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Commentary on Star Atlas in Galactic Perspective

Star Atlas in Galactic Perspective - Star Map in Galactic Perspective

Installed 28 Sep 2001. Latest update 30 Aug 2011.
Text changes or additions are in bold.

In April 1972, Apollo 16 astronauts set up a television camera near their lunar module (LM). The camera, called the big eye slowly panned back and forth (in a 350 degree arc) to record the astronauts' extra vehicular activities.

Each time the camera's field of view passed through what appeared to be a southerly direction there was a faint hazy irregular shaped something located a few degrees above the horizon. The following marked up picture shows the lunar lander, in situ, as well as a drawn-in likeness of the Faint Hazy Object (FHO) and the big eye camera.

Apollo 16 Big Eye
Apollo 16 Lunar Lander Showing a Likeness of the Faint Hazy Object

So what hazy astronomical body is South of the moon? Where large distances are involved, this question can be restated with respect to the Earth. (That is not exactly true.)

I broke out Menzel's A Field Guide to the Stars and Planets and pored over its polar map of the southern celestial hemisphere. The best I could come up with at the time, was one of the Magellanic clouds. (These are roughly 17 and 21 degrees away from the Earth's south celestial pole.)

The plane of the ecliptic is tilted 23.5 degrees (deg) with respect to earth's celestial equator. The ecliptic north pole is at 18 hrs RA, +66.5 deg Dec, and the ecliptic south pole is at 6 hrs RA, -66.5 deg Dec. [Thanks to Joe Harrington for calling attention to a coordinates mistake and for clearing up some polar nomenclature.

Most sources indicate that, the moon's orbit is tilted some five degrees with respect to the ecliptic. Thus, if you draw a five-degree-radius circle around the ecliptic south pole then the lunar south celestial pole should be somewhere on that circle. (See the larger red circle on the drawing below.)

According to a 1988 University of Texas at Austin source [Link no longer works.] (Page 12.) the moon's celestial axis is inclined to the pole of the ecliptic 1.5 degrees. (This would correspond to a location somewhere on the smaller red circle below.) [Added 09 Mar 2009.]

Southern Lunar Sky from Apollo 16 site
Southern Lunar Horizon and Approximate Location of Lunar South
Celestial Pole as seen from Apollo 16 landing site on 23 April 1972.
[Added 23 September 2005. Replaced 17 Mar 2009.]

WordIQ.com says that the lunar axis is tilted with respect to the normal [of its orbital plane?] by 1.54 degrees, and the coordinates for the lunar Northern Celestial Pole are RA 17 hours 47 min, Dec 65.46 deg. This would make the coordinates for its South Celestial Pole, to be RA 5 hours 47 min, Dec -65.46 deg. (These coordinates may be for a specified time.) The position associated with these coordinates is shown as a red dot which overlaps delta Dorado on the diagram above. The Distant Southern Lunar Horizon would have been nine degrees below that position.

On April 23, 1972 an observer located at the Apollo 16 landing site, facing South, should have seen the center of the Large Magellanic Cloud at about 12 degrees above the distant southern lunar horizon. (My memory from the Big Eye panorama places it at about four degrees above the local horizon. The approximated local southern horizon in the drawing has been shifted upwards to make the geometry come out right.

Coordinates for the Large Magellanic Cloud are:
Equatorial - RA 05 hrs 23.6 min, Dec -69 deg 45 min
Galactic - LII 280.4136 deg, BII -32.9310 deg

In 2002 I purchased a NASA book and video covering the Apollo 16 mission, but failed to see the hazy object anywhere in the video. Best I can tell, the focus clarity of the Big Eye mission video is degraded from that which was broadcast during the 1972 coverage.

Barring evidence to the contrary, and if I haven't stretched things too far, it would seem that my Faint Hazy Object was the Large Magellanic Cloud.

Back to 1972.

