RE: Our Interstellar Neigborhood

From: Lee Corbin (lcorbin@tsoft.com)
Date: Fri May 30 2003 - 22:09:49 MDT

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    Anders writes

    > Seems to fit my own impressions I got when I was doing starmaps
    > (http://www.nada.kth.se/~asa/Starmaps/

    Most excellent! About 30 years ago I worked out all the coordinates
    of the nearest 30 stars or so, and rotated them so that I could get
    an "objective" view of the nearby stars, looking down upon the
    galactic plane from above. So then I had to correct a lot of the
    imagery I had in mind as to "where" Alpha Centauri was with respect
    to the solar system and to the galactic center, than I had unconsciously
    picked up while reading SF.

    Your applet is perfect for this. Now you mention

    > The coordinate box enables or disables circles showing the distance 100, 1000 and 10000 lightyears from the sun, as well as the
    coordinate axes in a heliocentric coordinate system with the X axis pointing at the galactic center.
    <

    Okay, so the X axis (as it goes towards the right) is pointing to
    galactic center. (I have always understood that from our point of
    view at Sol, Alpha Centauri and Proxima are at about 45 degrees to
    the right when facing galactic center, and your applet seems to
    corroborate this, and, luckily for SF, they lie in about the same
    galactic plane as we do---i.e., the plane formed by the center of
    the galaxy, Sol, and Alpha Centauri, is about the same as the
    galactic plane.) But you have the "y" axis pointing down, and
    so, what direction is that pointing to in terms of our galaxy?

    If I assume, as you have written, that the X axis points to Galactic
    Center, and, then visually, the Y axis (if it were to point upwards
    on your diagram) should be pointing towards Deneb, approximately.
    Hey, and so when I adjust the distance to about 1000+ ly, there is
    Deneb where I want it! All right!

    So it must be that we are (i) looking down on the galactic plane,
    (ii) the *vertical* (not as you have shown it) Y axis is towards
    galactic rotation (towards Deneb), and thus the positive Z axis
    is towards the viewer, up out of the galactic plane. Is this
    all correct?

    Thanks,
    Lee

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