Recap

Cosmological principle

The cosmological principle is the notion that the universe's matter is isotropic and homogenous. It is more philosophical than theoretical.

Expanding universe

The expansion of the universe is intrinsic, meaning that it can expand faster than the speed of light.

Recessional velocity

It is the rate in which astronomical bodies outside the observer's galaxy recede from the observer. It can be measured by observing the wavelength shifts. If the object is moving to the observer, the electromagnetic waves are compressed, reducing its wavelength and increasing its frequency, and vice versa.

Solar time

There are 2 types of solar time - apparent solar time and mean solar time. Apparent solar time is the apparent time taken from observations on earth.