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| Patrick Powers... |
 Posted: Mon Jul 06, 2009 10:50 pm |
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I'm writing a novel where images are received from some unknown place
and time (never mind how). It seems to be some place on Earth but
can't be anywhere in the present. It could be past, future, or some
alternative reality. Anyway, assuming the images are from the Earth,
what could be determined about the location and time. The images come
in in real time, that is, one second here is one second there, time
flows at the same rate. There is about a five month offset in the
seasons.
Here is my thinking: If from Earth, it should be easy to get the
lattitude by observing the length of the days over about half a year.
How accurate would this be? +- 1 degree? I guess it depends on the
accuracy of the observations, so it can be almost whatever I like.
It would be more difficult to determine whether the images are from
the future or past. It seems it could be done by measuring the length
of a year. How much does this change every year? Not much.
How about observation of the sky? The pole of the earth changes
position relative to the heaven's. One night's oberservation would be
enough to determine the pole star or lack thereof. That would fix the
year within +- 500 years(?) mod 24,000 years.
Anything else? Longitude seems impossible to me, since the time
correspondence is arbitrary. |
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| dlzc... |
| Posted: Tue Jul 07, 2009 4:39 am |
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Dear Patrick Powers:
On Jul 7, 1:50 am, Patrick Powers <patmpow... at (no spam) gmail.com> wrote:
[quote:00b7717fb8]I'm writing a novel where images are received
from some unknown place
and time (never mind how). It seems to be
some place on Earth but can't be anywhere in
the present. It could be past, future, or some
alternative reality.
[/quote:00b7717fb8]
.... In which case, the heavens may be dissimilarly arranged, or the
length of year different.
[quote:00b7717fb8] Anyway, assuming the images are from the
Earth, what could be determined about the
location and time. The images come in in
real time, that is, one second here is one
second there, time flows at the same rate.
There is about a five month offset in the
seasons.
Here is my thinking: If from Earth, it should
be easy to get the lattitude by observing the
length of the days over about half a year.
[/quote:00b7717fb8]
No, you'd need about a year-and-a-half to establish latitude and aeon.
[quote:00b7717fb8]How accurate would this be? +- 1 degree?
I guess it depends on the accuracy of the
observations, so it can be almost whatever
I like.
[/quote:00b7717fb8]
Talk a little bit about the "data stream"... and is it two-way?
[quote:00b7717fb8]It would be more difficult to determine whether
the images are from the future or past. It
seems it could be done by measuring the length
of a year. How much does this change every
year? Not much.
[/quote:00b7717fb8]
The length of day about 2.2 billion years ago was about 16 hours, and
the lunar month was much shorter. As the Moon recedes, its effect on
Earth is diminished.
[quote:00b7717fb8]How about observation of the sky? The pole
of the earth changes position relative to the
heaven's. One night's oberservation would be
enough to determine the pole star or lack
thereof.
[/quote:00b7717fb8]
It doesn't disappear, and other stars will drift in (and eventually
out) of pole position. And none of the stars are fixed in the
heavens, the constellations change.
[quote:00b7717fb8] That would fix the year within +- 500 years(?)
mod 24,000 years.
[/quote:00b7717fb8]
Discounting severely different past histories...
You also have things like Barnard's star, and this new red dwarf that
will make its closest encounter (a little over a light year away) to
us in a million years or so.
[quote:00b7717fb8]Anything else? Longitude seems impossible
to me, since the time correspondence is
arbitrary.
[/quote:00b7717fb8]
The continents drift over millions of years, so yes, that is probably
not of interest in establishing *when*.
David A. Smith |
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| Mike Dworetsky... |
| Posted: Wed Jul 08, 2009 1:50 am |
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"Patrick Powers" <patmpowers at (no spam) gmail.com> wrote in message
news:1ea95071-b03b-4f54-97a1-adf41840e046 at (no spam) o18g2000pra.googlegroups.com...
[quote:d49d2a1850]I'm writing a novel where images are received from some unknown place
and time (never mind how). It seems to be some place on Earth but
can't be anywhere in the present. It could be past, future, or some
alternative reality. Anyway, assuming the images are from the Earth,
what could be determined about the location and time. The images come
in in real time, that is, one second here is one second there, time
flows at the same rate. There is about a five month offset in the
seasons.
[/quote:d49d2a1850]
Is there any way to control the direction of viewing? So that you can look
at sunset, sunrise, night sky such as Pole Star? Can you look at moon? Are
the features on it the same as we see now? Can telescopes be used to
magnify and intensify features in the "other" view ? (if e.g., Copernicus
crater is absent then the view is back in the Cretaceous or early Tertiary
(I can't recall exact age of this feature but it is comparatively young.
Similarly with Tycho.)
