hm. i'm pretty sure that this question was asked some times, but I can't found any answers.
seeing from the Moon's surface (sync orbit, near the surface), the Earth moves on a strange path on the sky. since Moon always shows the same side to Earth, I expected Earth to stay on one position on the sky. Okay, the Moon's orbit is not an exact circle, so I expected some small movements, but Earth, as Celestia shows, walks a path over 45deg in size.
why?
Earth from Moon
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Sounds like you have an older version of Celestia, in which the Moon was wrongly orientated with its equator parallel to the Earth's equator, rather than the plane of the ecliptic.
Since the Moon's orbit is inclined about 5 degrees to the plane of the ecliptic, the Earth appears to shift north and south in the Moon's sky by about five degrees during each month. With the old orientation, the Earth seemed to move 23+/-5 degrees north and south each month.
You can fix the Moon's orientation by replacing its definition in solarsys.ssc. The current definition reads:
Grant
Since the Moon's orbit is inclined about 5 degrees to the plane of the ecliptic, the Earth appears to shift north and south in the Moon's sky by about five degrees during each month. With the old orientation, the Earth seemed to move 23+/-5 degrees north and south each month.
You can fix the Moon's orientation by replacing its definition in solarsys.ssc. The current definition reads:
Code: Select all
"Moon" "Sol/Earth"
{
Texture "moon.jpg"
# Texture "clem-moon-4k.jpg"
# Texture "moon4k.dds"
BumpMap "moonbump1k.jpg"
BumpHeight 0.7
Radius 1737.53
Oblateness 0.002
CustomOrbit "moon"
EllipticalOrbit {
Period 27.321661
SemiMajorAxis 384400
Eccentricity 0.054900
Inclination 5.15
}
Obliquity 23.45 # mean axis
EquatorAscendingNode 0.0 # mean axis
RotationOffset 38
Albedo 0.12
}
Grant
Hello pint,
First let me be the first to welcome you to this forum.
The reason the Earth appears to wobble so dramatically across the sky when viewed from the moon is in fact due to your position on the moon. Also, the plane of orbit of the moon doesn't follow along the equator of the Earth and also the moon's orbit is moderately eccentric. All these factors contribute to the appearant "wobble". Likewise, the Sun appears to wobble thru a 23.5 degree 6 month cycle before completing it's cycle in another 6 months.![Smile :)](./images/smilies/icon_smile.gif)
First let me be the first to welcome you to this forum.
![Wink :wink:](./images/smilies/icon_wink.gif)
The reason the Earth appears to wobble so dramatically across the sky when viewed from the moon is in fact due to your position on the moon. Also, the plane of orbit of the moon doesn't follow along the equator of the Earth and also the moon's orbit is moderately eccentric. All these factors contribute to the appearant "wobble". Likewise, the Sun appears to wobble thru a 23.5 degree 6 month cycle before completing it's cycle in another 6 months.
![Smile :)](./images/smilies/icon_smile.gif)
I made a screen shot of the path of earth seen from the moon.
Actually, the shape of the trajectory can be very different one month to another.
http://www.shatters.net/gallery/view_photo.php?set_albumName=Calculus&id=ana_earth_from_moon_1_29
Another kind of phenomenon is the moon analemma
Look at this shot:
http://www.shatters.net/gallery/view_photo.php?set_albumName=Calculus&id=Moon_analemma_from_North_East_USA_June_2002_comet_7P_Pons_Winnecke_string
Actually, the shape of the trajectory can be very different one month to another.
http://www.shatters.net/gallery/view_photo.php?set_albumName=Calculus&id=ana_earth_from_moon_1_29
Another kind of phenomenon is the moon analemma
Look at this shot:
http://www.shatters.net/gallery/view_photo.php?set_albumName=Calculus&id=Moon_analemma_from_North_East_USA_June_2002_comet_7P_Pons_Winnecke_string
---Paul
My Gallery of Celestial Phenomena:
http://www.celestiaproject.net/gallery/view_al ... e=Calculus
My Gallery of Celestial Phenomena:
http://www.celestiaproject.net/gallery/view_al ... e=Calculus
granthutchison wrote:You can fix the Moon's orientation by replacing its definition in solarsys.ssc. The current definition reads:
Many thanks! But if I put that code into the solarsys.ssc, all planets disappear that comes after Earth in the file. something bad with that data, maybe the old version does not recognise some parts. now downloading the newest version.
I'm curious to see what the real situation is with that old Earth.
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granthutchison wrote:Oops. Are using 1.2.4? It was only after that that EquatorAscendingNode was introduced, so that may be the cause of your problem. Sorry, I should have anticipated that.
Grant
absolutely no problem. it was a lesson about backups :)
anyway, i had 1.2.5
now i have 1.3.0
Earth is much more lazy now :))
thx, pal!!