Room F, at Manchester Street School in Feilding, asks :-
What is the nearest galaxy to ours?
Patrick Bowman, a physicist who teaches the astronomy course at Massey University's Albany campus, responded.
A galaxy is a collection of stars, dust, planets and stellar remnants bound together by gravity. For example, all the individual stars that we see in the night sky belong to our own galaxy, the Milky Way. Our galaxy is flat (appearing as a band across the night sky), consists of bright arms of stars spiralling out from a central bulge, and is estimated to contain around 300 billion stars. Astronomers have found many distant objects that share these features, so it appears that our Galaxy is just one of many "spiral" galaxies.
The nearest large spiral galaxy to our own is the Andromeda galaxy, roughly 2.5 million light-years away. (A light-year is the distance light travels in one year, an enormous distance.) Andromeda is sometimes visible low in the northern sky.
However, there are other, smaller bodies nearby that also fit the definition I gave above. The two most obvious examples are the Large and Small Magellanic Clouds, both visible in the southern sky. They are classified as "irregular dwarf galaxies". At 170,000 light-years distance, the Large Magellanic Cloud is the closer of the two. These orbit the Milky Way, and so are referred to as "companion galaxies" or "satellite galaxies". The Milky Way has quite a few such companions. The current record holder for the nearest galaxy is another irregular dwarf galaxy: the Canis Major Dwarf Galaxy, named after the constellation it appears in. It was discovered in 2003 and is about 25,000 light-years from Earth or 42,000 light-years from the centre of the Milky Way. The Canis Major Dwarf Galaxy is being strongly affected by its close encounter with the Milky Way, and it seems some of it has already been absorbed by the larger galaxy.
When it has finished merging, the next contender for nearest galaxy will be the Sagittarius Dwarf Elliptical Galaxy.