[quote:d49d2a1850]Here is my thinking: If from Earth, it should be easy to get the
lattitude by observing the length of the days over about half a year.
How accurate would this be? +- 1 degree? I guess it depends on the
accuracy of the observations, so it can be almost whatever I like.
[/quote:d49d2a1850]
A couple of degrees, perhaps, but less accurate the closer you are to the
equator. In the tropics, the length of the day varies very little. You may
get more mileage out of measuring the angular sweep of sunrise/sunset from
solstice to solstice. This is around 47 degrees at the equator and
approaches 180 dgrees at the Arctic circle.
You can quickly tell whether you are in the southern hemisphere or northern
by seeing which direction the sun sets or rises in. If it rises up and to
the right, northern, and up and to the left, southern.
[quote:d49d2a1850]It would be more difficult to determine whether the images are from
the future or past. It seems it could be done by measuring the length
of a year. How much does this change every year? Not much.
[/quote:d49d2a1850]
Very little, even over thousands of years.
[quote:d49d2a1850]How about observation of the sky? The pole of the earth changes
position relative to the heaven's. One night's oberservation would be
enough to determine the pole star or lack thereof. That would fix the
year within +- 500 years(?) mod 24,000 years.
[/quote:d49d2a1850]
Yes, assuming that the time slip is only a few hundred to few thousand
years.
Some bright stars like Vega and Arcturus (or Alpha Cen in the south) have
significant proper motions and images of their constellations could help fix
a date in the range of a few thousand years, possibly with comparable or
better accuracy than the pole position, especially if the time shift is more
than 24,000 years.
If you can make accurate observations of the positions of planets you could
use the solar system as a multi-handed date clock. The idea has been around
in SF fro a long time (e.g., in Heinlein, Methuselah's Children). Current
numerical integrations can check forwards and backwards several million
years, especially useful if you discover the constellations are
unrecognisable.
[quote:d49d2a1850]Anything else? Longitude seems impossible to me, since the time
correspondence is arbitrary.
[/quote:d49d2a1850]
Yes, a local absolute time reference is needed and you won't have one.
Other natural observations that could help fix location would be determining
the types of plants, birds, and animals you might see. Aardvarks,
elephants, lions--Africa. Etc.
--
Mike Dworetsky
(Remove pants sp*mbl*ck to reply) |
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| Dr J R Stockton... |
| Posted: Wed Jul 08, 2009 4:12 pm |
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In sci.astro message <IdCdnVqOmf1E0snXnZ2dnUVZ8gmdnZ2d at (no spam) bt.com>, Wed, 8
Jul 2009 08:50:47, Mike Dworetsky <platinum198 at (no spam) pants.btinternet.com>
posted:
[quote:4b5c91ce34]"Patrick Powers" <patmpowers at (no spam) gmail.com> wrote in message
news:1ea95071-b03b-4f54-97a1-adf41840e046 at (no spam) o18g2000pra.googlegroups.com.
..
I'm writing a novel where images are received from some unknown place
and time (never mind how). It seems to be some place on Earth but
can't be anywhere in the present. It could be past, future, or some
alternative reality. Anyway, assuming the images are from the Earth,
what could be determined about the location and time. The images come
in in real time, that is, one second here is one second there, time
flows at the same rate. There is about a five month offset in the
seasons.
[/quote:4b5c91ce34]
By observing the phase of north/south movement of the Sun, the
fractional-year of the time difference can be found fairly well.
[quote:4b5c91ce34]You can quickly tell whether you are in the southern hemisphere or
northern by seeing which direction the sun sets or rises in. If it
rises up and to the right, northern, and up and to the left, southern.
[/quote:4b5c91ce34]
Provided that you first establish whether or not the magic viewer gives
a mirror image.
[quote:4b5c91ce34]Anything else? Longitude seems impossible to me, since the time
correspondence is arbitrary.
Yes, a local absolute time reference is needed and you won't have one.
[/quote:4b5c91ce34]
For a range of several thousand years including the present, you can
just wait for an eclipse of the Sun (partial annular or total),
carefully note its time of local day and the path of the Moon across the
Sun, and the duration of totality or annularity, and see which of Fred
Espenak's list of eclipses fit. That will, eventually, give exact date
and a fair idea of position.
--
(c) John Stockton, nr London, UK. ? at (no spam) merlyn.demon.co.uk Turnpike v6.05 MIME.
Web <URL:http://www.merlyn.demon.co.uk/> - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News. |
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| Steve Willner... |
| Posted: Fri Jul 10, 2009 12:32 pm |
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Guest
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In article <1ea95071-b03b-4f54-97a1-adf41840e046 at (no spam) o18g2000pra.googlegroups.com>,
Patrick Powers <patmpowers at (no spam) gmail.com> writes:
[quote:f91db981cb]I'm writing a novel where images are received from some unknown place
... assuming the images are from the Earth,
what could be determined about the location and time.
