Galactic scale

Distances in our solar system are hard to imagine. At its heart is our sun, some 864,938 miles in diameter. But if we imagine it as a 15 cm (6 inch) ball then on the same scale the following would be the size of the planets and their distances from the sun.

Mercury would be a tiny grain of sand 6.4 metres away away, Venus and Earth would be grains of sand 12 and 16.5 metres away and Mars a slightly smaler grain of sand 24 metres away. The gas giants Jupiter, Saturn, Uranus and Neptune would have diameters of about 1.75, 1.43, 0.63 and 0.63 centimetres and be at distances in metres from that scaled sun of 84, 155, 311 and 487.

In 1977 we launched the Voyager 1 and Voyager 2 Spacecrafts with missions to explore the outer gas giant planets of our Solar System. In August 2012 Voyager 1 which is travelling at 17 kilometres a second made an historic entry into interstellar space. Voyager 2 travelling at 15 km, a sec. did likewise in November 2018. They are both now out of our solar system and in the region between stars where scattered material remnants of stars that died millions of years ago reside. Both spacecrafts continue to emit data that takes hours to reach us on earth.

The stars of the milky way are all stars in our “Milky Way” galaxy

Our sun is one of about 200 billion linked stars in our galaxy, that we call the Milky Way. Our nearest neighbour star is Proxima Centauri. It is often referred to as Alpha Centauri C because it has links with a pair of binary stars (Alpha Centauri A and B) that rotate about one another. Light from that near neighbour takes 4.24 earth years to reach us. Light from its binary neighbours take 4.44 years to reach us. Such distances mean that even if we travelled at 20 km per second (faster than Voyager 1 and 2) it would take 15,000 earth years to get to that closest neighbour star.

The Milky Way is a Spiral Galaxy

The Milky Way galaxy is a pancake shaped galaxy with spiral arms and a bulge in the centre that includes a black hole whose mass is two million times that of our sun. The solar system is sited on an edge of one of its spiral arms and is located about two thirds of the way from the centre of the galaxy and just slightly above the equatorial or, if you prefer, pancake plane of the galaxy.

Our ancestors were more familiar with the night sky than we are. Very few of us now see the milky road of dense stars crossing the heavens. Only those living in or visiting remote areas get to see it. It is our view along the plane of our pancake like galaxy. The less dense stars we see are the one’s above and below us in that pancake formation.

On the scale we used for our solar system our pancake like galaxy would be about 68 million miles across and over 600 miles thick. Some pancake. The solar system is on this same scale located about 20 million miles from the centre of the pancake and about 9 miles above the pancake equatorial plane. The milky way galaxy rotates about its centre. It is estimated that the time our solar system takes to orbit the galaxy centre is between 200 and 250 million earth years. Toward the edge of our galaxy and diametrically opposite the solar system our galaxy is merging with one or perhaps two dwarf galaxies. I use the word merging because the vast distances between galactic stars mean collisions are improbable

The Andromeda Galaxy as photographed in our back garden using a 6 inch Newtonian Telescope. The light travelling at 300, 000 km per second had taken 2.537 million years to reach us.
We can clearly see a lot further than the horizon.

Let’s now change scale and consider our Milky Way galaxy as being just 15 cm (6 inches) in diameter. The Milky Way galaxy is one of about 30 in the “Local Group”. This group includes the well known Andromeda Galaxy (another spiral galaxy and on this new scale 20 cm in diameter and 4.9 metres away) and two galaxies that are clearly visible in the southern hemisphere namely the Large Magellanic Cloud (a tennis ball 30 cm away) and the Small Magellanic Cloud (a ping pong ball 35 cm away). These latter two galaxies are regarded as satellites of the Milky Way Galaxy.

A group of over 1000 galaxies called the Virgo Cluster is on this same scale about 55 metres away. This cluster is no bigger in size than the local group but with many more galaxies it has much more mass. This additional mass is pulling the “Local Group” toward it. The Virgo Cluster and Local Group together form part of what is called The Local Super Cluster covering 183 yards long on our scale.

The universe has many super clusters in all directions. The entire visible universe, on our galactic scale would be a large sphere about 28 miles in diameter and containing over 200 billion galaxies. Surely our earth and its life forms cannot be unique in such an extensive distribution of energy and matter.

Most of the smaller distances in space are measured in light years. Light in a vacuum travels at 299,792,458 metres per second. A Light year is the distance light travels in one earth year. It is just less than 6 trillion miles or just less than 10 trillion kilometres in metric. A parsec, the preferred unit in Astronomy, is about 3.26 Light Years. Hans Solo made reference to it in star wars.

You have to realise that when looking at the stars you are viewing objects as they were years ago, many of the millions of years ago. They are not a picture of what is but of many as was situations. Many of those stars seen will no longer be where we see them or even exist.

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