3. The basics of astronomy
Contents
3.1 The night sky
Have you ever studied the sky on a clear night?
At first, it may look like it is empty. However, if you do not focus your vision on any specific point, you will gradually notice more and more things in it. You will see bright dots, some of which are larger and brighter than others. These dots are actually stars, planets, and asteroids.
In this chapter, you will learn basic astronomic terms and concepts. If this seems like a daunting task, you can begin by reading the summary before delving into the chapter itself.
3.2 Basic concepts
The term universe means the world as we know it. In other words, the term universe encompasses space and all substances and energy contained inside it. According to our modern understanding, the universe was formed 14 billion years ago as a result of a gigantic explosion ("the Big Bang") and the rapid expansion that followed it.After a while, the gases that were created during the explosion began to concentrate, forming star systems or galaxies. There are millions of galaxies in the universe. They are like small islands dotted across the infinite, empty sea of space.
Our own galaxy is called the Milky Way. It consists of 100–400 billion stars. Its diameter is approximately 100 000 light years long, and it is over 10 000 light years wide.
The light year is a unit of distance that is widely used in astronomy. A light year represents the distance that light travels during a single year. This means that a single light year is an incomprehensibly long distance. Light travels at a speed of approximately 300 000 kilometers per second, meaning that the distance from the Earth to the Moon takes light only just over one second to travel. The distance between the Sun and the Earth takes light approximately eight minutes, whereas the distance between Earth and the next solar system takes four light years to travel.
3.3 The Sun
When looking at stars from the surface of the Earth, they seem to form groups or constellations.The closest star to us (aside from the Sun) is Proxima Centauri, which is over 4,2 light years away from planet Earth. It is too dim to distinguish with the naked eye. The brightest star in the night sky is Sirius, which is 8,7 light years away from Earth.
However, the star that is nearest to us is actually the Sun. It is a burning ball of gas over a million kilometers in size. The distance between the Earth and the Sun is approximately 150 000 (150 million) kilometers. The Sun was formed just under five billion years ago, making it a relatively young star.
When the Sun's fuel, hydrogen, eventually runs out, the Sun will expand into a red giant, swallowing the closest planets of our solar system, Mercury and Venus, and making the conditions on planet Earth extremely hot. When the outernmost layers of the sun are finally blown into space, it will shrink and form a white dwarf.
The video below shows activity on the surface of the Sun. The nuclear reactions that take place inside the star produce an enormous amount of energy, which is manifested as great flares on the star's surface.
3.4 Our solar system
Our solar system consists of a central star (the Sun), and the different celestial bodies that orbit it. Our solar system is thought to be approximately 4,6 billion years old.
The solar system was formed when the substances that floated freely in space slowly accumulated and compressed, forming the Sun and the eight planets that orbit it. Over 99,9 % of the solar system's total mass is located in the Sun. The Sun's gravity keeps the eight planets orbiting around it.
The solar system. Notice the asteroid belt between Mars and Jupiter. The Kuiper zone, located near the edge of our solar system, contains even more asteroids.
The closest planets to the Sun are rocky planets. They consist of a metal core, a molten mantle and a solid crust. In addition, these planets are located relatively close to the Sun. The four rocky planets of our solar system are (in order from the Sun) Mercury, Venus, Earth and Mars. All of these planets have atmospheres except for Mercury.
An asteroid belt is located between the rocky and gas planets. The asteroid belt consists of thousands of small planets. Another asteroid belt, the so-called Kuiper zone, is located at the edge of our solar system, beyond Neptune. The dwarf planet Pluto is one of the millions of asteroids in Kuiper zone.
Outside the asteroid belt, large gas planets can be found orbiting the Sun. The four gas planets of our solar system are (in order from the Sun) Jupiter, Saturn, Uranus and Neptune. They all consist of a large gas core surrounded by a gas atmosphere. They are multiple times larger than Earth. Some of them have rings and numerous moons. Due to their distance from the Sun, they do not receive a lot of heat. As a result, the surface temperature of each gas planet has been calculated to be over a hundred degrees below zero.
