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.

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.

Noun

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

comet
Noun

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

Noun

instrument used to tell direction.

demography
Noun

study of human populations.

Noun

height above or below sea level.

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.

Noun

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