Jay Ryan in Sky and Telescope a few years ago had some nice diagrams of how the orientation of the crescent moon can vary even for the same location, at different times of the year.
The moderator of this forum has asked that posters include a link to the Staff Report or Mailbag Item that is being discussed.
To include a link, it can be as simple as including the web page location in your post (make sure there is a space before and after the text of the URL).
The Staff Report can be found on-line at this link:
Why does the moon look different near the equator? (16-Jan-2001)
[Edited by C K Dexter Haven on 01-17-2001 at 01:37 PM]
Thanks Arnold. Why is that column not in “The complete Special Report/Mailbag Archive”? And, ah, why not this one as well, What is the definition of “down”? (revisited)?
The “complete” list of Mailbag articles (with RM’s link) excludes “recent” reports… unfortunately, that’s like the last 18 months or so.
For a list of “recent” Mailbag/Staff Reports, check here: http://www.straightdope.com/columns/index.html … you’ll have to scroll down past Cecil’s stuff.
Someday, we gotta get this updated.
It’s not on the “recent” list, either, since it hasn’t been (officially) posted yet. Where did you find it, RM?
It’s now been officially posted.
RM obviously subscribes and thus gets the week’s worth of columns, Staff Reports, etc early.
I’m sure Chronos has supplied enough information to answer this already, but I’m having trouble gleaning it. Here in the northern hemisphere, when the light side of the moon is on the right, it’s waxing, when on the left, it’s waning. Is it the opposite in the southern hemisphere? Do watches that show the moon phases have to run backwards in Australia?
Yes, that would be reversed in the Southern Hemisphere. Let’s picture a waxing moon, in the western sky shortly after sunset. Here in the north, the Sun is moving northward as it’s setting, so the path of the Sun (and the Moon, since they follow approximately the same path) in the sky would be something like this \ . The Moon is higher in the sky than the Sun, so the Sun is to its right, and the lit portion will be on the lower right.
In the Southern Hemisphere, however, the Sun and Moon are moving to the South as they’re setting, so the path is more like / . When that same moon is in the west there, the Sun is below it and to the left, so the lower left portion of the moon is lit.
I have no idea whether this is reflected in timepieces manufactured in or for the South, but I would tend to doubt it: Clockwise and counterclockwise were standardized the way that they were because a sundial shadow moves clockwise in the Northern Hemisphere, where most clockmakers lived, and I don’t think that they’d be any less Eurocentric for other aspects of clock construction.
Ah, but large grandfather clocks have mechanisms that display the phase of the moon. As Greg points out, that display would be backwards in the Southern hemisphere.
Does the moon’s orbit coincide with the celestial equator? If not, all this is a tad oversimplified, ain’t it?
Oversimplified? Well, the article did say that the positions were on average.
For instance, it says that the crescent moon would be in the five o’clock position (150 degrees) from New Orleans at sunset, but that depends on the moon’s height and its position in relation to the ecliptic, and the angle of the ecliptic to the horizon. The moon’s orbit is tilted five degrees from the ecliptic, which is tilted 23 degrees to the equator. On Mar. 17, 2010 at sunset, the crescent is at 186 degrees on the lunar face, just past six o’clock (180 degrees). On Oct. 9, 2010, the crescent is at 118 degrees, just before four o’clock (120 degrees). So, it does vary some–as that link in my first post illustrates.
Yes, it is a bit of a simplification, hence all of the “approximately” and “on average”. I’ve currently got another Staff Report in the works (no, I haven’t forgotten about that, Dex!) dealing with the effect of the Earth’s axial tilt on the position of the Sun in the sky, but I’m having a hard time figuring out how to explain it in a comprehensible manner. For now, just accept the simplified version: The more complicated details don’t have a qualitative effect for these purposes.
Chronos
One thing that doesn’t seem to be so obvious, is that (for the near term) the line of the ecliptic is stationary and we rotate under it–in other words the constellations of the zodiac rotate through at the same heights day in and day out. In the summer, the sun is by Aldebaran, high in the sky. Six months later, it’s winter, and the sun is far away from Aldebaran–but we can still see Aldebaran high in the winter nighttime sky.
Hey Chronos check out this website:
I assume that’s Thai, but the pictures seem good.