We’ve explored just how big our solar system is, as well as our neighbors, the terrestrial planets. Now, let’s take a step back (well, a couple hundred million mile-long step back), and explore the remaining four planets, also known as the Gas Giants, and beyond.

Now, these four planets are called gas giants because they’re basically made up of gassy sludge. They’re much larger than terrestrial planets and don’t have any defined outlines or “land”, because...well...they’re just made of gas!

The first gas giant is Jupiter, the largest planet in the entire solar system. Jupiter mainly consists of hydrogen, helium, ammonia, methane, and water vapor. It has at least 66 moons, including Ganymede, the largest moon in the solar system. Finally, Jupiter is FULL of gas storms. It’s white, red, and brown stripes aren’t just for decoration...they’re all giant gas storms. The great big spot in the middle of Jupiter, known as “The Great Red Spot”, is another large storm on Jupiter, which has been going on for at least 340 years. In fact, the great red spot is the largest in the solar system, just like a lot of other things on Jupiter!

Then comes Saturn, the second largest and one of the prettiest planets in the solar system. It also has the lowest density of all planets in the solar system. Imagine a swimming pool big enough to fit saturn. If Saturn were to enter that swimming pool, it would float on top of the water, because it's less dense than even water. This low density is because Saturn is mostly made up of hydrogen and helium. Finally, Saturn has a complex system of rings, which are made from ice, rock particles, and dust. It also has 60 moons, one of which contains active volcanoes.

Next, we have Uranus, the bluish green planet right after Saturn. Uranus’s atmosphere is made up of hydrogen, helium, and methane which is responsible for giving it that pretty bluish-green color. It’s got at least 27 moons, and contains mostly ice and rock in the inside. However, Uranus is a little strange because it looks like it’s flipped to the side. This is because of its axis of rotation, which is an imaginary line around which a body rotates. Unlike the Earth and other planets in the solar system, which have an axis of rotation which is perpendicular to its orbit, Uranus has an axis of rotation that is parallel to its orbit.

Finally, we’ve come to Neptune, the furthest planet from the Sun and the coldest planet in the Solar System. Like Uranus, Neptune is bluish-green in color due to all the methane in its atmosphere, and its atmosphere changes VERY rapidly. This is why Neptune gets a lot of storm spots, which are similar to the Great Red Spot in Uranus.

We’ve just gotten a sneak peek into all the planets in the solar system! However, the Solar system isn’t all about the sun, the planets, and their moons. There are plenty of other objects in the solar system which are just as fascinating and mysterious.

First of all, there are dwarf planets. These are planets that can range from the size of the moon to half the size of mercury. These planets also orbit the sun, but are even further from it than Neptune. Next, we have asteroids, which are huge chunks of irregularly shaped rocks in space. Most asteroids in our solar system are located in the asteroid belt, a circle of asteroids around the sun that separate the orbits of Mars and Jupiter. We’ve also got comets, which can be seen as dirty snowballs. These are made of dust and rock particles, frozen gases, and ice that orbits the sun (with enormous orbits that are even larger than Mercury’s orbit).

Finally, the solar system also contains a lot of meteoroids, meteors, and meteorites. Even though these all sound like the same kind of rock, it is important to make the distinction between these three. Meteoroids are small pieces of rock and dust, such as disintegrated comets. They seem relatively harmless, until they become meteors, which happens when they enter the Earth’s atmosphere. As a meteor enters the atmosphere, it creates friction with it, causing the meteor to burn up and create a bright streak. Yep, meteors are easily the most dangerous out of all three. Finally, a meteorite is very similar to a meteor, except it makes it all the way to the earth WITHOUT completely burning up.

Congratulations, we have finished exploring the entire solar system, and all the objects within it. But...how do they impact us? When we’re sitting here on Earth, how does outer space even affect us? These questions will be answered in the next video, where we will dive deeper into the Earth-Moon-Sun system, the system within our Solar System that affects us the most. Until next time!

Unless you’ve been living under a rock all this time, I’m sure you all know what the moon is. It's a natural satellite, which is any object that orbits a planet, which in this case, is the Earth. There are theories that it was most likely formed when the earth collided with debris that were about the size of Mars, and that gravity pulled all the debris together into a large ball that became the moon. The moon also contains a lot of craters, mountains, and smooth dark regions made up of hard lava from volcanic reactions. In fact, these smooth dark regions are the reason why we can see our good friend, the man on the moon.

You’ve definitely seen the moon appear almost every night, in a different position and a different shape from the last. Now, we’re going to dive into how and why it does that, as well as some very special phenomena that happen between the Earth, Moon, and Sun, called eclipses.

