HW 2 Intro to Astrology

What conditions must exist for a lunar eclipse to occur?

- the must be passing through Earth's orbital plane -it must be full moon Memorize tip : note the full , it has a "u" in the second spot of the word , so does lunar! Thus lunar = full.

There are 360 degrees in a full circle. -How many arcminutes are in a full circle? -How many arcseconds are in a full circle? -The Moon's angular size is about 1/2. What is this in arcminutes? -What is the Moon's angular size in arcseconds

-21600' (360*60) -1296000" (21600*60) -30'(1/2*60) -1800(30*60)

Observations of stellar parallax therefore provide direct evidence that:

-Earth orbits the sun -some stars are more distant than others

The Sun-centered system pictured in the lower window of the video offers a simple explanation for observations of apparent retrograde motion. Should these facts alone have been enough to convince the Greeks that Earth really does go around the Sun?

-No, because the Greeks had an Earth-centered model that also accounted for apparent retrograde motion. Detailed Answer: the Greeks explained retrograde motion by imagining the planets moved around small circles that in turn moved around larger circles around Earth, thus the Greeks had no reason to reject the model. Even though the Sun-created model offered a simpler explanation for apparent retrograde motion.

Notice that in the view through the camera, the parallax is larger (the apparent movement is larger)for the man than the trees, and that the mountains do not appear to shift at all.

-The amount of parallax depends on the object's distance, with larger parallax for nearer objects. Detailed Answer: The farther way an object, the smaller its parallax.

Although all the known stars rise in the east and set in the west, we might someday discover a star that will rise in the west and set in the east

-The statement does not make sense. The stars appear to rise and set because of Earth's rotation. So during the day, all the stars must move in the same direction.

Stellar Parallax is larger for stars that are more distant. Which statement best summarizes why stellar parallax occurs?

-We view nearby stars from different positions in Earth's orbit at different times of year.

Stellar parallax occurs in much the same way as parallax on Earth. Which statement best summarizes why stellar parallax occurs?

-We view nearby stars from different positions in Earth's orbits at different times of year. Tip: Therefore, stellar parallax provides direct proof that Earth is not Stationary at the center of the universe, but rather is a planet orbiting the Sun: if Earth did not move around the Sun , there would be no apparent shift in stellar positions.

Which of the following statements are true about summer compared to winter?

-You have more daylight and less darkness in summer -The Sun follows a longer and higher path through the sky in summer -Temperatures tend to be warmer in the summer Main takeaway: longer and higher path for the Sun through the sky, which means more concentrated sunlight. This leads to higher temperatures and shorter shadows.

Consider a Time when Mars is in the middle of one its periods of apparent retrograde motion. During this time, Mars appears _____________ in our sky and crosses the meridian around _____________

-brightest -midnight Detailed Answer: The middle of a period of apparent retrograde motion occurs when Mars is closest to Earth in its orbit(in a full phase viewed from Earth) , which is why is brightest in our sky at that time. It is also opposite the Sun in the sky at that time, which is why it crosses the meridian at midnight

At most times, Mars appears to move ______ eastward relative to the stars. The exceptions are during its periods of apparent retrograde motion, when Mars appears to move __________ relative to the stars

-eastward -westward Detailed Answer: Occurs when Earth passes Mars orbit happens each 1-2 years.

If you wanted to document the apparent retrograde motion of Mars, you would need to measure and record Mars's ___________ over a period of _________

-position among the constellation -several months Detailed answer: Apparent retrograde can be observed by noticing changes in Mar's position among the constellations and unfolds when Earth moves a significant fraction of its orbit... which takes several months.

What conditions must exist for a solar eclipse to occur?

-the Moon must be passing through Earth's orbital plane -it must be new moon Note: moon must be or be quite near one of the nodes of its orbit.

Suppose that instead of being inclined to Earth's orbit around the Sun, the Moon's orbit was in the same plane as Earth's orbit around the Sun. (Click "Show Moon with flat orbit" to see this situation.) In this hypothetical situation, approximately how many solar eclipses would occur each year?

