If you guessed the astronomical unit, you are correct. The au — the rough distance between the Earth and the Sun — was previously determined by a confusing calculation (“the radius of an unperturbed ...

If you want to find the size of a basketball, you can use a normal meter stick to measure the diameter. You should get a value of around 0.24 meters. Please don't use inches—they are just harder to ...

Scientists still define astronomical time in years, with some recent refinements. By C. Claiborne Ray Q. Do scientists actually speak of the age of the universe in years, or do they use some ...