Choosing the Observing Field

Most meteors are witnessed centrally in the field of vision. Thus it is important to choose the field center such that meteors appearing there can be easily distinguished from sporadics and associated to the shower(s) under study. In the vicinity of the radiant, shower meteors are slow moving and have short paths while at larger distances from the radiant they resemble sporadics. A field near the radiant seems therefore more favourable. As we have seen in Section 6.1, the main criterion, the direction of the path, also applies more accurately for meteors in the vicinity of the radiant.

From the above one could perhaps conclude that it is best to look directly at the radiant. But we must consider another point too. Which property distinguishes meteors from stars? Their motion. We witness faint meteors in between the hundreds of stars in our field due to their movement. If a faint star appeared for about one second we would not realize it. But that is exactly the scenario which happens when a meteor occurs in the immediate vicinity of the radiant! We need some degree of movement when witnessing a meteor. On the other hand, very fast-moving meteors are easily missed too. Medium velocity is optimal for perception.

Taking into account all the factors discussed above a distance from the centre of the field of view to the radiant(s) under study of 20° to 40° is optimal. Distances of more than 50° should be avoided.

Besides an elevation of 50° to 70° from the horizon and a radiant distance of 20° to 40°, there is an additional point to be taken into account. If you are going to observe several showers at the same time, which is quite possible, you have to take care that their radiants do not lie in one line as seen from your field centre. Otherwise meteors from these radiants cannot be distinguished by their path directions, and distinguishing them by their angular velocity and path length alone will become difficult and more uncertain. Observing, for instance, the Orionids with their radiant near Betelgeuze (beta Ori) and the epsilon-Geminids with their radiant near Pollux (beta Gem) the field centre should be in Taurus/Auriga/Perseus or Canis Minor/Monoceros/Canis Major rather than in Cancer/Ursa Major or Lepus/Eridanus.

When you have chosen the best-situated field you should follow its diurnal motion as long as conditions (elevation of the field about 50°-70°, artificial lights, obstructions, etc.) permit. If you are forced to change the field, note the time of this change and the new field. For analysis the time of such a change should be identical with the boundary of an observing interval.