Meteor Shower drift position

[izubiaurre]

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

Edited March 2, 2021 by izubiaurre

[alexwolf]

Please check the values of coordinates within range of activity days

[izubiaurre]

On 03/03/2021 at 07:41, alexwolf said:

Please check the values of coordinates within range of activity days

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? 

[alexwolf]

On 05/03/2021 at 16:28, izubiaurre said:

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? 

This is very good question! We compute coordinates of radiants for valid range of activity from RA/Dec (J2000.0) and drift values to get the correct location of radiants (please compare to official maps: https://www.imo.net/files/meteor-shower/cal2021.pdf). Outside valid range of activity we just place radiant in location of first day of activity, but this is of course not correct by astronomical reason and correct by didactic reason (we mark location of radiant, but people will no see meteors).

 

 

[izubiaurre]

On 16/03/2021 at 17:33, alexwolf said:

This is very good question! We compute coordinates of radiants for valid range of activity from RA/Dec (J2000.0) and drift values to get the correct location of radiants (please compare to official maps: https://www.imo.net/files/meteor-shower/cal2021.pdf). Outside valid range of activity we just place radiant in location of first day of activity, but this is of course not correct by astronomical reason and correct by didactic reason (we mark location of radiant, but people will no see meteors).

 

 

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.