precession

Seeing the previous posts mentioning Precession prompted me to wonder what
is the actual lowest star we can see from a certain location over the full
precession cycle.
for example I know that Vega gets close to the pole in the cycle so I think
this much mean that stars around the same Right ascension would be higher in
the sky than now and thus lower stars that are currenly too far south to
rise may do so, for example Theta Scorpio at -43% may be visible and other
stars we currently see may then be too low to see.
so if you have a latitude of 52% what would be the lowest star

it could be that I am completley wrong about this assumption.

thanks Paul

"Paul Forsdick" wrote in message
...
| Seeing the previous posts mentioning Precession prompted me to wonder what
| is the actual lowest star we can see from a certain location over the full
| precession cycle.
| for example I know that Vega gets close to the pole in the cycle so I
think
| this much mean that stars around the same Right ascension would be higher
in
| the sky than now and thus lower stars that are currenly too far south to
| rise may do so, for example Theta Scorpio at -43% may be visible and other
| stars we currently see may then be too low to see.
| so if you have a latitude of 52% what would be the lowest star
|
| it could be that I am completley wrong about this assumption.
|

Let's think it out.

Precession moves the equinox and solstice points around the entire ecliptic
once in the precession cycle. So every point on the ecliptic will at some
time be north of the celestial equator by the inclination of the earth's
axis (currently just over 23 degrees, but it does vary a degree or so either
way).

At the moment this "furthest north" point lies near the border between
Gemini and Taurus. So we in the Northern Hemisphere currently get the best
view we can of the area around Orion, and for a significant part of the
precession cycle the brightest star - Sirius - would be invisible from the
British Isles. But by a similar argument for most of the cycle Scorpio
would be further north than it is now and we currently get an unusually poor
view of it.

If you are at 52 N, you can see every star less than 38 degrees south of the
celestial equator (90 degrees - your latitude). Seeing as every part of the
ecliptic will at some time be 23 degrees north of the celestial equator, it
follows that at some time in the precessional cycle every star less than 23
+ 38 = 61 degrees south of the *ecliptic* will come into view. In some
parts of the sky this will be out a bit due to "North" and "South" being at
various times not exactly where they are now - I thought I'd better mention
it before someone else does. But if you have a star atlas with the South
Ecliptic Pole marked, or "planetarium" software which will show an ecliptic
coordinate grid, to a reasonable approximation you will (eventually) be able
to see every star more than about 30 degrees from the South Ecliptic Pole.
This is actually over 90% of the sky. [If there were no precession or the
poles were at right angles to the ecliptic place this figure would be about
80% - what we currently see throughout the year. This may seem surprising as
we are so far from the equator, but spherical geometry means that half of
the sky is within 30 degrees of the celestial equator and 71% within 45
degrees, plus we will see half of the remainder as being round the pole
nearest us.] Move 29 degrees nearer the equator so you reach the tropics,
and everywhere within the tropics you can at some point in the precessional
cycle see every star in the sky. And, of course, at the equator you see all
the stars in the sky at some time each year.

So in about 10 000 years time we will get a wonderful view of Scorpio, which
will take the place Taurus and Gemini currently occupy. At other times we
will be able to see the Southern Cross and various of the "Southern Birds".
But the area around Argo we will never see much better than we do now - we
currently get almost the best view we can of this part of the sky. And if
you want to see the Magellanic Clouds, I am afraid it is either a visit to
places south of here or a very long wait for them to "orbit" to our side of
the Galaxy...
--
- Yokel -

"Yokel" posts via a spam-trap account which is not read.

On Dec 31 2009, 11:53*pm, "Yokel"
wrote:
"Paul Forsdick" wrote in message

...
| Seeing the previous posts mentioning Precession prompted me to wonder what
| is the actual lowest star we can see from a certain location over the full
| precession cycle.
| for example I know that Vega gets close to the pole in the cycle so I
think
| this much mean that stars around the same Right ascension would be higher
in
| the sky *than now and thus lower stars *that are currenly too far south to
| rise may do so, for example Theta Scorpio at -43% may be visible and other
| stars we currently see may then be too low to see.
| so if you have a latitude of 52% what would be the lowest star
|
| it could be that I am completley wrong about this assumption.
|

Let's think it out.

