Size Comparison Of Astronomical Objects

The size of astronomical objects are so large and the distances are so great that they quickly exceed human comprehension. Each picture below shows increasingly larger objects as one moves further from the earth.

Inner planets of the solar system. These planets are the most dense in the solar system and, with the exception of Pluto, closest to the sun.


The outer planets (gas giants) of our solar system. They consist largely of frozen gases and are consequently the least dense in the solar system. However due to the extremely large masses they exert very strong gravitational force compared to the inner planets.


Our sun is a middle aged average sized star that has been around for about 5 billion years. it will use up all its fuel in another 4.5 Billion years.


The size of our sun (smallest sphere in the lower left) compared to other nearby stars:


Some of the still larger stars. Note that there life span is extremely short (millions of years) compared to our sun because they must burn hydrogen fuel at a prodigious rate to to balance against the incredibly strong gravitational force trying to compact the star because of their huge masses.

Shown below is the home of our solar system including the sun and all the planets. This is the milky way galaxy. It is a spiral galaxy which is home to between 200 - 400 billion stars (many of which most likely have their own planetary systems). The diameter of our galaxy is about 100,000 light years. Our sun is located on one of the smaller spiral arms of our galaxy within the outer region. Our whole solar system is orbiting the galactic center in a near circular orbit that takes about 220 million years to complete one revolution.

Shown below are far away galaxies taken by the Hubble telescope billions of light years from earth. There are billions of galaxies in the universe and each one contains billions of stars like the ones shown in the previous pictures. The closest distance between the earth and the nearest star in our own galaxy is 4.5 light years away. The distance our own milky way galaxy and our neighboring galaxies are several hundred thousand to millions of light-years away from the earth. The nearest large galaxy is about 2.9 million light years away.

Shown below are far away galaxies from the darkest area of the picture above. Given the immense distances, the speed of light and the time elapsed since the Big Bang, we can only see huge extremely bright objects up to approximately 14.5 billion light years away or slightly less than the estimated age of the universe. As we look at these distant objects we are looking back in time because light travels at a finite speed (3 x 108 meters/second) and consequently the incredible time it takes light to travel these immense distances to reach earth.