how to calculate the time of solar terms

Greetings all,

I actually have a computer-related job and not familiar with astronomy
at all and all my related knowledges are high-school level, I want to
write a program to calculate the exact time of solar terms (which have
actually special ecliptic longitude) if you provide a specific
Gregorian year.

I found a site[1] have this function but it is not so accurate
(absolute_value(correct - calcuated) can be as large as 10 hours or
more even the range is within 20 years). I want to find an algorithm
to calcultate the exact time (hopefully the delta should be in [10,
20] minutes). Any help is greatly appreciated. Thanks in advance!

Cheers,
Deephay

[1] http://www.nrel.gov/midc/solpos/solpos.html

"Deephay" wrote in message
oups.com...
Greetings all,

I actually have a computer-related job and not familiar with astronomy
at all and all my related knowledges are high-school level, I want to
write a program to calculate the exact time of solar terms (which have
actually special ecliptic longitude) if you provide a specific
Gregorian year.

I found a site[1] have this function but it is not so accurate
(absolute_value(correct - calcuated) can be as large as 10 hours or
more even the range is within 20 years). I want to find an algorithm
to calcultate the exact time (hopefully the delta should be in [10,
20] minutes). Any help is greatly appreciated. Thanks in advance!

Cheers,
Deephay

[1] http://www.nrel.gov/midc/solpos/solpos.html


Have you looked at the JPL HORIZONS web site?

http://ssd.jpl.nasa.gov/?horizons

On Aug 29, 7:30 pm, "Greg Neill" wrote:
"Deephay" wrote in message

oups.com...



Greetings all,

I actually have a computer-related job and not familiar with astronomy
at all and all my related knowledges are high-school level, I want to
write a program to calculate the exact time of solar terms (which have
actually special ecliptic longitude) if you provide a specific
Gregorian year.

I found a site[1] have this function but it is not so accurate
(absolute_value(correct - calcuated) can be as large as 10 hours or
more even the range is within 20 years). I want to find an algorithm
to calcultate the exact time (hopefully the delta should be in [10,
20] minutes). Any help is greatly appreciated. Thanks in advance!

Cheers,
Deephay

[1]http://www.nrel.gov/midc/solpos/solpos.html

Have you looked at the JPL HORIZONS web site?

http://ssd.jpl.nasa.gov/?horizons

Hi,
Thanks for the info, HORIZONS looks nice, but I want an offline
method.

"Deephay" wrote in message
oups.com...
On Aug 29, 7:30 pm, "Greg Neill" wrote:

Have you looked at the JPL HORIZONS web site?

http://ssd.jpl.nasa.gov/?horizons

Hi,
Thanks for the info, HORIZONS looks nice, but I want an offline
method.

What specifically are you wanting to calculate?
Depending upon what it is, it might require only
a short self-contained program or a solution
using terms of a pre-computed series (VSOP87
Theory).

On Aug 29, 8:06 pm, "Greg Neill" wrote:
"Deephay" wrote in message

oups.com...

On Aug 29, 7:30 pm, "Greg Neill" wrote:

Have you looked at the JPL HORIZONS web site?

http://ssd.jpl.nasa.gov/?horizons

Hi,
Thanks for the info, HORIZONS looks nice, but I want an offline
method.

What specifically are you wanting to calculate?
Depending upon what it is, it might require only
a short self-contained program or a solution
using terms of a pre-computed series (VSOP87
Theory).

I just want to calculate the ecliptic longitude (0 degree for Vernal
equinox) for a specific year
if you provide the longtitude & latitude of your location and the
result should be acurate for
a large range (1000 BC - 5000 AC, say). Thanks.

"Deephay" wrote in message
ups.com...

I just want to calculate the ecliptic longitude (0 degree for Vernal
equinox) for a specific year
if you provide the longtitude & latitude of your location and the
result should be acurate for
a large range (1000 BC - 5000 AC, say). Thanks.


I'm still not clear on what it is you want
to calculate. Is it the date and time of
the vernal equinox for a given year that you
want? The longitude of the Sun throughout
the year? Something else?

In article . com,
Deephay wrote:
On Aug 29, 8:06 pm, "Greg Neill" wrote:

What specifically are you wanting to calculate?
Depending upon what it is, it might require only
a short self-contained program or a solution
using terms of a pre-computed series (VSOP87
Theory).

I just want to calculate the ecliptic longitude (0 degree for Vernal
equinox) for a specific year

During any year, the Sun's ecliptic longitude varies between 0 and 360
degrees.... :-) .... it's 0 degrees at the March equinox, 90 degrees
at the June solstice, 180 degrees at the September equinox, and 270
degrees at the December solstice.

if you provide the longtitude & latitude of your location

The observer's longitude and latitude is not needed for the
computation of the Sun's ecliptic longitude.

Your requests are a bit vague and ambiguous - perhaps you need to
think over a bit what you really need, and why ?????

and the result should be acurate for
a large range (1000 BC - 5000 AC, say). Thanks.

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/

On Aug 29, 11:10 pm, "Greg Neill" wrote:
"Deephay" wrote in message

ups.com...

I just want to calculate the ecliptic longitude (0 degree for Vernal
equinox) for a specific year
if you provide the longtitude & latitude of your location and the
result should be acurate for
a large range (1000 BC - 5000 AC, say). Thanks.

I'm still not clear on what it is you want
to calculate. Is it the date and time of
the vernal equinox for a given year that you
want? The longitude of the Sun throughout
the year? Something else?

yes, that is what I mean. Thanks

On Aug 30, 1:13 am, (Paul Schlyter) wrote:
In article . com,

Deephay wrote:
On Aug 29, 8:06 pm, "Greg Neill" wrote:

What specifically are you wanting to calculate?
Depending upon what it is, it might require only
a short self-contained program or a solution
using terms of a pre-computed series (VSOP87
Theory).

I just want to calculate the ecliptic longitude (0 degree for Vernal
equinox) for a specific year

During any year, the Sun's ecliptic longitude varies between 0 and 360
degrees.... :-) .... it's 0 degrees at the March equinox, 90 degrees
at the June solstice, 180 degrees at the September equinox, and 270
degrees at the December solstice.

if you provide the longtitude & latitude of your location

The observer's longitude and latitude is not needed for the
computation of the Sun's ecliptic longitude.

sorry I made a mistake.


Your requests are a bit vague and ambiguous - perhaps you need to
think over a bit what you really need, and why ?????

I just want to calculate the exact time when Sun's ecliptic longitude
equals to (0, 15, 30 ... 330, 345) degree for one year.
Thanks a lot.

Cheers,
Deephay


and the result should be acurate for
a large range (1000 BC - 5000 AC, say). Thanks.

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/

"Deephay" wrote in message
ups.com...

I just want to calculate the exact time when Sun's ecliptic longitude
equals to (0, 15, 30 ... 330, 345) degree for one year.
Thanks a lot.

You might want to find a copy of Jean Meeus' Astronomical
Algorithms. In it you'll find methods for calculating
the ecliptic longitude of the Sun for a given date and time
(expressed in Julian Day format).

If you take such a method and wrap a search loop around
it, you can zero in on the time for any given longitude.