Precession moves the equinox and solstice points around the entire ecliptic
once in the precession cycle. *So every point on the ecliptic will at some
time be north of the celestial equator by the inclination of the earth's
axis (currently just over 23 degrees, but it does vary a degree or so either
way).


You are all over the place but that is not surprising when you
reference everything off rotational orientation (tilt) or combine it
with the orbital motion of the Earth,in your case,you are simply a
happy astrologer regurgitating what you learned without thinking about
the topic properly.So,this is 2010 and are all going to behave like
intelligent people for a change and not like the monkeys in the late
17th century who botched everything.

Answer me this,what causes the seasonal appearance and disappearance
of the certain constellations and I mean the specifics of orbital
motion and not some 'sidereal time' junk which tries to explain the
apparent motion of the constellations around Polaris via planetary
dynamics ?.











At the moment this "furthest north" point lies near the border between
Gemini and Taurus. *So we in the Northern Hemisphere currently get the best
view we can of the area around Orion, and for a significant part of the
precession cycle the brightest star - Sirius - would be invisible from the
British Isles. *But by a similar argument for most of the cycle Scorpio
would be further north than it is now and we currently get an unusually poor
view of it.

If you are at 52 N, you can see every star less than 38 degrees south of the
celestial equator (90 degrees - your latitude). *Seeing as every part of the
ecliptic will at some time be 23 degrees north of the celestial equator, it
follows that at some time in the precessional cycle every star less than 23
+ 38 = 61 degrees south of the *ecliptic* will come into view. *In some
parts of the sky this will be out a bit due to "North" and "South" being at
various times not exactly where they are now - I thought I'd better mention
it before someone else does. *But if you have a star atlas with the South
Ecliptic Pole marked, or "planetarium" software which will show an ecliptic
coordinate grid, to a reasonable approximation you will (eventually) be able
to see every star more than about 30 degrees from the South Ecliptic Pole..
This is actually over 90% of the sky. [If there were no precession or the
poles were at right angles to the ecliptic place this figure would be about
80% - what we currently see throughout the year. This may seem surprising as
we are so far from the equator, but spherical geometry means that half of
the sky is within 30 degrees of the celestial equator and 71% within 45
degrees, plus we will see half of the remainder as being round the pole
nearest us.] Move 29 degrees nearer the equator so you reach the tropics,
and everywhere within the tropics you can at some point in the precessional
cycle see every star in the sky. *And, of course, at the equator you see all
the stars in the sky at some time each year.

So in about 10 000 years time we will get a wonderful view of Scorpio, which
will take the place Taurus and Gemini currently occupy. *At other times we
will be able to see the Southern Cross and various of the "Southern Birds".
But the area around Argo we will never see much better than we do now - we
currently get almost the best view we can of this part of the sky. *And if
you want to see the Magellanic Clouds, I am afraid it is either a visit to
places south of here or a very long wait for them to "orbit" to our side of
the Galaxy...
--
* * * * * * * * - Yokel -

"Yokel" posts via a spam-trap account which is not read.

Hi Yokel

Thanks for the detailed Information

I thought I was on the right track

paul
"Yokel" wrote in message
...
"Paul Forsdick" wrote in message
...
| Seeing the previous posts mentioning Precession prompted me to wonder
what
| is the actual lowest star we can see from a certain location over the
full
| precession cycle.
| for example I know that Vega gets close to the pole in the cycle so I
think
| this much mean that stars around the same Right ascension would be
higher
in
| the sky than now and thus lower stars that are currenly too far south
to
| rise may do so, for example Theta Scorpio at -43% may be visible and
other
| stars we currently see may then be too low to see.
| so if you have a latitude of 52% what would be the lowest star
|
| it could be that I am completley wrong about this assumption.
|

Let's think it out.

