

The observed position of a meteor's radiant may be explained as follows. The Earth's velocity V_{e } is directed along the apex of the Earth's way. A meteor moving with a heliocentric velocity V_{H} from a radiant located at an angular distance b away from the apex will have a resultant geocentric velocity V_{G} given by V_{G}^{2} = V_{H}^{2} + V_{E}^{2} +2 V_{H }V_{E }cosb and the radiant will appear to be shifted to an angular distance c from the apex where sin c =(V_{H} sin b) / V_{G} The specifics of the Persied meteors, on the 12th August are described in the following diagram. The plane of the diagram is defined by the observer, the direction of the Earth's way and the radiant. V_{e }represents the Earth's velocity towards the apex (29.78km/s) and V_{G }represents the meteoroid's geocentric velocity (59km/s). The angle between the vectors V_{e } and V_{G} is the angle between the radiant and the apex of the Earth's way (40º). The construction allows us to derive the meteoroids heliocentric velocity, which turns out to be 41.25km/s and derive the angle between the apex and the heliocentric direction of the meteoroids (67.5º). Consequently, if the Earth's motion, about the Sun, was suddenly to be frozen, the Persied meteors would appear from a radiant in Cepheus and would travel considerably slower than normal. 