Astronomy Chapter 2

If we could observe background stars in daylight, how would the sun appear to move against the background because of our motion on an orbiting earth?

1 degree/day from W to E

Describe the three structures or carvings on made by past civilizations that show an understanding of astronomy

1. Carvings in North America The carvings of North America made by the ancestral Puebloans of modern day New Mexico, Arizona, Utah and Colorado created carvings that were illuminated by the sun on the first days of summer or winter. 2. the window made in Machu Picchu, In the ancient city of Machu Picchu in Peru, a narrow window carved in a rock 2 meters thick looks out on the sunrise only on December 21st each year. The window was thought to keep track of the seasons for farming, so that the people knew when to sow the seeds and keep track of the seasons. 3. Stonehenge Stonehenge of the British Isles shows the movement of where the Sun rises and sets, during important times throughout the year. It can be expected that this structure had a highly practical use, which was used to make life for the ancient inhabitants of the British Isles, easier.

If the stars Polaris and Arcturus are known to be 71 degrees apart, how far away from Polaris is the closest constellation in the Ursa Major?

25 degrees

If the unaided eye is sensitive enough to see about 600 stars in the entire sky, about how many stars would be seen in a given night from a single location from which the horizon is completely visible around the observer?

3000

In modern astronomy, the constellations are...

88 regions of the sky, covering the entire sky

The declination angle between the north celestial pole and the celestial equator is...

90 degrees

Why is a particular star overhead at 10:00pm on a given night rather than two hours later at midnight; how does this relate to Earth's orbit? Why are there different stars overhead at midnight on June 1st rather than at midnight on December 1st?

A particular star overhead at 10:00pm on a given night rather than two hours later at midnight relates to Earth's orbit because of Earth's diurnal motion. Diurnal motion is the daily motion of the sky. The constellations rise in the east and set in the west a few minutes earlier each day than they did on the previous night. If you look at the sky in the same spot after a month, the constellations are visibly different. After six months, you would see almost a complete new set of constellations. After a year passes, the sky will look the same as when it began. This happens because Earth rotates once a day around the axis from the North Pole to the South Pole while it revolves around the Sun once per year. That is also why there would be different stars overhead on June 1st and December 1st.

Which of the following was no obtained by people ancient civilizations form observations of the night sky? a. the relative distances of the Sun, Moon, and stars from Earth b. timing information, both daily and yearly c. patterns of stars in the sky about which myths and stories were devised d. directions for navigations

A. The relative distances of the Sun, Moon, and stars from Earth

How do the stars appear to move over the course of the night as seen from the north pole? As seen from the equator? Why are these two motions different?

As seen from the North Pole, over the course of the night the stars move in a parallel motion since all of the stars at this point are circumpolar. From the equator, they move across the sky in a semicircle overhead. Over the night, the stars travel along paths that are perpendicular (vertical) to the horizon. These two motions are different because of their different positions on the Earth, and the rotation of the celestial sphere due to it's rotation around the Earth. The tilt of the Earth and its movement contribute to this as well.

At what point on the horizon does the vernal equinox rise?Where on the horizon does it set?

During the vernal equinox, the Sun rises directly in the east and sets in the west. This is due to the intersection of the ecliptic and the celestial equator at one of the two precise equinoxes.

With respect to the stars, the rotation of the Earth carries you toward...

East

Which way are you moving with respect of the background stars because of the revolution of in its orbit around the sun?

Eastward

Which way are you moving with respect to the stars, during the rotation of the Earth?

Eastward

What statement correctly describes the relationship between stars and constellations?

Every star is located in a constellation

How many degrees is the angle from the horizon to the zenith? Does your answer depend on what point on the horizon you choose?

From the horizon to the zenith, there is a 90 degree angle. No, my answer does not depend on the point of the horizon that I choose. This is because your location on Earth is always 90 degrees, and your position underneath your zenith is always perpendicular.

Imagine that someone suggests sending spacecraft to land on the celestial sphere. How would you respond to such a suggestion?

I would say they should not do that because it is imaginary and there would be nothing for them to land on.

