Astronomy facts for kids

The Paranal Observatory of European Southern Observatory shooting a laser guide star to the Galactic Center

Astronomy is a natural science that explores everything beyond Earth's atmosphere. It studies amazing celestial objects and the incredible events happening in the cosmos. Astronomers use mathematics, physics, and chemistry to understand how these objects began and how they have changed over time.

Some of the things astronomers study include planets, moons, stars, nebulae (giant clouds of gas and dust), galaxies, meteoroids, asteroids, and comets. They also investigate powerful events like supernova explosions, gamma ray bursts, and quasars. Cosmology is a special part of astronomy that looks at the entire universe as a whole.

Astronomy is one of the oldest sciences. Ancient civilizations like the Egyptians, Babylonians, Greeks, and Maya carefully watched the night sky. They used these observations to create calendars and navigate.

Today, professional astronomy has two main parts: observational and theoretical. Observational astronomy gathers information by looking at objects in space. Theoretical astronomy uses computers and math to create models that explain these objects and events. Both parts work together to help us understand the universe better.

Astronomy is also special because many everyday people, called amateur astronomers, help with discoveries. They often find new comets or observe sudden events in space.

What is Astronomy?

The word "Astronomy" comes from ancient Greek words meaning "star" and "law" or "rule." So, it means the study of celestial objects. It's important not to confuse astronomy with astrology. Astrology is a belief that the positions of stars and planets affect human lives. Astronomy, however, is a science based on facts and physics.

Astronomy and Astrophysics

You might hear the words "astronomy" and "astrophysics" used almost interchangeably today. Both fields study objects and matter outside Earth. Astrophysics focuses more on the physical properties and processes of these objects. Many professional astronomers actually have degrees in physics!

A Journey Through Time: The History of Astronomy

Ancient Skywatchers

The Nebra sky disc (around 1800–1600 BCE) from ancient Europe. It shows the Sun, Moon, and stars, and helped people track the seasons.

Long before written history, people looked at the sky for practical reasons. They needed to know when to plant crops, so they created calendars. Places like Stonehenge show us that ancient people were very interested in the movements of the Sun and Moon. The Nebra sky disc is another example. It's an ancient calendar that helped define the year using the Moon's cycles.

Classical Discoveries

A Babylonian planisphere from the 7th century BCE. The Babylonians were skilled at tracking celestial movements.

Many early civilizations, including the Egyptians, Babylonians, and Greeks, built observatories and developed ideas about the universe. The Babylonians were very advanced in math and science. They even discovered that lunar eclipses happen in a regular pattern.

In ancient Greece, thinkers tried to explain why things happened in the sky. Around 300 BC, Aristarchus of Samos suggested that Earth and the planets orbited the Sun. This idea is called the heliocentric model. Later, Hipparchus created a catalog of over 1000 stars. He also invented early astronomical tools like the astrolabe. The Antikythera mechanism (around 150–80 BC) was an amazing ancient computer. It could predict the positions of the Sun, Moon, and planets.

After the Greek era, the idea that Earth was the center of the universe became popular. This was called the geocentric model or Ptolemaic system, named after Claudius Ptolemy. His book, the Almagest, was the main reference for over a thousand years. Even though it was later proven wrong, it made the best predictions for planet positions at the time.

Astronomy in the Middle Ages

A portrait of Alfraganus, an important Islamic astronomer. Islamic scholars made many contributions to astronomy.

Astronomy really thrived in the medieval Islamic world. They built observatories and translated important texts from India, Persia, and Greece. Islamic astronomers added their own discoveries. For example, Abd al-Rahman al-Sufi described the Andromeda Galaxy in 964 AD. Many stars still have Arabic names today.

In Europe, scholars like Richard of Wallingford invented early astronomical clocks. Nicole Oresme even discussed the idea that Earth might rotate. The Roman Catholic Church also supported astronomy for centuries, partly to figure out the correct date for Easter.

The Age of Telescopes

Galileo's first drawings of the Moon's surface from 1610. His telescope revealed mountains and craters.

During the Renaissance, Nicolaus Copernicus brought back the idea of a Sun-centered solar system. In 1610, Galileo Galilei used a new telescope to observe the phases of Venus. This observation strongly supported Copernicus's heliocentric model. Around the same time, Johannes Kepler figured out that planets move in ellipses, not perfect circles, around the Sun.