See, the moon is in constant motion, rotating and revolving around the Earth at the same time, just like how the Earth rotates and revolves around the Sun! The moon completes a revolution around the Earth every 27.3 days. It also rotates and revolves at the same speed, which means that we see the same face of the moon all the time...the face with the man on the moon!

Another special characteristic of the moon is that it glows at night, because it reflects light from the Sun. The Sun always lights half of the moon, but because the positions of the Earth and moon change, we see a different part of the lighted side of the moon every night. These are called the Phases of the Moon. They depend on the relative positions of the Earth, the Moon, and the Sun. When the lit portion of the moon appears to be getting larger and larger every day, this is called “waxing” or growing. When the lit portion of the moon appears to be getting smaller, the moon is “waning” or shrinking. It takes about 29.5 days for the moon to finish all of its phases. Here are the phases of the moon, in the order that they occur:

New Moon

Waxing Crescent

First Quarter

Waxing Gibbous

Full Moon

Waning Gibbous

Third Quarter

Waning Crescent

Now that we’ve got the phases of the moon down, let's talk about something special: eclipses. There are two types of eclipses, Solar and Lunar eclipses. Both types of eclipses are super rare, because the sun, the moon, and Earth all need to be perfectly aligned, which doesn’t happen very frequently. A solar eclipse occurs when the moon is between the Earth and the Sun. In this position, the moon blocks the light from the sun, casting a shadow on the Earth. During partial solar eclipses, the moon only covers part of the sun, making the sun look like a big, fiery crescent. However, during a total solar eclipse, when the moon completely covers the sun, this can create a ring of fire, when only the edges of the sun’s light can be seen by us. Kinda cool, right?

Onto Lunar Eclipses. Lunar eclipses occur more often than Solar Eclipses, but they’re still pretty uncommon. During these eclipses, the Earth obstructs sunlight from striking the moon. Sometimes, this causes us not to see the moon. But sometimes, it gets even cooler. In some Lunar eclipses, some light refracts through the Earth’s atmosphere, which causes the moon to glow red, perfect for a horror story.

We’ve just explored why the moon looks the way it looks each night, and what happens during those strange phenomena called eclipses as well. However, it’s time to take a step back and think about where this all came from. I mean seriously...where did the Earth and the moon and the sun and the rest of the solar system and the rest of the universe start? We’ll tackle this question in the next video, so see you then!

We’ve learned so much about how the universe looks today, especially the parts of the Universe that are our neighbors. We have a solar system with planets, stars, moons, and other objects, which orbit around each other and work together to help us live on Earth. But, how did it all start? Where did all this stuff come from? Everything had to start somewhere...right? There were many ideas throughout the centuries about the origin of the universe, but only few had much actual evidence to support them.

First, there was the constant state theory, which was that the Universe had already existed in a steady state, and that as it expands, new matter is created, in order to keep the density of the universe consistent. However, according to the Law of Conservation of Matter, the amount of matter stays consistent, and that matter cannot be created or destroyed. That, and a whole pile of evidence from the 60s and beyond have completely ruled out this possibility.

New evidence then gave rise to the Oscillating Model Theory. This was the theory that the universe is in a cycle of expanding and contracting. Think of blowing up a balloon, letting it deflate, and then blowing it up again. However, this theory was shot down as well, because while we do have evidence that the Universe is expanding, we have no evidence of it contracting at all.

Finally, we have the most famous and most plausible theory of them all: the Big Bang theory. According to the Big Bang theory, the Universe started around 14 billion years ago, from a single point even smaller than a little atom. It was extremely hot and dense, and then suddenly began to expand really quickly, which is called “the bang”. New matter cooled to form planets, moons, and stars, and the universe is still expanding today. This theory is the most widely accepted, and is constantly being refined as new evidence is discovered.

There’s quite a bit of evidence that suggests that the universe is expanding. Based on our movements, we perceive waves in different frequencies. This is called the Doppler Shift. Scientists used the Doppler shift of light waves to determine whether stars and galaxies are moving toward or further away from us. If stars are moving closer, they will appear blue, whereas if they move further, they will appear red. These scientists found that the light from galaxies outside our local group appeared red, which supports the theory that the entire universe is expanding.

Though all of this information seems plausible, and seems to make sense, the Big Bang Theory is just that, a theory. Though there is a lot of proof that this is what truly happened all those billions of years ago, we can’t go back in time and find out how true this theory really is. That’s why it’s up to you to keep researching this information, and come up with an opinion of your own about how the universe was really formed, and how everything around us began to exist. In the next unit, we are going to exit outer space and enter the Earth, to learn more about the properties of our own planet. See you then!