Fun Facts About Mercury: What Mercury Is Like and Its One-of-a-Kind Characteristics

Mercury is the smallest planet and it's packed with extremes: 88-day years, 176-day solar days, wild temperature swings, and even a comet-like tail. In this guide, you’ll find the most interesting Mercury facts (size, color, temperature, composition, moons) plus quick, practical tips for spotting Mercury in the sky. Since it stays close to the Sun, timing is everything – open the free Star Walk app to track Mercury’s position in seconds and catch it during the best viewing windows.

Contents

• Mercury facts in short
• 7 fun facts about Mercury we bet you didn’t know

  • Mercury doesn't have seasons like Earth
  • Mercury has a tail
  • Mercury is not the hottest planet
  • A day on Mercury lasts two Mercury years
  • Mercury can have two sunrises in a row
  • Mercury is a Budha planet
  • Mercury is the smallest – and it’s getting even smaller
• What’s Mercury like? Size, temperature, composition
  • How big is Mercury?
  • How hot is Mercury?
  • How long is a day on Mercury?
  • What is Mercury made of?
• What does Mercury look like?
• Mercury in the sky 2026: visibility guide
  • Mercury events in 2026

    • August 2: Mercury at greatest western elongation
    • August 11: Moon near Mercury
    • August 12: Mercury in a six-planet alignment
    • August 15: Jupiter near Mercury
    • August 25: Mercury near Regulus
    • September 12: Moon near Mercury
    • October 5–7: Venus near Mercury
• Mercury F.A.Q.
  • What color is Mercury?
  • How many moons does Mercury have?
  • How far is Mercury from the Sun?
  • When was Mercury discovered?
  • Why is Venus hotter than Mercury?
  • What does the Sun look like from Mercury?
• Most interesting facts about Mercury: to sum up

Mercury facts in short

• Planet type: terrestrial
• Radius: 2440 km (1516 miles)
• Mass: 3.3011×10^23 kg
• Aphelion: 69.8 million km (43.4 million miles)
• Perihelion: 46.0 million km (28.6 million miles)
• Average distance from the Earth: 77 million km (48 million miles)
• Surface temperature: -173°C to 427°C (−280 °F to 800 °F)
• Solar day length: 176 Earth days
• Sidereal day length: 59 Earth days
• Year length: 88 Earth days
• Age: 4.503 billion years
• Named after: Roman god of commerce

7 fun facts about Mercury we bet you didn’t know

Mercury doesn't have seasons like Earth

On Earth, the seasons occur because our planet is tilted, approximately 23.5 degrees relative to the ecliptic. In contrast, Mercury's axis is nearly straight, tilted only about 0.034°, meaning neither hemisphere can tilt more toward the Sun. To understand how it works, take a look at the article “What Causes the Seasons to Change?”.

However, Mercury still experiences a type of seasonal change: thermal seasons. Its orbit is highly elliptical, so it is sometimes much closer to the Sun and at other times much farther away. When Mercury reaches aphelion (its farthest point), it receives less sunlight and cools down. At perihelion (its closest point), Mercury receives much more sunlight and heats up. Mercury's distance from the Sun at its aphelion is approximately 1.5 times greater than its perihelion distance, which is why the difference is so noticeable.

Mercury has a tail

Many people know comets have tails. But have you heard about a planet that has one? Mercury has a cometlike tail produced when solar radiation and the solar wind release sodium atoms from the planet’s surface. It’s not easy to see: you’ll have to take a long-exposure photo using a telescope and a special filter.

Mercury is not the hottest planet

Mercury is the closest planet to the Sun, but it isn’t the hottest. The title goes to Venus. Here’s why: Mercury has only an extremely thin exosphere, so it can’t trap heat – the planet’s surface bakes in sunlight, then cools down fast at night. Venus, on the other hand, is wrapped in a thick carbon-dioxide atmosphere that creates an intense greenhouse effect, keeping the planet scorching hot day and night.

A day on Mercury lasts two Mercury years

Mercury spins once every about 59 Earth days, but one solar day – from sunrise to sunrise – takes about 176 Earth days. That’s roughly two Mercury years, since Mercury orbits the Sun in only about 88 Earth days. In other words, on Mercury, you could celebrate two birthdays before sunset.

