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From Galileo to Hubble and Beyond Important discoveries in astronomy over the centuries

Highlights of Important Astronomical Discoveries • The 20th and 21st centuries have been an incredible period of discovery in astronomy, cosmology, physics and many other scientific disciplines.

• The centuries leading up to modern times were especially pivotal in helping astronomers understand the movement of planets, their satellites, and the cosmos at large.

• Following are highlights of some of the key inventions and discoveries of the last several centuries that have helped shape our understanding of the universe.

Lippershey Invents the Refracting Telescope • In 1608 Hans Lippershey, a Dutch eyeglass maker, invented the refracting telescope.

• The invention of the telescope began a revolution in astronomy, and the device spread rapidly around Europe.

• Interestingly, the patent Lippershey filed in 1608 was never actually issued, as other spectacle-makers claimed to have invented the telescope.

Kepler’s Laws of Planetary Motion • German astronomer Johannes Kepler published the book New Astronomy in which he described the three laws of planetary motion, as follows:

1. Planets have an elliptical orbit with the Sun at one of the two foci. 2. A line joining a planet and the Sun sweeps out equal areas during equal intervals of time. 3. The square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit.

• Kepler’s scientific works would later become the foundation of Isaac Newton’s theory of universal gravitation.

Galileo Supports Copernican Heliocentrism • Galileo supported the Copernican theory of a Suncentered universe based on observations he made with his hand-built telescope.

• In the 2,000 years preceding Galileo’s discoveries the long-accepted theory was an Earth-centered one in which the sun and planets in our solar system revolved around the Earth.

• Among Galileo’s observations were craters on the moon, spots on the Sun and four of Jupiter’s satellites. Galileo’s findings were published in the pamphlet Sidereus Nuncius.

Isaac Newton and His Apple • In 1668 English physicist Isaac Newton built the first reflecting telescope.

• In 1687 he established the theory of gravitation and laws of motion, as outlined in his book Philosophiae Naturalis Principia Mathematica.

• Newton explained Kepler's laws of planetary motion in Principia, shedding light on the forces acting between the Sun, planets and their satellites.

• It is said that Newton was inspired to formulate his theory of gravitation after watching an apple fall from a tree. Although this has become something of a myth, accounts from Newton’s friends suggest there may be some truth behind the claim.

Edmond Halley and His Comet • In 1705 English astronomer Edmond Halley predicted that comets seen between the years 1456 to 1682 were one and the same.

• The comet returned in 1758 as Halley predicted it would, and was later named in his honor.

• Halley’s Comet is visible with the naked eye and reappears every 75-76 years; it is the only comet that a person may see twice in a lifetime.

Herschel Discovers Uranus • In 1781 German astronomer Frederick William Herschel discovered the planet Uranus and two of its major moons, Titania and Oberon.

• Herschel initially mistook the planet for a comet. • Uranus was the first planet discovered beyond Saturn up to that point.

• Among Herschel’s other accomplishments was his discovery of infrared radiation – an important contribution considering that half of the total energy Earth received from the Sun arrives in the form of infrared.

Big Bang Theory •

According to Big Bang Theory, all the matter in the Universe was once compressed into an infinitely dense and hot point, which began expanding approximately 13.7 billion years ago.

Big Bang Theory holds that space and time did not exist before the expansion of the universe, but rather came into existence after the expansion began.

Once the universe cooled sufficiently, elements formed, leading to the formation of stars, planets and other celestial objects.

Einstein’s theory of general relativity was pivotal in the development of the Big Bang theory. The theory is broadly accepted in the scientific community and was even pronounced to be in accordance with the Bible by the Catholic Church in 1951.

If You Believe They Put a Man on the Moon • On July 20, 1969 the extraordinary happened when the USA’s Apollo 11 spacecraft landed on the moon. Neil Armstrong became the first man to set foot on the moon. • There have been six manned landings on the moon, all of which occurred between 1969 and 1972. Twelve men in total have landed on the moon, including Neil Armstrong and "Buzz" Aldrin. • There have been many unmanned moon landings as well, including a “soft” landing of a rover on December 14, 2013 operated by the China National Space Administration.

Hubble Space Telescope Discoveries • Launched into orbit in 1990 and still in operation today, the Hubble Space Telescope has been an indispensable tool for astronomers, helping them determine the age of the universe and understand how dark energy is accelerating the universe’s expansion.

• The telescope was named after American astronomer Edwin Hubble, who discovered the expanding universe and determined that Andromeda is actually a galaxy rather than a nebula, as previously thought.

The Discovery of Exoplanets • Exoplanets, also known as extrasolar planets, are planets that revolve around other stars in our galaxy and beyond. • Astronomers weren’t able to prove the existence of exoplanets until the early 1990s; in 1992, several terrestrial-mass planets were found orbiting a pulsar known as PSR B1257+12. • • To date, more than a thousand confirmed exoplanets have been discovered, including 175 multi-planetary systems, and the Kepler space telescope launched in 2009 has discovered more than 3,500 additional candidate planets as of late 2013.

• Among the most common methods of locating exoplanets is the transit method, whereby astronomers look for dimming on the surface of a star to indicate the passing of a planet in front of the star from the perspective of the observer.

Our Accelerating Universe •

• In 2011 Adam Riess, Brian Schmidt, and Saul Perlmutter were awarded to the Nobel Prize in Physics for their discovery that the expansion of the universe is accelerating.

The scientists discovered that the expansion rate of the universe is a timescale, not a speed, and that the universe expands at a fixed rate, which essentially means that it takes a fixed amount of time for the universe to double in size.

In ten billion years, for example, any particular galaxy observed will be twice as far away; in twenty billion years it will be four times as far away, and in thirty billion years it will be eight times that far away, thus indicating that the acceleration of the universe is expanding.

The acceleration discovery is significant, as it changes our understanding of what the universe will look like billions of years from now.

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From Galileo to Hubble: Important discoveries in astronomy over the centuries | LabRoots presents an overview of some of the major discov...