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Learn about the Moon in a great new book New book chronicles the space program. Dave's Universe Year of Pluto. Groups Why Join? Astronomy Day. The Complete Star Atlas. The Andromeda Galaxy is speeding toward us, but it will take 4 billion years to get here. Meet the Milky Way's neighbor: the Andromeda Galaxy.
Ask Astro : How many satellite galaxies does the Milky Way have? Warning: Objects in the cosmos are larger than they appear. Our Galaxy has arms of younger stars and gas that appear to spiral out from the centre. In fact the objects in these spiral arms are in almost circular orbits about the centre of the Galaxy.
The Sun takes about million years to complete one orbit around the centre. About 30 percent of all galaxies have spiral arms. Spiral galaxies are rich in gas and dust. Some are viewed face-on so that the spiral arms are easily seen whereas others are viewed edge-on. The majority of galaxies show no spiral features, nor are they flattened disks; they take the form of ellipsoids. They show only small evidence for young stars, dust or gas. They are very different in size ranging from giant ellipticals with masses of about 1 million million times that of the Sun to dwarf ellipticals with masses closer to those of the globular clusters.
Some galaxies are neither ellipsoidal nor are they spirals. Some of these are obviously objects which have been tidally distorted by the presence of another near-by galaxy but there are some, such as the Magellanic Clouds, which have little symmetry to their structure. Some galaxies show evidence for the generation of enormous amounts of energy from the vicinity of their nucleus.
The Sagittarius Dwarf Elliptical Galaxy is the next closest , at ,,,,, km 70, light years from the Sun. The Large Magellanic Cloud, 1,,,,,, km , light years away, was once considered the nearest galaxy outside of the Milky Way.
The Small Magellanic Cloud is 1,,,,,, km , light years away. The distance to the LMC has come to play such a crucial role in establishing the extragalactic distance scale that several research groups are applying a variety of methods other than the Cepheids and RR Lyraes. These alternative techniques, which include the use of SN A, the so-called red clump stars, and eclipsing binaries are used to check the accuracy of the period-luminosity relationships. By using several different methods to determine distances, astronomers can increase the accuracy of and our confidence in the RR Lyrae and Cepheid methods, and the distances determined by them.
If you measure the distance to one object in the LMC, for example, you know the distances to all the millions of objects in the LMC fairly accurately. Of course, there are not all exactly the same, but the thickness of LMC, as seen from the Earth, is much smaller than the typical uncertainties in the distances to individual objects in the Milky Way.
Astronomers therefore often study LMC objects then calculate their true brightness from their apparent brightness and the latest the most accurate distance to the LMC. For example, astronomers have studied the supernova remnants to compare with theoretical models, or to derive a relationship between their size, energy, and brightness.
To get to the closest galaxy to ours, the Canis Major Dwarf, at Voyager's speed, it would take approximately ,, years to travel the distance of 25, light years! If we could travel at the speed of light, it would still take 25, years!
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