Precession moves the equinox and solstice points around the entire
ecliptic
once in the precession cycle. So every point on the ecliptic will at some
time be north of the celestial equator by the inclination of the earth's
axis (currently just over 23 degrees, but it does vary a degree or so
either
way).

At the moment this "furthest north" point lies near the border between
Gemini and Taurus. So we in the Northern Hemisphere currently get the
best
view we can of the area around Orion, and for a significant part of the
precession cycle the brightest star - Sirius - would be invisible from the
British Isles. But by a similar argument for most of the cycle Scorpio
would be further north than it is now and we currently get an unusually
poor
view of it.

If you are at 52 N, you can see every star less than 38 degrees south of
the
celestial equator (90 degrees - your latitude). Seeing as every part of
the
ecliptic will at some time be 23 degrees north of the celestial equator,
it
follows that at some time in the precessional cycle every star less than
23
+ 38 = 61 degrees south of the *ecliptic* will come into view. In some
parts of the sky this will be out a bit due to "North" and "South" being
at
various times not exactly where they are now - I thought I'd better
mention
it before someone else does. But if you have a star atlas with the South
Ecliptic Pole marked, or "planetarium" software which will show an
ecliptic
coordinate grid, to a reasonable approximation you will (eventually) be
able
to see every star more than about 30 degrees from the South Ecliptic Pole.
This is actually over 90% of the sky. [If there were no precession or the
poles were at right angles to the ecliptic place this figure would be
about
80% - what we currently see throughout the year. This may seem surprising
as
we are so far from the equator, but spherical geometry means that half of
the sky is within 30 degrees of the celestial equator and 71% within 45
degrees, plus we will see half of the remainder as being round the pole
nearest us.] Move 29 degrees nearer the equator so you reach the tropics,
and everywhere within the tropics you can at some point in the
precessional
cycle see every star in the sky. And, of course, at the equator you see
all
the stars in the sky at some time each year.

So in about 10 000 years time we will get a wonderful view of Scorpio,
which
will take the place Taurus and Gemini currently occupy. At other times we
will be able to see the Southern Cross and various of the "Southern
Birds".
But the area around Argo we will never see much better than we do now - we
currently get almost the best view we can of this part of the sky. And if
you want to see the Magellanic Clouds, I am afraid it is either a visit to
places south of here or a very long wait for them to "orbit" to our side
of
the Galaxy...
--
- Yokel -

"Yokel" posts via a spam-trap account which is not read.

It looks like we can would be be able to see Achernar in about 6000 years
and alpha and beta Centauri in about 11,000 years so it would just be
Canopus which never rises of the brightest stars
"Yokel" wrote in message
...
"Paul Forsdick" wrote in message
...
| Seeing the previous posts mentioning Precession prompted me to wonder
what
| is the actual lowest star we can see from a certain location over the
full
| precession cycle.
| for example I know that Vega gets close to the pole in the cycle so I
think
| this much mean that stars around the same Right ascension would be
higher
in
| the sky than now and thus lower stars that are currenly too far south
to
| rise may do so, for example Theta Scorpio at -43% may be visible and
other
| stars we currently see may then be too low to see.
| so if you have a latitude of 52% what would be the lowest star
|
| it could be that I am completley wrong about this assumption.
|

Let's think it out.

Precession moves the equinox and solstice points around the entire
ecliptic
once in the precession cycle. So every point on the ecliptic will at some
time be north of the celestial equator by the inclination of the earth's
axis (currently just over 23 degrees, but it does vary a degree or so
either
way).

At the moment this "furthest north" point lies near the border between
Gemini and Taurus. So we in the Northern Hemisphere currently get the
best
view we can of the area around Orion, and for a significant part of the
precession cycle the brightest star - Sirius - would be invisible from the
British Isles. But by a similar argument for most of the cycle Scorpio
would be further north than it is now and we currently get an unusually
poor
view of it.

