The Solar System: Observing the Planets

Solar System
Jonny Lindner, Germany

Our local planetary neighborhood, with its eight planets, began to form 4.6 billion years ago when a region of space filled with interstellar gas and dust collapsed in on itself under the force of its own gravitational pull, eventually igniting the Sun. During the Sun’s formation, other elements that were part of the initial gas-and-dust cloud coalesced into protoplanets of different sizes. It’s easy to imagine that at this initial stage, the whole scene must have looked pretty much like a crazy billiards game with protoplanets colliding, merging or exploding on impact. Because the intense heat prevented lighter elements from aggregating, heavy and rare elements formed near the center of this expanse, giving rise to the rocky inner planets: Mercury, Venus, Earth and Mars. Lighter and more common elements would in turn coalesce into the gas giants: Jupiter, Saturn, Uranus and Neptune. Our part of the neighborhood, the Earth, occupies a convenient place in the solar system: it’s right in the middle of the so-called habitable zone, a spot where the temperature allows liquid water to exist provided that other conditions, such as a thick enough atmosphere, are present.

Mars, Jupiter and Saturn are the most interesting planets to observe through a telescope and, provided you have one with decent magnification, you’ll be rewarded with a great set of details.

The rest of the planets won’t appear as much more than pale dots in the eyepiece. When the conditions are right, you can see the seasons change on Mars and observe the ice caps shrinking and growing. Jupiter is the easiest planet to observe. Equipped with only a pair of good binoculars, you’ll be able to discover the four major moons orbiting around this gas giant, just like Galileo Galilei first did with his telescope. With a more powerful instrument, the stripes in the planet’s atmosphere will be visible and you’ll also be able to see the Great Red Spot, an anticyclonic storm roughly the size of the Earth. Finally, Saturn is another interesting celestial object because its rings are clearly visible, and if your instrument allows it, you may even see the so-called Cassini division, an area of lower density visible as a dark gap in the middle of the rings.

Observing the planets requires that you understand their relative motion. The closer a planet is to the Sun, the faster it orbits around it. It takes the Earth 365 days to complete its orbital revolution around the Sun; Venus and Mars make the trip in 224 and 686 days, respectively. If Jupiter is on the other side of the Sun, you won’t be able to observe this giant for many months. The planetary model below allows you to see the positions of the planets on any given date and observe how they move relative to one another over time.

If the simulation doesn’t work or if you get an error, go to the original site: or use this alternative version that is lighter and faster to load.


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