Why does mercury have phases

The temperatures and solar radiation that characterize this planet are most likely too extreme for organisms to adapt to. If Earth were the size of a nickel, Mercury would be about as big as a blueberry.

From an average distance of 36 million miles 58 million kilometers , Mercury is 0. One astronomical unit abbreviated as AU , is the distance from the Sun to Earth. From this distance, it takes sunlight 3.

Mercury's highly eccentric, egg-shaped orbit takes the planet as close as 29 million miles 47 million kilometers and as far as 43 million miles 70 million kilometers from the Sun.

It speeds around the Sun every 88 days, traveling through space at nearly 29 miles 47 kilometers per second, faster than any other planet.

Mercury spins slowly on its axis and completes one rotation every 59 Earth days. But when Mercury is moving fastest in its elliptical orbit around the Sun and it is closest to the Sun , each rotation is not accompanied by sunrise and sunset like it is on most other planets. 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 for other parts of the surface. One Mercury solar day one full day-night cycle equals Earth days — just over two years on Mercury. Mercury's axis of rotation is tilted just 2 degrees with respect to the plane of its orbit around the Sun. That means it spins nearly perfectly upright and so does not experience seasons as many other planets do. Mercury formed about 4. Like its fellow terrestrial planets, Mercury has a central core, a rocky mantle, and a solid crust.

Mercury is the second densest planet, after Earth. It has a large metallic core with a radius of about 1, miles 2, kilometers , about 85 percent of the planet's radius. There is evidence that it is partly molten or liquid. Mercury's outer shell, comparable to Earth's outer shell called the mantle and crust , is only about kilometers miles thick. Mercury's surface resembles that of Earth's Moon, scarred by many impact craters resulting from collisions with meteoroids and comets.

Craters and features on Mercury are named after famous deceased artists, musicians, or authors, including children's author Dr. Seuss and dance pioneer Alvin Ailey. Very large impact basins, including Caloris miles or 1, kilometers in diameter and Rachmaninoff miles, or kilometers in diameter , were created by asteroid impacts on the planet's surface early in the solar system's history.

While there are large areas of smooth terrain, there are also cliffs, some hundreds of miles long and soaring up to a mile high. You will find more information about the physical properties of Mercury on another page. Mercury is the planet closest to the Sun , the innermost of all worlds in the solar system. Mercury revolves around the Sun in an elliptical orbit at a mean distance of 58 million km; the orbital period is 88 Earth days or 0. The Ecliptic is the projection of the Earth's orbit onto the celestial sphere.

Mercury's orbit is very eccentric. When at "perihelion" the orbital point where a planet is closest to the Sun , Mercury is about It is therefore about 1. For comparison, the eccentricity of the Earth's much more circular orbit is only 0.

Mercury, as the innermost planet, is also the fastest moving major planet in the solar system. Mercury's sidereal period is about 88 Earth days - this is the interval of time one body needs to complete one revolution around another body with reference to the stars.

The synodic period of Mercury is about Earth days - this is interval of time until Mercury again is in the same position relative to the Sun, as seen from the Earth the difference is caused by the simultaneous motion of the Earth in its orbit.

Both periods are the shortest of any major planet. The mysterious perihelion shift. An interesting property of Mercury's orbit is the observed perihelion shift , i. This effect is present in all planetary orbits and is mainly caused by the gravitational interaction with the other planets.

But it was discovered in the 19th century by means of very accurate positional observations, that the measured rate of Mercury's perihelion shift was different by about 43 arcseconds per century from what the classical Newtonian gravitational theory predicted. The origin of this discrepancy was long a great mystery. However, it has since been found that the motion conforms fully with Albert Einstein's General Theory of Relativity - when the "relativistic" terms are introduced, there is absolute agreement between observation and theory.

This phenomenon is therefore now completely understood and, in fact, constitutes one of the best proofs of the validity of Einstein's theory. Mercury's visibility. Mercury is the planet nearest the Sun and is the most difficult to observe, because it is always quite close to the Sun in the sky. When Mercury is west of the Sun, it can be seen rather low in the morning sky before sunrise; when it is east of the Sun, it is seen in the evening sky and sets soon after the Sun. View our Privacy Policy.

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