Cheap Astronomy - Dear CA #109: Planets

The 365 Days of Astronomy

Things that orbit the Sun and clear their orbits.

Dear Cheap Astronomy – What happens when worlds collide?

The outcome of a collision between two planets depends on the speed of the collision, the angle

of the collision and the relative masses of the two bodies and their composition – think rocky

planets versus gas giants for example. A small planet approaching a large planet slowly might

get tidally stretched and break up into pieces, but a fast moving one might impact before there’s

been time for gravitational stretching to break it up.

Dear Cheap Astronomy – Why is Mars’ sky red?

A good place to start is to think about the colours we are familiar with in Earth’s sky. In the

middle of the day, the overhead Sun is a bright white disk you can’t look at directly and the rest

of the sky is blue.

This is because most of the visible light from the Sun passes straight through the atmosphere,

which is transparent to those wavelengths, except at the very short end – so rather than passing

straight through, photons in the blue and violet parts of the visible spectrum are scattered –

meaning they are deflected off their straight line path and bounce around a lot, although most

eventually reach the ground.

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