Their eyes,
Refracting Telescopes (ones with class lenses)
Reflecting Telescopes (ones with mirrors)
Radio Telescopes
Imaging computer chips in conjunction with telescopes
Space based telescopes
Underground telescopes (to detect high energy or exotic particles from stars)
Gravity wave detectors
Astronomers use a method called parallax to measure the distance to nearby stars. By observing how a star's position changes when viewed from different points in Earth's orbit around the Sun, astronomers can calculate the star's distance based on the angle of this apparent shift.
I have usually seen them quoted in kilometers.
Distance.
Astronomers use the parallax method to measure distances to stars by observing how a star's position shifts against distant background stars as Earth orbits around the Sun. By measuring the angle of this shift and knowing the baseline distance between Earth's orbit positions, astronomers can calculate a star's distance using trigonometry. The parallax method is most effective for nearby stars within a few hundred light-years from Earth.
Because the angle of shift is very small and extremely difficult to measure, scientists usually use photography to measure the shift. The star is photographed at the beginning and end of a six-month period, and its position in relation to other stars is studied each time.
Because they cannot visit stars and measure their sizes with a tape measure!
the sun
Astronomers use a method called parallax to measure the distance to nearby stars. By observing how a star's position changes when viewed from different points in Earth's orbit around the Sun, astronomers can calculate the star's distance based on the angle of this apparent shift.
Usually light-years, or parsecs.
I have usually seen them quoted in kilometers.
They do not use units: they use the fact that stars are not galaxies. For example, you don't use units to measure the difference between children and countries.
Distance.
Astronomers use parallax to measure the distance to other stars by observing how a star appears to shift its position against the background of more distant stars as the Earth orbits the Sun. By measuring this apparent shift, astronomers can calculate the distance to the star based on the angle of the shift and the known distance between the Earth and the Sun.
Astronomers use luminosity to measure the total amount of energy a star emits in all directions. By knowing a star's luminosity, astronomers can calculate its distance, size, and temperature. Luminosity helps astronomers understand the life cycle of stars and their evolution.
The device that astronomers use to find the angle between the horizon and stars in the sky is called a sextant.
Astronomers measure distances from Earth to stars using a method called parallax, which involves observing the apparent shift in a star's position as Earth orbits the Sun. They also use techniques like spectroscopy and standard candles to estimate distances to stars that are farther away.
With a long measuring tape.