Mercury (in astronomy)

The Columbia Encyclopedia, 6th ed.

Mercury (in astronomy)

Mercury, in astronomy, nearest planet to the sun, at a mean distance of 36 million mi (58 million km); its period of revolution is 88 days. Mercury passes through phases similar to those of the moon as it completes each revolution about the sun, although the visible disk varies in size with respect to its distance from the earth. Because its greatest elongation is 28°, it is seen only for a short time after sunset or before sunrise. Since observation of Mercury is particularly unfavorable when it is near the horizon, the planet has often been studied in full daylight, with the sun's light blocked off.

Mercury has the most elliptic orbit of the planets in the solar system. Its great eccentricity of orbit and its great orbital speed provided one of the important tests of Einstein's general theory of relativity. Mercury's perihelion (its closest point to the sun) is observed to advance by 43″ each century more than can be explained from planetary perturbations using Newton's theory of gravitation, yet in nearly exact agreement with the prediction of the general theory.

Mercury is the smallest planet in the solar system, having a diameter of 3,031 mi (4,878 km); both Jupiter's moon Ganymede and Saturn's moon Titan are larger. Its mean density relatively high, a little less than that of the earth; its core is believed to occupy about 85% of its radius and to consist of a probably solid iron core, surrounded by a liquid iron layer, which is surrounded by a solid iron-sulfide layer. There is 10 times as much sulfur in its crust than is found on the surface of the earth. The planet has a dark surface that reflects relatively little light; it is believed that the surface has been darkened by the deposition of carbon-rich micrometeorites that originate from comets passing close to the sun. Mercury's small mass and proximity to the sun prevent it from having an appreciable atmosphere, although a slight amount of carbon dioxide has been detected.

The surface of Mercury is much like that of the moon, as was shown Mariner 10 in flybys in 1974–75 and Messenger in flybys in 2008–9 and in orbit in 2011–15. Most of its craters were formed during a period of heavy bombardment by small asteroids early in the solar system's history. Messenger, which became the first space probe to orbit Mercury, found solid evidence of ancient volcanism as well and corroborated that there is ice near the planet's north pole in craters where areas are in permanent shadow; measurements by earth-based radar in the 1990s had suggested that there was ice near the poles. Images from Messenger were used to produce (2016) a complete topographic map of Mercury.

It was long thought that Mercury's period of rotation on its axis was identical to its period of revolution, so that the same side of the planet always faced the sun. However, radar studies in 1965 showed a period of rotation of 58.6 days. This results in periods of daylight and night of 88 earth days each, with the daylight temperatures reaching as high as 800°F (450°C). Night temperatures are believed to drop as low as -300°F (-184°C).

Notes for this article

Add a new note
If you are trying to select text to create highlights or citations, remember that you must now click or tap on the first word, and then click or tap on the last word.
One moment ...
Default project is now your active project.
Project items
Notes
Cite this article

Cited article

Style
Citations are available only to our active members.
Buy instant access to cite pages or passages in MLA 8, MLA 7, APA and Chicago citation styles.

(Einhorn, 1992, p. 25)

(Einhorn 25)

(Einhorn 25)

1. Lois J. Einhorn, Abraham Lincoln, the Orator: Penetrating the Lincoln Legend (Westport, CT: Greenwood Press, 1992), 25, http://www.questia.com/read/27419298.

Note: primary sources have slightly different requirements for citation. Please see these guidelines for more information.

Cited article

Mercury (in astronomy)
Settings

Settings

Typeface
Text size Smaller Larger Reset View mode
Search within

Search within this article

Look up

Look up a word

  • Dictionary
  • Thesaurus
Please submit a word or phrase above.
Print this page

Print this page

Why can't I print more than one page at a time?

Help
Full screen
Items saved from this article
  • Highlights & Notes
  • Citations
Some of your highlights are legacy items.

Highlights saved before July 30, 2012 will not be displayed on their respective source pages.

You can easily re-create the highlights by opening the book page or article, selecting the text, and clicking “Highlight.”

matching results for page

    Questia reader help

    How to highlight and cite specific passages

    1. Click or tap the first word you want to select.
    2. Click or tap the last word you want to select, and you’ll see everything in between get selected.
    3. You’ll then get a menu of options like creating a highlight or a citation from that passage of text.

    OK, got it!

    Cited passage

    Style
    Citations are available only to our active members.
    Buy instant access to cite pages or passages in MLA 8, MLA 7, APA and Chicago citation styles.

    "Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences." (Einhorn, 1992, p. 25).

    "Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences." (Einhorn 25)

    "Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences." (Einhorn 25)

    "Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences."1

    1. Lois J. Einhorn, Abraham Lincoln, the Orator: Penetrating the Lincoln Legend (Westport, CT: Greenwood Press, 1992), 25, http://www.questia.com/read/27419298.

    Cited passage

    Thanks for trying Questia!

    Please continue trying out our research tools, but please note, full functionality is available only to our active members.

    Your work will be lost once you leave this Web page.

    Buy instant access to save your work.

    Already a member? Log in now.

    Search by... Author
    Show... All Results Primary Sources Peer-reviewed

    Oops!

    An unknown error has occurred. Please click the button below to reload the page. If the problem persists, please try again in a little while.