A galaxy is a big group of stars circling together around a very dense middle. Thomas Wright was the first one to figure it out in 1917 (so only a bit over a hundred years ago!). The middle of a galaxy is something very dense and heavy and it acts a little like our Sun in the Solar System. Many scientists believe there are black holes in centers of galaxies.
Black holes get created when a star goes supernova – that means it explodes. Then in some cases, the exploding star will collapse on itself, creating a small (well, in astronomical terms small), but extremely heavy object. It creates a ton of gravity and nothing can get away from it, not even light. The fact that even light isn’t fast and strong enough to leave is why they appear to be black.
Word galaxy comes from Greek word for ‘milky’. Our galaxy, Milky way, looks like a white stripe across our sky during the night. The Greeks had a myth that the stripe was created by milk from Hera’s breast.
There are billions of galaxies out there. Our nearest galactic neighbor is Andromeda.
There are four types of galaxies:
Spiral – it has a center and some arms that are made up of stars. The arms are arches that go around the center and outward
Barred spiral – it’s kind of like spiral galaxy, but there is a middle bar and there are only two arms, which start at each end of the bar
Elliptical – those galaxies are discs without any arms. They usually look pretty even inside
Irregular – any galaxy that does not fit on of the other three categories. Scientists believe that at least some of these are a result of two or more galaxies colliding.
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Galileo Galilei was an Italian (yay for Italians! I am half Italian 😊) astronomer and physicist. He was born in 1564 and was executed by the Catholic Church in 1642 for saying that Copernicus was right about the Sun being center of our Solar System.
Other than his fight with the Catholic Church, Galileo was famous for writing about what he saw through his telescopes:
He figured out that our galaxy, Milky Way, was made up of many stars
He noticed that the surface of the Moon wasn’t flat
He discovered the four largest moons of Jupiter, which we still call today the Galilean Moons
He was the first one to see Sun spots, which are dark spots on the surface of our star
He noticed that planets around us have dark and light phases, like the Moon, which helped him prove that they were circling the Sun rather than Earth.
Kangaroo rats don’t drink water. They get all of the water they need from food.
Word of the day ❗
Strand – line consisting of a complex of fibers twisted togehter.
The Moon is Earth’s natural satellite. That’s a huge rock that goes around our planet. It’s relatively pretty big – over quarter of the size of Earth. Because it’s so large, Earth and Moon are sometimes called a binary system. It takes the moon 28 days to travel once around Earth – and that’s basis for what they used to call a month (it changed a bit when the Romans created Julian calendar and divided year into 12 months).
I know that we can see the Moon from Earth and it’s easy to think that it shines. The Moon doesn’t create the light on its own though. It reflects Sun’s light. That is actually why we have phases of the Moon – that’s you can see different shapes.
The Moon has a hard, rocky surface, which means you can walk on it. There is no atmosphere though, so the temperatures change a lot and you need a special suit to protect your body. People actually have walked on the Moon. The first person to do it was Neil Armstrong and he did it in 1969.
The fact that the Moon is so large relative to Earth is very important to things that happen on our planet. One thing you probably have seen that the Moon causes are tides. The Moon pulls on water on Earth, making is move in its direction a bit. So when one shore is closer to the Moon, the water flows towards it, causing high tide – that’s when water goes higher on the beach. When Moon is on the other side of Earth, it pulls water away, causing low tide.
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He was a German mathematician and astronomer who lived between 1571 and 1630. He was Tycho Brahe’s student and assistant. He learned a lot about the first telescope and created refracting telescopes, knows also as Keplerian telescopes. His telescopes were used by Galileo in his work (more on that tomorrow).
His greatest work was on planetary motions. That’s how planets (and their moons) move and why. This research helped Isaac Newton come up with theory of gravity. He studied both theories of how the Solar System is built. He decided that Copernicus was right.
Like his teacher, Kepler was an astrologer and used to tell the future based on his observations of the sky (it’s all made-up, but some people still believe that and read their horoscopes).