If you are at 52 N, you can see every star less than 38 degrees south of
the
celestial equator (90 degrees - your latitude). Seeing as every part of
the
ecliptic will at some time be 23 degrees north of the celestial equator,
it
follows that at some time in the precessional cycle every star less than
23
+ 38 = 61 degrees south of the *ecliptic* will come into view. In some
parts of the sky this will be out a bit due to "North" and "South" being
at
various times not exactly where they are now - I thought I'd better
mention
it before someone else does. But if you have a star atlas with the South
Ecliptic Pole marked, or "planetarium" software which will show an
ecliptic
coordinate grid, to a reasonable approximation you will (eventually) be
able
to see every star more than about 30 degrees from the South Ecliptic Pole.
This is actually over 90% of the sky. [If there were no precession or the
poles were at right angles to the ecliptic place this figure would be
about
80% - what we currently see throughout the year. This may seem surprising
as
we are so far from the equator, but spherical geometry means that half of
the sky is within 30 degrees of the celestial equator and 71% within 45
degrees, plus we will see half of the remainder as being round the pole
nearest us.] Move 29 degrees nearer the equator so you reach the tropics,
and everywhere within the tropics you can at some point in the
precessional
cycle see every star in the sky. And, of course, at the equator you see
all
the stars in the sky at some time each year.

So in about 10 000 years time we will get a wonderful view of Scorpio,
which
will take the place Taurus and Gemini currently occupy. At other times we
will be able to see the Southern Cross and various of the "Southern
Birds".
But the area around Argo we will never see much better than we do now - we
currently get almost the best view we can of this part of the sky. And if
you want to see the Magellanic Clouds, I am afraid it is either a visit to
places south of here or a very long wait for them to "orbit" to our side
of
the Galaxy...
--
- Yokel -

"Yokel" posts via a spam-trap account which is not read.

"Paul Forsdick" wrote in message
...
| It looks like we can would be be able to see Achernar in about 6000
years
| and alpha and beta Centauri in about 11,000 years so it would just be
| Canopus which never rises of the brightest stars

Sounds reasonable to me. Canopus is close to the Magellanic Clouds and both
of those are too close to the South Ecliptic Pole to ever be seen from these
shores.

There is a far better way to see Achernar, etc. which does not involve a
wait of 6000 years. A few years ago I booked a holiday to the wild and
remote places of Central and NW Australia. Until you have seen the stars
from there or a similar remote location (if your night vision is up to it,
the stars shed so much light you can walk around purely by starlight), you
cannot really know how wonderful the night sky is. I can remember waking up
in the middle of the night in Purnulu (also known as the "Bungle Bungles")
and seeing even the patchy clouds glowing by starlight - this was also the
first time I saw Achernar with my own eyes. Another night in Windjana Gorge
(on the road between Derby and Fitzroy Crossing) you could make out the
pattern of grass patches and sand on the desert floor by the stars. If you
ever get the chance, don't miss it - it beats running the planetarium
software!

The one thing that did puzzle some of my travelling companions who had come
from Sydney is why we couldn't see the Southern Cross during the evenings -
we were there in October. The answer being that the Southern Cross is far
enough from the current South Celestial Pole that it sets for part of each
day from tropical Australia, and in October that happens to be the evenings.
But at that time of year Scorpio was a wondrous sight in the evening western
sky, especially as at the time I was there Venus and Mars were also on
display to the west with Jupiter and Saturn also visible.
--
- Yokel -

"Yokel" posts via a spam-trap account which is not read.

On Jan 3, 8:38*pm, "Yokel" wrote:

The one thing that did puzzle some of my travelling companions who had come
from Sydney is why we couldn't see the Southern Cross during the evenings -
we were there in October. *The answer being that the Southern Cross is far
enough from the current South Celestial Pole that it sets for part of each
day from tropical Australia, and in October that happens to be the evenings.

