Celestial Navigation

With modern GPS systems now (or soon to be) available on an average
person's wrist watch, this is purely a question of historic and
academic interest!

Can someone please re-iterate the calculations and easiest method
necessary to work out latitude and more importantly *longitude*
based on observations of the Sun and stars from a specific point on
the Earth's surface?

This is an 'all surface terrain' question (not just confined to
positions at sea), and I am assuming there is no 'dead reckoning'
info. available to the navigator and he/she does not have any almanacs
to hand, except an Astronomy handbook giving simple info like the R.A.
and declination of the 100 brightest stars and sunrise and sunset
times for various latitudes throughout the year, positions of bright
planets, etc.

In the northern hemisphere, I know geographic *latitude* can be simply
deduced from the elevations of Polaris (at night) or the midday Sun
(if you know its approximate declination) above the local horizon.
Also, if you have a chronometer keeping GMT, then simply taking the
transit time of the Sun due south at midday to equate to 1200 hrs
local time and working out its difference from GMT will give you a
very "rough" idea of your local time zone and hence approx.
*longitude* band.

How do you then further refine the calculations to make your longitude
deductions accurate to say within a *few degrees*? How do concepts
like hour angle and Greenwich Mean Sidereal Time (GMST) come into the
equation? As its purely for academic purposes, I do not wish to press
for too much complications in the methodology...so simple diagrams and
ideas would suffice.

Thanks.
Abdul Ahad

Celestial Navigation

A search on Google gives over 150,000 hits on this subject. You might read a
few and you should find your answers.

Abdul Ahad wrote:

With modern GPS systems now (or soon to be) available on an average
person's wrist watch, this is purely a question of historic and
academic interest!

Can someone please re-iterate the calculations and easiest method
necessary to work out latitude and more importantly *longitude*
based on observations of the Sun and stars from a specific point on
the Earth's surface?


See: http://pollux.nss.nima.mil/pubs/
http://www.irbs.com/bowditch/

"Land Navigation Handbook" by W. S. Kals
http://www.edu-observatory.org/eo/bkr/bkr.93.04

Latitude is fairly easy to work out, if you have some device like a
sextant or kamal to measure the maximum height of the sun (Hs) or other
object and doing a sight reduction. Sin(Hc) = Sin(dec) * Sin(lat) +
Cos(dec) * Cos(lat) * Cos(LHA) and Cos(Z) = [Sin(dec) - Sin(lat) *
Sin(Hc)] / [Cos(lat) * Cos(Hc)] where Hc = calculated altitude, dec =
declination, lat = latitude, LHA = Local Hour Angle, Z = azimuth. Use
your DR latitude for lat.

Latitude by Polaris works the same way. Remember that the height of
Polaris is several minutes from true 90 degrees.

Longitude. You need accurate GMT to find longitude. There are methods for
determining longitude like finding lunar distance, but these fill books.
There is no easy way to determine longitude other than accurate GMT.

RA = GHA (Aries) - GHA (Body), where GHA = Greenwich Hour Angle.

There are many excellent sites that go into detail about your question.
Type celestial navigation into Google.

Mike Boersma

Abdul Ahad wrote:

With modern GPS systems now (or soon to be) available on an average
person's wrist watch, this is purely a question of historic and
academic interest!

Can someone please re-iterate the calculations and easiest method
necessary to work out latitude and more importantly *longitude*
based on observations of the Sun and stars from a specific point on
the Earth's surface?

This is an 'all surface terrain' question (not just confined to
positions at sea), and I am assuming there is no 'dead reckoning'
info. available to the navigator and he/she does not have any almanacs
to hand, except an Astronomy handbook giving simple info like the R.A.
and declination of the 100 brightest stars and sunrise and sunset
times for various latitudes throughout the year, positions of bright
planets, etc.

In the northern hemisphere, I know geographic *latitude* can be simply
deduced from the elevations of Polaris (at night) or the midday Sun
(if you know its approximate declination) above the local horizon.
Also, if you have a chronometer keeping GMT, then simply taking the
transit time of the Sun due south at midday to equate to 1200 hrs
local time and working out its difference from GMT will give you a
very "rough" idea of your local time zone and hence approx.
*longitude* band.

How do you then further refine the calculations to make your longitude
deductions accurate to say within a *few degrees*? How do concepts
like hour angle and Greenwich Mean Sidereal Time (GMST) come into the
equation? As its purely for academic purposes, I do not wish to press
for too much complications in the methodology...so simple diagrams and
ideas would suffice.

Thanks.
Abdul Ahad

Banjopikr1 wrote:

Celestial Navigation

A search on Google gives over 150,000 hits on this subject. You might read a
few and you should find your answers.

Wouldn't it have been easier to not answer his question if you don't
have anything useful to say? Or perhaps you like to play the role of a
critical parent.


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Here are a couple sites explaining how celestial nav works:

http://home.t-online.de/home/h.umland/page2.htm
http://celestialnavigation.net/

There's also the Navigation mailing list, which is about traditional
navigation methods. This page explains how to subscribe, and has a
link to the message archive.

http://www.wa6pby.com/

--

Paul Hirose
To reply by email delete INVALID from address.

Paul Hirose wrote in message ...
Here are a couple sites explaining how celestial nav works:

http://home.t-online.de/home/h.umland/page2.htm
http://celestialnavigation.net/

There's also the Navigation mailing list, which is about traditional
navigation methods. This page explains how to subscribe, and has a
link to the message archive.

http://www.wa6pby.com/

Thank you all. Looks like there's tonnes of info still available on
"classical" navigation...in a modern era of GPS, WAP, 3G mobile,
Bluetooth, PDA, .... May reflect how much faith people have in the US
Defense Department's GPS constellation?!

Abdul

(Abdul Ahad) wrote in
om:


Thank you all. Looks like there's tonnes of info still available on
"classical" navigation...in a modern era of GPS, WAP, 3G mobile,
Bluetooth, PDA, .... May reflect how much faith people have in the US
Defense Department's GPS constellation?!

Abdul

Or, putting the anti-US cracks aside, they may have sufficient sense to
wonder what they'll do if their batteries run down

mike r

(Abdul Ahad) wrote in message . com...

Thank you all. Looks like there's tonnes of info still available on
"classical" navigation...in a modern era of GPS, WAP, 3G mobile,
Bluetooth, PDA, .... May reflect how much faith people have in the US
Defense Department's GPS constellation?!

Not at all. The principles remain valid (and sometimes
useful, depending on circumstances). Nothing deeper
than that.

It's sometimes fun to go back to first principles - and I
have indeed determined my location from first principles,
Polaris at night, then local noon (with an accurate clock)
the next day. You still have to correct for the equation
of time, but my planisphere has an analemma on it. Very
handy.

The numbers in my .sig are from GPS.

Laura Halliday VE7LDH "Que les nuages soient notre
Grid: CN89mg pied a terre..."
ICBM: 49 16.05 N 122 56.92 W - Hospital/Shafte

mike ring wrote:

Or, putting the anti-US cracks aside, they may have sufficient sense to
wonder what they'll do if their batteries run down

They will put in fresh ones, like everyone else does.