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furrysocks2

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About furrysocks2

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  1. Another thread using aaplus - for a given date, correcting J2000 RA/Dec coordinates for proper motion, precession, nutation and aberration:
  2. Confirmed - will be changed next release.
  3. From the source: If Alpha is in hours and Delta is in degrees, then PMAlpha should be in seconds and PMDelta in arcseconds. I'll query a documentation bug with the author.
  4. Terminology for units... "hours, minutes and seconds" vs "degrees, arcminutes and arcseconds". But you're right... That throws my RA way out... I wonder if it's an error in the documentation.
  5. 0.33466 is in as/yr - quoted on wikipedia as 334.66 mas/yr, so you shouldn't need to convert from milli...?
  6. Just a quicky... Right ascension and hour angle are not equivalent... hour angle = local sidereal time - right ascension. Local sidereal time should account for this. Of course, you'll use the hour angle when you're converting to horizontal coordinates.
  7. OK, in Cartes du Ciel, I set the time, searched for Theta Persei and double clicked it: My Initial - RA: 2.736663 (41.049946), Dec: 49.228448 2h44m11.987040s, 49º13'42.411100" CDC Astrometric J2000 - RA: 2.736938 (41.054063), Dec: 49.227725 2h44m12.975000s, 49º13'39.810000" Error (in arcseconds) - RA: -14.819400, Dec: 2.601100 My Mean - RA: 2.769718 (41.545775), Dec: 49.348461 2h46m10.986074s, 49º20'54.460414" CDC Mean Date - RA: 2.769812 (41.547183), Dec: 49.348450 2h46m11.324000s, 49º20'54.420000" Error (in arcseconds) - RA: -5.068896, Dec: 0.040414 My Final - RA: 2.770569 (41.558535), Dec: 49.352026 2h46m14.048310s, 49º21'7.293791" CDC Apparent - RA: 2.770662 (41.559937), Dec: 49.352025 2h46m14.385000s, 49º21'7.290000" Error (in arcseconds) - RA: -5.050353, Dec: 0.003791 Uncertain what the "Apparent Astrometric J2000" coordinates actually represent, as the error is large, but the other two match up nicely in Dec and both 5 arcseconds out in RA. Here's the code, with print lines removed for clarity: // Initial auto initial = mk_coord(HMS(2, 44, 11.98704), DMS(49, 13, 42.4111)); auto stellarium_0124_initial = mk_coord(HMS(2, 44, 12.7), DMS(49, 13, 40.9)); auto stellarium_0151_initial = mk_coord(HMS(2, 44, 12.71), DMS(49, 13, 40.9)); // Proper motion double J2000_0 = 2451545; double JD = 2462088.64832177; double pmAlpha = 0.33466 / 15; double pmDelta = -0.08999; CAA2DCoordinate proper_motion = CAAPrecession::AdjustPositionUsingUniformProperMotion((JD - J2000_0) / 365.25, initial.X, initial.Y, pmAlpha, pmDelta); // Precession CAA2DCoordinate precession = CAAPrecession::PrecessEquatorial(proper_motion.X, proper_motion.Y, J2000_0, JD); // Obliquity and Nutation double obliquity = CAANutation::MeanObliquityOfEcliptic(JD); double nutation_longitude = CAANutation::NutationInLongitude(JD); double nutation_ecliptic = CAANutation::NutationInObliquity(JD); CAA2DCoordinate D = precession; double alpha_nutation = CAANutation::NutationInRightAscension(D.X, D.Y, obliquity, nutation_longitude, nutation_ecliptic); double delta_nutation = CAANutation::NutationInDeclination(D.X, /*D.Y,*/ obliquity, nutation_longitude, nutation_ecliptic); // Aberration CAA2DCoordinate aberration = CAAAberration::EquatorialAberration(D.X, D.Y, JD, true); //Final auto result = mk_coord(precession.X + alpha_nutation/3600.0/15.0 + aberration.X, precession.Y + delta_nutation/3600.0 + aberration.Y); // Stellarium for comparison auto stellarium_0124 = mk_coord(HMS(2, 46, 11), DMS(49, 20, 55)); auto stellarium_0151 = mk_coord(HMS(2, 46, 11.06), DMS(49, 20, 55.5)); auto stellarium_0151_nutation = mk_coord(HMS(2, 46, 9.7), DMS(49, 20, 52.9)); // Cartes du Ciel for comparison auto cdc_astrometric_j2000 = mk_coord(HMS(2, 44, 12.975), DMS(49, 13, 39.81)); auto cdc_mean_date = mk_coord(HMS(2, 46, 11.324), DMS(49, 20, 54.42)); auto cdc_apparent = mk_coord(HMS(2, 46, 14.385), DMS(49, 21, 07.29)); Interestingly, applying nutation in Stellarium 0.15.1 changes both RA and Dec in a negative direction, whereas CDC mean->apparent and my own calculations both move in the positive direction. Perhaps also interestingly, CdC's "Apparent Astrometric J2000" is closer to the "RA/DE (J2000)" values in Stellarium than the values from SIMBAD, but I'm unsure why. // Initial auto initial = mk_coord(HMS(2, 44, 11.98704), DMS(49, 13, 42.4111)); auto stellarium_0124_initial = mk_coord(HMS(2, 44, 12.7), DMS(49, 13, 40.9)); auto stellarium_0151_initial = mk_coord(HMS(2, 44, 12.71), DMS(49, 13, 40.9)); ... // Cartes du Ciel for comparison auto cdc_astrometric_j2000 = mk_coord(HMS(2, 44, 12.975), DMS(49, 13, 39.81));
