Mercury Retrograde
Astrologers advise us not to sign any contracts during Mercury retrograde, which starts Thursday. NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Don't bother booking a vacation or trying to communicate critical information anytime in the next few weeks, because Mercury is in retrograde. Named after the Roman god of business and communication, Mercury rules over these astrological realms -- and it's known to wreak havoc with them.

The notion of Mercury in retrograde -- three times a year, the planet appears to be going backwards for about three weeks -- came from an earlier, outdated notion that Earth was the center of the universe. Nicolaus Copernicus' heliocentric model of the solar system, with the sun at the center, placed Earth among the planets orbiting a star, which led to the revelation that retrograde motion was nothing more than an illusion.

Mercury's reputation as a trickster traces to its eccentric orbit. Mercury's orbit did not match up with predictions, Kristin Dombek explained in the New York Times Magazine in January. When the planet traveled faster than expected, experts posited it was from the influence of a planet named Vulcan, or an asteroid field or a dust field, but all failed to explain the odd orbit. It took Albert Einstein's theory of general relativity to solve the mystery: The sun's mass warps space, which causes Mercury to speed up.

While Mercury's retrograde motion and the planet's orbit were finally explained, its reputation as a trickster has endured.

"The planet Mercury rules communication, travel, contracts, automobiles, and such. So, when Mercury is retrograde, remain flexible, [you should] allow time for extra travel and avoid signing contracts. Review projects and plans at these times, but wait until Mercury is direct again to make any final decisions," the Old Farmer's Almanac explained.

Not everything will be bad, astrologically speaking, during the Mercury retrograde period, which runs through Oct. 9. "Mercury rules anything that begins with "re": redo, reassess, repair, repeat, redesign, revisit. It's always human nature to want to hear that new opportunities are coming our way, but we really do need to focus on the quality of our work and improve it to the best it can be," Susan Miller, author of Astrology Zone, wrote.

During this Mercury retrograde period, astrologer Larry Schwimmer predicts political upheaval and a stock market slide. "Misinformation about the Iran nuclear deal will come out during the retrograde and cause huge protests and efforts to obstruct it once again. Expect another politician to make a Rick Perry-type gaffe," Schwimmer wrote in the Huffington Post. If you want to find out how Mercury retrograde affects your life, visit here.

Mars is another planet susceptible to the retrograde illusion. Earth travels faster than Mars, which causes our planet to lap the red planet. "About every 26 months, Earth comes up from behind and overtakes Mars...it will look like Mars is moving up and down. Then, as we move farther along our curved orbit and see the planet from a different angle, the illusion will disappear and we will once again see Mars move in a straight line," NASA explained.

There is no astronomical event associated with Mercury retrograde, but you can see the planet in the night sky if you live in the Southern Hemisphere.