Tanya Goomes, of Southland Girls' High School, asks :-
When the planets are spinning around the sun there must be a time when all the planets will line up. If this does happen would this affect the earth?
Alan Gilmore, an astronomer at the University of Canterbury's Mt John Observatory, responded.
The short answer is: Nothing. The planets are very large distances apart compared to their sizes and masses. So they have next to no effect on one another. The only effect we can measure is tiny variations in the orbits of planets due to the gravity pull of their neighbours.
The moon causes tides on the earth's oceans because it is very close. Tidal effects decrease very quickly with distance. In mathematical terms tides vary inversely as the the cube (the power of three) of the distance. So if the moon was twice as far away its tides would be one half times one half times one half which equals one eighth of the present tides.
The sun produces tides on the earth because it is massive, though distant. The sun's mass is a thousand times greater than the mass of all the planets put together.
The planets are too distant and too small to have any tidal effect on each other. So an alignment of planets would have no effect. It would make an interesting sight in the night sky. We would have Mars, Jupiter and Saturn (and in a telescope Uranus, Neptune and Pluto) all in the midnight sky. Mercury and Venus would be invisible, being in line with the sun on the daytime side of earth.