As a current astronomy student, I would simply recommend that you read An Introduction to Modern Astrophysics by Carroll and Ostlie. I've heard it said that it contains about 90% of everything any astronomer knows, with the other 10% being specialization. Once you've read through most of it, you'll at least be able to follow most astronomy papers. If you're comfortable with simple calculus and basic physics, you shouldn't have too much trouble with it.

It really doesn't involve any more science than any other movie, and I would hardly consider simply using science to be the defining characteristic of SF. SF uses science, or pretends to, in fantastic ways that are not currently possible in order to tell a story--usually one about the ramifications of fictional science or technology. Sending astronauts into low Earth orbit is not only possible, it's routinely done.

Gravity isn't science fiction. We actually do send people into space, and that kind of disaster could sort of happen. There's no speculative science, predictions of the future, or fantasy elements to it. And that's really cool--what seems so much like SF is actually a real-life job that some people do everyday.

I liked The Clone Wars, you insensitive clod!

I can't even type that jokingly without cringing.

And intelligent life is even rarer still. In 4 billion years of evolution, intelligent life (i.e., intelligent enough for high technology) has only evolved once and has only been around a few million years. But I don't think we're in serious danger of extinction any time soon. We're extremely adaptable, and once we establish self-sustaining colonies on other worlds, it's very unlikely that any act of nature will kill us off. That means the only plausible threat to our survival is ourselves, and we've been getting less violent throughout our history. That trend probably won't reverse any time soon.

I suspect that, once intelligent life does evolve, it probably survives more often than not. That means there probably aren't many species anywhere near our level of technology, as most are probably much, much older than us.

No, all units are lowercase in SI (in English), but abbreviations of units named after people are usually capitalized. For example, 1 joule per second (1 J/s) is equal to 1 watt (1 W).

While the Sun's heat probably played a role in ISON's destruction, I think the main reason it broke up was because of the Sun's tidal forces. ISON was within its Roche limit, where the tidal effects of the Sun were enough to overpower ISON's own gravity, tearing the comet apart. Most of it is probably orbiting the Sun right now as a very small ring.

The Simpsons manage to stay fresh and funny? When did that start again?

Granted I haven't watched the last few seasons, but I don't think that show has been funny in years.

Okay, I'll reword it. I don't understand why it's still used as much as it is.

It doesn't make any sense to me. It's a very limited, antiquated, and error-prone medium. Now that so many people have smartphones that are capable of email and IM, it doesn't really make sense that we should continue to use this. Why should I be forced to use such a tiny computer because you're not at your desk?

(I assume that "texting" refers specifically to SMS text messaging, as most people use the term, not as any message containing text.)

You could always have yourself castrated. But why do that when you could use your sexual energy to your advantage by conditioning yourself into having some kind of weird programming fetish.

With all the features people want in this thing, the battery will probably have to be pretty big or you won't get much use out of it. (It will be enough of a change to have to plug my watch in every night; I don't want to have to do it every few hours.) Which means the only way anyone is going to release something like this is if it has very limited features--maybe just time, date, a few basic alerts, etc., which means it probably won't be worth the cost. But then again, people will spend $500 on a watch that keeps worse time than the one that came with my breakfast cereal, so you never know.