It was Isaac Newton who finally explained why planets moved this way. He developed the law of gravitation and also invented the reflecting telescope. Newton and Richard Bentley suggested that stars were distant suns. Galileo also discovered that the Milky Way was made of countless stars.

Later, William Herschel discovered the planet Uranus in 1781, the first new planet found with a telescope. Scientists also developed new tools like the spectroscope and astrophotography. These allowed them to study the light from stars and discover what elements they were made of.

Discovering Galaxies

William Herschel's diagram of stars, showing his early ideas about the Milky Way.

In the late 1700s, William Herschel mapped stars and thought our solar system was near the center of a disk of stars, the Milky Way. For a long time, astronomers debated if fuzzy "spiral nebulae" were clouds within our galaxy or entirely separate "island Universes."

Photograph of the Great Andromeda "Nebula" by Isaac Roberts in 1888.

In 1912, Henrietta Leavitt discovered special stars called Cepheid variables. These stars change brightness in a predictable way, which helps measure their true brightness and distance. Using these stars, Harlow Shapley created the first accurate map of the Milky Way. Then, in the 1920s, Edwin Hubble used Cepheid variables to prove that the Andromeda Galaxy and others were indeed separate galaxies far beyond our own. This showed that the universe is full of countless galaxies.

Understanding the Universe's Beginning

The Hubble Extreme Deep Field shows thousands of galaxies, some very distant and ancient.

Albert Einstein's theory of general relativity in 1917 helped start modern ideas about the universe. In 1929, Edwin Hubble observed that galaxies are moving away from Earth, and the farther they are, the faster they move. This is called Hubble's law, and it means the universe is expanding.

This expansion suggested that the universe started from a very dense and hot point, an idea called the Big Bang. Scientists later found strong evidence for the Big Bang in 1965 with the discovery of cosmic microwave background radiation. This is a faint glow of heat left over from the early universe.

Theoretical astronomy also predicted amazing objects like black holes and neutron stars. These help explain mysterious phenomena like quasars and pulsars. Today, Space telescopes and projects like LIGO (which detected gravitational waves in 2015) continue to reveal new secrets of the cosmos.

How Astronomers Observe the Universe

Different types of observational astronomy use various wavelengths of light to see into space.

Observational astronomy uses different kinds of "light" or electromagnetic radiation to study space. We categorize astronomy by the type of radiation observed.

Radio Astronomy

The Very Large Array in New Mexico, a powerful radio telescope.

Radio astronomy uses very long wavelengths, much longer than visible light. These waves can pass through dust clouds that block visible light. Radio telescopes can detect invisible gases like hydrogen, as well as pulsars (spinning neutron stars), supernova remnants, and distant galaxies.

Infrared Astronomy

The Subaru Telescope (left) and Keck Observatory (center) on Mauna Kea, which observe in infrared and visible light.

Infrared astronomy detects infrared radiation, which is like heat. It's great for studying objects too cold to glow with visible light, such as planets, dusty disks around young stars, or stars hidden inside thick clouds of dust. Most infrared light is absorbed by Earth's atmosphere, so infrared telescopes are often in high, dry places or in space, like the James Webb Space Telescope. This telescope can see very distant, ancient galaxies because their light has stretched into infrared as the universe expanded.

Optical Astronomy

Optical astronomy is the oldest type, using the visible light we can see. Early astronomers drew what they saw. Later, they used cameras. Today, digital cameras like charge-coupled devices (CCDs) capture images. These telescopes can also see some near-ultraviolet and near-infrared light.

Ultraviolet Astronomy

Ultraviolet astronomy uses ultraviolet light. Earth's atmosphere absorbs most UV light, so these observations must be made from high in the atmosphere or from space. UV astronomy is perfect for studying very hot, bright stars.

X-ray Astronomy

An X-ray jet from a supermassive black hole, seen by NASA's Chandra X-ray Observatory.

