How do we know how many galaxies there are?

Counting stars Whatever instrument is used, the method of estimating the number of galaxies is the same. You take the portion of sky imaged by the telescope (in this case, Hubble). Then — using the ratio of the sliver of sky to the entire universe — you can determine the number of galaxies in the universe.

How can we see galaxies so far away?

So astronomers measure a galaxy’s redshift from its spectrum, use the Hubble constant plus a model of the universe to turn the redshift into a distance, and use the distance and the constant speed of light to infer how far back in time they are seeing the galaxy—the look-back time.

Could we see a galaxy that is 20 billion light years away?

Average distances between galaxies are increasing with time. Could we see a galaxy that is 20 billion light-years away? (Assume that we mean a “lookback time” of 20 billion years.) No, because it would be beyond the bounds of our observable universe.

Could we see a galaxy that is 25 billion light years away?

-No, because a galaxy could not possibly be that far away. No, because it would be beyond the bounds of our observable universe. -three-fourths of the age of the universe. -two billion years less than the age of the universe.

How can NASA see other galaxies?

The telescope has helped scientists understand how planets and galaxies form. Galaxies contain billions of stars. A picture called “Hubble Ultra Deep Field” shows some of the farthest galaxies ever seen. Pictures from Hubble help scientists learn more about the whole universe.

How far back in time can Hubble see?

about 10-15 billion light-years
The farthest that Hubble has seen so far is about 10-15 billion light-years away. The farthest area looked at is called the Hubble Deep Field.

How many galaxies are there in the universe?

So how many galaxies are there in the Universe? Currently, the observable Universe, which has a radius of 46.5 billion light-years, seems to contain at least two trillion galaxies. Our galaxy, the Milky Way, is just one among these numerous galaxies, and it isn’t even considered a big galaxy.

Is there a limit to how far away we can see Galaxies?

But there were other limits. The most distant galaxies are caught up in the expansion of the Universe, causing distant galaxies to redshift past the point where our optical and near-infrared telescopes (like Hubble) could detect them. Finite sizes and observing times meant that only the galaxies above a certain brightness threshold could be seen.

How many galaxies are beyond human observation capabilities?

Two trillion versus 176 billion means that more than 90\% of the galaxies within our Universe are beyond the detection capabilities of even humanity’s greatest observatory, even if we look for nearly a month at a time.

What is the largest type of Galaxy?

The largest of all galaxies tend to be giant ellipticals, which can measure up to one million light years across and contain one trillion stars or more. For the most part, irregular galaxies are quite small and all together account for about 25\% of galaxies in the known universe.