eli5: Does the light coming from the stars which are light years away still contain some heat or is it lost as the light travels?
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yes, the star light is heat in the form of radiation, but the stars are so far away that it dissipates by the time it reaches earth & is scattered when it hits the atmosphere
It contains energy, yes. But it’s such a small amount that, in practice, it’s negligible for faraway stars.
In dense star clusters, however, where there are thousands of stars packed tightly together, starlight is enough to heat the gas in the cluster.
Technically it’s not heat until the radiation interacts with matter, but yes, the light from distant stars heats whatever it falls on.
Need to clarify on some misunderstanding of the words “light” and “heat”.
What you call “light” IS electromagnetic radiation of some wave length.
What you call “heat” is, again, electromagnetic radiation of some wave length. Typically we call “heat radiation” light in the infrared spectrum, but to be precise light of any frequency can heat any surface that can absorb them (https://en.m.wikipedia.org/wiki/Infrared). And when I use the verb to “heat” it means to transfer energy that excites atoms and “makes them wiggle more”.
So, as an example, radiowaves used to transmit music are also light and they can also heat stuff. Any light of any spectrum can potentially heat stuff.
The main difference between starlight and sunlight is that starlight is dimmer because stars are so much farther away. It gets dimmer because it’s spreading out, so light isn’t being lost (unless there are dust clouds or red-shift). So if you had a star just like the sun but a million times farther away it would light and heat us in the just same way but a trillion times more weakly (because a million squared is a trillion).
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