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Gordon Rayner
scholastic sledgehammer
Reged: 03/24/07
Posts: 965
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Re: Sky Vistas : I do not have that book. Have seen it, but sticker shock made me pass on it. Perhaps I should reconsider. Do they have a correct description of Milky Way structure, that is, that the Milky Way is a barred spiral, rather than a top view of a whirlpool?
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GlennLeDrew
Pooh-Bah
Reged: 06/18/08
Posts: 1251
Loc: Ottawa, Ontario, Canada
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Gordon,
One should not place too much emphasis on how the *gross* structure of our Galaxy is treated. Why? From an observational standpoint, the dust-laden disk limits the in-plane horizon from about 400 to 15,000 light-years. Considering the average in-plane distance to which we can see in the visible, the fraction of the galactic disk open to our gaze is only about one percent of its 100,000 light-year diameter! Besides the occasional, relatively clear sight lines which allow to peer quite deep into the disk, for the most part our observational horizon is limited to the Sagittarius, Cygnus-Orion (Local) and Perseus arms.
For an observing guide to be considered out of date just because its treatment of the largely inaccessible inner Galaxy is incorrect is perhaps unfairly rigorous.
Cheers!
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Home-made 11X50 right angle bino, 8.1 deg. FOV
Modified 26X100 bino, 3.5 deg. FOV
Home-made Mk II RA bino, using interchangeable objectives and eyepieces
My Gallery
Mediocre minds discuss people. Good minds discuss events. Great minds discuss ideas.
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rookie
scholastic sledgehammer
Reged: 01/14/06
Posts: 878
Loc: St. Petersburg, FL
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Hi Gordon,
NASA's Spitzer Space Telescope sky survey identified the central core of the Milky Way to be barred. The press release was August 2005. Sky Vistas was published in 2004.
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SV
Scope: Celestron CPC8
Binoculars: Garrett GT80~45, Fujinon 16x70, Regals 10x42, Ultima 9x63, Nikon AE 8x40
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Crossen
member
Reged: 07/14/08
Posts: 87
Loc: Vienna
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Quote:
Re: Sky Vistas : . . . Do they have a correct description of Milky Way structure, that is, that the Milky Way is a barred spiral, rather than a top view of a whirlpool?
Gordon,
Right off hand, the only thing I recall saying in "Sky Vistas" about our Galaxy's central bar is on page 127 of the book: ". . . we live within a relatively loose-armed Sbc spiral galaxy with a small central bulge (that probably is barred rather than simply spheroidal)." I'd drop the "probably" if I had to rewrite that statement, though it does get across the fact that the bar is weak--nothing like the spectacular bar of NGC 1300.
I've long been familiar with the question of the central bar of the Milky Way, because one of the guest speakers at an advanced graduate course on the Milky Way that I took at the U of MN in the spring of 1992 was Leo Blitz of the U of MD, one of the early researchers into the matter. But as Glenn LeDrew implies in his post, the emphasis in "Sky Vistas" is on things actually seeable in giant binocs and RFT's and, because of interstellar dust, there are very few objects as far as 20,000 l-y away that we can see in the disc of our Galaxy. Only a few "pieces" of our Galaxy's central bulge are actually visible with the eye or binoculars above or below or through the dense dust of the Galactic plane, the largest and brightest being the Great Sgr Star Cloud. (The presence of the bar was inferred from IRAS surveys and from peculiarities in the rotation velocities of objects in and near the bulge observed at radio wavelengths.) Consequently the one chart of spiral structure in the book, on page 131, simply shows the distribution of associations, young open clusters, and large emission nebulae that "trace" the spiral arms in the immediate solar neighborhood.
"Sky Vistas" has a fairly large amount of text. But that text is devoted to describing what you can see with wide-field instruments, why these objects look they way they do and, further, why they're distributed in the sky the way they are (that is, trying to "see" the sky in 3-D). I tried to make the text as down-to-earth as possible while at the same time presenting a lot of solid scientific astronomy.
Craig Crossen
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