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匿名 發問於 教育及參考書小學及中學教育 · 1 十年前

information on the comets,meteors or Milky Way? URGENT!

URGENT! p.6 student.

3 個解答

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  • 1 十年前
    最愛解答

    -- Comets

    A comet is a small body in the solar system that orbits the Sun and (at least occasionally) exhibits a coma (or atmosphere) and/or a tail — both primarily from the effects of solar radiation upon the comet's nucleus, which itself is a minor body composed of rock, dust, and ice. Comets' orbits are constantly changing: their origins are in the outer solar system, and they have a propensity to be highly affected (or perturbed) by relatively close approaches to the major planets. Some are moved into sun grazing orbits that destroy the comets when they near the Sun, while others are thrown out of the solar system forever.

    -- Meteors

    A meteor is the visible event that occurs when a meteoroid or asteroid enters the earth's atmosphere and becomes brightly visible. For bodies with a size scale larger than the atmospheric mean free path (10 cm to several metres) the visibility is due to the heat produced by the ram pressure (not friction, as is commonly assumed) of atmospheric entry. Since the majority of meteors are from small sand-grain size meteoroid bodies, most visible signatures are caused by electron relaxation following the individual collisions between vaporized meteor atoms and atmospheric constituents. The meteor is just what we see.

    -- Milky Way

    The Milky Way is a barred spiral[1] galaxy of a Local Group of galaxies within the Virgo Supercluster. The main disk of the Milky Way Galaxy is about 80,000 to 100,000 light-years in diameter, about 250,000 to 300,000 light-years in circumference, and outside the Galactic core, about 1,000 light-years in thickness.[citation needed] The galaxy is estimated to contain 200[2] billion stars but this number might reach 400 billion[3] if small-mass stars predominate. As a guide to the relative physical scale of the Milky Way, if the galaxy were reduced to 130 km (80 mi) in diameter, the solar system would be a mere 2 mm (0.08 inches) in width. The Galactic Halo extends outward, but is limited in size by the orbits of the two Milky Way satellites, the Large and the Small Magellanic Clouds, whose perigalacticon is at ~180,000 light-years.[4] New discoveries indicate that the disk extends much farther than previously thought.

    The term "milky" originates from the hazy band of white light appearing across the celestial sphere visible from Earth, which comprises stars and other material lying within the galactic plane. The galaxy appears brightest in the direction of Sagittarius, towards the galactic center. Relative to the celestial equator, the Milky Way passes as far north as the constellation of Cassiopeia and as far south as the constellation of Crux, indicating the high inclination of Earth's equatorial plane and the plane of the ecliptic relative to the galactic plane. The fact that the Milky Way divides the night sky into two roughly equal hemispheres indicates that the solar system lies close to the galactic plane. The Milky Way's visual absolute magnitude is −20.9[5]

    Although the Milky Way is but one of billions of galaxies in the observable universe (between 1×1010 and 8×1010), the Galaxy has special significance to humanity as the home of the solar system. The Greek philosopher Democritus (450 BC–370 BC) was the first known person to claim that the Milky Way consists of distant stars.

    資料來源: Wikipedia
  • 1 十年前

    -- Comets

    A comet is a small body in the solar system that orbits the Sun and (at least occasionally) exhibits a coma (or atmosphere) and/or a tail — both primarily from the effects of solar radiation upon the comet's nucleus, which itself is a minor body composed of rock, dust, and ice. Comets' orbits are constantly changing: their origins are in the outer solar system, and they have a propensity to be highly affected (or perturbed) by relatively close approaches to the major planets. Some are moved into sun grazing orbits that destroy the comets when they near the Sun, while others are thrown out of the solar system forever.

    -- Meteors

    A meteor is the visible event that occurs when a meteoroid or asteroid enters the earth's atmosphere and becomes brightly visible. For bodies with a size scale larger than the atmospheric mean free path (10 cm to several metres) the visibility is due to the heat produced by the ram pressure (not friction, as is commonly assumed) of atmospheric entry. Since the majority of meteors are from small sand-grain size meteoroid bodies, most visible signatures are caused by electron relaxation following the individual collisions between vaporized meteor atoms and atmospheric constituents. The meteor is just what we see.

    -- Milky Way

    The Milky Way is a barred spiral[1] galaxy of a Local Group of galaxies within the Virgo Supercluster. The main disk of the Milky Way Galaxy is about 80,000 to 100,000 light-years in diameter, about 250,000 to 300,000 light-years in circumference, and outside the Galactic core, about 1,000 light-years in thickness.[citation needed] The galaxy is estimated to contain 200[2] billion stars but this number might reach 400 billion[3] if small-mass stars predominate. As a guide to the relative physical scale of the Milky Way, if the galaxy were reduced to 130 km (80 mi) in diameter, the solar system would be a mere 2 mm (0.08 inches) in width. The Galactic Halo extends outward, but is limited in size by the orbits of the two Milky Way satellites, the Large and the Small Magellanic Clouds, whose perigalacticon is at ~180,000 light-years.[4] New discoveries indicate that the disk extends much farther than previously thought.

    The term "milky" originates from the hazy band of white light appearing across the celestial sphere visible from Earth, which comprises stars and other material lying within the galactic plane. The galaxy appears brightest in the direction of Sagittarius, towards the galactic center. Relative to the celestial equator, the Milky Way passes as far north as the constellation of Cassiopeia and as far south as the constellation of Crux, indicating the high inclination of Earth's equatorial plane and the plane of the ecliptic relative to the galactic plane. The fact that the Milky Way divides the night sky into two roughly equal hemispheres indicates that the solar system lies close to the galactic plane. The Milky Way's visual absolute magnitude is −20.9[5]

    Although the Milky Way is but one of billions of galaxies in the observable universe (between 1×1010 and 8×1010), the Galaxy has special significance to humanity as the home of the solar system. The Greek philosopher Democritus (450 BC–370 BC) was the first known person to claim that the Milky Way consists of distant stars.

  • 1 十年前

    hellohello

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