Galactic Distances Our Eyes See The Light Part 1

How Big Is Our Galaxy?

In centuries gone by it was thought by some (not all) people that the Earth was at the centre of the known universe. As the use of telescopes became available it dawned on some that the Earth was actually going around the sun and that the sun was at the centre of the universe. We now know that the sun is at the centre of it’s own little solar system and that the Earth is the third planet away from the sun and that there are other stars and planets beyond us.

Some History.

As recently as the 16th century astronomers were sure that there was just one galaxy, the milky way galaxy, our galaxy so named because in the clear night sky the stars look like a streak of milk stretching from horizon to horizon. It is now known that stronger telescopes can distinguish other galaxies in the vast expanse of space. If for instance the space telescopes focus on a pinpoint in a void between the stars for several days they will pick up the faintest of light coming from even more galaxies and the surprising thing is that there are millions if not billions of galaxies in the newly visible cosmos.

Astronomers have come to realise something that I had worked out when I was around 10 years old using the laws of averages and probability. You now have some inkling as to my opinion of most so called astronomers. There are exceptions to the rule I admit, but most “have to see to believe”. We all know that assumptions can be dangerous but if you base those assumptions on known facts and use the law of averages and probability you can move ahead much faster.

The Enormity Of  The So Called Voids.

To get some idea of  the size of a galaxy, we need to appreciate the distances involved and the limitations imposed on us by current technology in actually being able to see things in the vastness of so called empty space. When we look at the Moon we are seeing light from the sun reflected off it’s surface and coming to our eyes. Normally light travels in straight lines and at a certain speed. It takes time to do this, light travels fast,very very fast indeed.

Some Facts About The Solar System And The Speed Of Light.

Visible light travels: 

In one second: 186,282·397 miles.

In one hour: 617,000,000 miles.

In one day: 148,080,000,000 miles.

In one year: 5,404,920,000,000 miles.

In fact all electromagnetic radiations obey this law in the so called vacuum of space, it is a constant and is denoted by the letter c.

The distance from Earth to the Moon is 238,857 miles (384,403 km).

The mean distance from Earth to the Sun is 93,000,000 miles (150,000,000 km).

     It takes light 8 minutes and 19 seconds to reach Earth from the Sun.

Light Embarks From The Sun And Arrives To Enlighten Us.

OK so armed with this information we can see that light is not instantaneous, that it has a finite speed and takes some time to travel those distances. In fact it takes 8 minutes and 19 seconds for light to travel the 93 million miles from the Sun to our eyes here on Earth.  In other words we are seeing the sun as it was approximately 8½ minutes ago, that tells us the important fact, that when looking at distant objects we are actually looking into the past.

If we were to cast our eyes on to other Stars or solar systems within our Milky Way Galaxy then the distances become even greater and require a new unit of measurement. It seems logical, that the time taken for light to travel in one year be used and so we have the light year (1Ly). In other words, light travelling at 186,282.397 miles per second in one year can travel 5,404,920,000,000 miles which = 1Ly, a very very long way indeed.

Note:  to get the distances in Kilometers multiply these figures by 1·609.

Limitations of Physical Travel, The Time Factor.

The nearest star to our Sun is Alpha Centauri which is 4·2421 light years away, travelling at the speed of light it would take us approximately 4 years and 3 months to get there. Now we are beginning to see the enormity of the distances within the Milky Way. The distance from our Sun to the centre of the galaxy is 24,000 to 28,000 light years. The sun travels around the centre of the galaxy at approximately 251 km per second and completes 1 orbit in 250,000,000 years this means that it has completed around 25 orbits in its lifetime (estimated to be around 4½ billion years). At 251 km per second the Sun travels 1 light year in around 1,400 years.

Using the data from many telescopes of varying types and lots of mathematics astronomers reckon the total diameter of the Milky Way Galaxy is in the order of 100,000 light years and is around 10,000 light years thick. These speeds and figures are truly mind bending but in the grand scheme of things they are minuscule. Everything in the cosmos is relative to the observer and the distance that observer can actually see. But you must remember that because we cannot see something it does not mean it isn’t there.

A look at the Hubble Space Telescope.

The Earth Is Merely A Passenger.

The Earth, tied to the Sun by gravitational “apron strings” is actually hitching a lift with a body that sustains it’s life. That body is a kind of space craft travelling through space at a respectable speed, it would be more accurate to say a velocity of 251km per second. The journey the Earth embarked on along with its life support so long ago has passed through, or collided with and skimmed, many different entities that have affected it in many subtle and in some cases devastating ways. It has orbited the Galactic centre just 25 times since it set out. There are things in inter stellar and inter galactic space that are travelling at much higher velocities and have no respect for the order of things in our solar system.

In other words, the past has demonstrated that all life on Earth can perish or thrive depending on the entity that has affected it. The laws of averages and probabilities tell us that we will encounter these good and not so good entities many times again in the future. The Earth and the Sun will recover most of these events but there is a more vulnerable entity that will have to use it’s huge brain to endure, after all, are we not dinosaurs?

The most important picture taken of so called empty space.

  Just another gem from sidewallfusion,

  Coming soon in part 2, the relativity of size and distance. An imaginary journey into inter galactic space just to take a look at the sheer magnificence of creation in its entirety, laid out in all it’s dimensional relativity. A lesson in humility for us all.

Some interesting reading from amazon.com

Astronomy

Galactic Astronomy (Princeton Series in Astrophysics)
Introductory Astronomy and Astrophysics (Saunders Golden Sunburst Series)
Galaxies and Cosmology (Astronomy and Astrophysics Library)
The Sun: An Introduction (Astronomy and Astrophysics Library)