The best planetary party for 18 years has begun. Like a 17th century astronomer, you can reach it by simply looking up.
Throughout the month of June, skywatchers can see Earth’s five closest planetary neighbors with the naked eye. About half an hour before sunrise, Mercury, Venus, Mars, Jupiter, and Saturn are aligned in their natural order from the sun stretching diagonally beginning low in the east. On June 3 and 4, the distance between Mercury and Saturn was only 91 degrees.
“Planets often move closer together and further apart, but that’s just a particularly amusing order. It’s just a coincidence,” said Michelle Thaller, a NASA astronomer. “It’s just kind of a really fun tour of the solar system that you can do for free.”
When celestial bodies appear close together from Earth, astronomers call the sight a conjunction. Conjunctions of a few planets are quite common and occur every few years or so, but the five planets only align once every two decades. The last time the five planets aligned was in December 2004, and the next alignment will not occur until 2040. Due to the different orbits and inclinations, the eight planets will never be perfectly aligned.
How to watch
Although a telescope or binoculars can help observe the sky, planets will shine brighter than surrounding stars and should be easy to spot with the naked eye. Go out about 30 minutes before sunrise and hope for a clear horizon. Darker skies are best, but planets will stand out even above city lights.
“Even in town they’re bright enough – you should be able to see them. Get on a friend’s balcony or on the roof. As long as you can get a nice clear horizon and clear sky, you can see it,” said Thaller said. said.
Mercury is the hardest to see of the planets due to its proximity to the sun. The small dark planet is usually lost in the glow of sunrise or sunset, but the planet will gradually move away from the sun as the month progresses. Thaller, who has only seen Mercury half a dozen times in his life, had his best performance near Dulles International Airport.
The best opportunity to see all five planets will occur on June 24. Mercury should be much easier to spot as it is moving away from the sun and will rise an hour before sunrise. As a bonus, Earth’s crescent moon will also position itself between Venus and Mars and act as a stand-in for Earth. Skywatchers can see a spectacular view of the six celestial bodies in order: Mercury, Venus, Earth’s moon, Mars, Jupiter and Saturn. The distance between Mercury and Saturn will be 107 degrees, according to Sky & Telescope.
Thaller said the rare planetary alignment poses no danger to Earth’s inhabitants, but the gravitational pull of all the planets to one side can be seen very faintly through the tides on Earth. Due to its distance, Venus exerts the greatest tidal force on Earth, although it is only a small fraction compared to our moon. Thaller said spacecraft can also feel extremely small forces — on the scale of fractions of atoms — when the gravity of planets pulls them together.
Observations of planetary conjunctions have been made for centuries and date back to the ancient Greeks observing the movements of these five planets with the naked eye. (Uranus, Neptune, and the dwarf planet Pluto weren’t discovered until after the invention of the telescope in the 17th century.) People back then thought they might be gods or spirits. The word “planet” is derived from the Greek word “planets”, which means “wanderer”.
“People noticed that they were different…most of the stars stayed in their positions relative to other stars, but these planets seem to be wandering around the sky,” Thaller said. “Sometimes they all happened to be lined up in one part of the sky.”