A fellow student tells you that in a picture of the constellation of Orion, the only stars in the constellation are those connected by the blue lines are a part of the constellation Orion. How would you respond?

I would tell the student that the definition of a constellation is broader in modern astronomy than it was in the past. The modern definition of astronomy is an irregular patch of sky with scattered stars. The stars in the picture of Orion that are not within the blue lines cannot be seen by the naked eye, but are still a part of the constellation. Any part of this grouping of stars lies within the Orion constellation.

Why can't a person in Antarctica use the Big Dipper to find the north direction?

If you are located on the south celestial pole, the stars around the pole but always remain below the horizon of an observer in the northern hemisphere. The Big Dipper is not circumpolar to Antarctica and cannot be seen in the southern hemisphere. The Big Dipper does not dip below the north horizon.

Is there any place on Earth where you could see the north celestial pole on the northern horizon? If so, where? Is there any place on Earth where you could see the north celestial pole on the western horizon? If so, where?

If you were standing on the equator, you would be able to see the north celestial pole on the north horizon. If you are anywhere on the north hemisphere, you can see the north celestial pole. However, if you are on the west celestial pole, the north it can never be seen because it always lies to the north. The same instance would occur if you were on the southern hemisphere, because the southern hemisphere lies below the north horizon.

Why is it convenient to divide the Earth into time zones?

It is convenient to divide Earth into time zones in areas of commerce, transportation and communication. In a time zone, all clocks and watches are set to the mean solar time for a meridian of longitude that runs through the center of the zone. Time zones around the world are generally centered on meridians of longitude at 15 degree intervals.

Give two reasons why it is warmer in the summer than in the winter.

It is warmer in the summer than it is in the winter of the extended daylight hours and because the sun is high in the hemisphere's sky. Because of this, the sunlight strikes the ground at a nearly perpendicular angle that heats the ground efficiently.

Which of the following points remains fixed in the sky relative to an observer's horizon?

North celestial pole

What are the vernal and autumnal equinoxes? What are the summer and winter solstices? How are these four points related to the ecliptic and the celestial equator?

On about March 21st every year when the Sun passes northward across the celestial equator the vernal equinox occurs marking the beginning of spring in the northern hemisphere. On about September 22nd, the sun moves southward across the celestial equator at the autumnal equinox, marking the moment when fall begins in the northern hemisphere. Both of these days have 12 hours of day and 12 hours of night all over the world. The sun moves on the ecliptic equator northward of the celestial equator during the vernal equinox, and southward of the celestial equator during the autumnal equinox. The point on the ecliptic farthest north of the celestial equator the summer solstice. When this occurs, the Sun is as far north of the celestial equator as it can get, and stops moving northward on the celestial equator. It occurs on about June 21st every year. On about December 21st every year, the Sun is farthest south of the celestial equator at the point of the winter solstice.

Describing as star as being in the constellation Cygnus (swan) tells a modern astronomer that the star is...

Somewhere in a particular region of the sky having definite boundaries

If a star is described as being the constellation Leo, a modern astronomer will know that it is...

Somewhere in a particular region of the sky having definite boundaries

How does the daily path of the Sun across the sky change with the seasons? Why does it change?

The daily path of the Sun across the sky changes with the seasons because the angle that the Sun's rays strike the Earth's surface change. In the summer, the suns ray sceom from directly overhead and higher in the sky. In the winter, the Sun's rays hit the ground from the Sun's lower position. This is caused by the tilt of the Earth and the Earth rotating around the Sun.

Why is the ecliptic plane tilted with respect to the celestial equator? Does the Sun appear to move along the ecliptic, the celestial equator, or neither? By about how many degrees the Sun appear to move on the celestial sphere each day?

The ecliptic plane is tilted with respect to the celestial equator and not the same as the Earth's equator. This is due to the 23 ½ degree tilt of Earth's rotation axis. As a result, the ecliptic and the celestial equator are inclined to each other by that same 23 ½ degree angle. The Sun appears to move along the ecliptic at a rate of about 1 degree per day with the motion of west to east, which is the opposite direction of the celestial sphere.

At which time of year will your shadow in sunlight at midday be shortest?

