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Random Astronomy Facts

When someone wants to describe a number as being really big they often use the word “astronomical”, presumably because astronomy involves so many big numbers. Big numbers are cool in themselves but more interesting when the significance of big numbers can be used to make a more relevant point. So that’s what i am going to try to do here, in my next instalment in my “random facts” series, which will probably be slightly less controversial than the last one!

One of the first questions people ask about the universe is how big it is. I will answer this question through the use of some of my random facts from my “Astronomy Random Facts” file (as explained in the entry “Random Environment Facts” from 2013-05-20).

Fact 1: There are 5 times as many stars as grains of sand on every beach on Earth. (source: Infinite Monkey Cage podcast, 20 Jun 2011)

Discussion: The IMC podcast is (was) hosted by well known astronomer Brian Cox so you would expect it to have a certain amount of credibility. But this number varies greatly depending on the source and method used to do the estimate. Some estimates suggest the number of grains of sand and stars is about the same. But either way, that is a lot of stars.

Remember that stars are huge balls of glowing plasma, just like our Sun. The Sun is 1.3 million times bigger (in volume) than the Earth and many stars are much bigger than even that. A star called VY Canis Majoris (a red hypergiant) is often quoted as the biggest known. It’s volume is almost 4 billion times bigger than the Sun or 7 thousand trillion times bigger than the Earth!

Plus the distance between stars is huge. Even in our galaxy the distance between stars is 50 million times bigger than the size of the star itself. And stars are grouped into galaxies where the distance between them is generally very large (millions of times greater than the distance between stars).

So, in summary, the universe has a vast number of really big stars separated by huge distances. So yes, the universe is big. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space. – Douglas Adams, The Hitchhiker’s Guide to the Galaxy

Fact 2: If you attempted to count to stars in a galaxy at a rate of one every second it would take around 3,000 years to count them all. And fact 3: The Hubble Space Telescope (HST) site estimates there is hundreds of billions of galaxies in the universe. A recent German super-computer simulation estimates that the number may be as high as 500 billion.

Discussion: Just to reinforce the number of stars out there, this is the same information presented in a different way. Again, the number is an estimate which varies greatly. The only thing which is certain is that it’s big!

I often wonder what people with “human-centric” worldviews think of this sort of thing. For example, the Bible strongly implies that the Universe is here for our benefit, yet we only experience a tiny fraction of it and practically the whole Universe is unsuitable for life as we know it. Why? How can that possibly fit in with a human-centric belief system?

Fact 4: It looks like we live in a flat universe where the total energy is zero.

Discussion: To many people this seems bizarre. How can the Universe have zero energy? After all, there are all those stars and other high energy phenomena, aren’t there? Yes, there is a lot of energy in the Universe but there is a lot of negative energy too. Gravitational energy is always stated as negative and it exactly balances the other forms as far as we can tell.

Is this merely coincidental or a side-effect of the measurement techniques, or is it something fundamentally important about the Universe? We don’t know for sure but it is interesting to note that something with near-zero energy can easily be created from a vacuum with no underlying cause according to quantum physics. Perhaps the whole Universe is a vacuum fluctuation.

Fact 5: Sun leaks 7 billion tonnes of coronal mass every second into space. And fact 6: The Sun would only burn for about 5000 years if it was made of coal.

Discussion: Stars like our Sun are truly mighty objects. Every second the Sun loses billions of tonnes of it’s mass into space yet it has been doing that for billions of years and that has barely made a difference.

But even with such a huge mass it could only produce energy at the rate it does for 5000 years if it utilised conventional combustion. The fact that it has “burned” for a million times as long yet has only used less than 1% of it’s total fuel shows how incredibly efficient nuclear fusion is. And that’s why we want to use this energy source (not quite the same but very similar to stars) for power production on Earth.

Fact 7: At its closest approach to Earth, Mars appears about as big as a tennis ball viewed from a distance of one and a half miles (two and a quarter kilometers).

Discussion: When I used to teach astronomy to the public there were two responses I commonly got when viewing the sky. The first was the delight that people could actually see those objects (especially Saturn) which they had only seen in books. And the second was disappointment in the image size and clarity we often had. The fact that we were observing from inside a city with a lot of street lights and heat sources didn’t help, of course!

But observational astronomy is just inherently difficult. Apart from the Moon everything is too far away to make detailed observation easy. Even the closest objects like Mars (technically the third closest large body after the Moon an Venus) is very small even in large telescopes. When I taught astronomy we didn’t have the HST photos we do now so expectations weren’t quite as high. It must be a lot more difficult now!

So Mars is very small and it’s sometimes difficult to see much more than a small orange disk, but what about genuinely distant objects? What about the closest star? Well that is about the same size as the Sun so it is about 100 times the diameter of Mars. That means that if Mars was a tennis ball, the star would be 6.5 meters across (about 20 feet). But the star is 40 trillion kilometers away compared with a mere 40 million for Mars. That is a million times further.

So the star is a hundred times bigger but a million times further away making it appear 10,000 times smaller. And that’s the closest star! In effect this means that stars tend to be just points of light in even the biggest telescope. The damn Universe is just too big to be convenient!

Last fact: Virtually every atom in your body (other than hydrogen) was created in the core of an exploding star over five billion years ago.

Discussion: As Carl Sagan said: we are all star stuff.

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