#14 - Unlike stars, planets do not generate light, but only

[jackieb]

Hey Jackieb,

The author's conclusion is that "there are celestial objects in this galaxy that generate light but are not stars", based on the fact that planets don't generate light, and there are other objects in the galaxy that aren't planets. The author sets up 3 categories of things: planets, stars, and "others" and they say that becuase the other things in the galaxy aren't planets (which don't generate light) these other things must generate light. But that's not necessarily true - there could be things in the galaxy which are not planets and which also don't generate light.

You said the author allows for some to not generate light, but they actually do not here, they assume that everything which is not a planet must also generate light - either because it is a star or because it is part of this 'other' category.

Hope that helps!

Hi Dana,

I'm sorry- I still don't understand how we know the author thinks ALL other celestial objects generate light. The conclusion says "there are celestial objects in this galaxy that generate light but are not stars." To me, the author is only saying there are some other celestial objects that generate light- not ALL of them have to. How do you know the assumption is all of them have to?

[Luke Haqq]

Hi jackieb!

To understand this one, perhaps it could be helpful to start with the conclusion and ask what's missing. The author concludes that "there are celestial objects in this galaxy that generate light but are not stars." How does the author arrive at this conclusion? We're just told that planets are unlike stars in that they do not generate light, and that there are other celestial objects that are not planets. The author's conclusion would follow if it were the case that all other celestial objects besides planets generate light.