Famous Astronomers

Famous Astronomers

Aristarchus • Circa 310-230 BC • Ancient Greece • Decided sun the center of the universe since he observed that the sun was larger than the Earth and moon (no one believed him) • Calculated distance to and size of sun and moon with correct methods, but he did not have capable instruments to make accurate estimations

Aristarchus http://outreach.atnf.csiro.au

Aristotle • circa 384-322 BC • Ancient Greece • Earth composed of Earth, air, water and fire • The imperfect Earth is a sphere and doesn’t move and planets go around Earth in perfect circles – one inside another

Aristotle http://onlinephys.com

Tycho Brahe • 1546-1601 • Denmark • Built an observatory carefully recorded his precise observations of the sky • Saw a supernova and a comet and his observations went against the idea that the heavens never change. • Came up with design of the solar system where planets orbit the sun, but the sun orbits the Earth

Brahe galileo.rice.edu/science.html

Nicolaus Copernicus • 1473-1543 • Poland • Developed a simple model of the solar system where the planets all went around the sun in perfect circles • Came up with the correct order of the planets and the idea that Earth rotates on an axis

Copernicus http://starchild.gsfc.nasa.gov

Galileo Galilei • 1564-1642 • Italy • Improved the telescope • Discovered mountains and craters on the moon, the phases of Venus, and the four largest moons of Jupiter • Studied sunspots on the sun • His studies helped prove that the heavens were imperfect and not everything goes around the Earth • He concluded (and published) that Copernicus’ model of the solar system was correct.

Galileo http://www.hyperhistory.com http://www.sydneyobservatory.com.au

Johannes Kepler • 1571-1630 • Germany • Was Brahe’s assistant • Using Brahe’s observations he established the three laws of planetary motion • Discovered planets orbit in an ellipse • Discovered planet’s speed depends on distance from the sun

Kepler http://jkepler33.blogspot.com

Isaac Newton • 1642-1727 • England • Developed theories of gravitation and 3 laws of motion, which explain how the planets move around the sun and not fly off into space • Created a reflecting telescope

Newton http://web.njit.edu http://museumvictoria.com.au

Ptolemy • Circa 90-168 • Egypt (he was Greek, but a Roman citizen) • Created model of universe with Earth in the center (he believed the Earth moved too) – the sun, moon and planets move in smaller circles (called epicycles) while circling the Earth • This was believed for 1500 years!

Ptolemy http://usersguidetotheuniverse.com/?p=606

Ptolemy http://abyss.uoregon.edu

Pythagoras • 580-500 BC • Ancient Greece (Samos) • Believed Earth is a sphere • Believed that each planet was attached to a concentric sphere (think nesting cups) and that as these spheres moved a sound is made • Recognized that Venus is both the morning star and the evening star

Hipparchus • 185-125 BC • Ancient Greece • Made a star catalog of star positions and brightness • Studied the motion of the moon and sun (eclipses, etc) • Studied equinoxes • Decided star locations changed over time due to the Earth wobbling as it spun like a top

Giovanni Cassini • 1625-1712 • Italy, but born in France • Calculated the distance to Mars • Co-discoverer of the Great Red Spot on Jupiter and also studied the motion of Jupiter’s atmosphere • discovered four satellites of Saturn and the gap in Saturn's rings now known as ``Cassini's division''

Christiaan Huygens • 1629-1695 • Netherlands • discovered Saturn's first satellite, Titan, and the true shape of Saturn's rings • First to draw the Orion Nebula including specific stars in the nebula

Edmond Halley • 1656-1742 • England • used his theory of cometary orbits to accurately predict that the comet of 1682 (later named ``Halley's comet'') would return

Charles Messier • 1730-1817 • France • discovered upwards of 21 comets • compiled a famous catalog of non comet objects he observed (nebulae, galaxies and star clusters) that are now called Messier Objects (named M1 through M110) • Examples of his discoveries: Crab Nebula and the Andromeda Galaxy

William Herschel • 1738-1822 • English, but born in Germany • Discovered Uranus and 2 of its moons • discovered 2 of Saturn's moons • discovered the ice caps of Mars, several asteroids and binary stars • cataloged 2,500 deep sky objects • Taught his sister, Caroline, astronomy and she discovered several comets

Guiseppe Piazzi • 1746-1826 • Italy • discovered the largest asteroid, Ceres • As professor of astronomy in Palermo he supervised the creation of an accurate star catalog with thousands of objects • Studies the motion of stars

UrbainLeVerrier • 1811-1877 • France • predicted the position of Neptune (also predicted at the same time by John Couch Adams) • one month after he announced his prediction the planet was found by a telescope in Germany • studied the orbit of Mercury and incorrectly believed that there was a planet between Mercury and the Sun (later named Vulcan)

Edwin Hubble • 1889-1953 • USA • Discovered that there are galaxies outside our own and came up with a method to classify galaxies • Noticed changes in the light emitted from galaxies which means the galaxies are moving away from each other at a rate constant to their distance – called Hubble’s Law • This lead scientists to conclude that the universe is expanding and find the age of the universe

Walter Baade • 1893-1960 • USA, born in Germany • Discovered 10 asteroids • established two different stellar classes (types of stars) • Identified supernovas as a new class of astronomical objects and believed that neutron stars formed from supernovae

Jan HendrikOort • 1900-1992 • Netherlands • Studied Milky Way – distance to center, mass, time for the sun to revolve around the galaxy • proposed existence of huge spherical cloud of icy comets (the Oort cloud) left behind from formation of the solar system

Gerard Kuiper • 1905-1973 • USA, born in Netherlands • Discovered moons of Neptune and Uranus • Discovered the atmosphere of Titan, Saturn's largest satellite • His studies led to the discovery of comet-like debris at the edge of the solar system, now called ``Kuiper's belt'‘ (where Pluto is)

Clyde Tombaugh • 1906-1997 • USA • Discovered the planet Pluto before he attended college • Pluto was the hypothetical Planet X that Percival Lowell believed existed • Discovered around 800 asteroids • Believed in UFOs

Fred Whipple • 1906-2004 • USA • Proposed the ``dirty snowball'' model of cometary structure • Helped discover 6 comets and an asteroid • Helped map the orbit of Pluto

Carl Sagan • 1934-1996 • USA • searched for extraterrestrial intelligence • Studied Venus • contributed to most of the space missions to explore Mars and the outer planets

Stephan Hawking • 1942- • Great Britain • Showed that according to the Theory of Relativity that space and time started with the Big Bang and will end in a black hole which unifies relativity with quantum theory • Based on this discovered black holes must emit some sort of radiation and will eventually disappear • The universe has no edge or boundary

2 Vocab Words Geocentric: • Earth centered model of the solar system (planets, sun go around Earth) Heliocentric: • Sun centered model of the solar system (planets ALL go around sun) florinickka.blogspot.com http://csep10.phys.utk.edu

Famous Astronomers