Planet Mercury

Mercury (planet)

Mercury is the smallest and innermost Planet in the Solar System. Its orbit around the Sun takes 87.97 days, the shortest of all the planets in the Solar System. It is named after the Roman deity Mercury, the messenger of the gods.

Like venus, Mercury orbits the Sun within Earth’s Orbit as an inferior planet, and its apparent distance from the Sun as viewed from Earth never exceeds 28°. This proximity to the Sun means the planet can only be seen near the western horizon after sunset or eastern horizon before sunrise, usually in twilight. At this time, it may appear as a bright star-like object, but is often far more difficult to observe than Venus. The planet telescopically displays the complete range of phases, similar to Venus and the Moon, as it moves in its inner orbit relative to Earth, which recurs over its synodic period of approximately 116 days.

Mercury rotates in a way that is unique in the Solar System. It is tidally locked with the Sun in a 3:2 spin-orbit resonance, meaning that relative to the fixed stars, it rotates on its axis exactly three times for every two revolutions it makes around the Sun. As seen from the Sun, in a frame of reference that rotates with the orbital motion, it appears to rotate only once every two Mercurian years. An observer on Mercury would therefore see only one day every two Mercurian years.


The smallest planet in our solar system and nearest to the Sun, Mercury is only slightly larger than Earth’s Moon.

From the surface of Mercury, the Sun would appear more than three times as large as it does when viewed from Earth, and the sunlight would be as much as seven times brighter. Despite its proximity to the Sun, Mercury is not the hottest planet in our solar system – that title belongs to nearby Venus, thanks to its dense atmosphere. Because of Mercury’s elliptical—egg-shaped—orbit and sluggish rotation, the morning Sun appears to rise briefly, set and rise again from some parts of the planet’s surface. The same thing happens in reverse at sunset.

Facts about Mercury

Mercury does not have any moons or rings.

Mercury is the smallest planet.

Mercury is the closest planet to the Sun.

Your weight on Mercury would be 38% of your weight on Earth.

A day on the surface of Mercury lasts 176 Earth days.

A year on Mercury takes 88 Earth days.

It’s not known who discovered Mercury.

A year on Mercury is just 88 days long.
One solar day (the time from noon tonoon on the planet’s surface) on Mercury lasts the equivalent of 176 Earth dayswhile the sidereal day (the time for 1 rotation in relation to a fixed point) lasts59 Earth days. Mercury is nearly tidally locked to the Sun and over time this has slowed the rotation of the planet to almost match its orbit around the Sun. Mercury also has the highest orbital eccentricity of all the planets with its distance from the Sun ranging from 46 to 70 million km.

Mercury is the smallest planet in the Solar System.
One of five planets visible with the naked eye a, Mercury is just 4,879 Kilometres across its equator, compared with 12,742 Kilometres for the Earth.

Mercury is the second densest planet.
Even though the planet is small, Mercury is very dense. Each cubic centimetre has a density of 5.4 grams, with only the Earth having a higher density. This is largely due to Mercury being composed mainly of heavy metals and rock.

Planet Mercury, explained

Named for the fleet-footed Roman messenger god, Mercury is the closest planet to the sun, zipping around our parent star at an average of 36 million miles away. However, Mercury’s orbit is not a perfect circle. The planet can pass as close as 29 million miles and as far away as 43 million miles.

Living up to its name, Mercury is the fastest planet in the solar system, speeding along at about 29 miles per second and completing each orbit around the sun in just 88 Earth days. Mercury is also the smallest planet in the solar system, measuring just 3,032 miles wide at its equator. That makes it only slightly larger than Earth’s moon.

Because Mercury is so small and so close to the sun, it is the most elusive of the five planets that are visible to the naked eye. You can only catch Mercury at dawn and dusk, and it usually does not rise far above the horizon. But that’s not the only time the tiny planet makes an appearance. Because of its position in the solar system, Mercury passes between Earth and the sun 13 times each century in an event known as a transit. During a transit of Mercury, observers on Earth can see the planet in silhouette as it seems to sweep across the sun’s disk.

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