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whatta
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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?
Last edited:
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
UMC Time, or Universal Meridian Time, is a system of timekeeping based on the position of the Prime Meridian, which runs through Greenwich, England. It is used as a standard time reference for astronomical observations and calculations.
Right Ascension is a celestial coordinate system used to measure the east-west position of a celestial object in the sky. It is measured in hours, minutes, and seconds, and is analogous to longitude on Earth.
Right Ascension is measured along the celestial equator, which is an imaginary line that follows the Earth's equator projected into space. The zero point of Right Ascension is defined as the position of the vernal equinox, one of the points where the celestial equator intersects with the ecliptic.
Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is measured in degrees, minutes, and seconds, with the Prime Meridian serving as the zero point. Longitude is used to determine time zones around the world.
Since UMC Time and Right Ascension are both based on the Prime Meridian, they are closely related to longitude. In fact, one hour of Right Ascension is equal to 15 degrees of longitude. This means that the Right Ascension of a celestial object can be converted into longitude, and vice versa.