Paul Clark

Hi

At ~ 15:30 yesterday (26/12) I noticed the moon low on the NE horizon, 'full
moon' had occured ~ 25 mins earlier.

On turning around I could see the sun low down in the SW.

I was therefore able to see the post-opposition moon and the sun at the
'same' time.

Is this a common occurence? Is this phenomenon a manifestation of the
differing orbital planes of the objects involved??

Regards
Paul

Mike Dworetsky

"Paul Clark" <dr.clark@dial.pipex.com> wrote in message
news:41d0628a$0$27827$cc9e4d1f@news.dial.pipex.com ...
> Hi
>
> At ~ 15:30 yesterday (26/12) I noticed the moon low on the NE horizon,
'full
> moon' had occured ~ 25 mins earlier.
>
> On turning around I could see the sun low down in the SW.
>
> I was therefore able to see the post-opposition moon and the sun at the
> 'same' time.
>
> Is this a common occurence? Is this phenomenon a manifestation of the
> differing orbital planes of the objects involved??
>
> Regards
> Paul
>
>

The definition of Full Moon is when the longitude of the Moon is 180 degrees
from the longitude of the Sun. But the Moon's orbit is inclined by nearly 6
degrees and it was N of the ecliptic at that time, so (especially in higher
northern latitudes such as in the UK) in these circumstances, the formally
defined Full Moon would be above the horizon before the Sun set below it.

Close examination of the Full Moon would reveal that there was a terminator,
shadows, etc along one side, i.e., the disk was not 100% illuminated.


--
Mike Dworetsky

(Remove "pants" spamblock to send e-mail)

Yokel

"Paul Clark" <dr.clark@dial.pipex.com> wrote in message
news:41d0628a$0$27827$cc9e4d1f@news.dial.pipex.com ...
| Hi
|
| At ~ 15:30 yesterday (26/12) I noticed the moon low on the NE horizon,
'full
| moon' had occured ~ 25 mins earlier.
|
| On turning around I could see the sun low down in the SW.
|
| I was therefore able to see the post-opposition moon and the sun at the
| 'same' time.
|
| Is this a common occurence? Is this phenomenon a manifestation of the
| differing orbital planes of the objects involved??
|

There are two effects here:

1) Our good friend refraction, which causes objects near the horizon to
appear between 0.5 and 1 degree above their "real" positions.

2) The moon's orbit is inclined to the ecliptic (plane of earth's orbit
round the sun) by about 5 degrees. The "nodes", or points where the orbital
planes intersect precess by a whole revolution in about 18-19 years (which
is why the times of year when eclipses take place drift earlier from year to
year). At the present time, the nodes are located such that the moon's
orbit is north of the ecliptic in the direction of Gemini and south of it in
the direction of Sagittarius, so the moon currently swings north and south
in declination through a greater range than the sun. This would be
especially noticeable from places such as Orkney and Shetland where in
midwinter the full moon will hardly set and in summer the full moon will
barely appear at all. In about 10 years time the opposite situation will
apply and you will have to be well north of the Arctic Circle to see the
"Midday (full) Moon" near the winter solstice.

So the moon is both several degrees north of the position directly opposite
of the sun and appears a little higher in the sky than it should (as does
the sun). At the solstices the ecliptic plane also makes the shallowest
angle with the horizon at sunrise/sunset, making the effect of the full moon
being north or south of it as great as possible. All these effects are
adding together to make possible the effect you observed.

The extreme north declination of the moon is heading for a maximum in the
next year or two, after which it will decrease. So you should be able to
see this effect at this time of year for a few years, then it will no longer
be possible for a decade or so as the moon will not go far enough north to
allow it. But instead for a time you may notice a similar effect with the
midsummer full moon.

