What is an ectotherm?

 

An ectotherm is an animal (perhaps a reptile or fish) which can't control their body temperature internally - they control their body temperature through their behaviour. This might be through a number of ways - including physically moving from one place to another, so from direct sunlight to shade so they don't overheat.

In the case of ectotherms, their internal temperature depends on that of their surroundings and their activity level depends on the external temperature. They're more active at higher temperatures and less active at lower temperatures.

As far as their metabolic rate is concerned, it's variable and they generate very little heat themselves.
 

How does the sun "burn" if there is no oxygen in space?

At first glance, an image of the sun may resemble a roaring fire. However when astronomers talk about the sun "burning" they are actually talking about a process called nuclear fusion. This process involves the forcing together of tiny hydrogen nuclei in the core. Nuclear fusion takes place in the core as nuclear fusion need high pressure and high temperatures, both of which are present in the sun's core.