Wednesday, November 16, 2005

The Known Extent of the Universe

Since this blog's theme is going to be my long time interest in all things related to space exploration, I thought I would start out with a review of where we are in space, and the structure of the universe. Most space enthusiasts probably already know all this stuff, but novices might find it interesting:

Everyone knows we are on Earth, orbiting the sun along with 10+/-2 planets (depending on the mood of the astronomy community - pluto/sedna/charon/qauoar regularly change designation from planet to comet and back!). The other stars in the sky are indeed other suns, with planetary systems of their own. We are beginning to detect planets in orbit around other star systems, though our ability to detect them is still coarse and limited to very large planets. What perhaps most people don't have a very good grasp of is the vast extent of the universe. The universe is enormous! It is impossible to convey with mere words how huge it is, but perhaps hurling numbers at the problem can help:

Our star exists in one spiral arm, off center of our galaxy, which is our local pie shaped group of stars. The milky way itself has a radius of about 50000LY, our star being 30000LY from the center. The galaxy contains over 100 billon stars. That's just our galaxy though.

At one time not very long ago (70 or so years) it was thought that our galaxy was the universe. But the galactic scale is only the beginning of what is observable. We discovered that some of the off-plane nebulae were actually extraordinarily distant conglomerations of stars, and that these objects were like the disk which our own star inhabited. The observable universe extends out quite a ways, and currently is jam-packed with about 40 billion galaxies. (Astronomy: A beginner’s guide to the universe, Chaisson McMillan, pg 419). While stars are very far from each other on the scale of planetary systems, galaxies, on a galactic scale, are about as close to each other as plates on a dinner table.

A few amazing Hubble pictures as an interlude, and to drive the point home:
  • Image 1

  • Image 2: The Tadpole Galaxy: One of my favorite desktop backgrounds


  • Image 3


  • These are from the Hubble deep field images. They are from minute areas of the sky exposed over hours (the photons come in very slowly from such distances).

    To be continued: More to come on this topic.

    1 Comments:

    Blogger Edwin said...

    Great beginning! One comment about the last statement though: the photons do not come in very slowly from the distant galaxies. The photons come in at the usual speed (c). There are just very few photons coming to Hubble from those distances.

    Monday, April 06, 2009 11:37:00 AM  

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