 Greetings and welcome to the Astronomy Picture of the Day podcast. Today's picture for January 8th of 2024 is titled The Phases of Venus. So what do we see here? Well, what we see is multiple images of the planet Venus. And Venus, much like our own moon, does go through a complete cycle of phases as it moves around the Sun. Now it really depends on our positioning and the positioning of Venus and the Sun, much like the moon phases do. Now this is very important. This is one of the discoveries that Galileo made back in the early 1600s with his small telescopes. Before this you could not see Venus as a phase. You need a telescope to be able to bring it close enough in appearance to be able to distinguish between the phases. And one of the things that Galileo noted is that Venus does go through phases just like our own moon. Now why was this so important? Well, the models at the time of the universe were either the heliocentric or Sun-centered model, or the geocentric or Earth-centered model. And under the geocentric model Venus would always appear as a crescent. That would be the only way to explain its motions through the sky and its position relative to the Sun. We would always have to see it as a crescent phase. However, under the heliocentric model with both Earth and Venus moving around the Sun, Venus could go through a complete cycle of phases. So that was one thing that really distinguished between these two models. One model could explain the observation, and one could not. So this really kind of showed that the geocentric model that had been used for over a millennium was really not correct. And were there other models that could still work? Well, there were some hybrid models that were used for a while, but at this point the heliocentric model was becoming much more accepted in the scientific community. Now here we see all these different images. We can see Venus is a very thin crescent in the lower images. And as we work around to the left it becomes a little bit more illuminated, reaching a quarter phase. And then as we go all the way around to the back we see it as a nearly full phase. Now the other thing that we note is that the size changes. Now the size changes because of the changing difference. When Venus appears as a crescent it is between us and the Sun. And that means it's closer to us. That's when Venus is at its closest and is going to appear the largest in the sky. Whereas when it's at the largest distance at the other side it will be on the opposite side of the Sun. Much more distant from Earth and it's going to appear significantly smaller. And you can see that big difference in size between the images that we see here. Venus being very large but a very thin crescent when it's close to us in the near part of its orbit. And being very small but nearly full when it is on the far side of its orbit. So here we see multiple images of that showing the cycle of the phases of Venus taken in 2015. But a cycle that repeats over and over again. So that was our picture of the day for January 8th of 2024. It was titled The Phases of Venus. We'll be back again tomorrow for the next picture previewed to be Thor's hat. So we'll see what that is about tomorrow. And until then have a great day everyone and I will see you in class.