X-ray astronomy looks at X-radiation, which comes from extremely hot and energetic events. Since X-rays are blocked by our atmosphere, telescopes for X-ray astronomy are on rockets or satellites. X-ray sources include black holes, supernova remnants, and hot gas in galaxy clusters. X-ray images of the Sun show its super-hot outer atmosphere, called the corona.

Gamma-ray Astronomy

Gamma-ray astronomy observes the shortest, most energetic waves in the universe. Gamma rays are detected by satellites or special ground telescopes that catch flashes of light when gamma rays hit the atmosphere. Gamma-ray bursts are the most powerful explosions in the universe. This field helps us understand cosmic rays and mysterious dark matter.

Beyond Light: Other Ways to Observe

The underground ANTARES neutrino telescope in the Mediterranean Sea.

Astronomers can also study space using things other than light.

• In neutrino astronomy, scientists use huge underground detectors to catch tiny particles called neutrinos. Most neutrinos come from the Sun, but some have been detected from supernova 1987A.
• Gravitational-wave astronomy uses special detectors like LIGO to sense gravitational waves. These are ripples in spacetime caused by massive, accelerating objects like colliding black holes. LIGO made its first detection in 2015.

Combining observations from light, neutrinos, and gravitational waves is called multi-messenger astronomy. It gives us a more complete picture of cosmic events.

Mapping the Sky: Astrometry and Celestial Mechanics

Using optical interferometry to precisely measure star positions.

Astrometry is one of the oldest parts of astronomy. It's about measuring the exact positions of objects in the sky. This was vital for celestial navigation (using stars to find your way) and making accurate calendars. By carefully tracking planets, we can understand their orbits and predict their future positions, a field called celestial mechanics. Measuring the tiny shift in a star's position as Earth orbits the Sun (called stellar parallax) helps us figure out distances in the universe.

Theoretical Astronomy: Explaining the Cosmos

Theoretical astronomers use math and computer simulations to understand what we observe. They create models to explain how stars work, how galaxies form, and how the universe changes. For example, the current "standard model of cosmology" helps explain the cosmic microwave background and the expansion of the universe. This model suggests that much of the universe is made of mysterious dark matter and dark energy.

Exploring the Universe: Subfields of Astronomy

Physical Cosmology: The Universe as a Whole

Physical cosmology studies the entire universe. It tries to understand how the cosmos formed and evolved. The Big Bang theory is central to this field. It says the universe started extremely dense and hot, then expanded over 13.8 billion years to its current state. Scientists are still trying to understand dark matter and dark energy, which seem to make up 96% of the universe's mass.

Extragalactic Astronomy: Beyond Our Galaxy

These blue, loop-shaped objects are multiple images of the same galaxy, bent and magnified by a gravitational lens.

This field studies objects outside our own galaxy. It looks at how galaxies form and change, their shapes, and how they group together into clusters. This helps us understand the universe's overall structure.

Galactic Astronomy: Our Home Galaxy

Galactic astronomy focuses on our own galaxy, the Milky Way. It's a barred spiral galaxy and part of a group of galaxies called the Local Group. The Milky Way is a huge spinning collection of gas, dust, stars, and other objects, all held together by gravity. Because we are inside it, much of the Milky Way is hidden from our view by dust. Studies show there's more mass in the Milky Way than we can see, suggesting the presence of a dark matter halo.

Stellar Astronomy: The Lives of Stars

The study of stars and their life cycles is key to understanding the universe. Astronomers study how stars are born in giant clouds of gas and dust, how they shine by nuclear fusion, and how they eventually die. Stars can end their lives in spectacular supernova explosions, or become dense white dwarfs or neutron stars. If a star is very massive, it can even become a black hole.

Solar Astronomy: Our Sun

An ultraviolet image of the Sun's active photosphere from NASA's TRACE space telescope.

Solar astronomy is the study of our own Sun. It's a typical main-sequence star and about 4.6 billion years old. Scientists study its sunspot cycle, how its brightness changes, and its different layers, from the core where fusion happens, to its outer atmosphere, the corona.

Planetary Science: Our Solar System and Beyond

The black spot is a dust devil climbing a crater wall on Mars. These swirling columns of Martian air create long, dark streaks.

