(2 in 1) How do scientists measure distances between stars/planets in our solar system and how do they measure the age?

Question

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

Answer 1

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.