Image text: The exact cause of the phenomenon is unknown, but it's thought to be linked to atmospheric refraction and you getting a really cool car.

The green flash is an atmospheric optical phenomena in which a small green spot will appear above or around the sun as it sets below the horizon.  The green flash occurs because of refraction of different colors of light.  Green light is higher frequency than red and orange light and so green light stays visible after the red and orange lights are blocked by the Earth.  Wikipedia has a great gallery of examples of the green flash. Personally, I have been looking for the green flash my whole life and have never seen it.  The name is slightly a misnomer as it is not really a flash at all, but stays for a few minutes.

The Tesla roadster is a new car from the Tesla Motors.  All of the Tesla Motors cars run entirely on electricity.  Check out the car here, as it is a pretty sweet little sports car.  No wonder the Black Hat Character wants to smash the other character over the head with the bottle he is holding to steal the car.

Image text: This is also one of only five identified situations in which a vuvuzela is actually appropriate.

For our international readers, "Toot my own horn" is an expression (possibly only used in America) that means to brag about ones self.

Vuvuzela is a noise maker that is native to South Africa and is featured heavily in any World Cup game.  Many vuvuzelas blown (played?) at the same time make a noise similar to that of a thousand bees.

Image text: Although really, the damage was done when the party planners took the hole punch to the elevator ribbon to hang up the sign.

The Space Elevator is an idea about how to quickly move ships, people and supplies into orbit without the

The Tower of Babel was an ancient building built so that it would be a testament to man's ability and would go so high, it would have its top among the heavens.  This is why the comic is referencing a "modern Babel" because the space elevator would have its top among the stars.

Tensile Strength is the maximum load that a material can support without fracture when being stretched.

Shear strength is the maximum shear stress which a material can withstand without rupture.  The comic is making a pun on this because the Black Hat character is using "shears" or scissors to cut the elevator ribbon.

This comic is also referencing how at a Grand Opening, there is a "ribbon cutting ceremony".  In the comic, there is a "ribbon cutting ceremony", however, the ribbon that is cut is not the ceremonial ribbon, but the space elevator ribbon.

Image text: The other two are still lost on the infinite plane of uniform density.

Let's see if we can work through this one.  The Black Hat character and a female accomplice knock out a Physics professor and put him in a frictionless vacuum.  The professor wakes up and tries to talk but the vacuum prevents him from being able to say anything.  In the first two frames of the bottom section, the professor tries to move, but falls down because the vacuum is frictionless as well.

EDIT: Please see the comments below for Rob and Paige's explanations of the comic who are much more attuned to physics jokes than I am.  Thanks Rob and Paige!

Image text: I bet he'll keep quiet for a couple weeks and then-- wait, did you nail a piece of scrap wood to my antique table a moment ago?

In this comic, we see the return of the Black Hat character, who this time is using his silent hammer invention for trouble.  The skeptics society is a group based on the fact that they must apply reason to all situations and only supports claims that have compelling and complete evidence.  Obviously, the Black Hat character knew this before puling this prank on the "Chair of the American Skeptics Society".  There does not appear to be such a title in real life, but Michael Shermer is the Executive Director of the Skeptics Society.

Additionally, it is probably not a coincidence that the Black Hat character returns on comic number 666.

Image meta text: Please do not try any of this and die or get arrested.

This comic references Titan, a moon of Saturn which has 14% of earth's gravity.  Because the gravity is less, it takes less lift to fly on Titan.

Also, the main character uses hot glue on his wings, similar to how Icarus of Greek Mythology flew too close to the sun with wings made of wax.  Just like Icarus, the character falls after subjected to high levels of heat.  In the comic's case, the heat was applied by a heat lamp from xkcd's resident troublemaker "Black Hat".

Image meta text: Hurricane forums are full of excited comments about central pressure and wind speed and comparisons to Camille and 1931 and 1938, with hastily-tacked-on notes about how it will be tragic if anyone dies and they hope it's a dud.

This comic has "Black Hat" reappear with a monologue about the things he enjoys to do.  There certainly is quite a bit of "rubbernecking" when a hurricane occurs.  Weather Channel certainly has its highest ratings of the year.