The five so-called naked eye planets -- Mercury, Venus, Mars, Jupiter and Saturn -- will appear to clump together later this month in a sight that might not be seen again for a century.
The grouping of the five will begin to be visible with unaided eyes around April 20, with the planets clustered closest by around May 4.
It could be 50 or 100 years before this happens again.
The display should be easy to see in most parts of the inhabited world, weather permitting, though those at extreme northern and southern latitudes may need binoculars or a small telescope, and Mercury could still be hard to spot.
What they should be able to see will be Mercury, Venus, Mars and Saturn all grouped within the span of 10 degrees of the sky, or about the width of a fist held at arm's length.
Jupiter will be a bit higher in the sky, about three fist-widths away, but still quite close.
The closest known planetary alignment in the last two millennia occurred on April 11, 1128, before most planets were identified as such, including Earth.
