FSS - Relative and Actual Distances of the Planets from the Sun Lesson
Relative and Actual Distances of the Planets from the Sun
"My Very Educated Mother Just Served Us Nine Pizzas" is a mnemonic device that has helped students learn the order of the planets for decades. Starting with the innermost planet and moving outward, Mercury is closest to the sun, followed by Venus, then Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and finally Pluto (Pluto was recently re-categorized as a "dwarf planet", but we'll still include it from time to time in our discussions).
One of the features of the solar system that is not well-represented, however, is the relative distances between the planets. The planets in our solar system are not evenly spaced apart, although many posters and drawings might suggest that they are. The distances between the planets vary greatly, and become larger the further away from the solar system one travels. For example, the distance between Mercury and Venus is approximately 50,000,000 km, while the distance between Uranus and Neptune is over 1.6 billion km - over three times as far apart as Mercury and Venus! Understanding these vast distances will help us understand differences between the "inner planets" and the "gas giants" later on, especially when we consider the composition of their atmospheres.
Another important point to keep in mind is that the planets' paths around the sun - their orbits - are not circular, but are actually elliptical. This oval-shaped path means that the planets are not fixed distances from the sun; the numbers provided above are actually based on average distances. A planet's perihelion is that point in its orbit at which it is closest to the sun, and its farthest distance from the sun is known as its aphelion. A common misconception is that summer occurs when the Earth is closest to the sun; in fact, the opposite is actually true. During the Northern hemisphere's summer, the Earth is actually at its aphelion.
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