| 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. |
| | If we were to compress the time since the Big Bang into one year, and make the time of the Big Bang January 1, |
| | Thus, all of human history is but a fleeting instant on the cosmic timescale. |
| | 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. |
| | 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 |
| | There are 200 billion "Suns" in a galaxy like our own Milky Way Galaxy. |
| | The Sun would hold 1.3 million Earths. |
| | Astronomers can see billions of galaxies. |
| | 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 |
| | Events of fantastic violence take place in the Universe. |
| | The entire Universe is expanding. |
| | In the last half-century we have come to believe that the Universe contains objects that are truly bizarre as measured in human terms |
| | Neutron Stars and Pulsars |
| | Exploding and Colliding Galaxies |
| | Only in the last 200 years have we begun to appreciate the age of the Universe |
| | Our Solar System is probably 4-5 billion years old. |
| | The Universe is probably 10-20 billion years old. |
| | 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 and Scale in the Universe |
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