If from Earth, it should be easy to get the
lattitude by observing the length of the days over about half a year.
[/quote:f91db981cb]
Or sun altitude at noon. If you could observe stars, you could get
the latitude in a single night; less than that if you have an idea of
which direction is which. This is equivalent to celestial navigation.
[quote:f91db981cb]How accurate would this be? +- 1 degree? I guess it depends on the
accuracy of the observations, so it can be almost whatever I like.
[/quote:f91db981cb]
Yep. Latitude accuracy will be basically equal to angular accuracy
of the measurements.
[quote:f91db981cb]It would be more difficult to determine whether the images are from
the future or past. It seems it could be done by measuring the length
of a year.
[/quote:f91db981cb]
As others have mentioned, length of day is probably what you want.
If you can see planets, you can probably get quite a good estimate
very quickly, at least for time ranges within several million years.
[quote:f91db981cb]How about observation of the sky? The pole of the earth changes
position relative to the heaven's. One night's oberservation would be
enough to determine the pole star or lack thereof. That would fix the
year within +- 500 years(?) mod 24,000 years.
[/quote:f91db981cb]
Much easier and more accurate to use planets, but precession would
work too. For longer time intervals, I think you need stellar proper
motions.
[quote:f91db981cb]Anything else? Longitude seems impossible to me, since the time
correspondence is arbitrary.
[/quote:f91db981cb]
Not so, if accurate celestial measurements are possible and the time
is within (I'm guessing) several thousand years. Look up "method of
lunar distances." The limitation will be the accuracy of
measurements (of the moon relative to stars) and the ability to
calculate the moon's orbit, which is quite complex.
If you can make telescopic observations, Jupiter's moons also provide
an absolute time clock. You might also get somewhere with an
ensemble of eclipsing binary stars.
I think you can have pretty much whatever accuracy your story
requires by limiting or expanding the types of observations that are
possible.
Good luck with the novel, and please let us know when it's published.
--
Steve Willner Phone 617-495-7123 swillner at (no spam) cfa.harvard.edu
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
email may be sent to your ISP.) |
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| Mike Dworetsky... |
| Posted: Sun Jul 12, 2009 2:26 am |
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"Steve Willner" <willner at (no spam) cfa.harvard.edu> wrote in message
news:h38fhp$l4l$1 at (no spam) news.eternal-september.org...
[quote:dc7d7f8670]In article
1ea95071-b03b-4f54-97a1-adf41840e046 at (no spam) o18g2000pra.googlegroups.com>,
Patrick Powers <patmpowers at (no spam) gmail.com> writes:
I'm writing a novel where images are received from some unknown place
... assuming the images are from the Earth,
what could be determined about the location and time.
If from Earth, it should be easy to get the
lattitude by observing the length of the days over about half a year.
Or sun altitude at noon. If you could observe stars, you could get
the latitude in a single night; less than that if you have an idea of
which direction is which. This is equivalent to celestial navigation.
How accurate would this be? +- 1 degree? I guess it depends on the
accuracy of the observations, so it can be almost whatever I like.
Yep. Latitude accuracy will be basically equal to angular accuracy
of the measurements.
It would be more difficult to determine whether the images are from
the future or past. It seems it could be done by measuring the length
of a year.
As others have mentioned, length of day is probably what you want.
If you can see planets, you can probably get quite a good estimate
very quickly, at least for time ranges within several million years.
How about observation of the sky? The pole of the earth changes
position relative to the heaven's. One night's oberservation would be
enough to determine the pole star or lack thereof. That would fix the
year within +- 500 years(?) mod 24,000 years.
Much easier and more accurate to use planets, but precession would
work too. For longer time intervals, I think you need stellar proper
motions.
Anything else? Longitude seems impossible to me, since the time
correspondence is arbitrary.
Not so, if accurate celestial measurements are possible and the time
is within (I'm guessing) several thousand years. Look up "method of
lunar distances." The limitation will be the accuracy of
measurements (of the moon relative to stars) and the ability to
calculate the moon's orbit, which is quite complex.
[/quote:dc7d7f8670]
In principle, this might be workable, but its use generally requires a good
idea of the approximate position by dead reckoning. If you literally have
no idea of the longitude to start with, and no certain idea of the date, it
is going to be very difficult.
Even on Earth, with all the equipment available in the 18th century (before
chronometers), lunar distances was a clumsy and exceedingly difficult
method, and they persisted with it because it was the only method available.
[quote:dc7d7f8670]If you can make telescopic observations, Jupiter's moons also provide
an absolute time clock. You might also get somewhere with an
ensemble of eclipsing binary stars.
I think you can have pretty much whatever accuracy your story
requires by limiting or expanding the types of observations that are
possible.
