NASA Goddard Planetary Scientist James O’ Donoghue created a nice animation showing the sidereal days and axial tilts of the solar system planets.
The sidereal days and axial tilts of Mercury-to-Neptune. Animation composed by Dr. James O’Donoghue using NASA imagery. Planets and dwarf planets to scale in size, rotation speed, and axial tilt (in order of distance from the Sun). There are many more dwarf planet candidates, but they aren’t mapped so aren’t included. Sidereal day lengths are shown.
The sidereal days and axial tilts of Mercury-to-Neptune. Animation composed by Dr. James O’Donoghue using NASA imagery. Planets and dwarf planets to scale in size, rotation speed, and axial tilt (in order of distance from the Sun). There are many more dwarf planet candidates, but they aren’t mapped so aren’t included. Sidereal day lengths are shown.
Update: new video by James O’ Donoghue, and even a better one: selected solar system objects to scale in size, rotation speed, and axial tilt.
Selected solar system objects to scale in size, rotation speed, and axial tilt.
A sidereal day is the length of time it takes a planet to rotate from the perspective of a distant star. For the planet Earth, a sidereal day is approximately 23 hours, 56 minutes, and 4 seconds. By contrast, solar time is reckoned by the movement of the Earth from the perspective of the Sun. The “solar day”, or simply “day” is 24 hours, so it is slightly longer than the sidereal day because of the amount the Earth moves each day in its orbit around the Sun.
The stellar day or “sidereal day” is shorter than the solar day. At time 1, the Sun and a certain distant star are both overheads. t time 2, the planet has rotated 360° and the distant star is overhead again but the Sun is not (from 1 to 2 = one stellar day). It is not until a little later, at time 3, that the Sun is overhead again (from 1 to 3 = one solar day). Image: Wikipedia
The seasons on Earth (or any other planet) occur because of the axial tilt.
How seasons occur: for half of the Earth tilted towards the Sun, one hemisphere receives more solar radiation from the Sun than the other. In the image above, it is summer in the southern hemisphere, while it’s winter in the northern hemisphere. The Earth’s axis is today tilted 23.5 degrees from the plane of its orbit around the Sun. But this tilt changes. During a cycle that averages about 40,000 years, the tilt of the axis varies between 22.1 and 24.5 degrees. Because this tilt changes, the seasons as we know them can become exaggerated. More tilt means more severe seasons-warmer summers and colder winters; less tilt means less severe seasons – cooler summers and milder winters. For half of the Earth tilted towards the Sun, one hemisphere receives more solar radiation from the Sun than the other. In the image above, it’s summer in the southern hemisphere, while it’s winter in the northern hemisphere.
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