In the intervening years, when eclipses take place near midsummer and
midwinter, the full moon will pass north of the antisolar postion at one
equinox and south of it at the other, but because the plane of the ecliptic
is at a steeper angle to the horizon at these times, the effect of the moon
being north or south of it will be less noticeable than at other times.
This is also an effect which is much less noticeable at the equator but has
its greatest effect near the Arctic and Antarctic circles where it is
possible to have the midnight sun and the full moon or to see neither
depending on location and the state of precession of the moon's orbit.
--
- Yokel -
oo oo
OOO OOO
OO 0 OO
) ( I ) (
) ( /\ ) (

"Yokel" now posts via a spam-trap account.
Replace my alias with stevejudd to reply.

Dr John Stockton

JRS: In article <cqrdhd$1ag$1@hercules.btinternet.com>, dated Tue, 28
Dec 2004 10:46:05, seen in news:uk.sci.astronomy, Mike Dworetsky
<platinum198@pants.btinternet.com> posted :
>
>The definition of Full Moon is when the longitude of the Moon is 180 degrees
>from the longitude of the Sun. But the Moon's orbit is inclined by nearly 6
>degrees and it was N of the ecliptic at that time, so (especially in higher
>northern latitudes such as in the UK) in these circumstances, the formally
>defined Full Moon would be above the horizon before the Sun set below it.


I don't think that we ever decided here how nearly circumpolar the Moon
could be from the UK - the next chance seems to be sometime in 2006, so
now should be a good time to start thinking.

--
© John Stockton, Surrey, UK. ?@merlyn.demon.co.uk Turnpike v4.00 MIME. ©
Web <URL:http://www.merlyn.demon.co.uk/> - w. FAQish topics, links, acronyms
PAS EXE etc : <URL:http://www.merlyn.demon.co.uk/programs/> - see 00index.htm
Dates - miscdate.htm moredate.htm js-dates.htm pas-time.htm critdate.htm etc.

Charles Gilman

A third factor is the human eye and brain. A shape must deviate
substantially from a true circle before it stops looking like one.

"Yokel" <yokel@surefish.co.uk> wrote in message
news:33e1nqF3q4f2tU3@individual.net...
>
> There are two effects here:
>
> 1) Our good friend refraction, which causes objects near the horizon
to
> appear between 0.5 and 1 degree above their "real" positions.
>
> 2) The moon's orbit is inclined to the ecliptic (plane of earth's orbit
> round the sun) by about 5 degrees. The "nodes", or points where the
orbital
> planes intersect precess by a whole revolution in about 18-19 years (which
> is why the times of year when eclipses take place drift earlier from year
to
> year). At the present time, the nodes are located such that the moon's
> orbit is north of the ecliptic in the direction of Gemini and south of it
in
> the direction of Sagittarius, so the moon currently swings north and south
> in declination through a greater range than the sun. This would be
> especially noticeable from places such as Orkney and Shetland where in
> midwinter the full moon will hardly set and in summer the full moon will
> barely appear at all. In about 10 years time the opposite situation will
> apply and you will have to be well north of the Arctic Circle to see the
> "Midday (full) Moon" near the winter solstice.
>
> So the moon is both several degrees north of the position directly
opposite
> of the sun and appears a little higher in the sky than it should (as does
> the sun). At the solstices the ecliptic plane also makes the shallowest
> angle with the horizon at sunrise/sunset, making the effect of the full
moon
> being north or south of it as great as possible. All these effects are
> adding together to make possible the effect you observed.
>
> The extreme north declination of the moon is heading for a maximum in the
> next year or two, after which it will decrease. So you should be able to
> see this effect at this time of year for a few years, then it will no
longer
> be possible for a decade or so as the moon will not go far enough north to
> allow it. But instead for a time you may notice a similar effect with the
> midsummer full moon.
>
> In the intervening years, when eclipses take place near midsummer and
> midwinter, the full moon will pass north of the antisolar postion at one
> equinox and south of it at the other, but because the plane of the
ecliptic
> is at a steeper angle to the horizon at these times, the effect of the
moon
> being north or south of it will be less noticeable than at other times.
> This is also an effect which is much less noticeable at the equator but
has
> its greatest effect near the Arctic and Antarctic circles where it is
> possible to have the midnight sun and the full moon or to see neither
> depending on location and the state of precession of the moon's orbit.
> --
> - Yokel -

