izubiaurre

So, if I'm understanding correctly, I have to calculate the position for the activity range and then add the drift value (driftAlpha * days passed since start of activity)? And, just not to confuse with values units, driftAlpha and driftDelta are in decimal degrees? For example, Quadrantids have DriftAlpha=3, DriftDelta= -1 values. So I have to understand that Alpha (Right Ascension) is increased by +3 decimal degress per day.

Now I can see the drifft affecting the RA and Dec values. Thanks! But now I have another question: should I apply the number of days (and hours and minutes) since J2000.0 times the drift to calculate the final RA and Dec for the given date within the activity days? Or, it is calculated for the first date and the drifft it is added for the rest of the dates until the end of the activity?

Hi, I'm making a function to calculate the topocentric position of any meteor shower for a given date, but when on the process of calculating the right-ascension and the declination it is somehow based on J2000.0 RA and declination values and a drift value for each of them. I don't really understand how this drift is applied in the calculations... For the information I have found, the drift values are per day (Stellarium handbook), but should I apply the number of days (and hours and minutes) since J2000.0 times the drift? Looking at Stellarium values of the Perseids, it seems that RA and Decl change day by day isn't as much as the drift should affect. Here some examples for Perseids meteor showers in Stellarium: 2000 January 1, 11:58:56 UTC: RA: 3h12m01.72s Dec: +57º69'59.4" 2000 January 2, 11:58:56 UTC: RA: 3h12m01.72s Dec: +57º59'59.4" 2000 January 3, 11:58:56 UTC: RA: 3h12m01.74s Dec: +57º59'59.4" 2000 February 1, 11:58:56 UTC: RA: 3h12m02.00s Dec: +58º00'00.8" 2000 March 1, 11:58:56 UTC: RA: 3h12m02.38s Dec: +58º00'02.6" Drift values (radiant drift/per day): RA: 0h04m48.0s Dec: +0º12'00" As can be seen here, the difference between RA and Dec values day by day, and month by month does not fall near the drift values. Maybe there's some other variable that I'm not counting and counters the effect of the drift? Thank you

Exactly. Thank you!

If I'm understanding correctly what you've said, no. Solar Longitude is the position (angle, 0º-360º) in the elliptic orbit around the sun starting at the vernal equinox. Also, it differs in the number of days each range 0º-90º, 90º-180º, 180º-270º and 270º-360º. Wikipedia

Hi, I'm trying to figure out if it's a way to calculate the date and time (JD) in a year for a solar longitude. I mean, I want to make a function that makes the calculations something like that: double SolarLongitudeToJD(int year, double solarLongitude) { // Here goes the code return JD; } I have searched in Jean Meeus book but found nothing about it (maybe it's the first time I haven't found any solution for my calculations in the book). I think that in the 24th chapter, there are the reverse calculation for what I trying to find: for a given date, various solar coordinates calculations, with the solar longitude between them. Thank you for advance.