Astronomy: Definition, Topics & Importance

Astronomy is the scientific study of the universe. The exploration of celestial bodies such as stars, planets, asteroids, galaxies or other so-called «celestial bodies» fall under this topic. Everything you see when you look at the sky is studied by astronomy.

Astronomy – importance in science

The word astronomy originates from ancient Greek «astronomy«, which translates to German as «Law of the Stars». Stargazing dates back to ancient Egypt and Mesopotamia.

The goal of astronomy is a deeper and better understanding of the universe. Moons, comets, planets, stars and solar systems are examined according to their structure, properties and movement.

For thousands of years people have been observing the sky and trying to interpret and explain the phenomena and processes. Great progress has been made over the years and old worldviews have been refuted.

Figure 1: Humans have been observing the sky for thousands of years (Source: pixabay.com)

The science of astronomy is divided into different disciplines because research has now progressed to the point where everything in the field of astronomy is studied, from the Big Bang to satellite orbits.

Astronomy – Topics

All subject areas of astronomy are linked to each other, but are still mostly considered and researched separately from each other.

The solar system

Astronomers have been observing others for a long time celestial bodies such as planets, moons and stars. Thanks to advancing technology, it is now possible for researchers to research far beyond the humanly visible part of the sky. There are always newer, state-of-the-art telescopes that are used to explore the vastness of the universe.

Figure 2: Telescope on a high mountain (Source: pixabay.com)

Planets, stars, asteroids and many other celestial bodies can be discovered and provide a better understanding of your own planet and the solar system. Researchers also regularly find so-called exoplanets. These are planets outside of our solar system. Again and again one hears about exoplanets in the habitable zone, or even earth-like planets. These are planets that orbit like Earth at a habitable distance from their own star.

planets

In our solar system there is 8 planets: Mercury, Venus, the Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Pluto was also considered a planet for a long time until it was downgraded to a dwarf planet in 2006. A planet is a celestial body that is in orbit around the sun and whose mass is so large that it is the dominant object in its orbit and has a spherical shape.

Geocentric and heliocentric world view

The geocentric world view states that the earth and thus man is the central fixed point of the universe and therefore all planets, moons and the sun orbit the earth. This worldview was replaced by the heliocentric worldview, which states that the sun is the center of the universe and all the planets revolve around it. Today we know that the sun is only the center of our solar system and the solar system in turn revolves around a black hole at the center of the Milky Way, our galaxy.

position of the sun and seasons

The sun is on average 150 million kilometers away from the earth. The farthest distance between the sun and the earth is 152 million kilometers, the shortest distance is 147 million kilometers. However, the distance has nothing to do with the seasons, although this is a common assumption. The seasons depend on the tilt angle of the Earth’s axis. This corresponds to 23.4° and is relatively constant. In summer in the northern hemisphere, the angle of incidence of the sun is steeper, so the days are longer than in the southern hemisphere, where the angle of incidence is flatter, with fewer hours of sunshine and longer nights.

The sun

The sun at the center of our solar system is classified as a «yellow dwarf» and is thus in the main sequence of sizes of stars. It consists mostly of hydrogen and helium and is around 110 times larger than Earth with a diameter of around 1.4 billion kilometers. The sun is so large that it accounts for over 99% of the total mass in our solar system.

Stars

Stars consist of hot gas and plasma and are distinguished by their size, temperature, and mass. Stars form from clouds of gas that collapse into each other due to their gravity. Depending on its size, a star lives for several trillion years and produces over the entire lifespan huge amounts of energy from nuclear fusion inside the star. At the end of a star’s life, the core collapses, creating a neutron star or even a black hole, depending on its size. The star’s outer layers are thrown out into the universe in an explosion. This explosion of a star will also supernova called.

Hertzsprung-Russell diagram

Stars are classified based on their own luminosity and spectral type. Depending on the strength of the star’s own glow and the light spectrum of the emitted light, a star can be classified into different classes such as dwarf, major class or giant. The Sun is characterized as a yellow dwarf in this diagram. You can also use this chart to determine the evolution of a star.

Big Bang and the structure of the universe

In cosmology, the structure of the universe and the beginning of the universe are studied. As the starting point of matter, space and time, the Big Bang is dated approximately 13.5 billion years ago. Based on observations of distant objects, it is suspected that the universe has been stretching and expanding ever since. Hence the theory of the infinite universe. However, proving such theories is incredibly difficult.

Stars form the center of all solar systems. Galaxies are made up of a large number of solar systems and a black hole is believed to be at the center of the galaxies. This assumption was proven in 2019, when a black hole was detected and photographed for the first time.

The reasons for this kind of phenomena and movements are clarified in astrophysics and astromechanics.

Hubble telescope

Through space travel, however, astronomical research could also be advanced. For example, through the Hubble Space Telescope or the James-Webb Space Telescope launched in January 2022, which is intended to inherit the Hubble Telescope. Through them, recordings such as the so-called «Hubble Deep Field Image» could be made.

Figure 4: «Hubble Deep Field Image» (Source: nasa.gov)

You can see galaxies millions of light years away from the Milky Way. Such images can be used to look far into the past and perhaps at some point the origin of the universe can be clarified. You can find more about the Hubble telescope in its own article.

Gravity and planetary orbits

Under the astrophysics we understand the physical background for that movement of the celestial objects. Gravity and planetary orbits can be described and predicted using astrophysics.

Also gravity and the gravitational laws are parts of astrophysics. In 1686, Isaac Newton established the law of gravitation, now referred to as Newton’s law of gravitation. The law states that every point mass attracts every other point mass with a force directed along the connecting line.

It provides explanations for the earth’s gravity, the moon’s orbit around the earth and the planetary movements around the sun. Phenomena such as the tides or the orbital disturbances of the moon can also be detected with the help of the Newton’s law of gravitation be explained.

Kepler’s laws

In addition to Newton’s laws are also the Kepler’s laws important when considering the behavior of celestial bodies. In Kepler’s three laws, the orbital behavior of planets around the sun is established as regularities. Based on the knowledge of the planetary orbits, satellite orbits are also established. You will also find detailed articles on Kepler’s laws and satellite orbits.