To my consternation, whenever I set the Field Guide aside for a while, I found that when I came back to its southern hemisphere polar plot, that I could never recall where I left the Magellanic clouds. (A polar plot is a polar plot and there is no obvious getting-on or getting-off point.)

Then I noted that the Milky Way, as projected on the polar plot, formed a long curved arc. Aesthetically, it looked nice but then I got "bent out of shape" at the celestial plot because the Milky Way is not bent out of shape. The distortion is even worse when you look at the Milky Way on a celestial equatorial projection (where the celestial equator is the undistorted aspect). You might want to stay home!

Here is an equatorial chart showing Messier objects and the Milky Way distortion. [Installed 26 Aug 2011.]

1000px Messier Objects
From: Wikipedia - List of Messier Objects   Three lines of Right Ascension have been emphasized.

I decided then and there that I would put together a star map where the Milky Way was the least distorted feature and let our celestial coordinates do the curvy stuff. Here is a scaled-down "extract" from the latest version of the Star Map. Details on construction of it's predecessor, and it, follows.
[Added 26 Aug 2011. Updated 30 Aug 2011.]

scaled down star map

A galactic coordinate system was drawn on a celestial sphere globe. Then the underlying celestial coordinates were transferred by eye onto what I call a oblique Mercator galactic projection. On this projection the gradual stretching out of galactic latitude begins at 30 degrees above and below the galactic equator. Latitude-wise the oblique mercator projection stops at plus/minus 80 degrees galactic latitude. Galactic polar plots were prepared which cover the regions from +30 degrees to the North Galactic Pole and from -30 degrees to the South Galactic Pole.

Lund Observatory kindly granted permission to overlay a stippled version of their 1958 Panorama of the Heavens on the map. The galactic coordinates used on the map were based on the system used in 1958. (That system has since been replaced with one whose zero galactic longitude is shifted some 32 degrees with respect to that used in 1958.

To eliminate the problem of constellations getting chopped in half at the edges, a 50 degree galactic longitude extension was added on the right hand side of the map.

The Star Atlas in Galactic Perspective (three maps) presents the Milky Way in a form that is insensitive to seasonal or time of day considerations. The distorted celestial coordinates make what I think is a useful tool for remembering constellation locations.

When the star atlas was being born, my navy boss, Robert G. Newbegin, IV, CDR USN was a Naval Aviator (an A-3 Driver) and a celestial navigator. He said that he liked the map but it had to have some way to locate the Zenith (the spot directly overhead) for any date and time. A Local Meridian Finder versus date and time graph was made to serve this purpose. Once you know your local meridian and your latitude, then locating your zenith is easy. (A copy of the Local Meridian Finder is at the bottom of this page.)

The 1972 Star Atlas was done in pen and ink and it has is a certain amount of eyeball subjectivity as to star sizes and positions. These subjectivities are gradually being "reduced." In most places the hand drawn names and Greek characters are being replaced with formal fonts. [Link to the original star atlas added on 23 September 2005.]

A newer Star Map is under construction on this site. In it, the stippled milky way has been replaced by a two color scheme that represents stellar density gradations. [Added 23 September 2005.]

How to use the Local Meridian Finder

The Local Meridian Finder has the calendar year laid out horizontally, the time of day vertically, and the local meridians (in hours of Right Ascension) are overlaid as diagonal lines. You pick the date and time and read off the Right Ascension for your local meridian. Use your geographical latitude as the Declination for your Zenith. (This graph can be used with any celestial star map.)

The Local Meridian Finder can also be used to tell when any given celestial object will be on a north-south line overhead. Follow the Right Ascension diagonal for your object until you reach your observation time of year. Read the time of day off the vertical axis on the left.

There's an online form to Convert Equatorial to Galactic Coordinates at Johns Hopkins University.
[Added 08 Oct 2005.]

Zenith Lookup

Send comments/questions to Bob Fritzius at fritzius@bellsouth.net
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