Mercury can have two sunrises in a row

Around perihelion, when Mercury is closest to the Sun, the planet moves fastest along its orbit. For a short time, this orbital motion can overtake its slow rotation. That's why from certain locations on its surface, the Sun may appear to slow down, stop, or even move backward across the sky. This phenomenon can create the illusion of double sunrises. The Sun rises, reverses, sets again, then rises once more.

Mercury is a Budha planet

In Sanskrit, Mercury is called Budha (not to be confused with Buddha, the founder of Buddhism). The Vedic texts call it Budha planet, and refer to it as a deity, the son of Soma (or Chandra, the Moon god) and Tara (wife of Bṛhaspati, the god of Jupiter).

Mercury is the smallest – and it’s getting even smaller

Mercury is the smallest planet in the Solar System, and it’s still shrinking. As the planet’s interior slowly cools, Mercury contracts, and its crust crumples like a drying apple. That process creates huge cliff-like “wrinkles” called lobate scarps – long ridges and steep slopes that cut across craters and plains, showing that Mercury has remained geologically active far longer than you might expect.

What’s Mercury like? Size, temperature, composition

How big is Mercury?

Mercury is the smallest planet in the Solar System in both mass and diameter. It’s 18 times less massive than the Earth, and its diameter barely reaches two-fifths of the Earth’s size. To give you a better understanding of Mercury’s size, let’s say that it’s only a third larger than the Moon.

Surprisingly enough, this small planet got even smaller over time. Cooling of its core has caused the entire planet to shrink, reducing Mercury’s radius by about 1-7 kilometers.

How hot is Mercury?

The temperature of Mercury’s surface varies more than on any other planet in our Solar System. It can range from −173 °C (−280 °F) at night to 427 °C (800 °F) during the day. This happens because the smallest planet has almost no atmosphere to trap heat, and it quickly loses the energy it receives from the Sun during the day.

Although Mercury is the closest planet to the Sun, it isn’t the hottest one (Venus is).

Do you know which object is the coldest, the biggest, or the fastest in the Solar System? Which planet hosts the highest mountain, and where is the largest ocean of liquid water (spoiler: not on the Earth)? Take this quiz and learn more about the space record holders!

Battle of the Solar System titans!🏆 Take this ultimate quiz to test your knowledge of the most remarkable objects in our Solar System. Giant planets, dwarfs, and moons – see who is the best at their own game. Ready to play?

Take the quiz!

How long is a day on Mercury?

A solar day – the amount of time it takes the Sun to rise, set, and rise to the same place again – on Mercury lasts about 176 Earth days. And here is another weird fact about Mercury: a solar day on this planet is about twice as long as a year, which lasts 88 Earth days. How come?

The smallest planet spins slowly about its axis – one rotation takes 59 Earth days. However, its sunrises and sunsets are quite different from those on Earth. Due to the planet’s unusual 3:2 rotation pattern (it rotates three times on its axis for every two orbits around the Sun) and its eccentric orbit, the Sun can appear to rise twice: once, shortly before setting, and then again from some parts of the surface. The same thing occurs in reverse at sunset. Thus, it takes much longer for the Sun to appear in the same place again, and one solar day lasts almost twice as long as a year.

Even though it spins slowly, Mercury travels around the Sun faster than any other planet – at 47 km/s (29 mi/s). In comparison, the second-fastest planet in our Solar System, Venus, has a speed of 35 km/s (21 mi/s).

What is Mercury made of?

Since Mercury is a terrestrial planet, it’s mainly composed of iron, nickel, and silicate rock. It has a large iron core, which is about 60% of the planet’s volume (in comparison, the Earth’s core is only 16%), and a 400-kilometer (250 miles) thick outer shell. By the way, Mercury’s core is about the same size as our Moon. Another similarity to the Moon is that the planet’s dry, rocky surface is full of craters.

Craters are the result of impacts with asteroids or other space objects – the density of craters on a surface generally indicates its age. Since Mercury’s surface is heavily cratered, it’s most likely ancient.

What does Mercury look like?

