[raybbr]

isn’t space a lot cooler? We are surrounded by a vacuum which, by definition, should be drawing plenty of energy from the planet.

[Telepathic Intruder]

Yes, basically. There's very little energy in the form of radiation reaching earth from space while the sun is down. Any radiation that is absorbed by the ground or atmosphere becomes heat. You have the 3°K from the CMBR and that's about it. Far more energy leaves the earth in the form of radiation.

As far as space being "cool", temperature is a property of mass only. Individual atoms in space can be hot, millions of degrees even, but the overall heat is low because atoms in space are rarefied. All the radiation coming from the sun doesn't become heat until it is absorbed by something.

[IronJack]

isn’t space a lot cooler?

To the degree (!) space is a vacuum, it is neither hot nor cold. In order for something to be either, there has to be some THING there to contain the thermal energy. Since a vacuum is the absence of any "thing," it can't be considered hot or cold.

However, a heated body in space would radiate thermal energy, which could be absorbed by nearby bodies and cause them to warm. That's how the sun warms the earth.