# Tag Info

52

From the PyEphem Quick Reference Guide: Rising and setting are sensitive to atmospheric refraction at the horizon, and therefore to the observer’s temp and pressure; set the pressure to zero to turn off refraction. It seems likely that, if you're using the default settings, the result returned is including atmospheric refraction, giving the results you ...

28

You made the same fundamental mistake that Anton Gromov made in his question on the sister Space Exploration StackExchange network site: You used the solar system barycenter rather than the Sun as the frame origin. Had you used the Sun, the apparent discrepancy would have dropped by almost two orders of magnitude. A much lesser flaw is that you apparently ...

22

Correct me if I am wrong, but if we count sunsets by the center of the Sun apparently crossing the horizon then the Sun is supposed to set every day at latitudes under the arctic circle. That is not how PyEphem defines sunrise and sunset. It defines sunrise as the time the top of the Sun would nominally first appear above an unobscured horizon (no mountains)...

13

This is because the summer and winter solstices (approx. June 21st and December 21st) do not correspond to the aphelion and perihelion (approx. July 5th and January 4th). Therefore, the average distance from the Sun is longer in the period from the Summer Solstice to Winter Solstice than vice versa, so the Earth is moving slower (on average) and it takes ...

9

Wikipedia's article on the Arctic Circle provides the explanation. Firstly, it says: because the sun appears as a disk and not a point, part of the midnight sun may be seen on the night of the northern summer solstice up to about 50 minutes (′) (90 km (56 mi)) south of the Arctic Circle. As the Arctic Circle is currently at roughly 66°34′N, this means a ...

