In Texas, teachers are expected to teach that the planets orbit the Sun, and that the Moon orbits the Earth. This topic is closely related to the changes in the night sky, the position of the planets, and lunar phases. This is a fairly simple topic, but is related to others that are much more complex seasons , lunar phases and so if students do not understand the movement of planets about the Sun or the Moon around the Earth, they will be unable to truly understand these other concepts.
Most moons in our solar system are named for mythological characters from a wide variety of cultures. The newest moons discovered at Saturn, for example, are named for Norse gods such as Bergelmir , a giant. Uranus is the exception. The International Astronomical Union approves an official name when the discovery is confirmed. Earth's Moon probably formed when a large body about the size of Mars collided with Earth, ejecting a lot of material from our planet into orbit.
Debris from the early Earth and the impacting body accumulated to form the Moon approximately 4. Usually the term moon brings to mind a spherical object, like Earth's Moon. The two moons of Mars, Phobos and Deimos , are different. While both have nearly circular orbits and travel close to the plane of the planet's equator, they are lumpy and dark.
Phobos is slowly drawing closer to Mars and could crash into the planet in 40 or 50 million years. Or the planet's gravity might break Phobos apart, creating a thin ring around Mars. Jupiter's menagerie of moons includes the largest in the solar system Ganymede , an ocean moon Europa and a volcanic moon Io.
Many of Jupiter's outer moons have highly elliptical orbits and orbit backwards opposite to the spin of the planet. Saturn, Uranus and Neptune also have some irregular moons, which orbit far from their respective planets. Saturn has two ocean moons — Enceladus and Titan. Both have subsurface oceans and Titan also has surface seas of lakes of ethane and methane. The chunks of ice and rock in Saturn's rings and the particles in the rings of the other outer planets are not considered moons, yet embedded in Saturn's rings are distinct moons or moonlets.
These shepherd moons help keep the rings in line. Titan, the second largest in the solar system, is the only moon with a thick atmosphere. In the realm of the ice giants, Uranus's inner moons appear to be about half water ice and half rock. In general, asteroids have orbits with smaller semimajor axes than do comets Figure 1. The majority of them lie between 2. As you can see in Table 1, the asteroid belt represented by its largest member, Ceres is in the middle of a gap between the orbits of Mars and Jupiter.
It is because these two planets are so far apart that stable orbits of small bodies can exist in the region between them. Figure 1: Solar System Orbits. We see the orbits of typical comets and asteroids compared with those of the planets Mercury, Venus, Earth, Mars, and Jupiter black circles. Shown in red are three comets: Halley, Kopff, and Encke.
In blue are the four largest asteroids: Ceres , Pallas, Vesta , and Hygeia. Comets generally have orbits of larger size and greater eccentricity than those of the asteroids.
Typically, the eccentricity of their orbits is 0. As they approach perihelion, the comets speed up and whip through the inner parts of their orbits more rapidly. The closest point in a satellite orbit around Earth is its perigee, and the farthest point is its apogee corresponding to perihelion and aphelion for an orbit around the Sun. The planets follow orbits around the Sun that are nearly circular and in the same plane.
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