| Comments |
| Lunation | 1051 |
|---|
| Phase | Waning Gibbous
Full + 23h |
|---|
| Age | 15d6h34m |
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Distance
Light Time
(from earth) | 364,243 km
1.21s |
|---|
| Elongation | 166.6° W |
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| % Illuminated | 98.4% |
|---|
| Morning Terminator Colongitude (λ E) | 98° |
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| Evening Terminator Colongitude (λ W) | 278° |
|---|
| Libration in Latitude | -4°07’ |
|---|
| Libration in Longitude | 5°43’ |
|---|
| Magnitude | -12.5 |
|---|
| Angular Size | 32.81' |
|---|
| Altitude | 19°12’ |
|---|
|
Virtual Moon Atlas graphic |
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Terrence Dickerson, in Exploring the Sky by Day, says that there is no difference in the Sun/Moon size between when it is on the horizon and when it is up in the sky.
When the sun and moon are close to the horizon, they look much larger than when they are high in the sky. Yet there is really no difference at all. Not a bit. Yet the sun and the moon are exactly the same size whether they are close to the horizon or not. It is an optical illusion.
I have already proved this is wrong for the Moon by the application of geometry and it should be wrong for the Sun also, and for the same reason (that we are closer to the body when it transits than we were when it rose or will be when it sets). To test out my hypothesis I went to Planetarium to get the diameters. I chose 23Dec07 since that is the night of the full Moon and I am hoping to be able to go out and photograph it low on the horizon (as low as the apartment buildings will permit) and when it transits.
| | Sun | Moon |
|---|
| Rise | 23Dec07
0714 EST
0.984 AU
32' 34.4" | 23Dec07
1600 EST
363,000 km
32' 31" |
|---|
| Transit | 23Dec07
1134 EST
0.984 AU
32' 34.4" | 24Dec07
0005 EST
357,000 km
33' 30" |
|---|
| Set | 23Dec07
1634 EST
0.984 AU
32' 34.4" | 24Dec07
0806 EST
365,000 km
32'60" |
|---|
We are coming up on aphelion so the Earth is getting closer to the Sun every second. We are also moving toward apogee so the Moon is getting farther away all the time.
I found that the Moon does appear larger when it is transiting and it is closer to earth at that time. But the Sun does not appear to change in size. I wondered if this might be a problem with Planetarium since Helio gives a different sun diameter so looked up those diameters and substituted them but the result was the same. I propose that the Sun really is subtending greater and lesser diameters as it rises and falls just like the Moon, but that it is so far away that the change is less than the resolution of my software and that we can't perceive the change.
Dickerson suggests using an aspirin tablet held at arm's length to prove that the Moon doesn't change size. He says that the tablet at that distance is slightly smaller than the Moon. Since he is also talking about the Sun on this page so should have included a warning not to try this with the Sun, but didn't.
It was bad weather last night so I went out tonight to photograph the Moon close to the horizon and plan to go out when it is culminating to prove that it is larger when it is overhead than it is when it is on the horizon. Unfortunately it is overcast so the images of the horizon Moon are not going to be great. Hopefully it will clear up before culmination.
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