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Date: 12 Aug 2006 23:58:55
From: Imagicka
Subject: A couple of questions.
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Greetings...
I have a question or two...
First: Why is it that we only see one side of the moon? That would
mean that it's rotational orbit around itself...is the same length of
time that it takes to orbit around the earth. Which is what? 28.1 days
or something like that? -- Is this why people think that the moon was
once a part of the earth? Are there anymore natural satellites (moons)
around other planets that have the same feature? -- Is there a site
with charts of these orbital information?
Also, is there a list of the number of stars that we can see in the
night's sky, charted by light polution? How many can we see in the
night's sky with the naked eye?
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Date: 13 Aug 2006 07:48:26
From: William Hamblen
Subject: Re: A couple of questions.
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On 12 Aug 2006 23:58:55 -0700, "Imagicka" <Imagicka23@gmail.com >
wrote:
>Are there anymore natural satellites (moons)
>around other planets that have the same feature? -- Is there a site
>with charts of these orbital information?
Nearly all of the satellites where astronomers have been able to
measure rotational periods have rotational periods the same as the
orbital periods. The reason is that the effects of the tides over a
long enough time will make the rotation the sane as the revolution.
See
http://nssdc.gsfc.nasa.gov/planetary/planetfact.html
for links to tables of data on planets and their satellites.
Bud
--
The night is just the shadow of the Earth.
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Date: 13 Aug 2006 05:36:04
From: AustinMN
Subject: Re: A couple of questions.
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Imagicka wrote:
> Greetings...
>
> I have a question or two...
>
> First: Why is it that we only see one side of the moon? That would
> mean that it's rotational orbit around itself...is the same length of
> time that it takes to orbit around the earth.
This was not always the case. It has become like it is because tidal
forces (caused by the earth on the moon) have caused it to slow to this
point. It will stay locked like this until acted on by some outside
force.
> Is this why people think that the moon was
> once a part of the earth?
No.
> Are there anymore natural satellites (moons)
> around other planets that have the same feature?
To the best of my knowledge, every moon of every planet in the solar
system has a rotational period that equals its orbital period.
Austin
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Date: 13 Aug 2006 00:59:28
From: DrBZU
Subject: Re: A couple of questions.
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The moon presents only one face to the Earth due to spin-orbit
coupling. This is a similar effect to the tides which are raised on
Earth due to the moons gravitational pull. The Earth exerts a tidal
effect on the moon too, but since the moons surface does not flow, its
spin gradually changes over many millions of years.
Imagicka wrote:
> Greetings...
>
> I have a question or two...
>
> First: Why is it that we only see one side of the moon? That would
> mean that it's rotational orbit around itself...is the same length of
> time that it takes to orbit around the earth. Which is what? 28.1 days
> or something like that? -- Is this why people think that the moon was
> once a part of the earth? Are there anymore natural satellites (moons)
> around other planets that have the same feature? -- Is there a site
> with charts of these orbital information?
>
> Also, is there a list of the number of stars that we can see in the
> night's sky, charted by light polution? How many can we see in the
> night's sky with the naked eye?
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Date: 13 Aug 2006 14:36:10
From: Greg Crinklaw
Subject: Re: A couple of questions.
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DrBZU wrote:
> The moon presents only one face to the Earth due to spin-orbit
> coupling. This is a similar effect to the tides which are raised on
> Earth due to the moons gravitational pull. The Earth exerts a tidal
> effect on the moon too, but since the moons surface does not flow, its
> spin gradually changes over many millions of years.
I don't think is has anything to so with "flowing surfaces." It's more
a matter of which of the Earth or Moon has the most mass (and therefore
momentum). The spin of the earth *is* changing due to this arrangement,
only more slowly.
Greg
--
Greg Crinklaw
Astronomical Software Developer
Cloudcroft, New Mexico, USA (33N, 106W, 2700m)
SkyTools: http://www.skyhound.com/cs.html
Observing: http://www.skyhound.com/sh/skyhound.html
Comets: http://www.skyhound.com/sh/comets.html
To reply take out your eye
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Date: 13 Aug 2006 07:31:22
From: Eugene Griessel
Subject: Re: A couple of questions.
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"Imagicka" <Imagicka23@gmail.com > wrote:
>First: Why is it that we only see one side of the moon? That would
>mean that it's rotational orbit around itself...is the same length of
>time that it takes to orbit around the earth. Which is what? 28.1 days
>or something like that? -- Is this why people think that the moon was
>once a part of the earth? Are there anymore natural satellites (moons)
>around other planets that have the same feature? -- Is there a site
>with charts of these orbital information?
The moon is just a little too close and a little to small to break
free of the earth's gravity and establish an independent rotation.
Basically it is trapped or locked by the earth in the axial rotation
it now finds itself in. And I guess the same conditions would apply
to other moons in the same sort of position.
>
>Also, is there a list of the number of stars that we can see in the
>night's sky, charted by light polution? How many can we see in the
>night's sky with the naked eye?
It depends on a number of factors - where you are being the first -
not only location but altitude and time, secondly your personal visual
acuity and thirdly pollution factors other than light such as aerosols
and smoke.