Yokel

"Dr John Stockton" <spam@merlyn.demon.co.uk> wrote in message
news:CzoMQ4SZce0BFw8S@merlyn.demon.co.uk...
| JRS: In article <cqrdhd$1ag$1@hercules.btinternet.com>, dated Tue, 28
| Dec 2004 10:46:05, seen in news:uk.sci.astronomy, Mike Dworetsky
| <platinum198@pants.btinternet.com> posted :
| >
| >The definition of Full Moon is when the longitude of the Moon is 180
degrees
| >from the longitude of the Sun. But the Moon's orbit is inclined by
nearly 6
| >degrees and it was N of the ecliptic at that time, so (especially in
higher
| >northern latitudes such as in the UK) in these circumstances, the
formally
| >defined Full Moon would be above the horizon before the Sun set below it.
|
|
| I don't think that we ever decided here how nearly circumpolar the Moon
| could be from the UK - the next chance seems to be sometime in 2006, so
| now should be a good time to start thinking.
|

The inclination of the Moon's orbit to the Ecliptic is about 5 degrees.
Therefore under the most favourable conditions you have to be above 60 deg N
or S to see the moon as "Circumpolar" (refraction adds a bit to the 5
degrees). Shetland and Fair Isle may qualify, Orkney distinctly marginal,
the British Mainland (which is less than 59 deg N) will not. However, from
northern Scotland it will be noticeable for the next few winters how little
time the December full moon spends below the horizon.
--
- Yokel -
oo oo
OOO OOO
OO 0 OO
) ( I ) (
) ( /\ ) (

"Yokel" now posts via a spam-trap account.
Replace my alias with stevejudd to reply.

Dr John Stockton

JRS: In article <33jl1aF428atjU1@individual.net>, dated Fri, 31 Dec
2004 00:33:08, seen in news:uk.sci.astronomy, Yokel
<yokel@surefish.co.uk> posted :
>
>"Dr John Stockton" <spam@merlyn.demon.co.uk> wrote in message
>news:CzoMQ4SZce0BFw8S@merlyn.demon.co.uk...

>| I don't think that we ever decided here how nearly circumpolar the Moon
>| could be from the UK - the next chance seems to be sometime in 2006, so
>| now should be a good time to start thinking.
>|
>
>The inclination of the Moon's orbit to the Ecliptic is about 5 degrees.
>Therefore under the most favourable conditions you have to be above 60 deg N
>or S to see the moon as "Circumpolar" (refraction adds a bit to the 5
>degrees). Shetland and Fair Isle may qualify, Orkney distinctly marginal,
>the British Mainland (which is less than 59 deg N) will not. However, from
>northern Scotland it will be noticeable for the next few winters how little
>time the December full moon spends below the horizon.

ISTR we already got further than that. Orkney seems out, Fair Isle is
scarcely further north. In Shetland, Muckle Flugga is at 60 deg 51' N,
and, ISTR, has or had a lighthouse. With 23.5 deg tilt + 5 deg tilt,
one needs to be at 68.5 deg, subtract for height and refraction, and it
looks hopeful, on the dubious assumption of fine weather[*]. But one
must also consider the radii : Earth 4000 mi, Moon 1000 mi, difference
3000 mi at 240000 mi which is 1 in 80 or about 0.7 deg adverse effect.

We may need first to invade the Faeroes; that gains well over a degree.

[*] What's the tide there when the Full Moon is to the North? Low tide
would help.

