My curious kids asked me this on the way to school and I honestly can’t answer it. Tried googling it but I keep getting the unit of measure as an answer rather than the method.
In: Planetary Science
if you look at something from 2 different places, and record and you know how far apart those 2 places are, you know the distance from each to the object. simple triangle
once you know how far away something is, you can make another triangle using that distance, and the angular size of the object in question. then the other side of the triangle is the diameter of the object
In ancient astronomy, a lot of geometry was used to calculate things like sizes and distances. The size of the earth was calculated by the different sizes of shadows at the same time of day at different points on the earth.
The size and distance of the moon were calculated by its angular size as it appears to us and its relation to the size of earths shadow (in a linar elcipse). Using that, the distance between earth and the sun was calculated by using basically Pythagoras. When the moon was in perfect half moon — the sun perfectly perpendicular to the moon from the earth, where was the sun relatively to the earth? Knowing the distance between the earth and the moon we could calculate the distance between the sun and the earth.
From there during the centuries until Newtons discoveries, mostly geometry was used. We saw the angular size of planets and calculated their distance using their rate of motion and their orbital period.
After Newton we started calculating masses using gravitational tugs. We actually discovered Neptune using math. We saw Uranus wobble in its orbit and we calculated what mass an object, and where should it be, to create this kind of interaction. We looked at the predicted spot and found a planet that was just too faint to see before.
Other masses were calculated using the planets moons and their orbits. Particularly Venus and Mars, I think.
These days we measure distances with more advanced methods like radar, measuring accelerations of probes and such. But it’s more like confirming calculations and honing in the numbers than discovering them.
Now the age thing is rather tricky. We don’t actually know the age of every planet in our solar system. Even now we estimate things. Pluto (though not a planet) we aren’t certain about its origin and we estimate that it may have been a rogue asteroid captured by the sun’s pull.
We estimate the age of planets by the age of the earth and the sun, suspecting that they formed roughly at similar times from the same dust and debris disc.
For nearby stars a method called Parallax is used.
If you held an object close to your face and observe it with only your left or right eye (the other one being closed) you’d notice that there’s a difference in the background behind the object. Basically measuring how far apart your eyes are and taking the angle from your eye to the object in front of you enables you to measure the distance to said object.
For more distant stars (>400ly) a range of methods are used that measure the brightness of the star. This is pretty self explanatory, objects with an intrinsic brightness will appear dimmer the farther they are.
For very distant stars it is by measuring something called redshift. If you take an slinky, imagine the it magically glows blue. The more you stretch it, the redder it becomes. Now imagine light travelling to us from distant objects. That light is stretched to the red part of the visible light spectrum because the universe is expanding and distant objects are moving away from us.
I imagine this one would be difficult to explain to the kids, I don’t really know how to explain this phenomenon in a more digestable way lol.
Hope that’s helpful
The keyword you are looking for is the cosmic distance ladder. There are a rather lot of different ways and they work best at different ranges.
https://en.m.wikipedia.org/wiki/Cosmic_distance_ladder
To the moon we can get absurdly accurate measurement by bouncing lasers off mirrors left by the Apollo missions. It’s accurate to something like 1.6mm.
To to Venus we can actually bounce radar off of it. That gives us some baseline from which we can calculate distances using angles between planets during different parts of the earth’s orbit. Actually at this point we have used radar to figure distances to all the planets except Pluto, but Pluto got kicked out anyway. If you don’t want to go too much into it you can just say -really- big RADAR dishes and that legitimately covers most of the solar system.
We can also use the parallax (differences in observed position between near and far stuff while the earth orbits the sun) to figure distance to nearby stars.
Further out we can use the light intensity of certain types of stars to gauge their distance. And several other methods for even further stuff. Since the ranges of different measurement techniques overlap we can link them together to estimate the distance across the whole range of objects we can see. Thus making a “ladder” with the different measurement methods as rungs.
We can also work backwards from the farthest objects using leftover radiation from the big bang.
And something -really- interesting is that our best estimates and theories allow us to calculate the range to a degree of accuracy that lets us know that when you work from the Earth out, and from the farthest stuff the the numbers don’t meet in the middle, called hubble tension. The space near us appears to be expanding a little too quickly. Something is wrong -somewhere- and no one really knows why.
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