The Universe is mind-bogglingly large. Light travels at almost 300, 000 kilometres per second (the actual speed is 299,792 km/second). A light-year is the distance that light travels in one Earth year. One light-year is about 9 trillion kilometres. While the spatial size of the Universe is yet to be known, the size of the observable Universe is currently estimated to be 93 billion light-years in diameter.
In 2003 scientists from the University of New South Wales, John Hopkins University in Baltimore, USA and the Royal Observatory in Edinburgh counted all the then known galaxies and estimated the number of stars in each, in one small region of the Universe close to Earth.
They then extrapolated the calculation across the then entire known Universe and came up with what is regarded was the most accurate estimate of the minimum total number of stars. Dr Simon Driver, who led the study at the Australian National University, said: "Even for a professional astronomer used to dealing in monster numbers, the total is mind boggling."
It is estimated that there are up to 400 billion stars in our galaxy, the Milky Way and somewhere between 100 and 500 billion galaxies in the Universe. This number is being refined as further discoveries take place. Celebrity astrophysicist Professor Brian Cox was quoted in Monday's Age as saying that there are approximately two trillion galaxies in the Universe.
In the 2003 calculations, astronomers calculated that there was a minimum of 70 thousand million million million - or seven followed by 22 zeros - stars. At the higher end of calculations there may be up to 200 sextillion stars.
Without a telescope it is estimated that we can only see around 5000 stars in the night sky from the darkest places of the Earth and just over 100 in city areas.
Mathematicians have calculated that there are significantly more stars in the Universe than there are grains of sand on every beach on the Earth.
To balance this, it used to be estimated that there are more atoms in a single grain of sand (approximately 50 000 000 000 000 000 000 - 50 quintillion) than there are stars in the Universe. With the number of identified galaxies and stars increasing as science extends its knowledge, it is probably safer to state that there are more atoms in 3 or 4 grains of sand than there are stars in the Universe.
Many people believe that the design and complexity of the Universe can only be explained via a cosmological argument in favour of a divine creator (God).
Whatever your beliefs, the size and complexity of the Universe is beyond the understanding of most people and is a true wonder to contemplate.