Good luck with the novel, and please let us know when it's published.
[/quote:dc7d7f8670]
Ditto.
[quote:dc7d7f8670]
--
Steve Willner Phone 617-495-7123 swillner at (no spam) cfa.harvard.edu
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
email may be sent to your ISP.)
[/quote:dc7d7f8670]
--
Mike Dworetsky
(Remove pants sp*mbl*ck to reply) |
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| Steve Willner... |
| Posted: Tue Jul 14, 2009 10:40 am |
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Guest
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In article <DOGdnUZ4gZ7dA8TXnZ2dnUVZ8tKdnZ2d at (no spam) bt.com>,
"Mike Dworetsky" <platinum198 at (no spam) pants.btinternet.com> writes:
[quote:6673efe653]Even on Earth, with all the equipment available in the 18th century (before
chronometers), lunar distances was a clumsy and exceedingly difficult
method, and they persisted with it because it was the only method available.
[/quote:6673efe653]
Wasn't the main difficulty doing the lunar calculations? Also doing
the measurements from the deck of a pitching, rolling ship, I
suppose, but that problem seems to have been overcome.
I don't see why you would need to know an approximate position in
advance. You would, however, have to know the date to the nearest
month (at least for a simple application), but that should be easy if
you can observe planets.
--
Steve Willner Phone 617-495-7123 swillner at (no spam) cfa.harvard.edu
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
email may be sent to your ISP.) |
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| William Hamblen... |
| Posted: Tue Jul 14, 2009 8:31 pm |
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On Tue, 14 Jul 2009 20:40:12 +0000 (UTC), willner at (no spam) cfa.harvard.edu
(Steve Willner) wrote:
[quote:5c417b1feb]In article <DOGdnUZ4gZ7dA8TXnZ2dnUVZ8tKdnZ2d at (no spam) bt.com>,
"Mike Dworetsky" <platinum198 at (no spam) pants.btinternet.com> writes:
Even on Earth, with all the equipment available in the 18th century (before
chronometers), lunar distances was a clumsy and exceedingly difficult
method, and they persisted with it because it was the only method available.
Wasn't the main difficulty doing the lunar calculations? Also doing
the measurements from the deck of a pitching, rolling ship, I
suppose, but that problem seems to have been overcome.
I don't see why you would need to know an approximate position in
advance. You would, however, have to know the date to the nearest
month (at least for a simple application), but that should be easy if
you can observe planets.
[/quote:5c417b1feb]
The apparent position of the Moon in the sky depends on where you are
on the Earth. To get initial condtions for your calculations you need
to have a reasonable position by dead reckoning. To get your
longitude to the nearest degree you need to know the time to the
nearest 4 minutes. To get the time to the nearest 4 minutes you need
to have the position of the Moon to the nearest 2 minutes of arc. It
is not easy. Nautical almanacs had tables that reduced the effort in
performing the calculations. They kept the tables for lunar distances
in the almanacs until surprisingly recent times.
Bud |
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| Steve Willner... |
| Posted: Thu Jul 16, 2009 10:53 am |
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In article <8peq55h02dtatv3mhc8apiia33f2b1tu2m at (no spam) 4ax.com>,
William Hamblen <william.hamblen at (no spam) earthlink.net> writes:
[quote:fcc9aaed6a]The apparent position of the Moon in the sky depends on where you are
on the Earth.
[/quote:fcc9aaed6a]
Yes; the correction is known as "horizontal parallax."
[quote:fcc9aaed6a]To get initial condtions for your calculations you need
to have a reasonable position by dead reckoning.
[/quote:fcc9aaed6a]
That may be the way navigators did it in practice, but I don't see
why it's necessary. You can derive horizontal parallax directly from
the observed declination and hour angle of the moon. You can also
derive it from measurements at different times from the same
location.
[quote:fcc9aaed6a]To get your longitude to the nearest degree you need to know the
time to the nearest 4 minutes. To get the time to the nearest 4
minutes you need to have the position of the Moon to the nearest 2
minutes of arc. It is not easy.
[/quote:fcc9aaed6a]
Agreed.
[quote:fcc9aaed6a]Nautical almanacs had tables that reduced the effort in performing
the calculations. They kept the tables for lunar distances in the
almanacs until surprisingly recent times.
[/quote:fcc9aaed6a]
Which suggests the method was useful despite the difficulties. For a
fixed location, multiple measurements might improve accuracy.
In thinking about this more, it occurred to me that another way to
estimate very long time scales in the OP scenario would be to look
for missing or extra craters on the lunar surface. Not at all
precise, of course, but perhaps easier to do than some of the other
methods.
--
Steve Willner Phone 617-495-7123 swillner at (no spam) cfa.harvard.edu
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
email may be sent to your ISP.) |
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