This map, drawn by Edmond Halley, was the first to chart lines of magnetic variation. (Yes, he also identified a comet.)
Map by Edmond Halley, courtesy the Louisiana State Museum

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  • On September 6, 1700, English scientist Edmond Halley returned from a one-year voyage on his science ship, the Paramour. Halley and his crew had sailed from the island of Great Britain to the southern tip of South America. Along the way, they measured the strength of Earth's magnetic field by comparing compass readings with the position of familiar stars. Halley then made a map of the unusual differences, so people could better understand the magnetic field that compasses use.

    Magnetism was just one of many things Edmond Halley worked to understand. He was the first to note that air pressure changes with elevation, for instance. Pressure difference is an important aspect of understanding climate and weather. Halley also pioneered demography, the numerical study of large groups of people in one place.

    Edmond Halley finished his career as Great Britain's astronomer royal. Most people remember him for identifying the cycle of a large comet that passes close to Earth about every 75 years. Halley's Comet will next pass us by in 2061.

  • Term Part of Speech Definition Encyclopedic Entry
    air pressure Noun

    force pressed on an object by air or atmosphere.

    aspect Noun

    view or interpretation.

    astronomer Noun

    person who studies space and the universe beyond Earth's atmosphere.

    climate Noun

    all weather conditions for a given location over a period of time.

    Encyclopedic Entry: climate
    comet Noun

    celestial object made up of ice, gas, and dust that orbits the sun and leaves a tail of debris.

    compass Noun

    instrument used to tell direction.

    Encyclopedic Entry: compass
    demography Noun

    study of human populations.

    elevation Noun

    height above or below sea level.

    Encyclopedic Entry: elevation
    identify Verb

    to recognize.

    journey Noun

    voyage or trip.

    magnetic field Noun

    area around and affected by a magnet or charged particle.

    star Noun

    large ball of gas and plasma that radiates energy through nuclear fusion, such as the sun.

    weather Noun

    state of the atmosphere, including temperature, atmospheric pressure, wind, humidity, precipitation, and cloudiness.

    Encyclopedic Entry: weather