Planetary science studies planets, moons, dwarf planets, comets, asteroids, and other objects orbiting the Sun. It also includes exoplanets, which are planets orbiting other stars. Our Solar System has been well-studied using telescopes and spacecraft. This field explores how planets form, how they get magnetic fields, and how internal heat drives geological processes like volcanism and erosion.

Connecting with Other Sciences

Astrochemistry: Molecules in Space

Astrochemistry combines astronomy and chemistry. It studies the different molecules found in the Universe and how they react with each other and with light. This helps us understand how the Solar System formed and what space is made of.

Astrobiology: Life Beyond Earth

Astrobiology (or exobiology) explores the origin of life and whether extraterrestrial life exists elsewhere. It uses astronomy, biochemistry, geology, and planetary science to look for signs of life on other worlds. This includes studying how life began on Earth and what makes a planet habitable.

Archaeoastronomy: Ancient Sky Knowledge

Archaeoastronomy is the study of how ancient cultures understood and used astronomy. It looks at archaeological sites and anthropological evidence to learn about their sky observations and their cultural meaning.

Amateur Astronomers: Stargazing Heroes

Amateur astronomers often build their own equipment and gather for "star parties."

Astronomy is one of the few sciences where everyday people, called amateur astronomers, make important contributions. They observe celestial objects and events, sometimes with their own telescopes. Popular targets include the Sun, Moon, planets, stars, comets, and meteor showers. Amateur astronomers have discovered comets, tracked minor planets, and observed variable stars. With modern digital cameras, many amateurs also create stunning astrophotography.

Mysteries of the Universe: Unsolved Problems

Even with all our knowledge, many big questions in astronomy remain unanswered. For example:

• What are dark matter and dark energy? These mysterious substances seem to control the universe's evolution.
• What is the ultimate fate of the universe? Will it expand forever, or will it eventually collapse?
• Why is there less lithium in the universe than predicted by the Big Bang model?
• Is our Solar System unique, or are there many others like it?
• How did the first galaxies form?
• What is the origin of supermassive black holes?
• Is there other life in the Universe, especially intelligent life?

These are exciting questions that future astronomers, maybe even you, will help answer!

See Also

In Spanish: Astronomía para niños

• Solar system
• Planet
• Satellite (natural) (word for moons of other planets)
• Comet
• Meteor
• Asteroid
• Star
• Black hole
• Galaxy
• Universe
• List of comets

Images for kids

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  The Paranal Observatory of European Southern Observatory is shooting a laser guide star to the Galactic Center.

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  Astronomical Observatory, New South Wales, Australia 1873.

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  The 19th-century Quito Astronomical Observatory is located 12 minutes south of the Equator in Quito, Ecuador.

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  A celestial map from the 17th century, by the Dutch cartographer Frederik de Wit.

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  The Suryaprajnaptisūtra, a 6th-century BC astronomy text of Jains at The Schoyen Collection, London. Above: its manuscript from c. 1500 AD.

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  Greek equatorial sundial, Alexandria on the Oxus, present-day Afghanistan 3rd–2nd century BC.

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  An astronomical chart from an early scientific manuscript, c. 1000.

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  The Very Large Array in New Mexico, an example of a radio telescope.

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  ALMA Observatory is one of the highest observatory sites on Earth. Atacama, Chile.

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  X-ray jet made from a supermassive black hole found by NASA's Chandra X-ray Observatory, made visible by light from the early Universe.

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  Astrophysics applies physics and chemistry to understand the measurements made by astronomy. Representation of the Observable Universe that includes images from Hubble and other telescopes.

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  Hubble Extreme Deep Field.

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  This image shows several blue, loop-shaped objects that are multiple images of the same galaxy, duplicated by the gravitational lens effect of the cluster of yellow galaxies near the middle of the photograph. The lens is produced by the cluster's gravitational field that bends light to magnify and distort the image of a more distant object.

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  Mz 3, often referred to as the Ant planetary nebula. Ejecting gas from the dying central star shows symmetrical patterns unlike the chaotic patterns of ordinary explosions.

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  An ultraviolet image of the Sun's active photosphere as viewed by the TRACE space telescope. NASA photo.

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  The black spot at the top is a dust devil climbing a crater wall on Mars. This moving, swirling column of Martian atmosphere (comparable to a terrestrial tornado) created the long, dark streak.