The Wright brothers are famous because they flew the first powered aircraft (that’s a simpler airplane).
Word of the Day ❗
Utter – without qualification.
Learn more about Moon landing from National Geographic Kids:
We have been talking since the beginning of last week about planets that go around the Sun. These planets and the Sun together make up the Solar System. First, let’s review the planets (starting with the closest on to the Sun):
Those are not the only objects in our system though. Do you remember me calling some of the planets outer planets? There is an asteroid belt between Mars and Jupiter. Asteroids are big rocks in space. Have you noticed that planets on the two sides of the asteroid belt are very different from each other? The inner planets (Mercury, Venus, Earth and Mars) are terrestrial planets, meaning they have hard rock surfaces. The outer planets are much larger and they are made up of gases, making them gas giants.
There are other stars around us, but we don’t orbit them. The nearest one is Alpha Centauri.
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He lived in Denmark between 1546 and 1601. He invented the telescope and built an observatory on island of Hven. He studied the stars and watched comets and supernova. Comets are objects travelling through space around a star. They have a hard core surrounded by dust. Supernova are exploding stars. Through his observations, Brahe discovered that objects outside the Solar System can change.
He was a strange scientist. He believed in astrology (that’s believing that how stars and planets move causes events in people’s lives). He was also not ok with Copernicus’ model of the Solar System, where all the planets went around the Sun. He believed that the Moon and the Sun went around the Earth, while other planets went around the Sun.
There are 4 components of human blood: plasma, red blood cells, white blood cells and platelets.
Word of the day ❗
Replenish – fill something that had been previously emptied.
I think it would be a nice idea to learn more about how telescopes work:
Neptune is the planet furthest from the Sun. It’s another gas giant and it’s a sister planet to Uranus. It is smaller in size than Uranus, but it is heavier. Neptune has 13 moons and that number keeps growing. Being a gas giant means that you can’t put your feet on the surface. Rather, you would fall through.
I finally learned why outer planets have so many moons and that number keeps growing! Each planet has its own gravity, as does the Sun. Outer planets are really big, so their gravity can catch rocks flying through the space. They are also far enough from the Sun that the Sun can’t steal those objects.
It’s day is shorter than ours – it’s only 16.1 hours. Its year, on the other hand, is crazy long: 164 Earth years!
Neptune has a hydrogen (mostly) and helium atmosphere. Strong winds and storms are common in there. Scientists managed to take a picture of one of those storms and called it the Great Dark Spot. It’s larger than Earth!
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Since we’ve been talking about astronomy, I thought it would be nice to talk about some really famous astronomers. We are going to start with Nicolaus Copernicus (but my mom always calls him Mikolaj Kopernik – apparently like her, he was Polish).
He was born in 1473 and died in 1543. He went to college first in Krakow and then moved to Italy. He was a polymath – he was not only a famous astronomer, but also a mathematician, economist, doctor and a few other things.
In astronomy, his greatest accomplishment was proving that our world is heliocentric. People used to think that stars and other planets move around Earth and Earth is the center of the universe. Copernicus, through his research, proved that it wasn’t true. He showed that planets actually go around the Sun. It was not a popular idea back then because the Catholic Church thought that God made Earth center of the universe.
Sharks don’t have bones. Their skeleton is made of cartilage.
Word of the day ❗
Polymath – a person of great learning in multiple fields of study.
Uranus is the seventh planet from the Sun. It’s twice as far from our star as Saturn. It is an ice giant – it is made up of ice and rocks on the inside and gas on the outside. It is the coldest planet in the Solar System. It takes Uranus almost 84 years to make a full circle around the Sun and its day is 17.2 hours long. Actually, Uranus’ day is kind of funny because it spins sideways:
It has 21 moons (and the number is growing). Like Saturn, it has rings. However, Uranus’ rings are much smaller and less visible. Uranus’ atmosphere is thick and a little stormy. The surface of the planet is pretty flat.
