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(meteorobs) Zenith Attraction, some numbers
At 11:03 PM 7/30/99 EDT, GeoZay wrote:
>
>Out of curiosity, which evening showers have a radiant shift as much as 15
>degrees? The biggest shift I can find amongst IMO's working list of showers
>with the radiant low on the horizon is the Draconids at 10.1 degrees, alpha
>Capricornids at 7.8 deg, S. Taurids at 5.3 deg, and N. Taurids at 4.5 deg.
>
>The Perseids will suffer a zenithal shift of 1.1 degrees with radiant low on
>the horizon and 0.3 deg relatively high up.
>geozay
>
To answer George's question, the Kappa Aquarids have the greatest zenith
attraction of any listed shower, with apparent radiant shift of 19 degrees
with the true radiant at the horizon. See the below (in which Rainer and I
agree quite well with regard to the calculated numbers):
** Resend from march 26, 1999 **
i got curious this afternoon [3/26/99] about the actual zenith attraction
numbers that we are dealing with in meteor shower observations, and so
produced the chart below.
This chart shows the heliocentric velocity (sun frame), apparent velocity
(Earth orbit frame), and Geocentric velocity (Earth surface frame) for each
shower. speeds are in km/sec, and directions are measured as the angle
between the shower radiant and the Apex of the Earth's Way (two dimensions
only). All data is derived from the published (Cook, 1973) geocentric
speeds and radiant coordinates for the date of shower maximum.
The difference in meteor speeds between Va and Vg range from about 1 km/sec
for very fast showers, up to about 5 km/sec for very slow showers, while
zenith attraction ranges from a maximum of only 1 deg for very fast
showers, up to a maximum of about 19 deg for the slowest shower (hence,
Lovell's number). The radiant shift can be quite severe for showers less
than about 25 km/sec, but is rather negligible for those showers of better
than 40 km/sec or so. In addition to the velocities mentioned above, the
three recorded numbers are the zenith attraction, dZa in degrees, for
radiant zenith angles of 30 deg, 60 deg, and 90 deg. This last places the
radiant at the horizon.
* key:
Vh = heliocentric speed (km/sec)
Va = apparent speed (km/sec)
Vg = geocentric speed (km/sec)
theta_h = heliocentric elongation angle from Apex point (deg)
theta_a = apparent elongation angle from Apex point (deg)
theta_g = geocentric elongation angle from Apex point (deg)
dZa(##) = radiant Zenith Attraction (deg), with the geocentric radiant at
## degrees of zenith angle.
* In the following arrangement:
Vh, theta_h | Va, theta_a | Vg, theta_g
dZa(30 deg) | dZa(60 deg) | dZa(90 deg)
* Quadrantids *
37.6, 108.4 | 40.0, 63.2 | 41.5, 63.2
0.6 | 1.2 | 2.1
* April Lyrids *
41.6, 101.1 | 46.3, 61.8 | 47.6, 61.8
0.4 | 0.9 | 1.6
* Eta Aquarids *
39.7, 44.3 | 64.5, 25.4 | 65.5, 25.4
0.2 | 0.5 | 0.9
* Northern Delta Aquarids *
41.7, 112.8 | 40.8, 70.3 | 42.3, 70.3
0.6 | 1.2 | 2.1
* Southern Delta Aquarids *
38.9, 110.6 | 39.9, 66.0 | 41.4, 66.0
0.6 | 1.2 | 2.1
* Alpha Capricornids *
35.6, 146.1 | 19.9, 89.2 | 22.8, 89.2
2.1 | 4.5 | 7.8
* Perseids *
40.3, 68.3 | 58.3, 39.9| 59.4, 39.9
0.3 | 0.6 | 1.1
* Kappa Aquarids *
35.5, 162.4 | 11.4, 110.2 | 16.0, 110.2
5.2 | 11.1 | 19.1
* Southern Taurids *
34.7, 136.0 | 24.6, 78.4 | 27.0, 78.4
1.4 | 3.1 | 5.3
* Northern Taurids *
36.3, 133.1 | 27.0, 79.1 | 29.2, 79.1
1.2 | 2.6 | 4.5
* Orionids *
40.2, 42.4 | 65.5, 24.5 | 66.4, 24.5
0.2 | 0.5 | 0.8
* October Draconids *
37.0, 152.9 | 17.1, 100.3 | 20.4, 100.3
2.7 | 5.8 | 10.1
* Leonids *
40.7, 17.8 | 69.8, 10.2 | 70.7, 10.2
0.2 | 0.4 | 0.7
* Geminids *
32.8, 117.7 | 32.5, 63.2 | 34.4, 63.2
0.9 | 1.9 | 3.3
* Ursids *
39.0, 127.6 | 31.5, 78.8 | 33.4, 78.8
0.9 | 1.9 | 3.4
Take care,
Jim
James Richardson
Tallahassee, Florida
richardson@digitalexp.com
Operations Manager / Radiometeor Project Coordinator
American Meteor Society (AMS)
http://www.amsmeteors.org
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