Can't any of you simply stop referencing planetary dynamics to the
apparent motion of the constellations around Polaris and treat the
matter like grown men for a change ?.

The seasonal disappearance of certain constellations is exactly just
that,a consequence of the orbital motion of the Earth and the slowing
360 degree turning of the planet with respect to the central Sun over
the course of an annual cycle and quite apart from the independent
motion of daily rotation.

Here is what you do,get a broom handle representing both daily
rotation and its orientation 'tilt'.Walk around a central object while
keeping the broom pointed in one direction and you will discover that
as you 'orbitally' complete a circuit you must walk forwards,then
sideways,backwards and forwards to complete a circuit and changing the
orientation of your body to the central object all the while (360
degree orbital component).

There are just two components to consider,count them,just two - the
Earth orbits the central Sun and orbitally turns through 360 degrees
rather than keeping the same face to the Sun,this is what causes the
seasonal disappearance of certain constellations,nothing more and
nothing less,if you can't interpret the images of Uranus on this
orbital point then believe whatever you wish -

http://astro.berkeley.edu/~imke/Infr..._2001_2005.jpg

99.999 % of people will not get it straight away but the change in
orientation is a signature of the orbital motion of Uranus as it turns
through 360 degrees and takes over 80 years to complete it.








But at that time of year Scorpio was a wondrous sight in the evening western
sky, especially as at the time I was there Venus and Mars were also on
display to the west with Jupiter and Saturn also visible.
--
* * * * * * * * - Yokel -

"Yokel" posts via a spam-trap account which is not read.

Hi Yokel

I think I may well try to do that in a few years

I notice the people in Britain in about the year 11350 will get Scorpio very
high but they will lose Rigel and by the year 12350 the belt of Orion will
not rise and by 15000 Betelgeuse is only about 1 degree above the hozizon

"Yokel" wrote in message
...
"Paul Forsdick" wrote in message
...
| It looks like we can would be be able to see Achernar in about 6000
years
| and alpha and beta Centauri in about 11,000 years so it would just be
| Canopus which never rises of the brightest stars

Sounds reasonable to me. Canopus is close to the Magellanic Clouds and
both
of those are too close to the South Ecliptic Pole to ever be seen from
these
shores.

There is a far better way to see Achernar, etc. which does not involve a
wait of 6000 years. A few years ago I booked a holiday to the wild and
remote places of Central and NW Australia. Until you have seen the stars
from there or a similar remote location (if your night vision is up to it,
the stars shed so much light you can walk around purely by starlight), you
cannot really know how wonderful the night sky is. I can remember waking
up
in the middle of the night in Purnulu (also known as the "Bungle Bungles")
and seeing even the patchy clouds glowing by starlight - this was also the
first time I saw Achernar with my own eyes. Another night in Windjana
Gorge
(on the road between Derby and Fitzroy Crossing) you could make out the
pattern of grass patches and sand on the desert floor by the stars. If
you
ever get the chance, don't miss it - it beats running the planetarium
software!

The one thing that did puzzle some of my travelling companions who had
come
from Sydney is why we couldn't see the Southern Cross during the
evenings -
we were there in October. The answer being that the Southern Cross is far
enough from the current South Celestial Pole that it sets for part of each
day from tropical Australia, and in October that happens to be the
evenings.
But at that time of year Scorpio was a wondrous sight in the evening
western
sky, especially as at the time I was there Venus and Mars were also on
display to the west with Jupiter and Saturn also visible.
--
- Yokel -

"Yokel" posts via a spam-trap account which is not read.

Paul Forsdick wrote:
Hi Yokel

I think I may well try to do that in a few years

I notice the people in Britain in about the year 11350 will get Scorpio very
high but they will lose Rigel and by the year 12350 the belt of Orion will
not rise and by 15000 Betelgeuse is only about 1 degree above the hozizon

Top posting??

Anyway, I wil start worrying about that in about 9000 years.