Phys 1404
We never see a crescent Jupiter from Earth because Jupiter __________.
is farther than Earth from the Sun Submit
What conditions must exist for a lunar eclipse to occur?
it must be full moon the Moon must be passing through Earth's orbital plane
What conditions must exist for a solar eclipse to occur?
it must be new moon the Moon must be passing through Earth's orbital plane
Why wasn't the Sun-centered model of Copernicus immediately adopted after he proposed it?
it was not noticeably more accurate than the old Ptolemaic model
Based on your answer to Part E, the time from one new moon to the next must be _________.
longer than the Moon's actual orbital period by about 1/12 of the 27-day orbital period
It is 1 p.m. on the spring equinox. What is the local sidereal time?
1 hours
Which of the following is not true about a scientific theory?
A theory is essentially an educated guess.
Why we observe a transit?
A transit occurs when a planet appears to pass in front of the Sun's disk as seen from Earth, so it can occur only when the planet is in inferior conjunction. Moreover, because Mercury and Venus's orbits are tilted relative to Earth's orbit, the planets usually are slightly north or south of the Sun at inferior conjunction. However, when the planet's orbit lines up just right, we get a transit.
Why does the local sky look like a dome?
Because we see half of celestial sphere at any time.
If you could change the layout of the solar system, which of the following would cause a lunar eclipse to occur at least once every month in this hypothetical situation?
Change the Moon's orbital plane so it is in the same plane as Earth's orbit around the Sun.
Kepler's first law states that the orbit of each planet is an ellipse with the Sun at one focus. Which of the following statements describe a characteristic of the solar system that is explained by Kepler's first law?
Earth is slightly closer to the Sun on one side of its orbit than on the other side. The Sun is located slightly off-center from the middle of each planet's orbit.
Earth is closer to the Sun in January than in July. Therefore, in accord with Kepler's second law:
Earth travels faster in its orbit around the Sun in January than in July.
Where does the Sun remain above the horizon all day (never setting) on the December solstice?
Everywhere between the Antarctic Circle (latitude 66.5°S) and the South Pole
Saturn, synodic period = 378.1 days.
Porb = 29.4 yr
Which of the following was not a major advantage of Copernicus's Sun-centered model over the Ptolemaic model?
It made significantly better predictions of planetary positions in our sky.
Which of the following planets has essentially no seasons at all?
Jupiter (axis tilt = 3.1°)
According to Kepler's third law,
Jupiter orbits the Sun at a faster speed than Saturn.
Which of the following is not true about scientific progress?
Science advances only through the scientific method.
Which of the following is not consistent with the major hallmarks of science?
Science consists of proven theories that are understood to be true explanations of reality.
Which of the following are the three key hallmarks of science?
Science progresses through the creation and testing of models of nature that explain the observations as simply as possible. Modern science seeks explanations for observed phenomena that rely solely on natural causes. Models must make testable predictions that will force us to revise or abandon the model if they do not agree with observations. Submit
why is it generally hotter in summer than in winter?
The Sun is higher in the sky in summer. We have more hours of daylight in summer.
Which of the following were key pieces of evidence that led to widespread acceptance of the Sun-centered model "extraordinary claim" during the period from about 1609 to 1630?
The fact that Kepler's laws allowed virtually perfect prediction of planetary positions. Galileo's telescopic observations.
What conditions must exist for a lunar eclipse to occur?
The phase of the Moon must be full and the Moon must be passing through Earth's orbital plane.
What conditions must exist for a solar eclipse to occur?
The phase of the Moon must be new and the Moon must be passing through Earth's orbital plane.
In the Greek geocentric model, the retrograde motion of a planet occurs when:
The planet actually goes backward in its orbit around Earth.
Suppose that Earth orbited the Sun 10 times as fast as it actually does but kept the same rotation period it has now. Which of the following would be true?
The sidereal day would still be 23 hours, 56 minutes, but the solar day would be a little over 24 1/2 hours.
You've now seen that Earth's varying distance cannot be the cause of our seasons. So what is the cause of the seasons?
The tilt of Earth's axis causes different portions of the Earth to receive more or less direct sunlight at different times of year.
Which of the following planets should have the most extreme seasons?
Uranus (axis tilt = 97.9°) Submit
A star's path through your sky depends on your latitude and the star's:
declination
A star that is located 30∘ north of the celestial equator has:
declination = 30∘.
In Ptolemy's Earth-centered model for the solar system, Venus's phase is never full as viewed from Earth because it always lies between Earth and the Sun. In reality, as Galileo first recognized, Venus is __________.
full whenever it is on the opposite side of the Sun from Earth
When we say that a planet has a highly eccentric orbit, we mean that:
in some parts of its orbit it is much closer to the Sun than in other parts.
If you know a star's declination, you can determine your latitude if you also:
measure its altitude when it crosses the meridian.
In Ptolemy's Earth-centered model, when would Venus appear directly behind the Sun as viewed from Earth?
never
When would you expect to see Venus high in the sky at midnight?
never
The Sun reaches the zenith (directly overhead) at midday ___________.
on the equator only on the March and September equinoxes everywhere within the tropics (between latitudes 23.5°N and 23.5°S) on two dates each year
The fact that we always see the same face of the Moon tells us that the Moon
rotates with the same period that it orbits Earth.