7

Would this not mean that information travels infinitely fast and thus contradict Relativity? Look more closely at equation 27 in the referenced document. I'll simplify this as $$\boldsymbol{\mathrm a} = \left(\sum_{B \ne A}\frac{GM_B\,(\boldsymbol{\mathrm r}_B - \boldsymbol{\mathrm r}_A)}{r_{AB}^{\,3}} \Bigl(1 + \text{other terms}\Bigr)\right) + \text{... 5 The PeakFinder app1 can do most of what you're looking for. It's available for Android and IOS as well as through a web browser. The app shows the paths across the sky for both the sun and moon2 and displays rise/set times taking into account the local topography and viewpoint elevation3. At least the Android version works without a network connection (... 5 Short answer is "no". I can model gravity by Newton's law of gravitation, and it gives extremely accurate results in most situations. Even though it is an approximation to the more accurate model of gravity in General Relativity, it is accurate enough to predict the location of the planets well enough for most purposes. The actual models used are ... 5 JPL HORIZONS gives the distance from the observer to the target as delta. In Table Settings this option is 20. Observer range & range-rate. For asteroids and comets, it can also give distance uncertainty (39. Range & range-rate 3-sigmas) as RNG_3sigma. You can choose units of au or km. For example, with Table Settings: QUANTITIES=1,20,39; range units=... 5 For those who don't have ready access to a copy of Astronomical Algorithms, Meeus's first approximation looks like:$$ \text{JDE} = 2541547.51 + 365.259636 ~k + 1.6 \times 10^{-8} ~k^2 $$where k, the number of anomalistic years since the January 2000 perihelion, is half of some integer. This neglects the influence of the Moon and other planets, so he adds a ... 5 This is a fairly standard ephemeris for e.g. times of maximum light of a variable star but you are getting some of the symbols mixed up. The ephemeris is normally written as:$$ T_{event} = T_0 + P\times E $$where T_{event} is the time of the given event (time maximum or minimum light, maximum positive radial velocity etc), T_0 is a reference time ... 4 Iorio (Preliminary constraints on the location of Telisto/Planet Nine from planetary orbital dynamics) has suggested transmissions from the New Horizons probe (currently beyond Pluto) could be used to test for the influence of the proposed new planet, and provide constraints to its possible position. It is estimated that the position of New Horizons could ... 4 The diagram below illustrates the reason, which is that the earth moves at different speeds during it revolution around the sun and the distribution of those speeds is not equal because the solstices/equinoxes are not located at symmetrical points on the ellipse vis-a-vis the speed symmetries, which are centered on the aphelion and perihelion. Diagram by ... 4 From the Wikipedia page on the Tropical year, The mean tropical year is approximately 365 days, 5 hours, 48 minutes, 45 seconds. Starting from the Tropical year proceeding after your birth date, you can calculate 27 Tropical years forward by adding that approximate amount of time 27 times over. 4 Probably the most reliable guide to vsop2000-p11.dat is the reference implementation vsop2000.for. The input line in question is the first of 5399 k=0 records contributing to x. Those are followed by 5842 k=1 records, 610 k=2 records, and so on up to k=8. Then y (k=0..8) and z (k=0..7) follow the same pattern. If I read the Fortran code correctly, the ... 4 There is a python package called Skyfield that loads, reads and interpolates the binary forms of the JPL Development Ephemerides or DEs for you, and does everything else you need to get the absolute best results possible from them. If you can use even a tiny bit of python then this would be the way to go rather than trying to figure out how to interpolate ... 4 This link even gives you the algorithm to calculate: link here Also, if you are comfortable with the VSOP, the VSOP2000 does have the moon data... the ephemerides can be downloaded from here 4 Do you need 1000 years? 50 years? 1-hour accuracy? 1-second accuracy? A simple linear interpolation for the perihelia from the year 2000 to 2050 gives a maximum error of about 1.3 days for the year 2009 and a mean absolute error of about 19.3 hours: et = 31558511.31638778 * year - 63116806104.00429 et is the so called ephemeris time (used by NAIF team in the ... 4 I post another answer because I think it should work better for you. Since I read in one your comment that you “only need a few years past and (mostly) future from 2021” and that you need “at least one-hour accuracy”, here’s my proposed method. I still don't know how many years you really need, but the following table shows the perihelia and aphelia with a 1-... 4 The Photographers Ephemeris is a very nice tool to give you the direction and time of both Moon and Sunset and -rise, made for exactly that purpose: plan and time shots to be at the right place and time for an awesome scenery. Other programmes and tools to tell you rise and set times are Stellarium heavens above time and date 3 Given a date and time, the position of the Moon can be calculated to provide the declination and right ascension. The sub-point of the Moon (the point on the Earth at which the Moon is at the zenith) is as follows: latitude = declination of the Moon longitude can be found by calculating the local mean sidereal time (LMST) that equals the Moon's right ... 3 Be aware there are differing formats. SPK is the newer format - the older text format seems to be deprecated. It's worth having a look at the documentation on this jplephem python library as it explains the format reasonably well. If you do use SPK, you'll need to read all of the documentation in NASA's SPK repository I'm not sure if this is from the same ... 3 There are many different ways of doing it. One way is to use the Keplerian elements and their rates obtained from the JPL Solar System Dynamics web site to determine the Cartesian coordinates of the planets in the ecliptic plane at a given time. Information and data to allow computation of approximate positions for the planets is provided in the document "... 3 It means that there is a moonset at that time on the third of February. At the equator, it is certain that the moon that set at 0041, rose the previous day (Feb 2nd), at about midday. (the moonset is about 50 minutes later each day, which means that there can be days with no moonset, but you can't have a day with two moonsets) On days with no moonset the ... 3 This excellent answer to Besides retarded gravitation, anything else to worry about when calculating MU69's orbit from scratch? in Space Exploration SE explains that we get the wrong answer if purely Newtonian mechanics is used except for slowing down the speed of gravity, but that's because one is neither treating gravity correctly nor using Newtonian ... 3 There is no easy formula for what you want. Astronomical Algorithms provides an algorithm for the times of perihelion and aphelion passages of the Earth-Moon barycenter. The times at which the Earth itself is closest to / furthest from the Sun is made much more complex by the fact that the Earth and Moon orbit one another as well as the Sun. Because ... 2 By trial and error I found that the following email text (including intermediate comment lines) is acceptable to HORIZONS:- !$$SOF EMAIL_ADDR = 'xxxxxx@gmail.com' !...Target= Mercury COMMAND= '199' !...Reference Site = Centre of Sun CENTER= '500@10' MAKE_EPHEM= 'YES' TABLE_TYPE= 'VECTORS' OUT_UNITS= 'KM-S' REF_PLANE= 'ECLIPTIC' REF_SYSTEM= 'J2000' VECT_CORR=...

2

The DE430 JPL ephemeris "memo" (https://ipnpr.jpl.nasa.gov/progress_report/42-196/196C.pdf) has details of how it is constructed and what from. Mercury and Venus's positions are tracked by tracking the spacecraft orbiting them (to sub-km accuracy). Mars, Jupiter and Saturn are also measured from the orbiting spacecraft such as Galileo and Cassini. The outer ...

Only top voted, non community-wiki answers of a minimum length are eligible