• Ashwini

GS2: The Milky Way: Where is our Solar System?

Updated: May 18, 2020

When observed from the Earth, the Milky Way looks like a hazy cloud but if viewed from a great distance, it would look like a flattened spiral with great curving arms slowly swirling around a glowing, disk-like centre. Presently, our Sun lies near the outer edge of one of these arms and rotates around the centre of the galaxy about once every 250 million years. And, we traverse through space, relative to an observer standing outside the galaxy, at about 200 km per second.

Image credit- Spitzer Space Telescope, NASA

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The Milky Way galaxy has a significant place for humans because it is our home. But when it comes to comparing it with the other galaxies out there in the Universe. A glance at the night sky reveals partially what is out there. Our ancestors described it as river or milk. It is a tough job to look through the Milky Way when our solar system is present on one arm of a disk of material and having a denser centre to the other side. The Milky Way does not sit still in space rather rotates constantly. It sails through a vast infinite size ocean with its robust hull and mast. The sun and the solar system travel with them. The solar system travels at an average speed of 515,000 mph (828,000 kmph) and still takes 250 million years to complete its orbit around the Giant Black Hole at the galactic centre. Our solar system lies 30,000 light-years from the galactic centre and about 20 light-years above the galactic plane. Our sister galaxy is Andromeda, which is thought to collide with ours in 4 Billion years. As geologists are busy mapping the landforms, in analogous manner astronomers are busy charting the spiral structure of our galaxy and others as well. This study from Earth itself was impossible until the infrared images from NASA’s Spitzer Space Telescope were received. The scientists discovered that the Milky Way’s elegant spiral structure is dominated by just two arms wrapping off the ends of a central bar of stars. Previously, it was thought to possess four major arms. The galaxy’s two major arms (Scutum-Centaurus and Perseus) can be seen attached to the ends of a thick central bar, while the two minor arms (Norma and Sagittarius) are less distinct and located between the major arms. The major arms consist of the highest densities of both young and old stars; the minor arms are primarily filled with gas and pockets of star-forming activity. Our Sun lies near a small, partial arm called the Orion Arm, or Orion Spur, located between the Sagittarius and Perseus arms.

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