<p>Recently I inherited quite a few old QuickBasic programs which perform various astronomical calculations.  I'm attempting to understand these programs and rewrite some of them in Python.  I do not have a deep background in astronomy.</p>

<p>A number of the programs take a parameter file as input, YEAR.DAT.  Below are 5 years of these files (each column represents one file).  I need help in figuring out the various data values.</p>

<p>YEAR.DAT</p>

<pre><code>year        2001         2008         2009         2010         2011 
delta t      66           65           66           66           67 
tilt         23.43909     23.43818     23.43805     23.43799     23.43786 
dow           1            2            4            5            6 
gst           6.71430      6.66860      6.71839      6.702509     6.68659 
x1          105.690      330.340      310.959      291.631      272.303 
bs           84           90           88           87           86 
fs          301          300          298          304          303 
x2          357.765      356.959      357.689      357.433      357.177 
x3          354.289      193.159      335.720      105.105      234.489 
jd      2451910.5    2454466.5    2454832.5    2455197.5    2455562.5 
</code></pre>

<p>I believe that all the values which are time dependent are for 0:00 hours on Jan. 1 of the year given.  </p>

<p>Here are the values I think I've figured out:</p>

<pre><code>tilt is the obilquity of the ecliptic
dow is the day of the week, where Monday is day 1
bs is the number of the day of the year when British Summer Time (BST) begins
fs is the number of the day of the year when BST ends
jd is the Julian day number (of 0:00 hours Jan. 1)
</code></pre>

<p>Values I'm unsure about:</p>

<pre><code>delta t is some sort of time delta, but I don't know what
gst seems to be Greenwich Mean Sidereal Time, but for what moment?
x1, x2, and x3 I'm clueless about
</code></pre>

<p>Here are my questions:</p>

<ol>
<li>What might delta t be?  </li>
<li>Is gst in fact Greenwich Mean Sidereal Time?  For what moment?  </li>
<li>What are x1, x2, and x3?  (This is low-priority question.)</li>
<li>How can delta t, gst, and, perhaps other values, be determined for 
    2018, 2019, ...?</li>
</ol>

<p>Any help will be greatly appreciated.</p>

<p>Roger House</p>

CC BY-SA 3.0
2016-11-06T19:53:35.897Z
Could you give an example of what the programs calculate? Maybe that might help. Alternatively, do you have the BASIC listings, do they offer any clues?
adrianmcmenamin
CC BY-SA 3.0
2016-11-07T13:39:16.753Z
You're asking us to debug a program without even giving us the code.  Have some mercy!
Carl Witthoft
CC BY-SA 3.0
2016-11-07T17:44:37.730Z
I feel your pain. I can't tell you how many times I've scratched my head while pouring over decades old programs with variable names like `xi`, `jas`, and `rp2`. Your best bet is to see how they're used and try to glean the information from context. You might also try changing some values and see how it affects the output. It's hard for us to determine these without the full code.
zephyr
CC BY-SA 3.0
2016-11-08T15:53:05.510Z
For delta T perhaps: http://eclipse.gsfc.nasa.gov/SEhelp/deltaT.html, Since the Earths axis tilt is 23.5 deg you might look at these numbers on context of the Earth.
scrappedcola
CC BY-SA 3.0
2016-11-08T18:52:25.523Z
Thanks to all of you for considering my query.  I should point out that in no way was I asking for analysis of code or help with debugging.  My hope was that someone with astronomical knowledge would recognize the values I posted, and indeed, this has been the case.  Both barrycarter and scrappedcola 2 have pointed me at what looks to be excellent information on delta t and gst.
Roger House
<fundamental-astronomy><coordinate><observational-astronomy><positional-astronomy>
Attempting to determine astronomy values in a parameter file
Roger House
# Attempting to determine astronomy values in a parameter file

(Asked by: username_0 on 2016-11-06)

Recently I inherited quite a few old QuickBasic programs which perform various astronomical calculations.  I'm attempting to understand these programs and rewrite some of them in Python.  I do not have a deep background in astronomy.
A number of the programs take a parameter file as input, YEAR.DAT.  Below are 5 years of these files (each column represents one file).  I need help in figuring out the various data values.
YEAR.DAT
year        2001         2008         2009         2010         2011 
delta t      66           65           66           66           67 
tilt         23.43909     23.43818     23.43805     23.43799     23.43786 
dow           1            2            4            5            6 
gst           6.71430      6.66860      6.71839      6.702509     6.68659 
x1          105.690      330.340      310.959      291.631      272.303 
bs           84           90           88           87           86 
fs          301          300          298          304          303 
x2          357.765      356.959      357.689      357.433      357.177 
x3          354.289      193.159      335.720      105.105      234.489 
jd      2451910.5    2454466.5    2454832.5    2455197.5    2455562.5 

I believe that all the values which are time dependent are for 0:00 hours on Jan. 1 of the year given.  
Here are the values I think I've figured out:
tilt is the obilquity of the ecliptic
dow is the day of the week, where Monday is day 1
bs is the number of the day of the year when British Summer Time (BST) begins
fs is the number of the day of the year when BST ends
jd is the Julian day number (of 0:00 hours Jan. 1)

Values I'm unsure about:
delta t is some sort of time delta, but I don't know what
gst seems to be Greenwich Mean Sidereal Time, but for what moment?
x1, x2, and x3 I'm clueless about

Here are my questions:

What might delta t be?  
Is gst in fact Greenwich Mean Sidereal Time?  For what moment?  
What are x1, x2, and x3?  (This is low-priority question.)
How can delta t, gst, and, perhaps other values, be determined for 
    2018, 2019, ...?

Any help will be greatly appreciated.
username_0

**Tags:** fundamental-astronomy, coordinate, observational-astronomy, positional-astronomy

> **Comments:**
> **username_1**: Could you give an example of what the programs calculate? Maybe that might help. Alternatively, do you have the BASIC listings, do they offer any clues?  
> **username_2**: You're asking us to debug a program without even giving us the code.  Have some mercy!  
> **username_3**: I feel your pain. I can't tell you how many times I've scratched my head while pouring over decades old programs with variable names like `xi`, `jas`, and `rp2`. Your best bet is to see how they're used and try to glean the information from context. You might also try changing some values and see how it affects the output. It's hard for us to determine these without the full code.  
> **username_4**: For delta T perhaps: http://eclipse.gsfc.nasa.gov/SEhelp/deltaT.html, Since the Earths axis tilt is 23.5 deg you might look at these numbers on context of the Earth.  
> **username_0**: Thanks to all of you for considering my query.  I should point out that in no way was I asking for analysis of code or help with debugging.  My hope was that someone with astronomical knowledge would recognize the values I posted, and indeed, this has been the case.  Both barrycarter and username_4 2 have pointed me at what looks to be excellent information on delta t and gst.  

---

## 0 answers

