Transits of earth viewed from Neptune & Uranus

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Transits of earth viewed from Neptune & Uranus

Postby jeffbee » Mon Jun 28, 2010 5:16 pm

Can anyone help please? According to my purchased copy of CyberSky 4, the Earth's shadow will by 'pointing' in the direction of Neptune early on August 21st 2010, and Uranus early on Sept 22nd 2010.
I would therefore expect that viewed from these planets, the Earth would be seen to transit the Sun. I have searched on t'internet and have retrieved no info regarding these transits.
Am I misunderstanding somehow or has it been overlooked?
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RE: Transits of earth viewed from Neptune & Uranus

Postby uea74 » Mon Jun 28, 2010 9:10 pm

Surely only to astronomers/observers on Neptune and Uranus would it be relevant, why would we report it here? It seems pretty irelevant as we cannot see it. The shadow would have to point directly at Neptune and Uranus not just towards them. The angles involved are very small a transit of the earth as seen from either planet must be very rare. If Neptune or Uranus are out of the plane of the ecliptic by much then never.

The distances are so vast that the penumbra would have no effect in shadowing either planet, unlike when the moon falls into the earths shadow.

Thinking about it any planet on the same side of the sun as us could "see" a transit of the earth, so that's Mars, Jupiter ans Saturn. Since the sun will be significantly bigger, they are closer, then there is more chance of observing one from them.

Also if you ignore planets the earth will always be performing a transit when observed from some point outside of the earths orbit. The observer may simply be in free space and not on a planet but would see a transit.

I suppose you experience a transit of the earth across the sun every night. It gets between you and the sun. Difference being that the angle subtended by the earth from your position is big enough to completely cover the sun.
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RE: Transits of earth viewed from Neptune & Uranus

Postby jeffbee » Tue Jun 29, 2010 3:13 pm

Thanks UAE74 - as there are no people on/near these planets as yet, it may not be [u]totally[/u] relevent, but just to be aware that Earth is in that position from these planets I find a little interesting, just like knowing that the sun if seen from Proxima Centauri, would appear as a bright, 0.4 magnitude star in the constellation Cassiopeia.
I know pics of Earth have been taken from spacecraft near Saturn - would be interesting if one could be taken from near these planets - regards.
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RE: Transits of earth viewed from Neptune & Uranus

Postby uea74 » Tue Jun 29, 2010 8:13 pm

Problem is that the sun would only subtend an angle of 0.0178 degrees from Neptune. The equivalent of 1mtr at 3.2Km. So the earth would have to cross this small disk exactly across the centre. I would not be surprised if the different angles that we circle the sun would mean that Neputune would never see a transit of the earth. The 3 bodies would have to line up to within 0.0178 deg to do so.

The sun may be a 0.4 mag star from Proxima Centurai but Cassiopeia wouldn't be Cassiopeia. It would be a different shape for an observer there, and what "constellation" our sun may be part of I cannot say.

The pole star at the time of ancient Egypt was not polaris as an example, and many constellations were different. Think that wikipedia shows what was polaris then, now and in a few thousand years and how the plough will alter.
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RE: Transits of earth viewed from Neptune & Uranus

Postby les » Thu Jul 01, 2010 10:50 am

HI There,
Ive checked out the skies from Alpha Centauri using Starry Night Backyard,and the thing that strikes you is, on the whole Earth based observers would still find most of the star patterns recognisable.The Sun is located in Cassiopea close to the border with Perseus(both groups still seem familiar albeit slightly distorted).The great constellatins such as Ursa Major,Orion,Cygnus and Ursa Minor are virtually unscathed.Of course the parallaxed veiw means that their are changes,for instance Arcturus has drifted north giving Bootes a very squat appearance.Procyon is in the middle of Gemini,which is a more scattered group, but Castor and Pollux are much closer together.Aldebaran is shifted within the Hyades giving Taurus a slightly boss eyed look.[:D]Altair is in Vulpecula.The biggest shock however is seeing Sirius near Betelgeuse!I think the biggest problem for a Earthling astronomer residing on a Centaurian planet wont be finding their way around but having two Solar like suns in the sky!
Regards Les.
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RE: Transits of earth viewed from Neptune & Uranus

Postby jeffbee » Thu Jul 01, 2010 3:00 pm

2 suns would be very interesting - more eclipses then, I would expect. Thanks les.
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