Radiation is one feature of space, but the universe is also full of objects that we can see. The most familiar objects to humans are planets and stars.
Stars (like our own sun) are immense balls of gas that produce their own radiation. They can range from red supergiants to cooling white dwarfs that are the leftovers of supernovas, or star explosions that occur when a big one runs out of gas to burn. These explosions spread elements throughout the universe and are the reason that elements such as iron exist. Star explosions can also give rise to incredibly dense objects called neutron stars. If these neutron stars send out pulses of radiation, they are called pulsar stars.
Planets are objects whose definition came under scrutiny in 2006, when astronomers were debating whether Pluto could be considered a planet or not. At the time, the International Astronomical Union (the governing body on Earth for these decisions) ruled that a planet is a celestial body that orbits the sun, is massive enough to have a nearly round shape, and has cleared its orbit of debris. Under this designation, Pluto and similar small objects are considered "dwarf planets."
The definition of extrasolar planets, or planets outside the solar system, is still not firmed up by the IAU, but essentially astronomers understand it to mean objects that behave like planets in our neighborhood. The first such planet was found in 1992 (in the constellation Pegasus) and since that time, hundreds of alien planets have been confirmed — with thousands more suspected.
Asteroids are rocks that are not quite big enough to be dwarf planets. In our own solar system, they are often considered to be leftovers from when our neighborhood was forming, and are most concentrated in a belt between the planets Mars and Jupiter. Younger solar systems also have collections of asteroids, but if planets are not there yet, astronomers can sometimes use the term "protoplanets" to indicate planets in formation.
In our solar system, comets (sometimes called dirty snowballs) are objects believed to originate from a vast collection of icy bodies called the Oort Cloud. As a comet approaches the sun, the heat of our star causes ices to melt and stream away from the comet. The ancients often associated comets with destruction or some sort of immense change on Earth, but the discovery of Halley's Comet and related "periodic" or returning comets showed that they were ordinary solar system phenomena.Radiation is one feature of space, but the universe is also full of objects that we can see. The most familiar objects to humans are planets and stars.
Stars (like our own sun) are immense balls of gas that produce their own radiation. They can range from red supergiants to cooling white dwarfs that are the leftovers of supernovas, or star explosions that occur when a big one runs out of gas to burn. These explosions spread elements throughout the universe and are the reason that elements such as iron exist. Star explosions can also give rise to incredibly dense objects called neutron stars. If these neutron stars send out pulses of radiation, they are called pulsar stars.
Planets are objects whose definition came under scrutiny in 2006, when astronomers were debating whether Pluto could be considered a planet or not. At the time, the International Astronomical Union (the governing body on Earth for these decisions) ruled that a planet is a celestial body that orbits the sun, is massive enough to have a nearly round shape, and has cleared its orbit of debris. Under this designation, Pluto and similar small objects are considered "dwarf planets."
The definition of extrasolar planets, or planets outside the solar system, is still not firmed up by the IAU, but essentially astronomers understand it to mean objects that behave like planets in our neighborhood. The first such planet was found in 1992 (in the constellation Pegasus) and since that time, hundreds of alien planets have been confirmed — with thousands more suspected.
Asteroids are rocks that are not quite big enough to be dwarf planets. In our own solar system, they are often considered to be leftovers from when our neighborhood was forming, and are most concentrated in a belt between the planets Mars and Jupiter. Younger solar systems also have collections of asteroids, but if planets are not there yet, astronomers can sometimes use the term "protoplanets" to indicate planets in formation.
In our solar system, comets (sometimes called dirty snowballs) are objects believed to originate from a vast collection of icy bodies called the Oort Cloud. As a comet approaches the sun, the heat of our star causes ices to melt and stream away from the comet. The ancients often associated comets with destruction or some sort of immense change on Earth, but the discovery of Halley's Comet and related "periodic" or returning comets showed that they were ordinary solar system phenomena.Radiation is one feature of space, but the universe is also full of objects that we can see. The most familiar objects to humans are planets and stars.
Stars (like our own sun) are immense balls of gas that produce their own radiation. They can range from red supergiants to cooling white dwarfs that are the leftovers of supernovas, or star explosions that occur when a big one runs out of gas to burn. These explosions spread elements throughout the universe and are the reason that elements such as iron exist. Star explosions can also give rise to incredibly dense objects called neutron stars. If these neutron stars send out pulses of radiation, they are called pulsar stars.
Planets are objects whose definition came under scrutiny in 2006, when astronomers were debating whether Pluto could be considered a planet or not. At the time, the International Astronomical Union (the governing body on Earth for these decisions) ruled that a planet is a celestial body that orbits the sun, is massive enough to have a nearly round shape, and has cleared its orbit of debris. Under this designation, Pluto and similar small objects are considered "dwarf planets."
The definition of extrasolar planets, or planets outside the solar system, is still not firmed up by the IAU, but essentially astronomers understand it to mean objects that behave like planets in our neighborhood. The first such planet was found in 1992 (in the constellation Pegasus) and since that time, hundreds of alien planets have been confirmed — with thousands more suspected.
Asteroids are rocks that are not quite big enough to be dwarf planets. In our own solar system, they are often considered to be leftovers from when our neighborhood was forming, and are most concentrated in a belt between the planets Mars and Jupiter. Younger solar systems also have collections of asteroids, but if planets are not there yet, astronomers can sometimes use the term "protoplanets" to indicate planets in formation.
In our solar system, comets (sometimes called dirty snowballs) are objects believed to originate from a vast collection of icy bodies called the Oort Cloud. As a comet approaches the sun, the heat of our star causes ices to melt and stream away from the comet. The ancients often associated comets with destruction or some sort of immense change on Earth, but the discovery of Halley's Comet and related "periodic" or returning comets showed that they were ordinary solar system phenomena.