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Rome – science
Some of the most important developments in science that come from Rome are related to building. They have perfected building an arch, which became basis for many constructions afterward. Those arches were very useful when they constructed aqueducts. Those are things that help move water from rivers to fields and cities. Speaking of delivering water to cities – they also came up with plumbing!
Many other cultures used to build those as well, but none as well as the Romans. In fact, many of those aqueducts still stand and portions of some are still in use. Romans didn’t only build great ‘roads’ for the water – they were the first ones to make durable (that means they were able to survive for a long time, including through bad weather) roads. Unlike other cultures before them, they didn’t make roads go around obstacles. They were really good at figuring out how to go through obstacles, such as building bridges over water and tunnels through mountains. Those roads are now over a thousand years old, but people still use many of them.
Romans were also great at building big structures. You may have heard about the Colloseum in Rome, the Pantheon or Hadrian’s Wall. Those took a lot of work and thinking! Did you know that they used to flood the stage of the Colloseum and have pretend navy battles in there.
Romans figured out how to tell time. They used sundials, which were kind of watches that used position of the sun to tell what time it is.
The Blue Whale is the largest mammal on Earth.
Word of the day ❗
Flexible – able to bend easily.
I am not feeling too well today, so I will be adding Uranus to my Solar System next week. For now, enjoy this video about the Solar System:
Saturn is the sixth planet from the Sun and it has 60 moons. Like in case of Jupiter, that number has been growing. I think I need to look further into this phenomenon… What makes Saturn special though are the rings around it. They are around the equator and made up of ice, dust and rocks. But mostly ice. It’s really cold in outer space after all!
You know how we said that it took Jupiter forever to get around the Sun? Well, it takes more than double that for Saturn to complete a full circle: 29.4 years! Its day is only a little bit longer than Jupiter’s – 10.7 hours.
Saturn is 95 times the mass of Earth. It is only slightly smaller in diameter than Jupiter though. The surface is made up of hydrogen and helium and is a gas. As you go in towards the core, the gases first turn into liquid and planet’s core is actually a hard rock.
One of Saturn’s moons is the second largest moon in the Solar System. It’s called Titan and has a dense atmosphere made of nitrogen. Humans can actually breath nitrogen without getting hurt – it makes up a large portion of Earth’s atmosphere, too.
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Rome – culture
Like the Greeks, Romans didn’t always have kings or emperors (who are kind of like kings). For a long time, their government was formed as a republic, with senators elected for a pre-set period of time. Does that sound familiar? A lot of countries around the world do that today. Romans also developed a law system that we make ours look like. They wrote down their laws and everybody had to follow them the same. One great idea that countries in the Western World still follow is that you assume somebody is innocent until proven guilty.
Famous writers named Virgil, Cicero, Horace and Ovid lived in Ancient Rome. A lot of books are still influenced by the way they wrote. Oh, and did I mention they spoke Latin? You may not have heard about this language yet, but you have probably heard words in Latin before. A lot of doctors still learn Latin because various medications and body parts have names in that language, so it’s easier to learn medicine if you can understand it.
Speaking of medicine: Romans were the first ones to have battlefield medics. Roman army was much more organized than those of other countries back then. Each soldier had a specific job and they were taught to fight together properly. They had soldiers whose job was to help wounded people during battle. This saved a lot of lives!
As you probably noticed, Romans were great at bringing order and structure to everything they did. Here is another thing that they decided needed to be put in order: days of the year. They have created the first calendar. It was called Julian calendar and it was a lot like ours. They were the ones that came up with the idea of a leap year! Currently, we used Georgian calendar, which is only slightly changed from Julian calendar.
Bamboo grows extremely fast. Some varieties can grow up to 3 feet in one day.
Jupiter is the 5th planet from the Sun. It already has 63 moons, but that number has been increasing. I wonder why? It’s humongous! It’s the biggest planet in the Solar System with mass 318 times that of Earth. It takes Jupiter 11.9 Earth years to make a full circle around the Sun. That’s really slow? Or, actually, it’s not moving all that slow, it’s just really far away from the Sun, so it takes forever to cover that distance. On the other hand, it spins rather fast – it takes it only 9.8 hours to spin ones. That’s one short day!
