How big is the universe?

You look to the skies and see a lot of stars, right? But how big do you think the universe is? Scientists would probably give you answers in 100 trillions of light years. Since the universe is expanding at something like 50 to 100 kilometers/sec/Megaparsec, the answer would change. Maybe we should think of size in terms of galaxies, stars, and planets.

For now, to avoid our heads from hurting while using our calculators trying to convert kilometers and megaparsec, taking in small facts at a time seems sensible. Especially since we are anthropic, or human-centric and think in thousands of years or 4.5 billion, the age of our earth.

Let’s start with our Milky Way galaxy. Our solar system is part of the galaxy, which has a star or our sun and a few plants revolving around it. Our galaxy has four hundred billion stars and it would take a hundred thousand years to cross it at the speed of light. There are probably 500 billion plants around the stars. Do the math. It’s a lot of stars and planets.

(Illustration Credit: NASA; ESA; and Z. Levay, STScI; Moon Image Credit: T. Rector; I. Dell’Antonio/NOAO/AURA/NSF)

Now that we have acquired our orientation, let me share with you a recent observation from the Hubble telescope. NASA decided to see if they could observe a square of sky (above illustration, XDF square next to the moon) by taking pictures over several years. This would provide a field of light from deep space that we were not able to see without this eXtreme Deep Field or XDF study. The universe is 13.7 billion years old and the XDF galaxies observed were some of the youngest galaxies, some 13.2 billion years old. The light is just reaching the earth now. There are 5,500 galaxies in just this patch of sky alone! How many galaxies would then be in the universe? How many stars? How many planets, just like earth? The picture below is what was observed in the XDF square in deep space.

XDF Image (Credit: NASA; ESA; G. Illingworth, UCO/Lick Observatory and the University of California, Santa Cruz; R. Bouwens, UCO/Lick Observatory and Leiden University; and the HUDF09 Team)

So when you look into the sky at night and see the observable landscape of our universe, this is the same sky that our ancestors observed over thousands or millions of years. But their view was limited. With the advancement of science, we are seeing stars and galaxies which have never been seen before. This is the history of the universe as if we dug up a dinosaur bone. Think about the possibilities. Not just what is on the earth, but what is on the quintillions of earths yet to be discovered. Sounds like a Star Trek episode.

So what is next in our collection of technology for observing the universe? Look forward to the James Webb Space telescope. The Hubble telescope is only a baby compared to the James Webb Space telescope. We will stretch our vision even further into the vast universe past our home and into the history of our beginnings. Exciting discoveries ahead if you are interested in your neighbors.

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