How Do We Measure the Size of the Galaxy with Limited Telescope Scans?

In summary, in a video discussing the SETI project, Michio Kaku mentions that our telescopes have only scanned 100 light years in detail for the purpose of detecting radio signals from intelligent life. However, the Hubble telescope has recorded images from galaxies billions of light years away. Therefore, we can estimate the size of our galaxy to be around 100,000 light years across based on the limited scanning we have done so far.
  • #1
flyingpig
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Homework Statement



It is said that telescopes have found that our galaxy is about a hundred thousand light years across. It is also said that our telescopes have only scanned a hundred light years of the galaxy.

I am just quoting from this video:

So my question is, how can we know that the galaxy is a hundred thousand light years across when we've only scanned a hundred light years
 
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  • #2
Hello flyingpig.

As usual, details are important.

In that video, Michio Kaku is speaking of the SETI (Search for Extra-Terrestrial Intelligence) project. Early in the video he says that we have only scanned perhaps 100 light years from Earth in some detail. What he refers to is scanning with radio telescopes for the purpose of detecting radio signals from some form of intelligent life.

He does not say that telescopes have only scanned 100 light years from earth.

The Hubble telescope has recorded optical images from galaxies which are billions of light years away.
 

What is the size of the observable universe?

The observable universe is estimated to be around 93 billion light-years in diameter. However, the actual size may be much larger as the expansion of the universe is still accelerating.

How far can we see into the observable universe?

The distance we can see into the observable universe is limited by the speed of light and the age of the universe. The farthest we can currently see is light that has been traveling for around 13.8 billion years, which is about 46.5 billion light-years away.

What is the composition of the observable universe?

The observable universe is mostly made up of dark energy, dark matter, and normal matter. Dark energy and dark matter are estimated to make up about 95% of the universe, while normal matter makes up the remaining 5%.

What is the age of the observable universe?

The current estimate for the age of the observable universe is around 13.8 billion years. This age is determined by studying the cosmic microwave background radiation, the oldest light in the universe.

How many galaxies are in the observable universe?

It is estimated that there are around 100 billion galaxies in the observable universe. However, this number may be much larger as we are still discovering new galaxies and the actual number may be impossible to determine.

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