12 Detailed explanation : Earth takes 12 months to orbit the sun thus the moon will do the same.

Suppose that instead of being inclined in Earth's orbit around the Sun, the Moon's orbit was in the plane as Earth's orbit around the Sun. In this hypothetical situation, approximately how many solar eclipses would occur each year?

12 Detailed explanation: Solar eclipses should happen each New Moon Cycle because there are 12 months and a New Moon occurs each month.

In reality, the Moon's orbit about Earth is tilted (by about 5 degrees) with respect to Earth's orbit about the Sun. As a result, the actual number of solar eclipses that occur each year is approximately______

2 Detailed Explanation: There are only two periods each year when eclipses are possible, lunar/new moon , solar/full moon.

In reality, the Moon's orbit about Earth is titled (by about 5degrees ) with respect to Earth's orbit about the Sun. As a result the actual number of solar eclipses occur each year is approximately _____

2 Detailed explanation : eclipses are only possible during the "the eclipse seasons"

If we hope to use parallax to measure distances to even more-distant stars, which of the following would be most useful?

A telescope that orbits the Sun in the outer Solar System. Detailed answer: A larger orbit would put the observation positions farther the Sun, making the star's parallax angle larger

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.

What is really happening in space during the periods when we see Mars going through apparent retrograde motion?

Earth is passing by Mars in its orbit around the Sun. Detailed Answer: Earth approaches the orbital position where it will pass Mars and end after Earth has passed Mars.

What is the basic reason that we have seasons on Earth?

Earth's axis is tilted relative to the ecliptic plane Detailed explanation: Earth's axis means that sunlight hits two hemisphere(Northern, Southern) differently as we orbit the sun. Leading to opposite seasons in the Northern and Southern Hemisphere.

Based on their inability to detect stellar parallax, the ancient Greeks concluded that________________

Either Earth is the center of the universe or stars are extremely far away. FYI: Most Greeks (with notable exceptions like Aristarchus) favored the first option because it was difficult for them to believe that stars were far away.

Stellar parallax exists only because Earth orbits the Sun. Therefore , if the ancient Greeks had measured stellar parallax , they would have known that their belief in an Earth-centered universe was wrong. Why didn't the ancient Greeks measure stellar parallax?

Even for the nearest stars , parallax angles are too small to measure with the naked eye.

Why didn't the ancient Greeks measure stellar parallax?

Even the nearest stars, parallax angles are to small to measure with the naked eye.

What happens to Earth's axis as we orbit around the Sun over the course of each year?

It remains pointed in the same direction at all time.

What is special about the June solstice?

It's the day on which the Northern Hemisphere receives its most direct sunlight.

Notice that the parallax is greater (the apparent movement is larger)for the person than the trees, and that the mountains do not appear to shift at all. Why?

The amount of parallax depends on an object's distance, with the greater parallax for nearer objects tip for parallax:the effect whereby the position or direction of an object appears to differ when viewed from different positions,

Notice that, as viewed through the camera, the positions of the man and the trees change (relative to distant mountains) as the photographer moves. Which of the following statement correctly describes what is really happening in this situation?

The photographer is moving, but the man and the trees are staying still. Detailed explanation: the photographer's motion causes her tp see parallax for the man and the trees, because their positions appear to shift even though they are not really moving.

Beijing and Philadelphia have about the same latitude but different longitudes. What can be said about the tonight's night sky in these two places?

The sky will look about the same

Which of the following locations for the telescope would allow you to measure distances to the most distant stars?

a telescope on Mars Detailed explanation: Parallax triangle is the Earth-Sun distance. Making the baseline distance larger would increase the parallax.

Suppose you live at a mid-latitude in the Southern Hemisphere (such as Australia, New Zealand, Chile, or South Africa).When will you have 12 hours of daylight and 12 hours of darkness.

on both the March and September equinoxes Memorization tip: Equinox means equal , March and September have the word equinoxes therefore both months will have the same hours of day and night.