The term mass is used a lot in astronomy but what does it actually mean? The mass of an object is a measure of the amount of “stuff”, atoms in this case, that it is made up of. It is measured in the SI Units of kilograms or kg.
Some examples of the mass of objects:-
A hydrogen atom has a mass of 0.000000000000000000000000000167 kg
1 litre of water has a mass of 1.0 kg
An average European has a mass of 70.8 kg