NATS1745 6.0 History ofAstronomy 2011-12
Chapter 10 Exam Review
1. What is the "Island Universe" theory?
a) Immanuel Kant said that elliptical nebulae seen in the sky are actually disk shaped star
systems (independent galaxies). Our galaxy is one of the many galaxies that exist. They are like
2. Why did theAncient Greeks use the word "galaxy" to describe the bright strip of light
across the sky? What do we call this strip of light today? What part of our galaxy does this
a) Galaxy means Milk in Greek; it was names by the Greeks due to its Milky appearance.
b) The light represents the disk of our galaxy.
3. What did William, Caroline and John Herschel produce together? What was Herschel
attempting to prove from this research? Why was he not able to prove this?
a) Used their giant telescopes to catalogue over 5000 “nebulae”
b) TO identify whether nebulae are distant star systems or nearby glowing gas clouds
c) B/c of large variety of nebulae and couldn’t come to conclusion about their composition
4. What did Herschel's map of the visible stars reveal about the shape of our galaxy?
a) Revealed our disk-shaped star system
5. What did Lord Rosse discover when he looked at the elliptical-shaped nebulae through
his Leviathan telescope?
a) Revealed many elliptical nebulae are “spiral nebulae”
6. What is a variable star? What characterizes the Cepheid variables? Explain briefly why
a) Star which fluctuate in brightness at regular time intervals
b) Cepheid: luminous variable stars which pulsate rapidly (at intervals of days to weeks) and has
highly opaque surface (its outward photons push surface outwards, which temporarily expands
star and reduces its opacity
7. What are the SMC and LMC? What did Henrietta Leavitt discover when she observed
Cepheids in the SMC? Why was this discovery so valuable? Who used her discovery to
determine the boundaries of our galaxy?
a) SMC is the Small Magellanic Cloud and LMC is the Large Magellanic Clouds (they are
galaxies). b) Assumed SMC Cepheids are equally distant from Earth, found brighter the Cepheid = longer
c) Discovering Cepheid period was valuable because it gives way its luminosity (and therefore
its distance, which is the distance to its star systems).
d) Harlow Shapley
8. What are the 3 components of our galaxy, according to Shapley's model? Where is the
Sun located in this model? Where is the Galaxy's centre? In what 2 ways is this model
a) Disk is 300,000 LY and implies all nebulae are systems WITHIN our galaxy and SMC is
INSIDE our galaxy
b) The sun resides in OUTSKIRTS of its disk
c) Milky Way centre is in Sagittarius.
d) He was wrong about where the spiral resided and the size of the disk (he estimated it was
three times bigger).
9. Why was Shapley convinced that the spiral nebulae are within our galaxy's boundaries?
a) Maps of spiral nebulae revealed spirals aren’t seen near the Milky Way disk
10. What is the Zone of Avoidance? What was Shapley's explanation for it? What was
Curtis'? Who was correct?
a) Spirals pushed from our disk by radiation pressure from high density of stars, creating ZOA,
therefore spirals are WITHIN our galaxy
b) Shapley said that spirals are pushed from our disk by radiation pressure from its high density
of stars, creating a “zone of avoidance”.
c) Curtis said: If the Milky Way’s disk contains a band of dust, and if the spirals are outside our
Galaxy, they aren’t seen in the “Zone ofAvoidance” because our vision is obscured by the dust.
11. What observation led Curtis to suspect that the disks of galaxies are filled with
interstellar dust? Where does this dust come from?
a) Completed a high-resolution survey of spiral nebulae, which revealed DUST in their disks
b) Our Galaxy’s disk filled with microscopic metallic grains (from dying stars) which absorb
12. What did Vesto Slipher observe about the spectra of spirals?
a) Slipher measured large redshift in the absorption lines of spiral, suggesting recessional speeds
as high as 1000 of km/secs.
13. In the Shapley-Curtis Debate, what did Shapley argue? What did Curtis argue? What 4 pieces of evidence did Curtis present?
a) Shapley argued: spirals are pushed from our disk by radiation pressure from its high density of
stars, creating a ZONE OF AVOIDANCE. Therefore, the spirals are WITHIN our galaxy. HE
ARGUED AGAINST ISLAND UNIVERSE.
b) Curtis argued if spirals are moving faster than stars in our Galaxy, the spirals must be
OUTSIDE our galaxy. CURTIS ARGUED FOR ISLAND UNIVERSE
c) 4 EVIDENCE CURTIS PRESENTED:
1) Spiral radial velocities are larger than star velocities
2) Spiral spectra are indicative of star systems
3) Faintness of what appear to be novae in spirals suggest they’re distant star systems
4) Spirals show evidence of obscuring matter in their disks; If Milky Way is such a spiral,
this explains Zone