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 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.