Novelist has some basic astro questions

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.

"Patrick Powers" wrote in message
...
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.

It's a whole lot easier to find latitude (only two t's) by observing
Polaris.
Magellan got lost when he couldn't see it from south of the equator,
but he still managed to almost circumnavigate the Earth.
Write what you know about, not what you are ignorant of or you
will not be successful.

Dear Patrick Powers:

On Jul 7, 1:50*am, Patrick Powers wrote:
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.

.... In which case, the heavens may be dissimilarly arranged, or the
length of year different.

*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.

No, you'd need about a year-and-a-half to establish latitude and aeon.

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.

Talk a little bit about the "data stream"... and is it two-way?

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.

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.

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.

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.

*That would fix the year within +- 500 years(?)
*mod 24,000 years.

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.

Anything else? *Longitude seems impossible
to me, since the time correspondence is
arbitrary.

The continents drift over millions of years, so yes, that is probably
not of interest in establishing *when*.

David A. Smith

Patrick Powers wrote:
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.

Depends on whether you're in the northern or southern hemisphere. If
you're in the north, then Polaris is pole star. In the south, the pole
star is something called Sigma Octanis, however it is too faint to be
seen properly by the naked eye. So instead, the entire Southern Cross
constellation serves as the southern pole locator.

Due to the Earth's precession, the pole star changes every few tens of
thousand years.

In the time of the ancient Greeks, the Southern Cross could be seen from
Greece. But now that it is the southern pole locator, it is no longer
visible from low northern latititudes.

Pole star - Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/Pole_star#South_pole

Anything else? Longitude seems impossible to me, since the time
correspondence is arbitrary.

Oh yeah, lots of things, depending on how far back in the past, you
should be able to see different kinds of vegetation and animal life. Ice
ages and ice-free ages.

If it's in the future, then there are certain things that can be
predicted. Such as certain stars becoming closer to or further than they
are now. Currently the closest star system is the Alpha & Proxima
Centauri system. In less than 10,000 years, Bernard's Star will be the
closest. In 20,000 years, the Lalande 21185 star will be the closest. In
27,000 years, the Alpha & Proxima Centauri system will be the closest
again, and even closer than they are now: they will then be within 3
light years vs. 4.2 light years right now. But the closest any star will
ever get to us will be in 1.36 million years, when Gliese 710 star will
be within 1 light year of us; GL 710 will in fact be closer to us than
our own Oort Cloud's outer boundary. Could mean a raindown of cometary
debris a few million years after that.

Yousuf Khan

Patrick Powers wrote:
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.

Depends on whether you're in the northern or southern hemisphere. If
you're in the north, then Polaris is pole star. In the south, the pole
star is something called Sigma Octanis, however it is too faint to be
seen properly by the naked eye. So instead, the entire Southern Cross
constellation serves as the southern pole locator.

Due to the Earth's precession, the pole star changes every few tens of
thousand years.

In the time of the ancient Greeks, the Southern Cross could be seen from
Greece. But now that it is the southern pole locator, it is no longer
visible from low northern latititudes.

Pole star - Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/Pole_star#South_pole

Anything else? Longitude seems impossible to me, since the time
correspondence is arbitrary.

Oh yeah, lots of things, depending on how far back in the past, you
should be able to see different kinds of vegetation and animal life. Ice
ages and ice-free ages.

If it's in the future, then there are certain things that can be
predicted. Such as certain stars becoming closer to or further than they
are now. Currently the closest star system is the Alpha & Proxima
Centauri system. In less than 10,000 years, Bernard's Star will be the
closest. In 20,000 years, the Lalande 21185 star will be the closest. In
27,000 years, the Alpha & Proxima Centauri system will be the closest
again, and even closer than they are now: they will then be within 3
light years vs. 4.2 light years right now. But the closest any star will
ever get to us will be in 1.36 million years, when Gliese 710 star will
be within 1 light year of us; GL 710 will in fact be closer to us than
our own Oort Cloud's outer boundary. Could mean a raindown of cometary
debris a few million years after that.

Yousuf Khan

"Patrick Powers" wrote in message
...
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.


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.)

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.


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.

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.

Very little, even over thousands of 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.

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.

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.

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)

In sci.astro message , Wed, 8
Jul 2009 08:50:47, Mike Dworetsky
posted:
"Patrick Powers" wrote in message
.
..
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.

By observing the phase of north/south movement of the Sun, the
fractional-year of the time difference can be found fairly well.



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.

Provided that you first establish whether or not the magic viewer gives
a mirror image.



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.

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. 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.

"Dr J R Stockton" wrote in message
nvalid...
In sci.astro message , Wed, 8
Jul 2009 08:50:47, Mike Dworetsky
posted:
"Patrick Powers" wrote in message
.
..
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.

By observing the phase of north/south movement of the Sun, the
fractional-year of the time difference can be found fairly well.



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.

Provided that you first establish whether or not the magic viewer gives
a mirror image.


Or check that Orion looks "upside down".


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.

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.


I did not include that idea largely because it would involve a lot of
waiting and if you are writing a novel you don't want the protagonists to
have to wait around for decades for an answer (not usually, anyways).

Possibly the "solar system as a giant clock" would be easier to manage.
This assumes the views are of Earth and they can view at night.

And initially it isn't even clear if they are viewing Earth or some
analogue. If the time shift is more than a few thousand years, even a study
of eclipses might not work very well.

--
Mike Dworetsky

(Remove pants sp*mbl*ck to reply)

In article ,
Patrick Powers 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.

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
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.)

"Steve Willner" wrote in message
...
In article
,
Patrick Powers 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.

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.

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.

Ditto.


--
Steve Willner Phone 617-495-7123
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.)


--
Mike Dworetsky

(Remove pants sp*mbl*ck to reply)