Obtain a list of stars ranked according to their visual magnitude -
tick of those observable from your personal viewing site, a
planisphere is helpful here or one of the many computer programs
available. Then start working your way upwards from the 6th magnitude
stars (or downward from 1st magnitudes) until you can see one - and
the rest should then be naked-eye visible. Given fair conditions you
should be able to see around 2000 - but in a modern urban environment
this could be lower than 200!
Eugene L Griessel
Never test for an error condition you don't know how to handle.
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Date: 13 Aug 2006 15:02:00
From: Bob May
Subject: Re: A couple of questions.
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The number of stars visible depends upon the obscuring effects of the sky.
The stars are listed with their magnitude (brightness of the star - charts
show stars as different sized according to their magnitude) and you can look
at a sky and see what stars are visible and that determines the cutoff point
of the sky's stars at that time.
--
Why do penguins walk so far to get to their nesting grounds?
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Date: 14 Aug 2006 01:51:48
From: Eugene Griessel
Subject: Re: A couple of questions.
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"Bob May" <bobmay@nethere.com > wrote:
>Why do penguins walk so far to get to their nesting grounds?
Tradition - and it's only the emperors that do it. Other penguins are
content to reproduce without the walk.
Eugene L Griessel
INDECISION is the key to FLEXIBILITY.
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Date: 14 Aug 2006 14:16:08
From: Dave
Subject: Re: A couple of questions.
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Although it is a long walk in the winter, in the spring when the
offspring leave to the water it is a short journey because the ice pathway
has melted. I wonder if it is because they need a safe nursery platform, so
their offspring would not be facing an early dip in water before they are
ready. It sounds like one of the great dangers is leopard seals, so a
controlled delay in entry to water would be an advantage. They all leave for
the water as a group, which should offer some form of 'heard protection'
(only so many chicks a seal can eat at one time). If penguins camped
adjacent to water, then the seals would have an easier time capturing more
chicks over a longer period of time.
I've never been to Antarctica, and don't know if more stable ground is
easily available.
Dave
"Eugene Griessel" <eugene@dynagen..co..za > wrote in message
news:44dfd6dc.322299@news.uunet.co.za...
> "Bob May" <bobmay@nethere.com> wrote:
>
>>Why do penguins walk so far to get to their nesting grounds?
>
> Tradition - and it's only the emperors that do it. Other penguins are
> content to reproduce without the walk.
>
> Eugene L Griessel
>
> INDECISION is the key to FLEXIBILITY.
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Date: 14 Aug 2006 20:44:45
From: Brian Tung
Subject: Re: A couple of questions.
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Imagicka wrote:
> First: Why is it that we only see one side of the moon? That would
> mean that it's rotational orbit around itself...is the same length of
> time that it takes to orbit around the earth. Which is what? 28.1 days
> or something like that? -- Is this why people think that the moon was
> once a part of the earth? Are there anymore natural satellites (moons)
> around other planets that have the same feature? -- Is there a site
> with charts of these orbital information?
That's an involved question with a longish answer. Here was my original
take on it, and I don't have much reason to change it:
http://astro.isi.edu/notes/tides.html
Actually, most people no longer think the Moon was part of the Earth,
at least not in the simplistic sense where the proto-Earth splits into
two parts, with one of the parts becoming the Moon. The most popular
theory these days is that another large body struck the Earth early in
its history, and part of the impact ejecta coalesced to form the Moon.
The rest of it settled back down into the Earth, or was thrown out of
orbit entirely.
> Also, is there a list of the number of stars that we can see in the
> night's sky, charted by light polution? How many can we see in the
> night's sky with the naked eye?
About 9,000 stars can be seen down to magnitude 6.5. That number goes
down by about a factor of three for every magnitude below that, so (for
instance), about 3,000 stars can be seen down to magnitude 5.5, about
1,000 down to magnitude 4.5, etc. That isn't a perfect fit to the
actual counts, but it's close enough for government work. :)
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
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Date: 14 Aug 2006 09:27:16
From: Morris Jones
Subject: Re: A couple of questions.
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Imagicka wrote:
> Also, is there a list of the number of stars that we can see in the
> night's sky, charted by light polution? How many can we see in the
> night's sky with the naked eye?
Sky & Telescope had an article on the subject a few years ago. I'd love
to have a reprint of it myself. It varies quite a bit by season and
latitude, but if I recall correctly it comes out to roughly 1,700
visible on a typical evening from a very good location.
On a typical Los Angeles evening it might about 20. :)
Mojo
--
Morris Jones
Monrovia, CA
http://www.whiteoaks.com
Old Town Astronomers http://www.otastro.org
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Date: 15 Aug 2006 09:01:47
From: Helpful person
Subject: Re: A couple of questions.
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Imagicka wrote:
>
> Also, is there a list of the number of stars that we can see in the
> night's sky, charted by light polution? How many can we see in the
> night's sky with the naked eye?
Is the red shift still thought to be responsible for the night sky
being dark?
Please visit my web site at www.richardfisher.com
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