How do astronomers measure distances within the solar system?

Astronomers measure distances within the solar system using methods such as radar ranging and parallax.

Radar ranging is a direct method used to measure distances within the solar system. This technique involves sending a beam of radio waves towards a planet or other celestial body and then timing how long it takes for the signal to bounce back. The speed of light is known (approximately 300,000 kilometres per second), so by multiplying the time it takes for the signal to return by the speed of light, and then dividing by two (because the signal has to travel to the object and back), astronomers can calculate the distance to the object.

Another method used is parallax, which is an indirect method of measuring distances. Parallax is the apparent shift in position of an object when viewed from two different locations. Astronomers use the Earth's orbit around the Sun as the baseline for these two locations. By observing a planet when the Earth is at opposite sides of its orbit (six months apart), and measuring the angle of the apparent shift in position, they can use trigonometry to calculate the distance to the planet.

These methods are very accurate for measuring distances within our solar system. However, for distances beyond the solar system, astronomers have to use other methods, such as observing the brightness of stars and their spectral lines, or using the redshift of distant galaxies. These methods are based on certain assumptions and are therefore less accurate, but they are the best tools we have for measuring such vast distances.