The Astrophysics Spectator

Issue 2.03, January 19, 2005

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January 12, 2005

This week we develop a sense of astronomical distance. The dramatic scales of size encountered in astronomy fall outside of all human experience. Even when distance is expressed as time, as is done in expressing distance as light years, is has values that are far outside our experience: light emitted from the Sun at the beginning of the Roman empire has now traveled less than one tenth of the way to the center of our Galaxy. To confuse us more, our science fiction presents space travel as simple and fast, with astronauts traveling between the stars in hours or days.

Three pages are added to the “Distance” path with this issue of The Astrophysics Spectator. These pages break astronomical distance into three scales: the scale of the Solar System, the scale of our Galaxy, and the scale of the Universe. Each of theses scales has a natural size that is many factors of ten larger than the previous scale. By addressing each scale in turn, we can develop a sense of astronomical distance without being overwhelmed.

Last week in the commentary I discussed the shortcomings of Intelligent Design arguments. This week I discuss a similar type of argument employed in astrophysics that I call “Natural Design.”

Jim Brainerd

Current News

Huygens Probe Lands on Titan (January 14, 2005). The Huygens probe successfully landed on the surface of Titan, sending back pictures of the moon's surface for 90 minutes before losing contact with its parent craft, the Cassini spacecraft. (continue)

Current Commentary

The Lure of Natural Design. Many scientists assume that there is a natural explanation for the universe we see. At some point, however, such a belief is an act of faith, because our vision of the universe will always be limited. We are then left with descriptions of the universe that have no explanation. (continue)

New Background

Distances in the Solar System. This page, which is the first page of the “Distance” path, discusses the relative sizes of the planets, their orbits, and their systems of moons. The natural size scale in the Solar System is the size of Earth's orbit, which defines the Astronomical Unit. (continue)

Distances in the Galaxy. The scale of the galaxy is many factors of ten larger than the scale of the Solar System. In fact, the size of our Galaxy relative to the size of the Solar System is about the same as the size of the Solar System relative to the size of a man. This page discusses the natural unit of distance within the Galaxy, the parsec. (continue)

Extragalactic Distances. The observable universe has a size that is a billion times the size of our Galaxy. This page discusses the intergalactic distance scale and the distance scale of the observable universe. (continue)

Bibliography. The bibliography page is a new page added under the Background link that lists the references used in writing the pages of this web site. The bibliography is only of references that the author finds useful. This page will be updated weekly. (continue)


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