Entry 2438, on 2026-04-14 at 22:11:38 (Rating 1, Science)
I see a lot of weird stuff while on the internet, especially on social media sites (I use Facebook and X a lot). I've got to admit that it is hard to know who is serious and who isn't today, because I honestly sometimes can't tell the difference between serious comments and satire! But I came across one comment recently which did seem serious. It was about "space being fake". The person seemed to be claiming that the universe was really just the Earth with a small amount of space above it, then maybe a solid barrier, although they were a bit vague about that.
So I thought, apart from just taking the word of astronomers, how would we really know how big the universe is? Is there a way the average person could figure it out without investing millions or even billions in fancy, professional level, equipment?
So the answer is yes. I have been an amateur astronomer for many years and I must admit, I have never done these observations myself, because they do take a lot of time and effort, but theoretically I could do them if I wanted to.
So here's how I would do it...
Let's assume the stars are at varying distances from the Earth rather than being holes in that solid sphere which my conspiracy theorist friend thinks they are. In that case we could use parallax to estimate the distance to the star. So we could assume the brighter stars are probably closer and the dimmer ones more distant. Because stars vary in brightness, this isn't always true, but on average it is.
We must also accept that the Earth orbits the Sun once per year. Again, this is an assumption, but like all the others we will get crazy results if the assumptions aren't true, so let's just proceed.
Choose a day, let's say mid-summer, and look at the position of the bright star in relation to a variety of dimmer stars, then do the same thing thing six months later at mid-winter. During that time the Earth has moved 300 million kilometers from one side of its orbit to the other (the Sun-Earth distance is about 150 million kilometers).
To understand parallax, try this: hold your finger up in from of your face and look at where it is in relation to a wall when looking through your left eye, then your right. Notice how it moves? Now move your finger further away, and repeat, then closer to your eye and repeat again. The amount it seems to move is proportional to the distance from your eye. Now substitute your left eye for the Earth at mid-summer, your right eye for it at mid-winter, the finger for the close star and the wall for the distant stars.
The first problem is we cannot be sure that the dim stars are really distant and the bright ones close, but if we repeat the process with enough stars we will get a statistical measurement that we can use. The second problem is that when this was first tried no parallax was seen, but that was because the stars are so incredibly distant that the parallax was small. With better techniques it was observed and the closest star moved 0.768 arc seconds, the equivalent of the width of a coin about 2 kilometers away!
Do the calculations and it turns out that star is about 40 trillion kilometers away. This is just "slightly" more than the "space is fake" person claimed, but he was only off by a factor of about a billion, so nice try! Also remember this is the closest star (apart from the Sun). The most distant star measured with this technique is about 500 thousand trillion kilometers away.
By the way, the more skeptical of you might be asking, how do we know the distance to the Sun, which we need to do the calculation? Well, it was measured quite accurately in 1672 using simple trigonometry from observations from opposite sides of the Earth to estimate the distance to Mars, then a further trig calculation to use Earth and Mars to get the distance to the Sun. It's simple maths which no one would debate, although the measurements themselves need to be very precise. But they got a number just 7% smaller than the one we have today.
Oh, one more thing too: how do we know the size of the Earth, because the "opposite sides of the Earth" observation needs that. Well, that was established by one of my heroes, Eratosthenes, in 240 BCE. He paid someone to step out the distance between the cities Alexandria and Syene, then he measured the length of a shadow at those two points at the same time. The shadow at the city closer to the equator was shorter and by using some more trigonometry he estimated the size of the Earth just a few percent different to the modern figure.
It was utterly brilliant and not only showed the diameter of the Earth, but also proved it wasn't flat, another crazy belief some people still have (I'm not joking, there really are some people who think the Earth is flat).
So everything I have listed here just needs some very simple maths and a bit of effort. To make the parallax observations you would also need a telescope, but a decent amateur level one would be sufficient. There is nothing you need to accept from an authority, everything can be done by any careful, moderately intelligent person.
By the way, even the more distant star I mentioned above is still exceptionally close by the standards of the universe as a whole! How do we know about even greater distances? Well, maybe that's a subject for my next blog post.
Comment 1 (8559) by Dad on 2026-04-15 at 10:10:40:
Owen why are you wasting your time doing useless calculations. There is only one person who knows the answer to the dimensions of the universe. The person who created it.
Comment 2 (8560) by OJB on 2026-04-15 at 10:12:26:
Well he hasn't been very forthcoming with that information, or a lot of other stuff we want to know, so I guess we just have to figure it out ourselves! :)
Comment 3 (8561) by Anonymous on 2026-04-15 at 11:33:27:
First you say we don't need to take anyone's word for it then you say we have to believe Eratosthanes and whoever did the Mars measurement. Which is it?
Comment 4 (8562) by OJB on 2026-04-15 at 11:58:50:
Maybe I didn't mention that you could also do those experiments. Eratosthanes measured the size of the Earth using a couple of sticks. How hard can it be?
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