 Greetings and welcome to the Introduction to Astronomy. In this week's Astronomy of Other Cultures we are going to continue looking at Egyptian astronomy and specifically talk a little bit about the pyramids. So, what do we know about the pyramids? Well, I'm not going to go into a lot of detail as to construction or anything like that here. What I really want to look at is a little bit of the astronomy here. So, what do we know about the pyramids? Well, one of the things that we do know is that they are aligned almost perfectly north, south, east, and west, and in fact to about one-fifteenth of a degree. So, how can you get such an accurate alignment? And there are many different theories. Obviously, we don't know for sure because we don't have written records that show what was going on when the pyramids were being built or how things were being done. So, one thought is that you could use the sun to do this because on the equinox the shadow will run directly east-west. So, if you lined up the sun directly on the equinox you could determine east and west very precisely. So, that's one thought as to how we could do this and over multiple observations and with a lot of practice and work on this then you could determine things to a very high level of accuracy. Now, are there other alignments with the pyramids? And that's a good question and we really don't know. Why? Because we're looking way back and we don't have records of construction as to what was intended on certain things. There are certainly possible alignments with the sun but we also need to take into account changes because there are what we see with things with the sun and the stars is that things will constantly change. Things like procession which causes the north pole of earth to change and we have to see what that would have been like thousands of years ago when the pyramids were being built. And we also have to take into account the earth's axis. The tilt changes. So, this tilt is not constant. We say it's 23 and a half degrees. Well, that's the current value but it does change from time to time and it undergoes slow changes. Not drastic ones but there are changes. Now, we have to calculate all this and take that into account to really try to determine if there are any alignments. And then the question is whether those alignments are just by chance or if they were truly intended to be aligned that way. Pretty certain that the north-south east-west alignment was intended but whether other alignments or lining up with the sun are just a coincidence because it is lined up north-south and east-west or if there was more intention there is a very good question. Now, one of the things we like to look at and that sometimes comes up as an alignment is a relationship in the pattern of the pyramids to the stars in Orion and that's because there are three of the primary pyramids that we see here that are lined up in rough spacing to the stars in Orion's belt. Now, we think that this probably is not the case that it really has nothing to do with the relationship with Orion or trying to match Orion in the sky. Actually, it's slightly inverted from what you would see in the sky so it's not exactly lined up and the lining up is close but not exactly precise. Some of the pyramids are off by a little bit so it's very difficult to see that there's actually any kind of alignment there or relation to the stars in Orion just that we happen to have three pyramids spaced out in one area. So let's go ahead and finish up with our summary here and what we look at is that we talked about the pyramids and how they really are accurately aligned with the cardinal directions north, south, east, and west. There are some possible alignments with the sun but the resemblance of the positions of pyramids with Orion and especially the stars in Orion's belt is probably just a coincidence. So that concludes this lecture on the Egyptian astronomy and the pyramids. We'll be back again next time for another study of other cultures in astronomy. So until then, have a great day everyone and I will see you in class.