![]() ![]() So if I select "mean" coordinates for CdC I get the same as Stellarium. I had forgotten about the annual aberration (parallax doesn't have an effect on stars), which is near the maximum of 20 arcseconds this time of the year and can explain that apparent RA difference of about 1.5min. Of the pole) accurately predict transit times in practice.Īh, thanks for the explanation. Only apparent coordinates (which include precession and nutation ( Stellarium can't hitĠh HA exactly because the JD step-size is too large.) Of course, ![]() Which presumably is "mean place at the beginning of the year In CdC because it is nearly the same as Stellarium's place, The attachment uses "mean place for equinox at date" Transit - but only if you use the same type of place in both Refraction too, which has been excluded up to this point.)ĬdC and Stellarium do predict approximately the same time of The apparent place with these two effects added back in. Removes only the effects of the observer's location (diurnalĪberration, geocentric parallax). Roughly speaking, mean place is the position that removes allĮffects of the Earth and the observer's location. Pressure and temperature settings for refraction go to (In both CdC and Stellarium, you can adjust the atmospheric ![]() Refraction is not included in mean place or apparent place. Still it does not agree with Stellarium, Setting Winnipeg as location at that time, Stellarium shows a 0h1m39s hour angle for polaris, and only shows it crossing the meridian close to what CdC calculates as "mean" RA. Hmm, what exactly is the difference between mean and apparent coordinates? I would expect it might be something like the effect of atmospheric refraction, yet it is not (CdC does not seem to calculate it, at least I haven't found such a setting - and in any case it would not affect RA at the point of crossing the meridian). That you're using Mean Coordinates instead, since that's the difference To duplicate this result, be sure to first go to Setup > Chart, coordinatesĪnd set the type of coordinates to Apparent. That the apparent RA is the same as the LST, the hour angle is correctly ![]() In the attached CdC screenshot, when the system time has been tweaked so Stellarium does return a 0 hour angle as I would expect.Įdited by ecuador, 08 January 2016 - 01:48 PM. How can you possibly have an object with an RA the same as the LST NOT be on the meridian? It is more than 1.5 minutes off. So I changed the time to get the RA of Polaris to match the Local Sidereal Time. I saw that the current epoch Polaris position RA calculation agreed more or less (5 second difference) and Cartes du Ciel gave it as 02h51m35s. However, that only accounted for about 3/4 of the difference with Stellarium, there was still about 1.5 min difference. In looking at why it differs from Stellarium and my app, I found out that Cartes du Ciel does not calculate atmospheric refraction when showing the Hour Angle. In any case, I first compared to Stellarium and it agrees with my app to within a couple of seconds, so Cartes is the odd one out. I had a user of my Polar alignment app for iOS ask me why there was a 6 minute difference to the Polaris Hour Angle calculation compared to Cartes du Ciel. ![]()
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