How well defined is a meteor-shower radiant?

How well defined is a meteor-shower radiant? Is it a point on the sky or a several-degree-wide spot?

Radiants are spots, not points. A meteor shower’s radiant is the location on the sky where all the meteors would appear to come from if we could see them approaching in the very far distance. However, the members of a meteoroid stream do not travel perfectly in parallel; over the centuries their orbits become increasingly scattered. Their nonparallel paths mean that the shower’s perspective point is not really a point.

For example, the International Meteor Organization’s Handbook for Visual Meteor Observations lists radiant diameters of 3° for the Perseids, 2° for the Leonids, 4° for the Geminids and Eta Aquarids, “complex” for the Orionids and Taurids, and “diffuse” or unknown for many others.

— Alan MacRobert

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