The Local Group consists of two giant spiral galaxies; the Milky Way and the Andromeda Galaxy; a few medium sized galaxies; M33, Large Magellanic Cloud, and Small Magellanic Cloud; and approximately forty dwarf galaxies. The total number is not known because some small dwarf galaxies may be so faint that they have not been detected yet, but mainly because a large part of the sky is covered by our own galaxy and there may be a number of galaxies, even large ones, lurking behind the dust and gas clouds of the Milky Way.
Of the Local Group, our Milky Way and Andromeda are by far the most massive. The two closest galaxies to the Milky Way are called the Magellanic Clouds, which may be viewed as satellite galaxies to the Milky Way at a distance of a little less than 200,000 light years. They are only visible in the Southern Hemisphere, but can easily be seen by the naked-eye and their brightest stars can be seen with binoculars. They are irregular galaxies and are much smaller than the Milky Way.
LMC & SMC
The LMC & SMC:
The Large Magellanic Cloud, together with its apparent neighbor and relative, the Small Magellanic Cloud, are conspicuous objects in the southern hemisphere, looking like separated pieces of the Milky Way for the naked eye. They were certainly known since the earliest times by the ancient southerners, but these people produced little documents which are still preserved. Both Magellanic Clouds are irregular dwarf galaxies orbiting our Milky Way galaxy, and thus are members of our Local Group of galaxies. The Large Magellanic Cloud, at its distance of 179,000 light years, was longly considered the nearest external galaxy, until in 1994, the Sagittarius Dwarf Elliptical Galaxy was discovered at only about 80,000 light years.
Galaxy groups stay together as groups, and are defined as groups, due to the gravitational interaction, i.e. dynamics, they impose on each other. Usually a group has two or three massive galaxies that dominate the dynamics of the group and a variety of smaller galaxies which more or less orbit the massive ones or are exchanged between them, or in some cases are flung out of the system altogether when they fly close to a massive galaxy. It is also possible that the massive one devours a dwarf galaxy that comes too close.
Sometimes other nearby groups are included in the Local Group and then we talk about the Extended Local Group of Galaxies. These other groups may have played an important role in the Local Group dynamics, or may still do so.
- The idea of a galaxy was first realized by Thomas Wright in 1917.
- Galaxies pass through each other all the time but because the stars are so spread out, the chances of them actually touching is very unlikely.
- Elliptical galaxies contain some of the oldest stars because they do not have the ability to form new stars.
- Elliptical galaxies often appear to have one bright star in the middle but it is actually a collection of stars.
- Elliptical galaxies are so bright that if Earth were located inside of one, there would always be day light everywhere no matter the time of day.
- Irregular galaxies are those that do not fit in any other type.
- A lot of irregular galaxies probably began as an elliptical or spiral galaxy that crashed into another galaxy.
- From the southern hemisphere of Earth, two other galaxies can be seen with the naked eye.
- A small galaxy is one that contains less than a billion stars.
- Our galaxy, the Milky Way, is a spiral galaxy.
- The largest galaxies in the universe may be up to two million light-years long.
- Sometimes galaxies merge with other galaxies to form a galactic merger.
- The origin of galaxies is debatable but most astronomers believe they were caused by the big bang.
- There are four galaxies that can be seen from Earth with the naked eye: the Milky Way, the Andromeda Galaxy, and the Small and Large Magellanic Clouds.
- The closest galaxy to the Milky Way is about 80,000 light-years away.