Question

The heat from the Sun reaches the Earth through empty space. This must mean the heat transfer being used is radiation.

Answer 1

Yes — in empty space heat is transferred by radiation. Conduction and convection need matter (molecules or a fluid) to carry thermal energy, so they cannot operate through a vacuum.

What actually happens: the Sun emits electromagnetic radiation (photons) across a spectrum (visible light, near‑IR, some UV). That radiation travels through space and is absorbed by the Earth and its atmosphere, raising their internal energy (i.e. heating them). The Sun’s surface (~5778 K) acts roughly like a blackbody; the solar flux at Earth’s orbit is about 1361 W/m² (the “solar constant”), averaging to roughly 340 W/m² over the whole Earth and, after reflection by clouds and surface (albedo), about 239 W/m² is absorbed.

After the radiation is absorbed, conduction and convection in the atmosphere and oceans redistribute the heat, and the Earth in turn emits thermal (longwave IR) radiation back to space. (A small additional energy flux comes from the solar wind — charged particles — but it is negligible compared with the radiative flux.)