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Queen's University
Physics, Engineering Physics and Astronomy
ASTR 101

Venus • Venus has great importance as it demonstrated to Galileo that Venus orbited the sun, due to its phases, thus reinforcing the heliocentric Copernican model  Venus can only be viewed with a telescope, however it is covered in a thick cloud layer which prevents observing the planet's surface  Clouds of Venus have a high albedo which is why Venus appears so bright(third brightest object we can see, other than sun and moon) • Edmund Halley, the man who first observed Halley's comet, suggested that the transit of Venus could be used to work out its distance from us and the sun  Transit of Venus: When Venus passes between Earth and the Sun, a shadow is cast on the sun, producing a small black spot moving across the sun  Transits are rare as the orbital plane of Venus is not the same as Earth's  Halley realized the duration of a transit (how long it takes for Venus to travel across the sun) depends on where you were observing it  The difference in duration between two observers allowed for parallax measurements of the distance from Earth to Venus (provided you knew the distance between the two observers)  Once you know the distance between Earth and Venus, you know the distance of all planets in the solar system due to the scale model made by Kepler and Copernicus (Method attempted by Captain Cook)  Sadly, this method did not work since Venus's atmosphere blurred it's edges, making it impossible to make an accurate measurement of when the transit began  Today, we use radar signals to determine how far a solar object is from us by measuring how long it takes for the signal to bounce off the object and return  Venus is the closest planet to us; it's rocky surface allows for clear radar signals The Rotation of Venus: • Venus is rotating in a retrograde motion, meaning it is rotating in the opposite direction as it orbits the sun  Despite rotating extremely slowly (once every 243 days), Venus is uniformly hot unlike other planets (rotation calculated using Doppler Radar)  Example: Earth temperatures drop when it's night time, however the face of Venus that is away from the Sun remains hot  Venus remains hot due to its thick atmosphere which circulates the warm air over the surface of the planet, trapping in heat  Known as the greenhouse effect, which is seen on Earth at a much smaller scale • Rotation of Venus was worked out by a radio telescope in Puerto Rico, which provided measurements of the distance between Earth and Venus as well as topographic profiles of Venus's surface  More detail obtained by telescopes sent to orbit Venus  Surprisingly, Venus does not have developed geology like Earth, however there are continents and less defined plate boundaries  Suggested the anhydrous rocks on Venus are more rigid and limit tectonic activity (anhydrous since Venus is closer to the sun) • Soviet Union managed to land a probe on Venus however it only lasted a few hours as Venus's atmosphere is composed of sulfuric, hydrochloric, and hydrofluoric acid  Obtained images of the surface and rock data The Greenhouse Effect: • Despite reflective cloud cover, Venus is extremely hot due to the runaway greenhouse effect  Most prominent greenhouse gas on Venus is carbon dioxide • Some of the sun's rays are reflected off Earth's surface, whereas others are absorbed, thus heating up the surface  Heated objects produce infrared
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