Question

The way Edwin Hubble showed that other galaxies existed was to measure a distance to a galaxy and show that it was greater than any estimates of the size of our own Milky Way. The first galaxy for which he measured a distance was M31, the galaxy in __________. He did that measurement using a class of stars called _________, whose variations in luminosity could be used to estimate their distance. Astronomer continued that work, measuring those kinds of stars in other nearby galaxies with other telescopes. Such measurements have recently been done in even more distant galaxies using ____________. Another way to measure distances is to find objects that behave like “standard bulbs;” one especially useful candidate for such a “bulb” is a ___________. Radio astronomers can measure the distance to a galaxy by noting the width of its 21-cm hydrogen line and applying the __________.

Answer 1

In 1925 Edwin Hubble gave hubble' s law which states that the distance to a galaxy is proportional to its velocity. v = H*d where H is the Hubble's constant, v is velocity and d is distance in megaparsec.

The first galaxy to which Hubble measured distance was Andromeda galaxy it is in constellation Andromeda it is named after this constellation. He used a class of stars called cepheid variables.these stars pulsate in a given period using their luminosity and period we can measure distance to the galaxy.

Hubble's telescope is used to measure distance to more distant galaxies.

Galaxies have extremely bright supernovae which are explosions caused in last stages of evolution of a star. These supernovae are called cosmic lightbulbs as their magnitude is very high and used to measure distance to galaxies.

21cm line of hydrogen can be seen in radio spectrum of galaxy and by measuring width of this line we can determine doppler shift in the line.This is used to calculate rotational velocity of the galaxy. once velocity is known Hubble's law can be used to calculate distance to galaxy.