These colors are not what Mercury would look like to the naked eye. The photo was enhanced with color to show chemical, mineralogical, and physical differences of its surface.
Mercury is notoriously tricky to spot. It stays close to the horizon and never rises high overhead. Depending on where you live, it might require careful planning in order to get a glimpse of it. Even Copernicus, the astronomer who first proposed that the Earth orbits the Sun, reportedly lamented that he never got a clear view of it. The low-lying fog over the river near him often blocked his view. That should tell you something about just how maddeningly hard this little planet is to see.
WHEN AND WHERE TO LOOK
Mercury is the closest planet to the Sun, so when we view it from Earth, it barely gets far enough away from the Sun for us to get a brief peek. The only way to catch a glimpse of it is to find a location where you have a good view of the horizon with no obstructions. It’s mostly visible during dawn and dusk for no more than 90 minutes before sunrise or after sunset.
ORIGINS OF THE NAME
Mercury is named after the Roman god of speed, and indeed, Mercury is one of the fastest-moving planets. We also trace the name “Wednesday” to Mercury. Wednesday comes from the Old English word “Wōdnesdæg”, meaning Woden’s (aka Odin’s) day in honor of the Germanic god. Woden is translated from the Latin dies Mercurii, meaning “day of Mercury.”
In Hindu culture, Mercury is known as Budha (not Buddha), the god of awareness and intellect. It also lends its name to the day we call Wednesday, which they call Budhvar.
In ancient Mesopotamia, it was named Nabu, after the god of writing and wisdom. And the ancient Greeks had two names for it. They called it Apollo when it was visible in the morning sky, and Hermes when it was visible in the evening sky. They didn’t realize they were the same planet until about 350 BCE.
WHAT DOES IT MEAN WHEN MERCURY IS IN RETROGRADE?
A simplified diagram of Mercury’s orbit. Imagine what its motion looks like from Earth.
Astrology places a lot of meaning on the idea of Mercury being in retrograde, but there is a simple scientific explanation for this phenomenon.
Retrograde means moving backward. Imagine yourself looking toward the Sun, watching Mercury trace its tight orbit around it. It vanishes in the Sun’s glare as it passes in front, then becomes visible as it heads to the right. When this happens, we see Mercury before sunrise on the eastern horizon. Each morning, we see it higher and higher in the sky as its orbit takes it farther from the Sun’s glare. But as it makes that circular orbit, it reaches the side of the Sun and appears to us that it has come to a standstill, not moving for many nights. Then, as its orbit swings around toward the back of the Sun, it appears to us to have reversed course, and each morning it appears lower and lower on the horizon until it vanishes behind the Sun.
About three to four weeks later, Mercury emerges from behind the Sun and becomes visible after sunset on the western horizon. Every evening, we see it higher and higher in the sky as it moves to the left of the Sun. As it curves along its orbit and moves toward Earth, it appears to come to a standstill. It then swings around toward the front of the Sun, appearing lower and lower in the sky each night until it gets swallowed in the Sun’s glare once again.
This celestial dance happens three or four times each calendar year. From an astronomical standpoint, retrograde is an optical illusion with no known physical effect on Earth. Mercury is too small and too far away for its motions to be felt by us. Ancient skywatchers noticed this strange backward motion thousands of years ago and tried to make sense of it as best they could, which led to the idea that this phenomenon could influence our personal lives.
A WORLD OF EXTREMES
Mercury may seem like a boring planet that is scorched by the Sun, but nothing could be further from the truth. Yet, everything about this planet is extreme compared to our lived experience on Earth.
Mercury orbits the Sun in just 88 Earth days, allowing it to put in four laps in the time that it takes us to make just one. However, it rotates so slowly that a Mercury day is about 176 Earth days long (from sunrise to sunrise), making one day twice as long as one year.
Because Mercury has no atmosphere to regulate and distribute heat, surface temperatures are wildly extreme. On the sun-facing side of the planet, temperatures reach about 800º F, while the dark side of the planet drops to -290º F. This difference of roughly 1,000º is the greatest temperature swing in our entire solar system. It may get hotter on Venus, but its dense atmosphere keeps the temperatures consistently high.
Close-up images of Mercury reveal a surface that resembles our Moon. It is covered with impact craters that have been well preserved for billions of years, thanks to its lack of an atmosphere. There is no weather or geological activity that would erode or bury the craters.
It may be the smallest planet, but it’s the second densest planet after Earth. This leads scientists to believe it has an enormous iron core that occupies a larger portion of its interior than that of any other planet.
WORTH THE FLEETING GLANCE
Even though it takes some effort to see Mercury with the naked eye, it’s a thrill to see it. It’s quite amazing to catch a glimpse of that tiny planet that’s zipping around the Sun, sizzling on one side while sitting in a deep freeze on the other. Most people have never seen it. When you do, you’ve joined a pretty small club of intentional sky watchers who took the time to look up at just the right moment — and that’s worth something.