  8. I have compiled a C++ program against aaplus and its output is shown below: Initial - RA: 2.736663 (41.049946), Dec: 49.228448 2h44m11.987040s, 49º13'42.411100" Stellarium (0.12.4) - RA: 2.736861 (41.052917), Dec: 49.228028 2h44m12.700000s, 49º13'40.900000" Error (in arcseconds) - RA: -10.694400, Dec: 1.511100 Stellarium (0.15.1) - RA: 2.736864 (41.052958), Dec: 49.228028 2h44m12.710000s, 49º13'40.900000" Error (in arcseconds) - RA: -10.844400, Dec: 1.511100 Proper motion - RA: 2.736842 (41.052630), Dec: 49.227726 2h44m12.631081s, 49º13'39.813364" Precession - RA: 2.769718 (41.545775), Dec: 49.348461 2h46m10.986074s, 49º20'54.460414" Nutation (in arcseconds) - RA: 15.845633, Dec: 6.219740 Aberration (in arcseconds) - RA: 30.087910, Dec: 6.613637 Total corrections (in arcseconds) - RA: 45.933543, Dec: 12.833377 Final - RA: 2.770569 (41.558535), Dec: 49.352026 2h46m14.048310s, 49º21'7.293791" Stellarium (0.12.4) - RA: 2.769722 (41.545833), Dec: 49.348611 2h46m11.000000s, 49º20'55.000000" Error (in arcseconds) - RA: 45.724647, Dec: 12.293791 Error (pre-nutation/aberration, in arcseconds) - RA: -0.208896, Dec: -0.539586 Stellarium (0.15.1) - RA: 2.769739 (41.546083), Dec: 49.348750 2h46m11.060000s, 49º20'55.500000" Error (in arcseconds) - RA: 44.824647, Dec: 11.793791 Error (pre-nutation/aberration, in arcseconds) - RA: -1.108896, Dec: -1.039586 Stellarium (0.15.1 w/ nutation) - RA: 2.769361 (41.540417), Dec: 49.348028 2h46m9.700000s, 49º20'52.900000" Error (in arcseconds) - RA: 65.224647, Dec: 14.393791 Error (pre-nutation/aberration, in arcseconds) - RA: 19.291104, Dec: 1.560414 OK... there's a lot here - note: I'm sticking to equatorial coordinates and not converting to topocentric horizontal coordinates. firstly, I note that the J2000 RA/Dec in Stellarium differs from the SIMBAD J2000 coordinates by ~10.7-8 arcseconds RA and 1.5 arcseconds Dec - they differ between 0.12.4 and 0.15.1 only by 0.01 seconds in RA which will due to rounding so can be ignored, so it would be interesting to know what catalog Stellarium uses, or whether there is an option I'm missing. compared to the book, the total nutation and aberration corrections I have calculated are within 0.0455" in RA and 0.0816" in Dec - very minimal difference the closest match appears to be between my pre-nutation/aberration value and Stellarium 0.12.4's "RA/DE (of Date)" values, which would lead me to assume 0.12.4 does not account for nutation/aberration (google suggests this was introduced in 0.14.0 or just before) - but this confuses me a little given the difference in initial RA/Dec... perhaps it is using different RA/Dec values than are displayed, or different values for proper motion that happen to coincide the next closest match appears to be between my pre-nutation/aberration value and Stellarium 0.15.1's "RA/DE (of Date)" values, without checking the "Include nutation" checkbox... this is again quite good but the same confusion as above therefore arises, given the difference in starting RA/Dec, particularly RA. looking then at Stellarium 0.15.1 with "Include nutation" checked, the error between "RA/DE (of Date)" and my calculated values including nutation/aberration is the largest error of all these data points, which is confusing given that the corrections I calculated match the book very well, leading me to wonder whether or not Stellarium is calculating nutation correctly or not - my pre-nutation/aberration values more closely match Stellarium 0.15.1's calculations with nutation. A very quick prod of Cartes du Ciel appears to give figures that match more closely to those I have calculated, but is very configurable wrt coordinates - warrants a closer look...