The solar system was formed when the substances that floated freely in space slowly accumulated and compressed, forming the Sun and the eight planets that orbit it. Over 99,9 % of the solar system's total mass is located in the Sun. The Sun's gravity keeps the eight planets orbiting around it.
The solar system. Notice the asteroid belt between Mars and Jupiter. The Kuiper zone, located near the edge of our solar system, contains even more asteroids.
The closest planets to the Sun are rocky planets. They consist of a metal core, a molten mantle and a solid crust. In addition, these planets are located relatively close to the Sun. The four rocky planets of our solar system are (in order from the Sun) Mercury, Venus, Earth and Mars. All of these planets have atmospheres except for Mercury.
An asteroid belt is located between the rocky and gas planets. The asteroid belt consists of thousands of small planets. Another asteroid belt, the so-called Kuiper zone, is located at the edge of our solar system, beyond Neptune. The dwarf planet Pluto is one of the millions of asteroids in Kuiper zone.
Outside the asteroid belt, large gas planets can be found orbiting the Sun. The four gas planets of our solar system are (in order from the Sun) Jupiter, Saturn, Uranus and Neptune. They all consist of a large gas core surrounded by a gas atmosphere. They are multiple times larger than Earth. Some of them have rings and numerous moons. Due to their distance from the Sun, they do not receive a lot of heat. As a result, the surface temperature of each gas planet has been calculated to be over a hundred degrees below zero.
3.5 The rocky planets
The rocky planets of our solar system: Mercury, Venus, Earth and Mars.
Mercury is the smallest planet in our solar system. It is also the planet that is located closest to the Sun. As a result of its closeness to the Sun, its orbit is the shortest in the solar system: a year on Mercury only takes approximately 88 Earth days. The days on Mercury are longer than those on Earth. This is a result of the planet's slow spin rate. A day on Mercury is approximately 58 Earth days long. Mercury is the only rocky planet without a gas atmosphere, which subjects the planet to large temperature changes. The difference in temperature between day and night can be as stark as 600 degrees, with days as hot as 420 degrees and nights as cold as -170 degrees. Mercury has no moon.
The size and composition of Venus resemble those of planet Earth. It is the brightest "star-like" object on the night sky, and it can sometimes be seen even during the day. The temperature on the planet's surface can reach over 500 degrees Celsius. This is due to the high carbon dioxide concentration of the planet's atmosphere, which results in a powerful greenhouse effect. Venus does not have a moon.
Earth is a blue planet. Most of its surface is covered by liquid water. It has an atmosphere and a magnetic field that protect it from solar radiation and meteoroids. It is the only planet where life has been found. Its orbit around the Sun lasts for 365 days and 6 hours. It rotates around its axis over the course of 23 hours, 56 minutes, and 4 seconds. The average temperature on the planet's surface is 14 degrees. It has one moon.
The red color of Mars is caused by iron dust found on its surface and in its atmosphere. It accomodates water in both gaseous and solid form. Its atmosphere is thin and consists mainly of carbon dioxide. The average temperature on the planet's surface is -55 degrees Celsius. Mars has two moons, Phobos and Deimos.
3.6 The gas planets
The gas planets of our solar system: Jupiter, Saturn, Uranus and Neptune.
Jupiter is the largest planet in our solar system. It is made of gaseous hydrogen and helium. It is surrounded by thin rings, which are invisible when viewing the planet from Earth.
Saturn is a planet that has been compressed at its poles. It is the second largest planet in our solar system. Its composition is similar to that of its neighbor Jupiter. It is surrounded by rings.
Uranus is the only planet that is named after a Greek god (all the other planets are named after Roman gods). Although in popular imagination it is often considered an ice giant, it actually contains very little ice.
Neptune is the outermost planet of our solar system. It cannot be distinguished with the naked eye from planet Earth.
Summary
- The universe is large, and the distances within it are often measured in light years.
- The universe consists of many star systems or galaxies, which in turn each consist of billions of stars.
- The central star of our solar system is called the Sun.
- Eight planets orbit around the sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
- Planets can be divided into rocky planets and gas planets based on their composition.
- Our solar system consists of a central star (the Sun), planets (as well as their moons and satellites), and small asteroids.
- Key words: universe, galaxy, light year, solar system, rocky planets, gas planets.