1. “Volume” is a measurement of the amount of space an object occupies. The sun has a whopping volume of about 1,409,272,569,059,860,000 cubic kilometers (338,102,469,632,763,000 cubic miles). The Earth has a volume of about 1,083,206,916,846 cubic kilometers (259,875,159,532 cubic miles).

      According to some astronomers, about 1.3 million Earths could fit inside the sun. According to other astronomers, only about 960,000 Earths could fit inside the sun.

      How can both of these facts be true?

      The first group of astronomers is only considering volume. If you divide the volume of the sun by the volume of the Earth, you get about 1.3 million.

      The second group of astronomers is considering the shape of the Earth as well as its volume. If all the Earths packed inside the sun maintained their spherical shape, there would be a lot of wasted space between the curved spheres. This empty space would prevent more than about 960,000 spherical Earths from occupying the spherical sun.

    2. The mass and volume of the sun are so huge that some astronomers describe the solar system as “the sun plus some debris.” What are some examples of the “debris” of the solar system?

      Planets! The gas giants of the outer solar system (such as Jupiter) account for most of the non-sun volume of the solar system. Rocky inner planets (such as Earth) and icy dwarf planets (such as Eris) have much less volume.

      Moons! Most planets have natural satellites, called moons, that orbit them. Some moons are tiny. The diameter of Saturn’s moonlet S/2009 S 1 is only about 400 meters (1,300 feet). Some moons are larger than planets. Ganymede, the solar system’s biggest moon (it orbits Jupiter), is larger than Mercury, the solar system’s smallest planet.

      Asteroids! These spherical and potato-shaped rocky bodies orbit the sun in a “belt” between the planets Mars and Jupiter.

      Comets! These “dirty snowballs” (or “snowy dirtballs”) spend most of their long, bizarre orbits in the outer reaches of the solar system. They swing by the sun, losing some of their gassy, icy tails, in regular patterns. Short-period comets take fewer than 200 years to orbit the sun. Halley’s Comet is a short-period comet that swings by the sun about every 75 years. Long-period comets take more than 200 years to orbit the sun, and are much more unpredictable. Comet Kohoutek is a long-period comet that takes about 75,000 years to orbit the sun.

    3. The sun is a middle-aged star. It was born about 4.6 billion years ago, and has about 5 billion years left before it dies.

      Do you think the sun’s volume will get bigger or smaller as it gets older?


      First, the sun will get bigger—so big it will be called a “red giant.” The red giant sun will expand as far as the orbits of Mercury and Venus—and might even gobble up Earth as well.

      Then, the sun will shrink—so small it will be called a “white dwarf.” The red giant sun will fling off its outer layers of gas and compress into a tiny ball of carbon with a volume about the same as Earth.

  • Term Part of Speech Definition Encyclopedic Entry
    asteroid Noun

    irregularly shaped planetary body, ranging from 6 meters (20 feet) to 933 kilometers (580 miles) in diameter, orbiting the sun between Mars and Jupiter.

    astronomy Noun

    the study of space beyond Earth's atmosphere.

    comet Noun

    celestial object made up of ice, gas, and dust that orbits the sun and leaves a tail of debris.

    dwarf planet Noun

    celestial body that is nearly spherical but does not meet other definitions for a planet.

    Earth Noun

    our planet, the third from the Sun. The Earth is the only place in the known universe that supports life.

    Encyclopedic Entry: Earth
    gas giant Noun

    one of the four enormous outermost planets in the solar system (Jupiter, Saturn, Neptune, Uranus), composed mostly of gases instead of rock. Also called a Jovian planet.

    mass Noun

    measure of the amount of matter in a physical object.

    moon Noun

    natural satellite of a planet.

    Encyclopedic Entry: moon
    orbit Noun

    path of one object around a more massive object.

    planet Noun

    large, spherical celestial body that regularly rotates around a star.

    Encyclopedic Entry: planet
    red giant Noun

    "main sequence" star with huge surface area, low surface temperature, and reddish color.

    solar system Noun

    the sun and the planets, asteroids, comets, and other bodies that orbit around it.

    sphere Noun

    round object.

    star Noun

    large ball of gas and plasma that radiates energy through nuclear fusion, such as the sun.

    sun Noun

    star at the center of our solar system.

    volume Noun

    space an object occupies.

    white dwarf Noun

    small, dense "main sequence" star that has used up most of its nuclear fuel.