  9. In a spreadsheet, I get: Working backwards from your proper motion value, I think I see that you're using the value 0.33466 in seconds per year, but it is in fact a value in arcseconds per year. I might be wrong, but check your units again just in case.
  10. Error in az seems a bit much, I can tell why you're still looking at it. Alt is "ok" but az, could be out by an entire fov with a small sensor. A few thoughts? Using Calculator, I can't get your proper-motion-adjusted RA to match your initial RA - can you check that one? For completeness, can you print out a value corrected for mean equinox? (ie after proper-motion, before nutation etc) Ignoring the Alt/Az for a second, how do your final RA/Dec compare with Stellarium's "RA/Dec (on date)" values? Are you sure you've set Stellarium location correctly? Have you got "Include nutation" and "Topocentric coordinates" both checked in Stellarium Configuration>Tools? Note that you can tick "Use decimal degrees" in Stellarium to make it easier to compare if you want. If you're still having issues, if you can repost your up-to-date code, I'll try compiling it against aaplus in C++.
  11. One degree = 60 arcminutes = 3600 arcseconds, and one hour = 60 minutes = 3600 seconds = 15 degrees = 900 arcminutes = 54000 arcseconds. For 2h44m11.986s, I'd convert to decimal hours first (2.74... or whatever) and then x15. The proper motion for Theta Persei on Wikipedia is quoted in mas/yr, or milliarcseconds per year, for both RA and dec. So for RA, you have to divide by 15 to get seconds per year if that's what you need to work with. You do have to be careful with units, and note that for trig functions, you typically need to convert to radians.
  12. Only briefly, a bit short on time - any reason you adjust for aberration before proper motion? I thought in the book it came after that and mean equinox. I've played with rise/set for planets not long ago, Perseus should be visible, so seems a bit odd. Keep me posted if you make progress, I'll let you know when I get a chance to get back to it.
  13. I'm getting confused at the first step. I don't know how far I'll get but basically trying to go independently from SIMBAD to Stellarium, ignoring the values in the book. I'm using astropy (SkyCoord, Angle, etc...). I'm also outputting error wrt the values in your test run above. Initial coords... 02h44m11.987s +49d13m42.4111s 2.73666306667, 49.2284475278 Error in RA: 0.0155999999095 arcsec Error in Dec: -0.0689000000989 arcsec Proper motion per year: 0.33466arcsec, -0.08999arcsec Final epoch: 2028-11-13T03:33:35.000 t = 0.28866935857 (28.866935857 Julian years) Effect of proper motion: 9.66061arcsec, -2.59774arcsec Taking into account proper motion... 02h44m12.6311s +49d13m39.8134s 2.73684196683, 49.2277259346 Error in RA: -29.9470312962 arcsec Error in Dec: -6.81113783235 arcsec Converted to final mean equinox... 02h46m10.9898s +49d20m54.5153s 2.7697193958, 49.3484764704 Error in RA: -29.9937433338 arcsec Error in Dec: -6.70072111622 arcsec Can you explain exactly how you reach this line: Variations of the proper motion: 2.73739654148241 right-ascension, 49.2296179172985 declination Unless I've misunderstood something, your value for dec appears to be greater than the starting dec by approx 4.14" though proper motion is -ve in dec, and your change in RA is 4x greater than I'd expect.
  14. Odd, you're welcome to send me code snippets if you like.
  15. Check your proper motion... try 0.02231 instead of 0.03425 and -0.08999 instead of -0.0895. Differences between your code and book look like (lack of) rounding, whereas I reckon Stellarium will have different values for the proper motion as Meeus and SIMBAD/Wikipedia disagree.