Themes > Science > Astronomy > Modern Astronomy > The Copernican Model > A Sense of Time and Scale in the Universe


Our modern perception of the Universe has been drastically reshaped from the corresponding perception of only a few hundred years ago.

Changing Perceptions of the Universe

Our understanding of the Universe with respect to it size, temporal duration, the kinds of events that take place in it, and the kinds of objects that it contains has undergone serious revision in the last few centuries:
  • Only in the last 400 years or so have we realized that the earth is not the "center", and that the Universe is immense.

    1. The Sun would hold 1.3 million Earths.
    2. There are 200 billion "Suns" in a galaxy like our own Milky Way Galaxy.
    3. Astronomers can see billions of galaxies.
    4. We don't know whether the Universe has an "end" or not; we are not completely sure even of the full meaning of the question.

  • Only in the last 50 years have we realized that the Universe is not static.

    1. The entire Universe is expanding.
    2. Events of fantastic violence take place in the Universe.

  • In the last half-century we have come to believe that the Universe contains objects that are truly bizarre as measured in human terms.

    1. Neutron Stars and Pulsars
    2. Black Holes
    3. Quasars
    4. Exploding and Colliding Galaxies

  • Only in the last 200 years have we begun to appreciate the age of the Universe.

    1. The Universe is probably 10-20 billion years old.
    2. Our Solar System is probably 4-5 billion years old.

Thus, the Universe of the modern astronomer would be largely unrecognizable to her counterpart from a few centuries ago. We can only speculate whether our present understanding of the Universe will appear as quaint 400 years from now as the views from 400 years ago appear to us.

A Sense of Scale

If the solar system were the size of a table, the Andromedae Galaxy would lie at 10 times the distance to the moon and the most distant galaxies would lie at 60 times the distance to the Sun.

A Sense of Time

If we were to compress the time since the Big Bang into one year, and make the time of the Big Bang January 1,
  • The Earth was formed in mid-September.
  • The mammals appeared on December 26.
  • All human prehistory (from the first known stone tools) and history have occurred in the last 1/2 hour of New Year's Eve.
Thus, all of human history is but a fleeting instant on the cosmic timescale.


Information supplied by: http://csep10.phys.utk.edu