When was the last time all the planets were aligned and approximately when will they be aligned again?
When astrologers speak of the planets being aligned (something which doesn't really concern astronomers) they don't mean that the planets will actually all lie on a straight line at some instant of time. One calculation of alignments within around thirty degrees (about as close as they can get) shows that the last such alignment was in 561 BC, and the next will be in 2854. The eight planets plus Pluto are somewhat aligned every 500 years, and are grouped within 30 degrees every one to three alignments.
If you'd like to read more, here's my source (archived from the original): National Solar Observatory Sacramento Peak page on planetary alignments
Through the years, there have been many ridiculous claims about planetary alignments - for instance, that they cause earthquakes, or that they briefly allow people on Earth to be weightless. Such claims are nonsense. The other planets are all too far away to have such dramatic effects on the Earth.
Here are some more pages discussing planetary alignments and explaining how they aren't actually very important:
- http://imagine.gsfc.nasa.gov/ask_astro/solar_system.html (see "When will the next alignment of the planets be?", about a quarter of the way down the page)
This page was last updated by Sean Marshall on January 21, 2016.