Components of the universe

What’s the Scale of the Universe?

Everything that exists anywhere in space and time constitutes the Universe. What’s the scale of the entire universe? Let’s start with our own star, the Sun. Our sun is 865,370 miles in diameter. In comparison, our Earth is only 7,917.5 miles in diameter. Our planet is on average 93 million miles away from our sun. We call this distance 1 Astronomical Unit (1 AU). Now that’s a long way off already. Let’s notch it up a bit…

Our sun, earth, moon, the other planets and their moons, and many more heavenly bodies like asteroids and comets – indeed, every bit of matter that goes around our sun – together constitutes our Solar System. The solar system is estimated to be about 178.62 billion miles, or 1921.56 AU, in diameter. Let’s notch it up a bit more…

Galaxies

A galaxy consists of stars, dust, gas and other matter held together by the forces of gravity. Galaxies have a diameter anywhere from a few thousand to several hundred thousand light-years. Galaxies are flung far apart from one another, often measured in Parsecs and Megaparsecs, where one parsec is 3.26 light-years and a megaparsec is a million times that!

On a dark night in the northern hemisphere you might be able to discern the shape of our own galaxy, the Milky Way, in the form of a spiral. You may also spot the galaxy nearest to us, the Andromeda Galaxy, which is 2.5 million light-years away. But the billions of other galaxies are too far away to spot without powerful telescopes.

Galaxies are classified by their appearance and shape. The most common shapes are Spiral, Elliptical and Irregular. Others can be sausage-shaped or flattened balls, or like rugby balls.

Our Milky Way galaxy and the nearby Andromeda galaxy are spiral. The Small and Large Magellanic Cloud are examples of irregular galaxies. Most other galaxies simply have alphanumeric names, as seen in the pictures below

Check Point

1. One Astronomical Unit (AU) is –
   1. Roughly 93 million miles
   2. The average distance between the sun and earth
   3. A unit of distance in space
   4. All of the above
2. The shape of the Milky Way Galaxy is –
   1. Irregular
   2. Spiral
   3. Elliptical
3. Distances between galaxies can be measured in –
   1. Parsecs
   2. Megaparsecs
   3. Light-years
   4. All of the above
4. The Milky Way galaxy is about –
   1. 100,000 to 150,000 light-years across
   2. 93 million miles across
   3. 93 billion light-years across
   4. 93 million light-years across
5. The galaxy nearest to our galaxy is –
   1. Milky Way
   2. Messier
   3. Andromeda
   4. NGC 3923

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