History of Astronomy Flashcards
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Read the first 7 History of Astronomy flashcards as text
Edwin Hubble's observations in the 1920s proved that 'spiral nebulae' such as Andromeda were actually distant galaxies. Which type of variable star did he use to measure their distances?
Answer: Cepheid variables
Hubble used Cepheid variable stars, whose period-luminosity relationship (discovered by Henrietta Swan Leavitt) allowed him to calculate that the Andromeda nebula was far outside the Milky Way.
Which ancient Greek thinker first proposed a heliocentric model of the solar system, more than 1,700 years before Copernicus?
Answer: Aristarchus of Samos
Aristarchus of Samos proposed a heliocentric model around 270 BCE, also estimating the relative sizes of the Sun and Moon, but his model was largely rejected in favor of the geocentric view.
William Herschel discovered which planet in 1781, the first planet found in recorded history rather than known since antiquity?
Answer: Uranus
William Herschel discovered Uranus on March 13, 1781, using a homemade telescope, making it the first planet discovered in modern times and doubling the known size of the solar system.
Annie Jump Cannon developed the Harvard stellar classification system (OBAFGKM). What physical property of stars does this sequence primarily reflect?
Answer: Surface temperature
The OBAFGKM sequence orders stars by decreasing surface temperature, with O-type stars being the hottest (>30,000 K) and M-type stars being the coolest (~3,000 K).
Henrietta Swan Leavitt's 1908 discovery of the period-luminosity relationship in Cepheid variable stars allowed astronomers to determine what?
Answer: Distances to objects beyond the Milky Way
By relating the pulsation period of a Cepheid to its intrinsic brightness, Leavitt created a 'standard candle' that enabled accurate distance measurements to nearby galaxies.
Arno Penzias and Robert Wilson accidentally discovered the cosmic microwave background radiation in 1965. What were they originally trying to do when they made this discovery?
Answer: Reduce antenna noise for a satellite communication system
Penzias and Wilson were engineers at Bell Labs trying to eliminate background noise from a sensitive microwave antenna, when they detected the 2.7 K thermal radiation permeating all of space.
The Hubble Space Telescope was launched in April 1990, but its initial images were blurry due to a flaw in its primary mirror. How was this corrected?
Answer: Corrective optics were installed by Space Shuttle astronauts in 1993
During Space Shuttle mission STS-61 in December 1993, astronauts installed COSTAR (Corrective Optics Space Telescope Axial Replacement) to compensate for the 2.2-micron spherical aberration in the primary mirror.