North Texas Space Walk

The Aphelion is the point in the orbit of a planet where it is most distant from the sun

This is a collection of many irregularly shaped bodies of various sizes, most of them rather small. Ceres is the largest known object in the asteroid belt, big enough to be considered a dwarf planet (Ceres may be added to the scale model at a later date). The total mass of all objects in the asteroid belt is only about 3% of Earth’s moon, with about 60% of that mass contained in the 4 largest objects.

A dwarf planet is an object that is massive enough to be gravitationally rounded, but not large enough to clear out the orbital neighborhood around it of other objects of comparable size except its own moons. There are nine objects currently considered to be dwarf planets, with 8 in Kuiper Belt (Pluto,  Eris,  Haumea,  Makemake,  Gonggong,  Quaoar,  Sedna, and Orcus) and 1 in the Asteroid belt (Ceres).

Eccentricity is a measure of how circular an orbit is. An eccentricity of 0 represents a perfectly circular orbit. Eccentricity of an orbit cannot be greater than 1. An eccentricity of 1 is an object that will either be captured into an orbit (eccentricity becomes less than 1), or escaped from an orbit (eccentricity becomes greater than 1 and is no longer in orbit).

A gas giant is a giant planet composed mainly of hydrogen and helium. There are two gas giants in the solar system, Jupiter and Saturn

The ice giants are giant planets composed mainly of elements heavier than hydrogen and helium. The term “ice” in astrophysics refers to volatile chemical compounds with freezing points higher than 100^o K (-173^o C, -280^o F). These include water, ammonia, and methane. There are two ice giants in the solar system, Uranus and Neptune. Uranus is slightly larger in diameter than Neptune, but Neptune is more massive.

The inner planets consists of the smaller, rocky planets that are relatively close to the sun, and inside the asteroid belt. Mercury, Venus, Earth, and Mars are considered the inner planets.

This is a large belt in the outer solar system, starting at the orbit of Neptune and extending about 2 Billion miles beyond. It is much wider than the asteroid belt and contains much more (20-200x) the mass of the Asteroid belt. The Kuiper belt is home to most of the objects consider by astronomers as Dwarf Planets (like Pluto).

The outer planets consist of all the planets outside of the asteroid belt. These consist of the gas giants, Jupiter and Mercury, and the ice giants, Uranus and Neptune

The Perihelion is the point in the orbit of a planet where it is closest to the sun

This is the amount of time it takes a celestial body to rotate about its axis once, relative to the distant stars. This is basically a 360^o rotation of the object. A sidereal day on Earth is slightly less (23 hrs, 56 min, 4 sec) than its synodic day (also called a solar day), as the Earth has to rotate a little more than 360^o to get the sun back into the same position in the sky

This is the amount of time it takes a planet to complete one complete revolution around the sun, relative to the distant stars

This is the time it takes a celestial object to rotate once relative to the object it is orbiting. Because the object moves along its orbital path while also rotating, its alignment with deep space and its alignment with the body it is orbiting will be slightly off. It will take slightly more (prograde), or slightly less (retrograde) than 360^o rotation to align back up with the object it is orbiting. The 24 hour day on Earth, for example, represents a synodic day. It is the time it takes to get the sun back into the same position in the sky.

This is the amount of time it takes a planet to return to the same position relative to the Sun as observed from Earth.