How can we describe the location of an object in the local sky?
specifying its altitude and azimuth
The shadow cast by a simple stick or obelisk allowed ancient people to
tell the time of day
If there is going to be a total lunar eclipse tonight, then you know that:
the Moon's phase is full.
An original observation of Galileo's that helped to overturn the ancient Earth-centered model was
the phases of Venus
In the demonstration, 360∘ of rotation (one full rotation) represents a sidereal day. You can actually measure the length of the sidereal day by measuring the time from when __________ crosses your meridian on one day (or night) until it crosses the meridian on the next day (or night).
the star Sirius the star Vega
Suppose you know the declination of a bright star that is now crossing your meridian. What else must you measure to determine your latitude?
the star's altitude
The time from one spring equinox to the next is the:
tropical year.
As shown in the figure, a solar day requires about an extra 1° of rotation, or a total of about 361° of rotation for Earth. Therefore, a solar day is longer than a sidereal day by about __________.
1/360 of 24 hours
You observe a star that has an hour angle of 13 hours (13h) when the local sidereal time is 11:15. What is the star's right ascension?
22 hours 15 minutes
The local sidereal time is 19:30. When will Vega cross your meridian?
23 hours 5 minutes
At latitude 50∘N, the celestial equator crosses the meridian at altitude:
40∘ in the south.
In Carl Sagan's statement "Extraordinary claims require extraordinary evidence," what does he mean by "extraordinary evidence"?
Evidence that is extremely strong.
In which of the four time periods did the Sun-centered model gain widespread acceptance, meaning that nearly everyone who looked at the evidence concluded that it was correct?
Later Copernican Revolution (about 1609-1630)
which of the following planets would you expect to have seasons most like Earth's?
Mars (axis tilt = 25.2°)
For what planets do we sometimes observe a transit?
Mercury Venus
Why is the writing on maps and globes usually oriented so that the Northern Hemisphere is at the top, even though there is no up or down in space? How does this relate to the fact that the June solstice has traditionally been called the summer solstice?
North is at the top on the most maps traditionally, maps are mostly made by people in the Northern hemisphere. The June solstice is traditionally called the summer solstice for the same reason.
Kepler's second law states that as a planet orbits the Sun, it sweeps out equal areas in equal times. Which of the following statements describe a characteristic of the solar system that is explained by Kepler's second law?
Pluto moves faster when it is closer to the Sun than when it is farther from the Sun.
In spring, the axis points toward
Polaris
Mercury, synodic period = 115.9 days.
Porb = 0.241 yr
An asteroid with synodic period = 429 days.
Porb = 6.73 yr
Which of the following changes would cause the solar day to be shorter (rather than longer) than the sidereal day?
Reversing the direction of Earth's rotation
which statement best describes how variation in the Earth-Sun distance affects the seasons?
The variation in Earth-Sun distance over the course of each year has virtually no effect on the seasons.
Kepler's third law states that a planet's orbital period, p, is related to its average (semimajor axis) orbital distance, a, according to the mathematical relationship p2=a3. Which of the following statements describe a characteristic of the solar system that is explained by Kepler's third law?
Venus orbits the Sun faster than Earth orbits the Sun. Inner planets orbit the Sun at higher speed than outer planets.
Which of the following can you observe about Venus with the naked eye?
Venus sometimes shines brightly in the western sky shortly after sunset Venus sometimes shines brightly in the eastern sky shortly before dawn
In Ptolemy's Earth-centered model for the solar system, Venus always stays close to the Sun in the sky and, because it always stays between Earth and the Sun, its phases range only between new and crescent. The following statements are all true and were all observed by Galileo. Which one provides evidence that Venus orbits the Sun and not Earth?
We sometimes see gibbous (nearly but not quite full) Venus.
The Moon takes about 1 month to orbit Earth (more precisely, about 27 1/3 days), and it travels in the same direction that Earth orbits the Sun. Therefore, during the time it takes the Moon to complete one orbit around Earth, Earth moves __________ around its orbit of the Sun.
about 1/12 of the way
Imagine that Venus is in its full phase today. If we could see it, at what time would the full Venus be highest in the sky?
at noon
When would a new Venus be highest in the sky?
at noon
Jupiter is brightest when it is:
at opposition.
Tycho Brahe's contribution to astronomy included:
collecting data that enabled Kepler to discover the laws of planetary motion.
When Einstein's theory of gravity (general relativity) gained acceptance, it demonstrated that Newton's theory had been
incomplete
Consider the hypothetical observation "a planet beyond Saturn rises in west, sets in east." This observation is not consistent with a Sun-centered model, because in this model __________.
the rise and set of all objects depends only on Earth's rotation
The Orion Nebula has declination of about -5.5∘ and right ascension of 5h25m. If you are at latitude 40∘ N and the local sidereal time is 7:00, approximately where does the Orion Nebula appear in your sky?
west of the meridian by about 25∘