Video Transcript: Motions of the Sky

It's been a testament to God's faithfulness to us and the whole world that He's crafted this environment and these laws that can be relied upon.  In fact, it's one of the fundamental assumptions of all of science, is that the laws we measure today, are the same in the future, or will be the same in the future, and have been the same throughout the past.  In a sense, one of the fundamental assumptions of science is that the creator of our universe is faithful that these things don't change.  

So there's a problem, though, when it comes to making sense of these motions in the sky and understanding them and that problem is that we're often disconnected from our sky.  I mean, we live in a world of artificial lights and electricity.  We use our watches to tell what time it is, and our virtual calendars, you know, to tell what day it is and what I need to do next week.  It didn't used to be that way, of course, right?  People used to rely on the motion of the Sun throughout the year to know when to celebrate certain festivals or when they needed to plant their seeds in the ground.  And so what we need to do is have a little bit of reintroduction to the night sky.  And that's what we're going to do in this particular video.  

We're going to look at the motion of the Sun, the stars, and the planets; that’s the three main things we're going to look at in this particular video.  So let's start by considering the motion of the Sun.  In the first picture in the gallery, you can see an indicator of the motion of the Sun over the course of a single day.  If you took a picture every couple hours, you would see the Sun making this kind of path across the sky.  Of course, every day the Sun rises in the east, and sets in the west.  And that's true for everyone everywhere.  But that's not the only thing that happens in the sky in the day.  This motion, while generally true, it changes from day to day, and week to week, and month to month.  You wouldn't really notice it except probably on a month to month sort of timescale because the sun gets higher and lower in the sky.  So in the second picture in the gallery, you can kind of see what I'm talking about.  

Throughout the course of the year, the Sun, the kind of arc across the sky that the Sun takes, it changes its position in the sky.  It gets higher and lower.  So on the far right, you see the path since the Sun's path on the winter solstice.  This is the lowest point that the Sun reaches in the sky.  And as we'll see later, it depends on your exact location on Earth, how low the sun really gets, but this is its lowest point.  It still makes this arc across the sky where it rises in the east and sets in the west, but it's much, much lower in the sky.  Now, over the course of the year, that Sun's path gets higher and higher until you reach the Equinox. The Equinox is when the sun is rising due east and setting due west.  And it's kind of the marker in between the seasons of summer and winter.  So when the sun is low, it's wintertime; that's the winter solstice, and then the sun makes its way further and further up higher in the sky and you reach the spring equinox.  And equinox means, it's like Latin probably, for equal day and night because when the sun rises in the east and sets in the west.  You get exactly 12 hours of daylight and 12 hours of nighttime.  But the Sun keeps going further up higher in the sky until you reach the summer solstice and this is when the Sun is highest in the sky.  

So we see multiple different motions happening.  There's this daily motion of the Sun rising and setting but the sun also shows this annual motion where it goes higher and lower over the course of the year. Of course, after it reaches the summer solstice, it starts getting lower and lower until you see it reaches the autumnal equinox, which is like autumn, the Fall Equinox, and then goes back down to the Winter Solstice.  So the Sun does an interesting motion over the course of the year.

Now how about the stars?  Stars are far, far away, right?  And so their motion in the sky is relatively simple and it's dominated by the fact that the earth is rotating.  And so the stars are all really far away.  I mean, imagine if you're sitting in a room, maybe on a swivel chair, and you imagine spinning your chair around on its axis, that's like the earth rotating.  And as you do that, all the things you see in your room, maybe pictures on the wall, or the window, or the door, all of those, as you spin, they look like it's all going around you.  From your point of view, it's all spinning around you as you rotate.  And so that's what's happening with the stars, they're all far away but it looks like they're rotating around us as the Earth rotates.  So much like the Sun, the stars rise in the east and set in the west. 

Now one of the really cool things that you can do to kind of capture this motion of stars is you can take a long exposure photograph.  A lot of the pictures that we'll see in this class are pictures where a camera has been left open for a long period of time.  And if you were to do this, if you just put a camera outside at night and pointed it up, and left the camera open, the stars would be moving in that picture.  And that's what this third picture in the gallery is showing.  This is what we call star trails, because the star light is kind of smeared out as the stars are moving in the sky.  And you can see the exact path that the stars are taking as they move.  

One of the things you'll notice in the picture is that it looks like all the stars are going around in circles like around a specific point.  And that point is very specific.  It's called the north celestial pole, or the North Star, if you're in the northern hemisphere.  In the southern hemisphere, it's the other side of the sky and we call it the south celestial pole or what's located near there as the Southern Cross.  What's special about this particular point is that it is this point out in space where the North Pole of the Earth is pointing directly towards.  So as the Earth rotates on this axis, that axis, kind of like an imaginary line extending out into space, and it points right to that point that north celestial pole and south celestial pole.  So as the Earth rotates, all the stars look like they're rotating around that point.  And the motion of stars doesn't really change throughout the year.  It's basically the same night after night.  But what does change is, as the Earth orbits around the Sun, our perspective on the sky changes. 

So during one time of the year the Sun is in our sky and we can't see any of the stars that are behind the Sun.  Six months later, the Earth is on the other side of the Sun and now we can see those constellations and those stars.  So roughly at any given time, we can only see half of the stars in the sky, and then we wait until the other time of the year and we can see more and more stars.  So over the course of the year, we can eventually see all the stars that are in our entire sky, you know, ones that the sun is in blocking.  So there are some changes that happen over the course of the year, but not nearly the kind of changes that we see with the Sun's motion.  Now, let's take a look at the planets.

