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2

The HORIZONS web interface allows for you to change the observer location to other bodies in the solar system. Select "Observer location [change] and read the instructions carefully. I was able to generate an ephemeris showing the Sun's position for the Viking lander location by entering in "Viking 1@499". Mars is designated by "@499&...


2

The advantages of using Julian dates (and what to do with the "- 2450000" part) have been described well in previous answers but if you're curious about the "barycentric" part here's an example. Let's say I'm observing an eclipsing binary to measure the period which might be changing. Six months later I observe the system again. The ...


3

Adding to the answers above: One of the problems here is that Julian Day Numbers start at noon of a particular Gregorian Date. For the dates under consideration January 31, 2010 starts on JDN 2455227.5 February 1, 2010 starts on JDN 2455228.5 You mentioned needing a reliable source for date algorithms. I recommend https://www.researchgate.net/publication/...


7

Julian dates offer one nice feature: All astronomical observations recorded by humankind have a positive timestamp. A key downside of Julian dates is that current timestamps on computers that use 64 bit IEEE Standard for Floating-Point Arithmetic (IEEE 754) have a resolution of 40 microseconds. Almost all computers use the IEEE 754 floating point standard. ...


5

That is a simple offset in order to work with smaller numbers. Add that number (2450000) again to each value in the day column and you have the unmodified value of BJD.


12

The formula in the wikipedia article explicitly uses integer division with round toward zero. Python's integer division uses round toward negative infinity (i.e., floor). The wikipedia article formula repeatedly uses (m-14)/12. This evaluates to -1 for months 1 and 2 (January and February), zero otherwise. You can use the wikipedia article formula in python3 ...


7

The formula is correct. However, the "problem" is with Python1. https://stackoverflow.com/questions/5535206/negative-integer-division-surprising-result. Here is the fix to the formula: jd = (1461 * (y + 4800 + int(float(m-14)/12))) // 4 + (367 * (m - 2 - 12 * (int(float(m-14)/12)))) // 12 - (3 * ((y + 4900 + int(float(m-14)/12)) // 100)) // 4 + d -...


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