In space, Mercury looks roughly similar to the Moon, a little grayer and bigger than our natural satellite. In NASA images of Mercury, you can see bright impact craters with “rays” of pulverized rock spreading outward. Mercury’s surface is also shaped by long ridges, fractures, and jagged cliff-like scarps — features that, along with countless craters, create the planet’s rugged landscape. With only an extremely thin exosphere to soften the sunlight, shadows are razor-sharp, and the landscape has a stark, high-contrast look.

In the sky, to the naked eye, Mercury looks like a bright “star” low above the horizon, often tinted yellow or orange by Earth’s atmosphere. In binoculars, it remains star-like. In a small telescope, you can see Mercury’s phases (like the Moon’s): it changes from a thin crescent to a half phase and a gibbous shape as it moves around the Sun. The best views come during twilight, when Mercury is highest above the horizon, and the sky is still relatively dark.

Mercury in the sky 2026: visibility guide

Here is a quick visibility guide for Mercury in the upcoming months of 2026:

• August: Mercury is visible in the morning sky, best seen from the Northern Hemisphere. It reaches its greatest elongation on August 2. Mercury reaches superior conjunction on August 27, getting lost in the Sun’s glare.
• September: Mercury reappears in the evening sky by mid-September.
• October: The planet rises higher in the sky, reaching the greatest elongation on October 12. On October 24, Mercury begins retrograde motion.
• November: Mercury reaches inferior conjunction on November 4 and disappears into the Sun’s glare. The planet ends retrograde motion on November 13, and reaches its greatest elongation on November 21, appearing in the morning sky.
• December: Mercury remains a morning object until mid-December, gradually slipping back into the sunrise glow.

Mercury events in 2026

Mercury often stays close to the Sun, so it can be difficult to spot, but it is worth the effort! Mercury can be seen near the Moon, bright stars, and other planets. To quickly check whether Mercury is visible now from your location (and exactly where to look), use the Star Walk 2 planetary guide. Just type the name of a planet in the search field, and the app will show you its position in the sky.

August 2: Mercury at greatest western elongation

On August 2, Mercury (mag 0.1) will reach the greatest western elongation, at a distance of 19°28′ from the Sun. The planet usually appears close to the Sun in our sky, but on this date, at 08:07 GMT, it will be at its greatest apparent angular separation from the Sun.

Mercury will be visible in the constellation Gemini before sunrise. During morning twilight, look for a bright dot near the east-northeastern horizon. Two prominent stars nearby will be Castor and Pollux — the brightest stars in Gemini.

Here are the best times to view Mercury on August 2, 2026. As the table shows, the visibility window varies significantly by location. The visibility window begins when Mercury reaches an altitude of 7° and ends when the Sun reaches 6° below the horizon. The “best moment” is the end of this window, and the listed Mercury altitude refers to that moment. Times in the table are local and rounded to whole minutes, so the displayed interval may differ slightly from the listed window length.

August 11: Moon near Mercury

• Conjunction time: 12:47 GMT (08:47 AM EDT)
• Conjunction distance: 2°08′
• Close approach time: 14:05 GMT (10:05 AM EDT)
• Close approach distance: 1°58′

On August 11, a very thin waning crescent Moon will pass close to Mercury (mag –0.9) in the constellation Cancer. The pair will rise shortly before sunrise, low above the eastern horizon. About 30 minutes later, bright Jupiter (mag –1.8) will follow them into the morning sky.

There is one catch: both the Moon and Mercury will be very close to the Sun. Your chances of seeing them will depend heavily on your location and how clear your eastern horizon is. From many places south of the equator, Mercury will rise around or after the start of civil twilight, when the sky is already brightening.

August 12: Mercury in a six-planet alignment

Around August 12, Mercury will join Jupiter, Mars, Uranus, Saturn, and Neptune in the morning sky. Mercury will appear low above the eastern horizon shortly before sunrise, so you’ll need a clear, unobstructed view and precise timing to spot it. For the best viewing time in your location and complete observing tips, see our guide to the August 2026 planetary alignment.

August 15: Jupiter near Mercury

• Conjunction time: 09:16 GMT (05:16 AM EDT)
• Conjunction distance: 0°34′
• Close approach time: 10:42 GMT (06:42 AM EDT)
• Close approach distance: 0°33′

On August 15, Jupiter (mag –1.8) and Mercury (mag –1.3) will appear close together in the constellation Cancer. The two planets will be visible shortly before sunrise, very low above the eastern horizon. Both planets are bright enough for the naked-eye viewing, but binoculars may be helpful in the morning twilight.

