Astronomy Chapter 2 & 3

 The stars stay in "fixed" positions on the celestial sphere because they 

are so far away that our eyes don’t notice their motions through space

Celestial sphere

a useful illusion used to map the stars and other objects in the sky

Ecliptic

the Sun’s apparent path along the celestial sphere

If Earth’s rotation slowed down so that it completed exactly one rotation about its axis in 100 hours (instead of 24), what would be the typical time interval between sunrise and sunset?

50 hours

How many arcminutes are in 1°?

60

How many arcseconds are in 1 arcminute?

60

Is there any place on Earth where we can see stars rise in the west and set in the east (rather than rising in the east and setting in the west)? Why or why not?

No, because the rising and setting of stars is caused by Earth's west to east rotation

Circumpolar star

A star that always remains above your horizon 

Earth rotates once each ________, Earth orbits the Sun once each ________, and the Moon orbits Earth about once each ________ 

day, year, month 

Seasons on Earth are caused by ________

Earth's axis tilt 

When it is summer in the Northern Hemisphere, it is ________ in the Southern Hemisphere 

winter

The Northern and Southern hemispheres have equal illumination from the Sun ________

on the March and September equinoxes

Suppose that Earth's rotation axis were tilted by 45 degrees instead of 23.5 degrees. Which of the following would be true, and why?

The seasons would be more extreme, because the Sun's rays would be more direct in summer and less direct in winter.

Why do we see essentially the same face of the Moon at all times? 

Because the Moon's rotational and orbital periods are equal 

Suppose you live on the Moon. About how long is a day (i.e., from sunrise to sunrise)? 

A month

If the plane of the Moon's orbit around the Earth was perfectly aligned with the ecliptic plane (instead of being tilted by about 5°), a solar eclipse would be visible on some parts of Earth ________

about once a month

The conditions required for a solar eclipse are ________

(1) the phase of the Moon must be new; (2) the nodes of the Moon's orbit must be nearly aligned with Earth and the Sun 

The conditions required for a lunar eclipse are ________

(1) the phase of the Moon must be full; (2) the nodes of the Moon's orbit must be nearly aligned with Earth and the Sun 

People of central Africa learned to predict rainfall patterns by tracking rainfall amounts and ________ 

observing the orientation of the crescent Moon relative to the horizon 

At the Sun Dagger in New Mexico, a dagger-shaped beam of sunlight pierced a spiral ________

at noon on the summer solstice 

Why did Ptolemy have the planets orbiting Earth on "circles upon circles" in his model of the universe? 

To explain the fact that planets sometimes appear to move westward, rather than eastward, relative to the stars in our sky 

Which of the following was an important reason why most ancient Greeks rejected the notion that the Earth orbits the Sun? 

They could not measure small changes in the positions of stars that occur as Earth orbits the Sun. 

During the Dark Ages in Europe, the scientific work of the ancient Greeks was preserved and further developed primarily by scholars in ________

Baghdad (Iraq) 

Which of the following statements can in principle be tested by scientific experiment(s)? 

The locations of the Sun and planets among the constellations at your birth predict your personality and health. 

The Greek philosopher Plato asserted that all heavenly objects move in perfect circles at constant speeds around the Earth. Which of the following observations most directly challenged this model? 

The apparent retrograde motion of planets 

Which person below discovered that the orbits of planets are ellipses? 

Kepler 

Which person below did the following? He tried fitting perfect circles to Tycho's data, but in doing so found discrepancies of up to 8 arc minutes. Because he was confident that Tycho's data had uncertainties of only 1 arc minute, he abandoned perfect circles, which led him to a model using elliptical orbits. 

Kelper

Which person below created a model of the solar system that put the Sun in the center, but that was not very accurate because he assumed that the orbits of the planets must be perfect circles? 

Copernicus

Kepler's second law, which states that as a planet moves around its orbit it sweeps out equal areas in equal times, implies that ________

a planet travels faster when it is nearer to the Sun and slower when it is farther from the Sun 

In its original form, Kepler's third law states that p2 = a3. What units must p and a use? 

p must be years and a must be astronomical units. 

According to Kepler's third law (p2 = a3), a hypothetical planet that is twice as far from the Sun as Earth should have an orbital period of ________

between 2 and 3 Earth years 

According to Kepler's third law (p2 = a3), an asteroid with an orbital period of 8 years lies at an average distance from the Sun equal to ________

4 astronomical units 

Which of the following statements best describes the accomplishments of these three people? 

Tycho collected the data, Kepler provided the model in the form of laws, Newton explained the model in terms of gravity.