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| Tutorial ID | Title | Tutorial | Video Tutorial | Revision Notes | Revision Questions | |
|---|---|---|---|---|---|---|
| 22.1 | Earth and Other Celestial Bodies |
In these revision notes for Earth and Other Celestial Bodies, we cover the following key points:
The Earth is a planet that belongs to a Solar System - a system of linked celestial bodies revolving around the Sun (the source of energy for the entire system), which is a common star. Other components of the solar system include: planets, natural satellites, asteroids, comets and meteors.
The Sun itelf, belongs to a system of billions of linked stars (and all the other celestial bodies linked to each individual star). This type of system is known as a "galaxy". Our solar system is a tiny part of this gigantic system where the galaxy we belong to is known as the Milky Way. All galaxies together form the Universe.
Planets are big spherical shaped celestial bodies that revolve around the Sun. The trajectory of planets is known as its' orbit and it has an elliptic shape.
Our Solar System has the Sun as source of energy and 8 planets revolving around it: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Pluto is no longer considered a planet.
The planets of the solar system are classified in two categories: earthy planets (Mercury, Venus, Earth and Mars) and giant planets (Jupiter, Saturn, Uranus and Neptune). Each planet has its own special features.
Giant Planets are farther from the Sun than earthy ones. Giant planets have lower density that earthy ones. They can be considered as gaseous gigantic balls floating in space held together by the high gravity produced by the gas itself. Matter in solid state exists only in their center (core). Giant planets are mainly composed of hydrogen and helium.
Earthy Planets are closer to the Sun. These planets are relatively small compared to giant ones. They are enveloped by a solid core (ground) and contain heavier materials than hydrogen and helium. Most metals we know are found under their surface.
Natural satellites are celestial bodies revolving around specific planets. Currently, there are 218 known natural satellites that revolve around the 8 planets of our Solar System. Mercury and Venus have no natural satellites while Jupiter has more artificial satellites than all the other planets (79).
The smallest natural satellites have irregular shapes; they look like rocks detached from the surface of Earth while larger ones have a planet-like spherical shape.
There are other types of celestial bodies besides planets and natural satellites floating on the space of our Solar System. They include
Asteroids which are small celestial bodies not linked to any planet that revolve around the Sun. Most asteroids in our Solar System are found between Mars and Jupiter, in a zone known as the asteroid belt. The asteroid belt occupies the space where there once was (or there will one day be) a planet.
Asteroids are classified in three groups based on their matter composition. They are C-, S-, and M-types.
When an asteroid enters the Earths' atmosphere, it heats up due to the friction with air and eventually burns out producing a moving light in the sky. In scientific terms, they are called meteors while in popular terminology they are known as falling stars.
There is a formula known as Titius-Bode Law which is used to predict the distance between a planet and its corresponding star in any given solar system. The formula suggests that, extending outward, each planet should be approximately twice as far from the star as the one before. Its mathematical form when applied is our Solar System is
where n = minus infinity for Mercury, n = 0 for Venus, n = 1 for Earth, n = 2 for Mars, n = 3 for Jupiter, n = 4 for Saturn, n = 5 for Uranus and n = 6 for Neptune. This distance is measured in au (au stands for astronomical unit = 150 million km that represents a rounded value of Sun-Earth distance). The formula fits perfectly for the first 5 planets but lacks accuracy for the next three.
Comets are celestial bodies made up of various material's and ices mixed with space dust. They have diameters ranging from a few hundred meters to several tens of kilometers. Comets revolve around the Sun following stretched orbits. When a comet get closer to the Sun, its temperature increases; the frozen ice begins to evaporate. As a result, a long bright cloud is formed around the nucleus of comet, forming a bright tail behind it. When a comet approaches the Sun at a distance comparable to the distance of the Earth from the Sun, the tail elongates up to several ten millions of kilometers producing an amazing view.
1. Calculate the revolving speed of Moon around the Earth in km/h if the distance Earth-Moon is 384 000 km and period of Moon revolution around the Earth is 27.32 days.
Correct Answer: A
2. What is the volume of Mercury if its average density is 5420 kg/m3 and its mass is 0.325 × 1024 kg?
Correct Answer: D
3. Calculate the distance Venus-Sun in kilometres using the Titius-Bode formula.
Correct Answer: C
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