Astro Glossary

Halley, Edmund

A British astronomer who calculated that comets follow elongated orbits around the Sun — orbits that sometimes bring them back into view from Earth. Halley calculated that one comet had visited the inner solar system several times and predicted that it would return in 1758. When it did (many years after Halley’s death), astronomers named it Halley’s Comet in his honor.

Have You Seen the Stars Tonight

Helioseismology

The study of the interior of the Sun by measuring waves that ripple across its surface. The waves are generated by the motions of giant bubbles of hot gas in the Sun's outer layer, known as the convective zone, which extends about a third of the way from the surface to the Sun's center. The waves can travel all the way around the Sun, causing "jiggles" when they reach the surface. The individual waves can reveal details about the Sun's structure, interior temperatures, composition, and more. Astronomers measure the waves through tiny changes in the motion of the Sun's surface toward or away from Earth. Studying similar waves on other stars is known as asteroseismology.

Hercules, the Strongman

A constellation named for Hercules, a character from Roman mythology, that is best viewed in spring and summer.

Herschel, William

A British astronomer who discovered Uranus and several of its major moons, such as Titania and Oberon.

Historical Events

History

History of Astronomy

Holidays and Festivals

Hubble Space Telescope

The first of NASA’s four Great Observatories. Astronauts aboard space shuttle Discovery deployed Hubble Space Telescope on April 25, 1990. It was the first big telescope designed to escape the blurring effects of Earth’s atmosphere, allowing it to see the universe more clearly than any other telescope. Its observations showed that the universe is about 13.7 billion years old. They also provided some of the first evidence of “dark energy” — a force that’s causing the universe to expand faster as it ages. Several repair and refurbishing missions by shuttle astronauts have kept the telescope going and vastly improved its scientific capabilities. It is expected to continue operating until around 2015.