When was the last time that the planets were in a line?

On Tue, 18 May 1999 you wrote:

> when was the last time the planets were in line.

It really depends on what you mean by the planets being "in line". I
assume you are referring to a news report a couple of months ago about
all the planets appearing in a line as viewed from Earth. In reality,
the planets are pretty much always in a line that wraps the entire way
around the sky. This line is called the "ecliptic", and it represents the
plane that all planets orbit around the sun on (except for Pluto). In
March/April, though, most of the planets were in the evening sky, so this
line was much more noticeable than normal.

As viewed from space, though, the planets were not aligned at all, but
spread throughout their orbits around the sun.

Close alignments of the planets, called "conjunctions", are not
extremely rare, although the true rate depends on which planets you are
talking about. Mars passes every other planet (as viewed from the Earth)
about every 2 or 3 years, while Uranus passes Neptune only once every 150
to 200 years or so. But the much-publicized "alignment" this Spring was
not very rare at all.

Thanks for writing!

Sincerely,
Kurtis Williams

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