Why do celestial objects rotate

It is to do with something called angular moment. Gravity is the central force in the Universe, because it is the only one which has a significant pull over large distances.

When things collapse under their own gravity in space i. Even if it spins by a tiny amount, as it collapses, angular momentum conservation will mean it spins more and more quickly - just like an spinning ice-skater pulling their arms into their body and spinning more quickly.

This means that all coherent masses are spinning - e. The Universe is a complex place so something may be slowing down because the gravity of other objects is putting on the brakes or some things may appear not to be rotating e.

Huge clouds of gas and dust tend not to be spinning as a whole because they are expanding to fill the available volume - like a bad smell in room! However they might have little pockets which start are turbulent, collapse under their own gravity, spin and form stars. I'm not sure if you want an object that doesn't spin at all, or one that somehow doesn't spin on its axis. In the former, any structure large enough e. For chaotic spinning often called tumbling , one example is Hyperion , a small moon of Saturn.

All celestial objects are formed from larger, more diffuse collections of matter such as a nebula which collapses to form a star. These larger objects typically have some very small net angular momentum spin. That total angular momentum is conserved, and as the object collapses it causes the rate of spin to accelerate in order to maintain the same degree of angular momentum.

It's the same phenomenon as the spinning ice skater pulling in their arms except in this case the amount of contraction is a factor of millions so even though a proto-stellar nebula may not be rotating much the sheer size difference between a star and a nebula will result in the star rotating a considerable amount.

However they do not completely lose their rotation and end up rotating with a period that is the same as the orbital period, so that they face always the same side towards the other body. The best know example is the Moon that shows always the same side to Earh. The phenomenon is called tidal locking. Tidal locking may happen to both the main body, and the smaller one orbiting it, but is much faster for the smaller one.

Double locking is faster when the two bodies have similar mass. But why do they spin in the same direction? When our solar system was nothing but a cloud of gas and dust, what was likely a shock wave from a nearby supernova bounced up against it and caused it to collapse.

As it collapsed, its own gravitational forces pulled it into a flat, spinning disk. And since everything in our solar system was formed from that same disk, its momentum sent nearly everything spinning in the same direction.

Notable exceptions include Uranus and Venus, whose odd spins probably stem from subsequent collisions with asteroids. Our planets have continued spinning because of inertia. The big bang gave linear motion. Gravity turned it into orbital motion. To answer this question — or ask a new one — email lastword newscientist.

Questions should be scientific enquiries about everyday phenomena, and both questions and answers should be concise. We reserve the right to edit items for clarity and style. Please include a postal address, daytime telephone number and email address. In addition, they all rotate in the same general direction, with the exceptions of Venus and Uranus. These differences are believed to stem from collisions that occurred late in the planets' formation. A similar collision is believed to have led to the formation of our moon.

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