--
© John Stockton, Surrey, UK. ?@merlyn.demon.co.uk Turnpike v4.00 MIME. ©
Web <URL:http://www.merlyn.demon.co.uk/> - FAQqish topics, acronyms & links;
some Astro stuff via astro.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

Grimble Gromble

"Dr John Stockton" <spam@merlyn.demon.co.uk> wrote in message
news:FWXdp$XjKa1BFw3M@merlyn.demon.co.uk...
> JRS: In article <33jl1aF428atjU1@individual.net>, dated Fri, 31 Dec
> 2004 00:33:08, seen in news:uk.sci.astronomy, Yokel
> <yokel@surefish.co.uk> posted :
>>
>>"Dr John Stockton" <spam@merlyn.demon.co.uk> wrote in message
>>news:CzoMQ4SZce0BFw8S@merlyn.demon.co.uk...
>
>>| I don't think that we ever decided here how nearly circumpolar the Moon
>>| could be from the UK - the next chance seems to be sometime in 2006, so
>>| now should be a good time to start thinking.
>>|
>>
>>The inclination of the Moon's orbit to the Ecliptic is about 5 degrees.
>>Therefore under the most favourable conditions you have to be above 60 deg
>>N
>>or S to see the moon as "Circumpolar" (refraction adds a bit to the 5
>>degrees). Shetland and Fair Isle may qualify, Orkney distinctly marginal,
>>the British Mainland (which is less than 59 deg N) will not. However,
>>from
>>northern Scotland it will be noticeable for the next few winters how
>>little
>>time the December full moon spends below the horizon.
>
> ISTR we already got further than that. Orkney seems out, Fair Isle is
> scarcely further north. In Shetland, Muckle Flugga is at 60 deg 51' N,
> and, ISTR, has or had a lighthouse. With 23.5 deg tilt + 5 deg tilt,
> one needs to be at 68.5 deg, subtract for height and refraction, and it
> looks hopeful, on the dubious assumption of fine weather[*]. But one
> must also consider the radii : Earth 4000 mi, Moon 1000 mi, difference
> 3000 mi at 240000 mi which is 1 in 80 or about 0.7 deg adverse effect.
>
> We may need first to invade the Faeroes; that gains well over a degree.
>
>
>[*] What's the tide there when the Full Moon is to the North? Low tide
> would help.

Are you sure? High tide would add a few metres of altitude.
Grim

Dr John Stockton

JRS: In article <ncmBd.227$RE.206@newsfe2-win.ntli.net>, dated Sat, 1
Jan 2005 00:32:19, seen in news:uk.sci.astronomy, Grimble Gromble
<grimble.gromble@virgin.net> posted :
>>
>> ISTR we already got further than that. Orkney seems out, Fair Isle is
>> scarcely further north. In Shetland, Muckle Flugga is at 60 deg 51' N,
>> and, ISTR, has or had a lighthouse. With 23.5 deg tilt + 5 deg tilt,
>> one needs to be at 68.5 deg, subtract for height and refraction, and it
>> looks hopeful, on the dubious assumption of fine weather[*]. But one
>> must also consider the radii : Earth 4000 mi, Moon 1000 mi, difference
>> 3000 mi at 240000 mi which is 1 in 80 or about 0.7 deg adverse effect.
>>
>> We may need first to invade the Faeroes; that gains well over a degree.
>>
>>
>>[*] What's the tide there when the Full Moon is to the North? Low tide
>> would help.
>
>Are you sure? High tide would add a few metres of altitude.

AIUI, it's a lighthouse, not a lightship. One wants the northern
horizon to be lowered.

If one were to row out to the limit of territorial waters, the tidal
state would be unimportant; 12 miles would not help much, but 200 miles
is three degrees.


On a different tack, I see that someone in .fr has telescopically
photographed ISS in transit across the Full Moon.

--
© John Stockton, Surrey, UK. ?@merlyn.demon.co.uk Delphi 3 Turnpike 4 ©
<URL:http://www.merlyn.demon.co.uk/> TP/BP/Delphi/&c., FAQqy topics & links;
<URL:http://www.bancoems.com/CompLangPascalDelphiMisc-MiniFAQ.htm> clpdmFAQ;
<URL:http://www.borland.com/newsgroups/guide.html> news:borland.* Guidelines

