Local Authors > Brandon Sanderson
Timespan for Stormlight Archives? (Spoilers)
cromptj:
That is assuming that it is the same size as the Earth
Cheese Ninja:
It doesn't matter if it's the same size, bigger, or smaller than Earth. If it takes 20 hours to rotate, then it has a 20 hour day.
Let's use Mars and Mercury as examples:
Mars has a 24.6229 hour day and is only has 11% of Earth's mass. Mercury has a 1407.5 hour day and has about the same mass as Mars. Mercury has nearly the same density of Earth. Mar's radius is 0.533 Earths, and Mercury's radius is 0.3829 Earths.
The mass only matters for gravity.
happyman:
--- Quote from: Cheese Ninja on August 21, 2011, 11:28:02 PM ---It doesn't matter if it's the same size, bigger, or smaller than Earth. If it takes 20 hours to rotate, then it has a 20 hour day.
Let's use Mars and Mercury as examples:
Mars has a 24.6229 hour day and is only has 11% of Earth's mass. Mercury has a 1407.5 hour day and has about the same mass as Mars. Mercury has nearly the same density of Earth. Mar's radius is 0.533 Earths, and Mercury's radius is 0.3829 Earths.
The mass only matters for gravity.
--- End quote ---
This is exactly correct, barring some extraordinarily small effects from General Relativity.
Gravity depends only on mass, and the length of the day depends only on how rapidly the planet is turning. The two can be changed quite independent of each other. In fact, even black holes have these two parameters independent.
Tortellini:
--- Quote from: Cheese Ninja on August 21, 2011, 11:28:02 PM ---It doesn't matter if it's the same size, bigger, or smaller than Earth. If it takes 20 hours to rotate, then it has a 20 hour day.
Let's use Mars and Mercury as examples:
Mars has a 24.6229 hour day and is only has 11% of Earth's mass. Mercury has a 1407.5 hour day and has about the same mass as Mars. Mercury has nearly the same density of Earth. Mar's radius is 0.533 Earths, and Mercury's radius is 0.3829 Earths.
The mass only matters for gravity.
--- End quote ---
Actually, Mars has twice the mass of Mercury. Yet at the same time, they both have almost the same surface gravity! Density of the planet also plays a role and can have significant impacts apparently. Source of all my apparent smartness: http://en.wikipedia.org/wiki/List_of_gravitationally_rounded_objects_of_the_Solar_System
The things I learn on this forum... ;)
Cheese Ninja:
I used wikipedia too, but I just kept jumping between Mars and Mercury's pages, so I'm not too surprised I screwed something up.
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