Both Andromeda and the Milky Way, along with 20 smaller galaxies belong to the "local group of galaxies". It can be seen with the naked eye as a spindle-shaped "cloud" the width of the full Moon. Like the Milky Way, M31 is a giant spiral-shaped disk of stars, with a bulbous central hub of older stars. M31 has long been known to have a bright and extremely dense grouping of a few million stars clustered at the very center of its spherical hub.
July 17, 2001 - UniSci News
An individual team including an astronomer from the Observatoire de Paris has recently observed for the first time individual stars in a very dense zone of an external galaxy, enabling for the first time an eagerly awaited comparison with the corresponding zone of our galaxy, the Milky Way.
With the advent of the refurbished Hubble Space Telescope (HST), it has become possible to study individual stars at the distance of the Andromeda galaxy (Messier 31). Resolving stars at still greater distances will require the next generation of ground- or space-based telescopes.
A team of astronomers (including Pascale Jablonka from Paris-Meudon Observatory and UMR 8631 of CNRS) took this opportunity to study with the Hubble Space Telescope at visible (WFPC2) and infrared (NICMOS) wavelengths, metal-rich stellar populations in globular clusters and field stars close to or in the bulge of M31.
They obtained images of the central part (bulge) of M 31 in two colors, and have analyzed these images, which include two globular clusters. These analyses pioneered the field of studies in extremely crowded environments, a difficult observation.
They give the first precise picture of a galaxy bulge besides the one of our own galaxy. With these images, they are able to:
* Derive estimates for metallicities and ages for stellar clusters close to the bulge.
* Compare the properties of stars in cluster with those of the stars surrounding the cluster (field stars).
* Deduce some features of the spiral galaxy formation scenario of the clusters and of their host galaxy (M31 is a spiral galaxy similar to our Galaxy).
The figure shows the visible (V) and infrared (I) images of two bright globular clusters, G170 and G177, projected on the bulge of M31.
The field of view of WFPC2 and NICMOS cameras enables us to see a number of bulge stars around the clusters. By comparing the images obtained in two diferent colors V and I, it is possible to build a color-magnitude diagram (an example is shown), and several conclusions can be deduced from the shape of this diagram.
Several conclusions can be drawn, in particular that the globular clusters seen from the ground in projection on M31 bulge are genuine bulge clusters which formed from the same gaseous material as the bulge field stars. No intermediate age population has been detected.
The clusters' very high chemical enrichment and old age indicate that they were formed, as was the bulge, in the very early stages of the galaxy's history. The bulge field stellar population presents a large dispersion in abundance and an apparent sharp cut at low metallicity, very similar to what is seen in the bulge of our own galaxy.
This large constellation of the northern hemisphere belongs to the constellation family of Perseus. The name of the alpha star of Andromeda Sirrah (or Alpheratz) has been taken form the Arabic meaning "horse's navel". The reason for this is because in former times this star has been associated with the constellation of Pegasus, next to Andromeda. Nowadays it marks the head of the royal daughter. Sirrah is a blue-white star (spectraltype B8IVpMnHg) with mag 2.06 .
Stars and other objects
The binary gamma And gives splendid view even in smaller telescopes for the two components can easily be separated. The brighter component has mag 2.2 whereas the fainter shows a brightness of mag 5.0 . As they are of different color they certainly make a showpiece of a double in the sky.
The 56 And. is a fainter pair, both being of 6th magnitude.
The planetary nebula NGC 7662 is one of the easiest to view with smaller amateur instruments. Using a high magnification it reveals a fuzzy blue-green elliptical disk.
The stars of the open star cluster NGC 752 are scattered over a large area. Therefore it is best viewed with binoculars. The member stars (about 100) show magnitudes between 9 and 10. NGC 752 is located near 56 And.
This constellation is best known for the Andromeda Galaxy, M31, one of the most famous objects in the sky, which can most easily be found (it can be seen even with the naked eye once you get a bit out of a lightpolluted city) and gives a brilliant view in each optical instrument. As it is the nearest spiral galaxy to us, it allows therefore an intensive study of the properties of spiral galaxies. Because we sit within our galaxy we cannot so easily observe the properties of ours but the Andromeda galaxy helps to understand our galaxy as well.
The Andromeda Galaxy has two satellites: M110 (NGC 205) and M32. M110 is located one degree northwest of M31 and M32 can be found half a degree south of M31. Both are elliptical galaxies. Detailed information to all three galaxies can be found in the Messier database about M 31, M 32 and M110.
Andromeda was the daughter of King Cepheus and Queen Cassiopeia of Ethiopia. Her mother Queen Cassiopeia was an exceedingly vain lady who dared to boast that she was more beautiful than even the Nereids, a group of fifty sea nymphs of exquisite beauty. The Nereids were so affronted at the presumption of the vain queen that they begged Poseidon to punish her.
In response to the pleas of the Nereids, Poseidon sent the sea monster Cetus to ravage Ethiopia. When King Cepheus asked the Oracle at Ammon what he must do to appease the anger of the god, he was told that he must sacrifice his beautiful virgin daughter to the sea monster. So he chained Andromeda to a rock on the Mediterranean shore at Jaffa (the present-day city of Tel Aviv) to await the approach of the monster.
Andromeda was saved by the hero Perseus who slew the monster and claimed the hand of Andromeda in marriage.
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