Grimble Gromble

"Dr John Stockton" <spam@merlyn.demon.co.uk> wrote in message
news:eOhbPqa4Ex1BFwEE@merlyn.demon.co.uk...
> JRS: In article <ncmBd.227$RE.206@newsfe2-win.ntli.net>, dated Sat, 1
> Jan 2005 00:32:19, seen in news:uk.sci.astronomy, Grimble Gromble
> <grimble.gromble@virgin.net> posted :
>>>
>>> ISTR we already got further than that. Orkney seems out, Fair Isle is
>>> scarcely further north. In Shetland, Muckle Flugga is at 60 deg 51' N,
>>> and, ISTR, has or had a lighthouse. With 23.5 deg tilt + 5 deg tilt,
>>> one needs to be at 68.5 deg, subtract for height and refraction, and it
>>> looks hopeful, on the dubious assumption of fine weather[*]. But one
>>> must also consider the radii : Earth 4000 mi, Moon 1000 mi, difference
>>> 3000 mi at 240000 mi which is 1 in 80 or about 0.7 deg adverse effect.
>>>
>>> We may need first to invade the Faeroes; that gains well over a degree.
>>>
>>>
>>>[*] What's the tide there when the Full Moon is to the North? Low tide
>>> would help.
>>
>>Are you sure? High tide would add a few metres of altitude.
>
> AIUI, it's a lighthouse, not a lightship. One wants the northern
> horizon to be lowered.
>
> If one were to row out to the limit of territorial waters, the tidal
> state would be unimportant; 12 miles would not help much, but 200 miles
> is three degrees.

I was actually referring to the tidal movement of the ground, not the water.
A larger tide would increase the angle between the ground and the earth's
spin axis, equivalent to a tiny (very very tiny) increase in latitude.
Surely anything is better than invading the Faeroes?
Grim

Charles Gilman

Firstly, there is no noticeable movement of the ground due to tides. If it
moves at all, the far greater movement of the sea described by Dr. Stockton
counteracts the advantages. Secondly, an increase in angle to the axis means
a decrease in latitude. The poles are on the axis, and the maximum angle to
the axis is at the equator.

"Grimble Gromble" <grimble.gromble@virgin.net> wrote in message
news:4nQBd.238$JM.99@newsfe1-gui.ntli.net...
>
> I was actually referring to the tidal movement of the ground, not the
water.
> A larger tide would increase the angle between the ground and the earth's
> spin axis, equivalent to a tiny (very very tiny) increase in latitude.
> Surely anything is better than invading the Faeroes?
> Grim

Grimble Gromble

There is movement of the ground due to tides and though you don't notice it,
it is of the order of a metre (anything from a half to a few - but somewhere
in that ballpark).

The angle I was referring to was that between the rotational axis and the
plane of the ground's surface which does increase under increasing tidal
forces. The surface of the ground at the poles is perpendicular to the axis
(90 deg latitude and 90 deg angle). That at the equator (0 deg latitude and
0 deg angle) is parallel to the axis. Tidal forces tend to tilt the
direction of the ground surface closer to the direction of the ground
surface at the poles - equivalent to an increase in latitude though bringing
the ground closer to the plane of the equator (more oblate). The reverse is
true at 'low tide'.
Grim

"Charles Gilman" <charles@gilman-ebr.freeserve.co.uk> wrote in message
news:crausl$8t2$1@newsg3.svr.pol.co.uk...
> Firstly, there is no noticeable movement of the ground due to tides. If it
> moves at all, the far greater movement of the sea described by Dr.
> Stockton
> counteracts the advantages. Secondly, an increase in angle to the axis
> means
> a decrease in latitude. The poles are on the axis, and the maximum angle
> to
> the axis is at the equator.
>
> "Grimble Gromble" <grimble.gromble@virgin.net> wrote in message
> news:4nQBd.238$JM.99@newsfe1-gui.ntli.net...
>>
>> I was actually referring to the tidal movement of the ground, not the
> water.
>> A larger tide would increase the angle between the ground and the earth's
>> spin axis, equivalent to a tiny (very very tiny) increase in latitude.
>> Surely anything is better than invading the Faeroes?
>> Grim
>
>