You may or may not have seen planets in the night sky because planets look more or less just like stars. In fact, in this picture, the fourth picture in the gallery, you can see that here's an evening sky shortly after sunset and Venus, Mars, and Saturn are like bright stars.  And you can see others bright stars labeled in the picture and they look essentially the same.  So it begs the question, how did people know that these were planets? I mean, they look just like stars.  Well, the key is that these star-like things have a very peculiar motion.  While the stars rise and set and look basically the same all year and year after year, the planets move relative to the stars.  But they move in kind of a weird way.  I mean, it's probably not very surprising that they move since they orbit the sun, but the way they move is really quite strange.  Over the course of a year, and from year to year, planets will move relative to the stars.  But at very special times, the planet will do a bizarre loop where it slows down in its motion, turns around - and this is over the course of many days and weeks - it'll move relative to the stars night after night, turn around, make a loop in the sky, and then keep going forward.  So in the fifth picture in the gallery, you can see several pictures illustrating the location of Mars relative to the stars, going from August 27 2007, to April of 2008.  So that's what that's almost a whole year. And you can see its motion from month to month it turns around and does this loop.  This kind of motion is called retrograde motion.  And trying to make sense of and explain this retrograde motion preoccupied astronomers for hundreds, in fact, thousands of years.  We'll learn more about what exactly is causing this retrograde motion and how we can understand it later on.  So planets exhibit a very strange behavior. 

Now, one of the things that you're going to read about is how ancient astronomers have known about these planets.  And there's basically seven objects that have been called planet-like objects.  And those are the seven objects in our sky that we can see with just our eyes and that exhibit unusual motion.  So that's the Sun, we've seen; the Moon, which we'll look at next and see the phases of the moon. Those are the two bright… they’re not really planets but they're bright objects in our sky.  And then the five other ones, which is Venus… well, Mercury, Venus, Mars, Jupiter, and Saturn.  Those were all visible to the very first people who looked at the sky.  And by carefully looking at the sky, and watching the motion of those bright looking stars, you can tell there's something different about them, which is how they earned the name, planet, which means wanderer.

So there's one more thing I'd like to address in this particular video, which is going to come up several times throughout our course and that is, in the readings in our course, you're going to see that you're reading from a secular astronomer’s perspective.  And so you're going to encounter things that may feel like they're in conflict with our understanding of scriptures.  And that's intentional.  Our work is continuously challenged by secular reasoning and the secular view of the world.  What I'd like to address in particular, though, is in the reading for this particular lesson, you're going to encounter for the first time, this notion of ages and times that are very old, like 60,000 years ago, in later readings, we'll read about things that are involved millions and billions of years, and I want to address that because there's a lot of argument and disagreement among Christians about these old ages and how they may mesh with an interpretation of Genesis.  And it's such a divisive issue that I struggle with how to address it in the most positive way.  And so here's, here's how I think we should approach it in our class. 

And that is this: there are several things I think we can all agree on it.  The first thing we can agree on is that faithful God-fearing Christians fall on both sides of the debate about whether our universe is 6,000 years old or whether it's 14 billion years old.  I personally know Christians who I know love the Lord and Jesus Christ is a part of their lives and they know that the world of the universe is only 6,000 years old, as the Bible suggests, with the six days of creation.  But I also know astronomers who are committed Christians who have given their life to Jesus Christ and have earned their PhD in Astronomy and they know that God has created the universe over the course of 14 billion years and continues to create it today.  God fearing Christians are on both sides of this issue.  I know that personally and now you do, too.  

The second thing that I think we have to agree on is that the universe and our planet have the appearance of age, right?  There are some people who say, “Well, oh, no, it's just, you know, it doesn't really look old if you interpret it a different way.”  But there's really no way around it; our universe looks old.  It looks old. Okay, that's something we have to agree on.  

The third thing we have to agree on is that God is capable of creating the universe any way He wants.  It's totally up to him and He's all powerful to do it.  He absolutely could have created the universe 6,000 years ago with the appearance of looking older than it is.  He also could have created the universe 14 billion years ago and communicated his message in Genesis the way He did.  He could have chosen to do it anyway He wanted to.

The last thing we need to take away from this, I think it's really important, and that is scientists, they don't just sit in a room somewhere and say, “Hmm, how can we disprove God today?”  You know, “How can we fight those Christians and turn the screws and try to disprove God?”  Instead, scientists examine through observations of the physical world, and they try to make sense out of how that physical world works.  Throughout the history of science, committed Christians, we have played a significant and important role and we'll see that that's certainly the case in astronomy as well.

Now, the other piece of that is that while scientists don't set out to disprove that God exists, they also limit themselves intentionally to only the things that can be measured in a physical universe.  And as people of faith, we acknowledge that there is more to our universe than simply what can be seen with our eyes.  And here's what is so cool.  And this is where we're headed.  By the end of this class, this is what you're going to see that’s just so awesome, is that through the process of science, which is limited to only looking at the physical reality, astronomers have found clear evidence that there are things beyond what we can physically observe.  And they still haven't been able to make sense of those things. But they have found conclusive proof that our understanding of the physical universe seems to be limited and that there might be something beyond this physical universe that we can observe and measure.  

It's tremendously exciting.  And so I am very motivated and excited about when we bring the science together with our faith, how both get enriched in a whole new way.  And so my hope is that we can move past any of these potentially divisive questions about age and instead look at the amazing beauty and profound mystery that arises when we bring these seemingly contradictory things together.

All right. We'll see you next time.