Page 53 - Curriculum Visions Dynamic Book

first simple life appeared on the Earth.
Light coming from places that are more than 10 billion
light-years away has not yet had time to travel to the Earth. That is why we talk about the “observable” Universe.
We know only about the billions of galaxies within this distance. It is certain that there are many, many more.
One interesting result of this is that light from distant galaxies provides a natural “time machine” for seeing far back in time.
The more distant the object, the longer it has taken
for light to get from it to us, and therefore the nearer the start of the Universe that light was emitted. So, this light gives us a snapshot of the early Universe, not a snapshot of what it is like now. To know what it is like now, we have to assume that everywhere is similar to conditions in our neighborhood of space.
An expanding Universe
When we start to investigate distant objects, we notice something curious. Every time a remote galaxy is measured, its distance from us is greater than when it was measured before.
No matter in which direction we look, the same is true. In effect, everything we see in the Universe is speeding away from every other thing, just like points on the surface of an inflating balloon. So, we cannot escape the dramatic conclusion that in the past everything was much closer. The implications of this were first deduced by Edwin Powell Hubble in the form of Hubble’s Law (see page 42). It is as though we are all part of some gigantic explosion that happened in the past.
 This is spiral galaxy NGC 4414. It was observed on
13 different occasions over the course of 2 months to accurately measure the distance to it, which was found to be 19.1 megaparsecs, or about 60 million light-years. This measurement contributes to astronomers’ overall knowledge of the rate of expansion of the Universe.
53