[extropy-chat] Question for Amara

Henrique Moraes Machado hemm at openlink.com.br
Tue Apr 12 13:30:00 UTC 2005

Thank you. This is the kind of scenery I was thinking of.

----- Original Message ----- 
From: ""Hal Finney"" <hal at finney.org>
To: <extropy-chat at lists.extropy.org>
Sent: Monday, April 11, 2005 6:00 PM
Subject: Re: [extropy-chat] Question for Amara

> Henrique writes:
> > Amara, since you're an astronomer, I think you would be the most
> > appropriate person to ask.  A hypothetical question. If our planet had
> > rings, how would (if...) they be viewed from the surface? Would they
> > glow at night? Would they be dark bands in the sky? Would they shadow
> > the sunlight and affect the climate?
> I am not Amara but I will offer some speculations.  Suppose we had a
> Saturn-like ring system around our planet.  What would it look like?
> The rings would probably orbit in a plane near to but not exactly the
> same as the equator.  This would cause their appearance to be different
> from different spots on the Earth.  Directly beneath the ring plane,
> they would not be visible because they are too thin from that angle.
> >From the more distant latitudes, they would be viewed from an oblique
> angle and should be relatively visible.  From the poles they might not
> be visible though, being below the horizon.
> Generally, the ring plane and the equatorial plane would both be fixed
> relative to the distant stars.  However, if this hypothetical Earth,
> like ours, had inclined poles, the appearance of the rings would change
> during the year.
> There would be two factors.  One is the angle of the ring plane with
> respect to the ecliptic, the plane of the Earth's orbit around the sun.
> This would cause the sun's angle with respect to the rings to change
> during the year.  When the sun was aligned with the ring plane, they
> would be invisible, which would happen twice a year.  3 months later the
> sun would be at maximum angle from the ring plane and the rings would
> be at their brightest.
> The other factor arises if the ring plane is different from the equatorial
> plane.  During the course of the year, the time of day at which a given
> observer is at maximum angle from the rings would change.  So at some
> times of year the rings would be more visible at sunrise and at other
> times they would be more visible at sunset.  These two year-based effects
> would interact in a complicated way causing the ring's visibility from
> different points on the Earth to vary from season to season.
> I'd imagine that the rings would not be visible during mid day, the sun
> being too bright.  They would be most noticeable just before sunrise and
> after sunset, when much of the rings would be illuminated overhead.
> If the rings are as big as Saturn's and extend several planetary
> diameters out, then portions of them should be visible all night long.
> The Earth's shadow will block out the overhead portion at midnight,
> but parts should still be visible rising in the east and the west,
> at least in middle latitudes.
> The rings would be whatever color the dust is they are made of, probably
> grayish like the moon.  Against the dark night sky they would look bright
> white and colorless, like a full moon overhead.  At the horizons they
> would shade into an orangeish color.
> I suspect that the shadowing effects of the rings would have some limited
> localized affect on climate.  Certain latitudes might consistently
> find that their noontime winter sun had to shine through the rings.
> Even if the rings were low density and this effect were small, it could
> still change the temperature profile and cause localized adaptations by
> planet and animal life.
> All in all the rings would be a remarkable sight, one which would probably
> have made a big difference in the historical course of understanding
> astronomy.  The Earth's shadow would be visible every night in a very
> obvious way, more so than the occasional lunar eclipse.  The change in
> visibility with different latitudes would also be more conspicuous than
> the variation in sun angles we are stuck with, and would point to the
> roundness of the Earth.
> Hal
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