The Milky Way is only one of the billions of galaxies in our observable universe, but it holds a significant place to humanity. We call this barred spiral galaxy our home, as do hundreds of billions of other stars.
Appearance and composition
In the night sky, we can see the Milky Way plane as a band of light, which looks like other galaxies when viewed from above. The Milky Way has a very bright central part and spiral arms. Like any other spiral galaxies, our home galaxy has a halo, a central bulge, and a disk. The Galactic center and the halo are filled with old stars, whereas the disk contains dust, gas, and young stars.
Size
It is estimated that the Milky Way’s stellar disk is around 100,000 light-years (9.5×1017 km) in diameter. On the average, it is believed to be roughly 1,000 ly (9.5×1015 km) thick. Our galaxy contains approximately 200-400 billion stars. The exact number depends largely on the number of low-mass stars. So how big is our Solar System relative to the Milky Way? Well, if you reduce our galaxy to 130 km in diameter, our Solar System would only measure 2 mm in width.
Age
It is almost impossible to determine the age of the Milky Way. However, the age of the oldest star discovered in our galaxy provides a clue - it’s roughly 13.2 billion years old. In 2004, astronomers used the Ultraviolet Visual Echelle Spectrograph (UVES) of the Very Large Telescope (VLT) to measure beryllium in two stars in the globular cluster NGC 6397.
The astronomers found that the elapsed time between the formation of the oldest stars in the Galaxy and the oldest stars in the cluster was about 200-300 million years. The team of astronomers included the approximate age of the stars in the globular cluster (13.4 ± 0.8 billion years) and assumed that the age of the first generation stars in our galaxy is 13.6 ± 0.8 billion years.
Environment
The Milky Way belongs to a group of 50 galaxies called the Local Group, which is part of the Virgo Supercluster. The milky Way is orbited by two smaller galaxies and several dwarf galaxies. The Large Magellanic Cloud larger of the two galaxies 20,000 light-years in diameter. The smaller one is the Small Magellanic Cloud. These two galaxies are connected by a stream of neutral hydrogen gas known as the Magellanic Stream.
The following are only some of the dwarf galaxies that orbit the Milky Way: Canis Major Dwarf, Ursa Minor Dwarf, Sagittarius Dwarf Elliptical Galaxy, Sculptor Dwarf, Fornax Dwarf, Sextans Dwarf, and Leo I Dwarf.
