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A world is a huge object that orbits a star. To be a planet, things must be huge enough for heaviness to have squeezed it right into a spherical, or round, shape,. It must likewise be big enough for gravity to have actually swept up any type of rocky or icy objects native its path, or orbit, approximately the star.Scientists think planets start to type when a thick cloud the dust and gas, referred to as a nebula, spins around a newly created star. Gradually, gravity causes the bits of issue in the nebula to clump together. Slowly, these clumps accumulate and grow. Eventually, these clumps end up being planets.Earth is one of eight planets the circle the star we call the sun. Together, the sun, the planets, and smaller objects such together moons make up our solar system.The 4 planets closest come the sun—Mercury, Venus, Earth, and also Mars—are dubbed terrestrial planets. These planets are solid and also rocky like earth (terra means “earth” in Latin). Earth is the biggest of the 4 terrestrial planets, and Mercury is the smallest. All room surrounded through a class of gas, or atmosphere. Their settings vary in thickness from Mercury’s very thin environment to Venus’, which is thick with clouds the sulfuric acid.The 4 planets the are much more distant from the sun—Jupiter, Saturn, Uranus, and Neptune—are dubbed gas giants. Gas giants are substantial compared with Earth, and they perform not have actually solid surfaces. They are big balls that gas. Jupiter and also Saturn are composed largely of hydrogen and helium. Uranus and Neptune have higher proportions that water vapor, ammonia, and also methane. Each of the four gas giants also has a ring system. A planet’s rings are made that ice, dust, and little rocks. Saturn’s ring mechanism is the largest.Every planet other than Mercury and Venus contends least one organic satellite, or moon. A planet’s moon orbits it together it revolves around the sun. Jupiter, Saturn, and Uranus each have actually dozens the moons.In addition to orbiting a star, planets likewise rotate, or spin, roughly an axis. An axis is one invisible line that runs through the facility of a planet. One complete rotation is referred to as a day. A day on earth is about 24 hours. A day on Jupiter takes just 9.8 hours. Venus has actually the longest day of any kind of planet in our solar system. That takes 243 planet days because that Venus to make a finish turn on its axis.Unlike stars, planets execute not endure nuclear fusion, the process of combining tiny particles dubbed atoms to relax energy. Nuclear combination creates radiation (heat and light) and makes stars glow. Due to the fact that planets do not have nuclear fusion, they do not develop their own light. Instead, lock shine through light reflect from a star. As soon as we watch planets in the night sky, such together Venus, the so-called "Evening Star," we"re seeing reflected sunlight.
You are watching: Objects revolving around and reflecting light from the sun
Exoplanets
Because there room trillions of stars in the universe, there are an extremely likely billions the planets. Yet until the beforehand 1990s, the only well-known planets were in ours solar system. Because then, however, scientists have discovered much more than 400 planets orbiting other stars. These are referred to as extrasolar planets, or exoplanets.Exoplanets appear to be fairly small native our approach on Earth. Telescopes normally cannot watch exoplanets directly, so astronomers have had to come up with techniques to recognize them. One an approach astronomers usage is to look because that a slim wobble in a star’s movement. This wobble is the an outcome of the gravitational traction of a surrounding planet. Many of the exoplanets found so far are gas giants.
Vocabulary
accumulate | verb | to gather or collect. |
ammonia | noun | a gas (NH3) crucial to food production. |
ancient | adjective | very old. |
astronomer | noun | person that studies an are and the universe past Earth"s atmosphere. |
atmosphere | noun | layers that gases surrounding a world or various other celestial body. |
atom | noun | the straightforward unit of an element, written of three significant parts: electrons, protons, and neutrons. |
axis | noun | an invisible line around which an item spins. |
billion | noun | 1,000,000,000 |
day | noun | time it takes because that a world to finish a single rotation approximately its axis. |
dense | adjective | having parts or molecules that space packed carefully together. |
detect | verb | to notice. |
distant | adjective | far away. |
dozen | noun | a team of 12. |
dust | noun | microscopic particles of rocks or minerals drifting in space. Additionally called cosmic dust or room dust. |
dwarf planet | noun | celestial body the is virtually spherical however does not fulfill other definitions for a planet. |
Earth | noun | our planet, the third from the Sun. The planet is the only location in the well-known universe the supports life. |
earth | noun | soil or dirt. |
energy | noun | capacity to execute work. |
eventually | adverb | at some suggest in the future. |
exoplanet | noun | planet exterior the solar system, orbiting a star various other than the sun. Likewise called one extrasolar planet. |
extrasolar planet | noun | planet external the solar system, orbiting a star various other than the sun. Also called an exoplanet. |
gas | noun | state of issue with no fixed shape that will certainly fill any kind of container uniformly. Gas molecules space in constant, random motion. |
gas giant | noun | one the the four enormous outermost planets in the solar system (Jupiter, Saturn, Neptune, Uranus), composed mainly of gases rather of rock. Additionally called a Jovian planet. |
gradually | adverb | slowly, or at a measure up pace. |
gravitational pull | noun | physical attraction between two substantial objects. |
gravity | noun | physical force through which objects attract, or traction toward, every other. |
helium | noun | a light, colorless gas with the chemical symbol He. |
hydrogen | noun | chemical aspect with the price H, who most typical isotope consists of a single electron and also a solitary proton. |
International huge Union | noun | organization promoting and also safeguarding the scientific research of astronomy through international cooperation. |
Jupiter | noun | largest planet in the solar system, the fifth planet native the Sun. |
Latin | noun | language of old Rome and the roman inn Empire. |
Mars | noun | fourth earth from the sun, between Earth and Jupiter. |
matter | noun | material that provides up a substance. |
Mercury | noun | smallest planet in the solar system, and also closest come the sun. |
methane | noun | chemical compound the is the basic ingredient of organic gas. |
Moon | noun | Earth"s only organic satellite. |
moon | noun | natural satellite of a planet. |
natural satellite | noun | moon, or a celestial body that orbits an additional celestial body (its primary). |
nebula | noun | cloud of gas and dust in space. |
Neptune | noun | eighth earth from the sun in ours solar system. |
nuclear fusion | noun | process where the nuclei of one element, usually hydrogen, fuse through each other to kind the nuclei of an additional element, commonly helium. |
orbit | verb | to move in a circular pattern roughly a an ext massive object. |
planet | noun | large, spherical celestial human body that on regular basis rotates about a star. |
Pluto | noun | dwarf world in ours solar system. |
proportion | noun | amount. |
radiation | noun | energy, emitted as waves or particles, radiating external from a source. |
reflect | verb | to cant or return light from a surface. |
revolve | verb | to orbit or spin around something. |
ring system | noun | thin one of dust, gas, and rocks the orbit a planet. |
rotate | verb | to turn roughly a center allude or axis. |
Saturn | noun | sixth planet from the sun. |
solar orbit | noun | revolution of an object around the sun. |
solar system | noun | the sun and the planets, asteroids, comets, and also other bodies that orbit approximately it. |
spherical | adjective | rounded and also three-dimensional. |
star | noun | large round of gas and also plasma the radiates energy through nuclear fusion, such together the sun. |
sulfuric acid | noun | toxic chemistry made the hydrogen, sulfur, and also oxygen. |
sun | noun | star in ~ the center of our solar system. |
telescope | noun | scientific tool that supplies mirrors come view distant objects. |
terrestrial planet | noun | one of the 4 planets closest to the sun: Mercury, Venus, Earth, or Mars. |