 Greetings and welcome to the Introduction to Astronomy. In this week's Misconception in Astronomy, we are going to talk about comets and address the misconception that the tail of a comet actually trails behind a comet. That might be what you expect, but that is not what always happens. So let's take a look at comet tails. First of all, what is a comet? Comets are balls of ice and other generally carbonaceous materials, and when they pass near our sun, the material is vaporized, and that gives us the comet that we say, see. That material is pushed away from the comet and gives us these tails, and we can actually see two tails here. We see one going pretty much straight back from the head of the comet, and another that kind of curves off to the side here. So this is the material from the comet itself. We cannot actually see the head of a comet unless we take a spacecraft up there to go see it. It's buried within this, and is usually only a few kilometers in size. Now since this is material that is pushed back by the sun, it is the solar wind and the sun that is doing this, the tail always points away from the sun. So where is the sun in this image? The sun has to be off in this direction, opposite to where we see the tails. And that means that we will always see the tails opposite in the sky to the sun. Now let's take a look at this in terms of an animation, and we can watch the tails here, and you'll note that as the comet here starts to come in, the tails are lagging behind the comet. But as it loops around the sun and it leaves, then the tails lead the comet. So the tails do not follow along as you might expect, they actually always point away from the sun. And you can see that in this image that we see both of those two tails that are present. Now let's take a look at those two tails briefly. We saw two tails here, we saw one going straight back. That is the ion tail, and that consists of individual atoms and ions. So that goes straight back from the sun and is individual particles. On the other hand, the dust tail is somewhat larger particles, and therefore it lags behind in the orbit. So what we know just from looking at this, we know the sun is off in this direction. So that's where the sun is. But we also know that the direction of motion of the comet is off in this direction. So that's because we know that these are lagging behind. So just from looking at the comet and tails, we can get those two pieces of information. So let's go ahead and finish up with our summary, and what we've looked at this time is that a comet tail will always point away from the sun. So that comet tail does not lag behind the comet. In the inward journey, it would be as you might expect, the tail follows the comet. However, when the comet heads back out to the outer solar system, the tail will actually lead the comet and go before the rest of the comet. So that concludes this discussion on comet tails and this misconception that the comet tails always lag behind the comet. We'll be back again next time for another misconception in astronomy. So until then, have a great day everyone, and I will see you in class.