Halley's Comet visits Earth's atmosphere once every 76 years. What branch of the Earth sciences is the main group that studies these phenomena

Halley’s Comet is probably one of the best researched and the best studied comets which passes close to our planet Earth once per every 76 years. It was first discovered centuries ago by many historic civilizations, including the Babylonian, the Byzantine, Chinese, and other ones

the arctic is a region of the planet, north of the arctic circle, and includes the arctic ocean, greenland, baffin island, other smaller northern islands, and the far northern parts of europe, russia (siberia), alaska and canada.

a. spokes of a wheel.

as indicated in the question radial contains rad, also found in radius, so the fracture's would span the radius.