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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:

This page was last updated by Sean Marshall on January 21, 2016.

About the Author

Dave Kornreich

Dave was the founder of Ask an Astronomer. He got his PhD from Cornell in 2001 and is now an assistant professor in the Department of Physics and Physical Science at Humboldt State University in California. There he runs his own version of Ask the Astronomer. He also helps us out with the odd cosmology question.

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