Re: lunar eclipse
Jim_Cobb [EMAIL PROTECTED] writes: I noticed that this time disagrees with the time given in the almanac, so I thought I should provide more information so as not to impugn the reputation of the excellent xephem program. The 16:08:17 UT time is what xephem computes as the time of the full moon. I do not know how to get it to reveal the maximum eclipse time. Well, that's interesting. I would have defined full moon as the time when the moon is most nearly opposite the sun, which would be the same as the time of maximum ecclipse. How else can it be defined? There must be something like a projection into the ecliptic. Art Carlson
Re: Analemmatic dial
Tom, With regard to your posting: Message text written by INTERNET:[EMAIL PROTECTED] comfortable arm-chair. If an analemmatic dial is planned for a vertical declining wall at 55° North, and the latitude on the earth's surface where this plane would be horizontal to the surface is 35° South, these two defining planes would be parallel to each other. Therefore, as the gnomon's Not true if the vertical wall declines. Declination will bring the southern latitude closer to the equator - until it equals the equator when the declination is 90 degrees. Fred Sawyer
Re: lunar eclipse
Philip P. Pappas, II wrote: There will be a total penumbral lunar eclipse on Jan. 31. The moon will pass entirely through the lighter part of the Earth's shadow without any of it being in the umbra or darkest portion. I don't know the exact time of the event. This is a somewhat rare event. I thought that this would be an excellent opportunity for you dialists to check the functioning of your sundials (moondials) and to test some of the theories that we discussed last week. (ie. Does the use of the EOT improve accuracy.) The reason that this eclipse is particularly good for sundial readings is that the moon will be brighter during totality than a normal eclipse and should cast a more distinct shadow. Of course the sun/earth/moon alignment will be better than during a partial eclipse also. Does anybody know the times for this eclipse? John Carmichael According to the xephem program, the eclipse occurs at 16:08:17 UT. The geocentric latitude of the moon at that time is -0:59:16 degrees (very close to -1 degree). Attached is a gif file showing the position of the moon and the umbra and penumbra at the time of the full moon. This picture was produced by the xephem program. It may be interesting to investigate correction by the EOT as well as correction by EOT for six months from now--the moon will be near the place the sun will occupy in six months, and I'm having a hard time deciding which EOT correction should be used (I know, Ishould be able to decide this...). Finally, also according to xephem, the moon will have zero geocentric latitude (i.e. it will be at the node) on Feb 1 at 11:19:12 UT. You might see whether the moondial is even more accurate at this time. -- --- -- | Jim Cobb | 540 Arapeen Dr. #100 | [EMAIL PROTECTED] | | Parametric | Salt Lake City, UT | (801)-588-4632 | | Technology Corp. | 84108-1202 | Fax (801)-588-4650 | --- -- I have the oldest typewriter in the world. It types in pencil. - Steven Wright Attachment converted: MAC Hard Disk:pen-eclipse.gif (GIFf/JVWR) (000108DE)
Re: lunar eclipse
Here is the eclipse info from the 1999 Astronomical Almanac (p. A 79). I meant to include this in the last message, but sent it off too soon... Circumstances of the Eclipse d h m s UT of geocentric opposition in right ascension, January 31 16 38 02.180 Julian date = 2451210.1930807838 d h m Moon enters penumbraJanuary 31 14 04.5 Middle of eclipse 31 16 17.5UT Moon leaves penumbra31 18 30.3 [...] Penumbral magnitude of the eclipse: 1.028 Jim --- -- | Jim Cobb | 540 Arapeen Dr. #100 | [EMAIL PROTECTED] | | Parametric| Salt Lake City, UT | (801)-588-4632 | | Technology Corp. | 84108-1202 | Fax (801)-588-4650 | --- -- The difference between common sense and stupidity? Common sense has its limits.
Re: Analemmatic dial
Frank Evans mentions making an analemmatic dial on a vertical wall. An article by Peter Drinkwater with just this title was published in the journal of the British Sundial Society in July 1994 (vol.89.2, p.2). Peter Tandy At 02:45 PM 1/25/99 +, you wrote: Greetings, fellow dialists, Douglas Hunt asked about an analemmatic dial on a slope. Yes, well, I've been planning an analemmatic dial on a vertical surface for quite a while. Trouble is, the plan has not left my armchair for the wall opposite my kitchen window, where I can watch it while I wash up. I'm in 55 north, nearly on the Greenwich meridian. The wall declines 34 degrees east of south, taking the morning sun. The solution seems to be to work out the layout for a dial in 35 degrees south latitude, as suggested by Tom McHugh and Tony Moss. The peg gnomon thus sticks out horizontally from the wall. This solution was proposed to me by Fred Sawyer at last year's meeting of the British Sundial Society at Dunchurch when I asked for his help (I hope I'm citing you correctly, Fred). But the minor axis of the analemma ellipse must lie in the earth's axis and with my declining wall I think it must be along what is hermetically called in the trade the style distance, in its case 21.4 degrees from the vertical. So, for further developments, watch this space. Or else go and find some wet paint and watch it dry. And that reminds me. Geordie, it seemed, was leading his donkey home but called on the way at an Irish club, where he remained for several hours. On emerging he found his donkey had been painted green. Returning inside he demanded to know the culprit. An Irishman measuring two pick handles across the shoulders put down his pint of stout and rose to acknowledge the deed. I just wanted to say, said Geordie, thinking quickly, that your first coat's dry. -- Frank Evans
light experiment
Hi guys, it's me again: Just thought of another fun experiment we can do during the Jan. 31 lunar eclipse. One person wrote saying that he doubted there would be enough light during a prenumbral eclipse to cast a shadow on a sundial. If you have a photometer, you could measure the minimum amount of light in foot-candles (or lumens) that is needed to cast a shadow. You can also note how far into the eclipse this occurs. I realize that results should vary depending on local ambient light pollution. Knowing, in foot-candles, the minimum amount of light needed to activate a sundial, how far away from the sun would you have to go until the sun doesn't cast a shadow? John Carmichael
Moon Shadows
Greetings Dialers: I'm certain that the penumbrally eclipsed moon will be bright enough to cast a shadow on the 31st. The planet Venus, when it is close by can cast a shadow and it is only a -4 magnitude object. Troy Heck
