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Where can I find a triplet of UTC Time, Right Ascension (of zenith) and Longitude, preferably with many, many safe decimal places?
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Based on what? To do that, the program needs to know position of Earth relative to stars at some moment. The minimum of data to perform such a computation is a triplet I want.russ_watters said:Any good astronomy program will tell you the RA of the zenith to several decimal places (what's a "safe decimal place"?).
I assume english translation of this is that at "JDJD 2451545.0 (J2000)" local sidereal time of longitude 0 was equal to 0.997269566329084 of UT1 time, which was... ? it is said also that UT1 could be found as UTC (January 1, 2000, 11:58:55.816 UTC) + DUT1 but I have no idea where to look this DUT1 up :( somebody please help me with this mess before I kill myself. EDIT: according to this graph it was around +0.35 sec, but exact value would be nice.The ratio of UT1 to mean sidereal time is defined to be 0.997269566329084 − 5.8684×10^−11T + 5.9×10^−15T^2, where T is the number of Julian centuries of 36525 days each that have elapsed since JD 2451545.0 (J2000).
if ((year < 1582) || ((year == 1582) && ((mon < 9) || (mon == 9 && mday < 5)))) {
b = 0;
} else {
a = ((int) (y / 100));
b = 2 - a + (a / 4);
}
return (((long) (365.25 * (y + 4716))) + ((int) (30.6001 * (m + 1))) +
mday + b - 1524.5) +
((sec + 60L * (min + 60L * hour)) / 86400.0);
* GMST -- Calculate Greenwich Mean Siderial Time for a given
instant expressed as a Julian date and fraction. */
double gmst(double jd)
{
double t, theta0;
/* Time, in Julian centuries of 36525 ephemeris days,
measured from the epoch 1900 January 0.5 ET. */
t = ((floor(jd + 0.5) - 0.5) - 2415020.0) / JulianCentury;
theta0 = 6.6460656 + 2400.051262 * t + 0.00002581 * t * t;
t = (jd + 0.5) - (floor(jd + 0.5));
theta0 += (t * 24.0) * 1.002737908;
theta0 = (theta0 - 24.0 * (floor(theta0 / 24.0)));
return theta0;
}
Your screenshot sais, "Altitude 88°". Zenith is 90°, isn't it.russ_watters said:The cursor disappeared when I did the printscreen, but rest assured, it was right on the zenith.
Date: February 13, 2007, 12:05:08 pm
Julian date: 2454144.95856
Stellarium output /15 (1): 20.5457510321
Yoursky output (2): 20.5457282109
Taking 20h away and converting to minutes:
(1) 32.7450619233
(2) 32.7436926529
Date: February 13, 2007, 1:05:08 am
Julian date: 2454144.50023
Stellarium output /15 (1): 9.51563402541
Yoursky output (2): 9.51561121915
Taking 9h away and converting to minutes:
(1) 30.9380415245
(2) 30.9366731487
Date: February 13, 2007, 2:05:08 am
Julian date: 2454144.50356
Stellarium output /15 (1): 9.59585307131
Yoursky output (2): 9.59583026493
Taking 9h away and converting to minutes:
(1) 35.7511842786
(2) 35.7498158961