ASP History of Astronomy 2 — Questions and Answers
Question 1: 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?
- RR Lyrae variables
- Cepheid variables (Correct answer)
- Mira variables
- W Virginis variables
Correct 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.
Question 2: Which ancient Greek thinker first proposed a heliocentric model of the solar system, more than 1,700 years before Copernicus?
- Plato
- Aristotle
- Aristarchus of Samos (Correct answer)
- Thales of Miletus
Correct 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.
Question 3: William Herschel discovered which planet in 1781, the first planet found in recorded history rather than known since antiquity?
- Neptune
- Saturn
- Uranus (Correct answer)
- Pluto
Correct 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.
Question 4: Annie Jump Cannon developed the Harvard stellar classification system (OBAFGKM). What physical property of stars does this sequence primarily reflect?
- Luminosity
- Distance
- Surface temperature (Correct answer)
- Chemical composition
Correct 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).
Question 5: Henrietta Swan Leavitt's 1908 discovery of the period-luminosity relationship in Cepheid variable stars allowed astronomers to determine what?
- The temperature of stars
- The composition of stellar atmospheres
- Distances to objects beyond the Milky Way (Correct answer)
- The age of star clusters
Correct 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.
Question 6: 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?
- Detect radio emissions from the Milky Way's center
- Reduce antenna noise for a satellite communication system (Correct answer)
- Search for signals from distant quasars
- Measure the temperature of interstellar gas
Correct 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.
Question 7: 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?
- The telescope was brought back to Earth and the mirror was reground
- Corrective optics were installed by Space Shuttle astronauts in 1993 (Correct answer)
- Software algorithms on the ground digitally sharpened the images
- A second, smaller mirror was added during a 1992 robotic mission
Correct 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.
ASP History of Astronomy 2
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?