Jupiter is not a terrestrial planet, like the former four. It’s a gas giant made up of hydrogen and helium. That means there is no surface you could walk on! It’s hard to imagine a ball gas having a weather, but Jupiter does have very strong storms. One of them, called The Great Red Spot, has been going on for hundreds of years now. Now that’s quite a storm! The energy for the storms comes from the nuclear fusion of gases in it, much like what happens on the Sun.
Jupiter’s moons are fascinating! Four of them were discovered by Galileo centuries ago and now they are called Galilean Moons. One of them, called Ganymede, is larger than Mercury. Europa, on the other hand, has salt water (much like what you can find in Earth’s oceans) underneath ice. Scientists think that there may be some sort of life on Europa.
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Rome – religion
When Roman Republic started, the Romans believed in many gods. Their religion was a lot like that of Ancient Greeks. They even had 12 most important gods, which were their versions of the Olympians:
Jupiter – Greeks called him Zeus
Juno – which is Hera
Mars – Roman version of Ares
Mercury – who was a lot like Hermes
Neptune – like Poseidon, the god of the seas
Venus – Roman version of Aphrodite
Apollo – he actually managed to keep his name! He was also the favorite of Roman emperors
Diana – a lot like Artemis
Minerva – goddess of wisdom, although she was not as important as her Greek version, Athena
Ceres – goddess of agriculture, so Greek Demeter (did you know that word cereal came from her name?)
Vulcan – I think you can guess by now who was he in Greek mythology. Yes, it was Hephaestus!
Bacchus – Roman version of Greek Dionysus
A very important story to Rome was a myth about brothers Remus and Romulus. According to the story, they were raised by a wolf. When they grew up, they created a city. Romulus killed his brother and took over the city. The city was named after him and he created the Roman legion (their military) and the senate.
The Romans didn’t like Christians in the beginning. They used to kill and torture them. However, it changed when Emperor Constantine converted to Christianity and made it official religion of Rome.
Mars is the fourth planet from the Sun. It’s mass is 11% of Earth’s mass (isn’t that tiny?). Its day is 24.6 Earth hours (wow! that’s close!) and it takes 1.9 years to go once around the Sun (can you imagine having to wait almost two years for your birthday???).
Mars has two moons, named Phobos and Deimos. Like previous three planets, it has a rocky surface. Its atmosphere is much thinner than that of Earth and it is made up mostly of carbon dioxide. Because there isn’t much of an atmosphere there, the surface of this planet is much colder than that of Earth. Surface of Mars is covered by sand and the winds get very strong, leading to huge dust storms.
Mars’ surface is in many ways similar to Earth and there are even signs that they used to have water. This planet has the tallest mountain in our Solar System, which is 3 times as tall as Mount Everest, tallest mountain on Earth.
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Rome – history
Rome was a very important civilization. It was located where Italy is currently. Roman Republic was created in year 509 BC. Their form of government was revolutionary because they didn’t have a king who was born to rule and stayed in power until he died. Instead, they elected senators, who made decisions for the country as a group for a limited amount of time. After that time, called term, new group would be elected. We will talk more about this subject on Wednesday, when we discuss culture of Rome.
In year 45 BC, Julius Cesar took over the Roman Republic and put himself in charge. This changed how the country was ruled and in year 27 BC, Julius Augustus became the first emperor of Rome. A lot of the government stayed the same, but now the emperor had the power to make final decisions.
As an empire, Rome kept growing and conquering lands around, including much of Europe and Egypt. Eventually, the country became to large for one emperor to rule. Remember: they didn’t have airplanes, phones or the internet. They had to have somebody deliver all messages by horse! So the two halves were: Rome with the capital in Rome and Eastern Roman Empire, better known in history as Byzantium with the capital in Constantinople (currently it’s city of Istanbul in Turkey).
In year 476 AD, Western Roman Empire fell as a result of wars with the barbarians. This started the Dark Ages in Europe. We will talk about Eastern Roman Empire more next week.