August 25: Mercury near Regulus

• Conjunction time: 07:32 GMT (03:32 AM EDT)
• Conjunction distance: 1°23′
• Close approach time: 13:23 GMT (09:23 AM EDT)
• Close approach distance: 1°18′

On August 25, Mercury (mag −1.8) will pass close to Regulus (mag 1.4) in the constellation Leo. Unfortunately, the pair will be too close to the Sun to observe safely, as the zodiac constellation Leo hosts the Sun from August 10 to September 15. At the time of the close approach, Mercury will be only about 3° from the Sun, making the pair unobservable. Never try to view this event with binoculars or a telescope.

September 12: Moon near Mercury

• Close approach time: 03:49 GMT (September 11, 11:49 PM EDT)
• Close approach distance: 3°24′
• Conjunction time: 07:31 GMT (03:31 AM EDT)
• Conjunction distance: 3°51′

On September 12, a very thin waxing crescent Moon, just one day after the New Moon, will pass close to Mercury (mag –0.6) in the constellation Virgo. The pair will appear in the sky shortly after sunset, low above the western horizon. Higher above, about 28°–29° from Mercury, you’ll be able to spot bright yellowish Venus (mag –4.7).

There is one catch: both the Moon and Mercury will be very close to the Sun. Your chances of seeing them will depend heavily on your location and how clear your western horizon is. The event will generally be easier to observe from the Southern Hemisphere, where the pair will remain higher in the sky after sunset.

October 5–7: Venus near Mercury

• Conjunction time: October 5, 14:50 GMT (10:50 AM EDT)
• Conjunction distance: 5°28′
• Close approach time: October 7, 04:09 GMT (12:09 AM EDT)
• Close approach distance: 5°02′

On October 5–7, Venus (mag –4.6) and Mercury (mag 0.0) will appear near each other in the constellation Virgo after sunset. The event strongly favors the Southern Hemisphere: there, both planets will stand fairly high above the western horizon after sunset. In the Northern Hemisphere, however, the pair will be very low or already below the horizon by the time the sky gets dark enough, making the conjunction difficult or impossible to observe.

Mercury F.A.Q.

What color is Mercury?

Mercury is primarily dark gray. A planet’s color depends on the color of its surface and its reflective abilities. Unfortunately, Mercury’s rocky exterior, covered with dust, doesn’t give a wide variety of colors.

How many moons does Mercury have?

Mercury doesn’t have any moons. Because it orbits so close to the Sun, the Sun’s strong gravity would pull away or destabilize any potential moon, preventing Mercury from keeping one for long.

How far is Mercury from the Sun?

Its average distance from the Sun is about 58 million km (36 million miles). Thus, among other planets in the Solar System, Mercury is the closest one to the star.

When was Mercury discovered?

Mercury has been observed since ancient times. The earliest recorded observation occurred in 265 BCE. The first people who observed Mercury through a telescope were Galileo Galilei and Thomas Harriot in the 17th century.

Why is Venus hotter than Mercury?

Despite Mercury being the closest planet to the Sun, Venus is hotter because of the thick Venusian atmosphere trapping heat. Mercury, in its turn, has no significant atmosphere and can’t hold the Sun’s energy.

What does the Sun look like from Mercury?

If you could stand on Mercury, at aphelion (the farthest Mercury can get from the Sun), you would see the Sun twice as big as it appears from the Earth. At perihelion (the closest distance), the Sun would appear three times as large as it does on our planet.

Most interesting facts about Mercury: to sum up

Mercury is full of surprises. It’s the closest planet to the Sun, yet not the hottest. It’s small, yet it has a giant iron core the size of the Moon. Mercury has no moons and almost no atmosphere. It is also difficult to observe because it stays close to the Sun and near the horizon. But we've made it easier for you – use the free Star Walk 2 app to find Mercury in seconds from your exact location.

You can also watch the fun and educational cartoon about Mercury that explains the main facts about the planet in simple words.

Wishing you clear skies and happy observations!