The first day of summer, about June 21st

What is the celestial equator? How is it related to Earth's equator? How are the north and south celestial poles related to Earth's axis of rotation?

The great circle on the celestial sphere 90 degrees from the celestial poles. It is related to Earth's equator because if we were to project the Earth's equator into space, we would see the celestial equator. The north and south celestial poles are related to Earth's axis of rotation because if were to project Earth's north and south poles into space, we would obtain the north celestial pole and the south celestial pole. Thus, the two celestial poles where Earth's axis of rotation intersects the celestial sphere.

What is the celestial sphere? Why is this ancient concept used today?

The imaginary sphere of very large radius centered in the observer; the apparent sphere of the sky It is still helpful because if you imagine that the Earth is stationary and the celestial sphere rotates around us, it is relatively easy to specify the directions to different objects in the sky and to visualize the motions of these objects.

What is the (fictitious) mean sun? What path does it follow on the celestial sphere? Why is it a better timekeeper than the actual Sun in the sky?

The mean sun is a fictitious object that moves eastward at a constant speed along the celestial equator, completing one circuit of the sky with respect to the vernal equinox in one tropical year. It is a better timekeeper than the actual sun in the sky because it moves at a constant rate.

What is the precession of the equinoxes? What causes it? How long does it take for the vernal equinox to move one degree along the ecliptic?

The precession of the equinoxes is the slow westward motion of the equinoxes along the ecliptic. It is caused by the precession of the Earth.

How are constellations useful to astronomers? How many stars are not a part of constellations?

They provide a convenient framework for stating the position of an object in the Heavens.This is useful because a good majority of the rest of the sky is constantly in motion, where these stars are always in the same place and can help to locate other objects in the sky. There are not any stars that are not apart of a constellation. This is because the modern constellations cover the entire sky, so every star can be found in a constellation. However, our Sun is an exception to this rule because it seems to move through different constellations in the daytime.

Where on Earth do you have to be in order to see the Sun at zenith? As seen from such a location, will the Sun be at the zenith every day?

To be at the Sun's zenith, you must be standing between the Tropic of Capricorn at 23 ½ degrees south latitude and the Tropic of Cancer at 23 ½ degrees. This happens hear at least once a day per year at high noon. Outside of the tropics, the Sun is never directly overhead is either south or north of the zenith locations.

Where on Earth do you have to be in order to see the north celestial pole directly overhead? What is the maximum point possible elevation of the Sun above the horizon at that last location? On what date can this maximum elevation be observed?

To see the north celestial pole directly overhead, it would have to be your zenith. This can only happen at the Earth's north pole, which is located at the north celestial pole. The maximum possible elevation above the sun at that location is 23 ½ degrees because of the tilt of the Earth's axis of rotation. This maximum elevation can be observed on the summer solstice in the northern hemisphere. This occurs when the sun stops moving northward on the celestial sphere.

Where would you have to look to see your zenith? Where on Earth would you have to be for the celestial equator to pass through your zenith? Where on Earth would you have to be for the south celestial pole to be at your zenith?

To see zenith, on Earth you would have to look directly overhead wherever you are standing. To see the celestial equator pass through your zenith, you would need to be 35 degrees north latitude, or 35 degrees north of the equator. For the south celestial pole to be at my zenith, I would have to be 35 degrees south of the equator.

If the daytime sky were not bright, in which direction would we see the Sun move along the ecliptic over the course of a year, relative to the background stars?

Toward the E

The constellation whose stars are pointers to the north celestial pole in the northern hemisphere is...

Ursa Major, the Big Dipper

During any given night, some stars will be observed to pass through the...

Zenith

Which of the following directions remains fixed in the sky, relative to an observer's horizon?

Zenith

Which of the following lines or points is always directly over your head, no matter where on the Earth that you go?

Zenith

The right ascension of a star is one coordinate of its position measured along the...

celestial equator

The declination of a star in our sky is defined as the angle between the...

celestial equator and the star, measured along a great circle passing through both celestial poles

What basic pattern do stars seem to trace out if you watch (or photograph) stars near the celestial pole for several hours a day?

circles, with the north celestial pole at the center

The apparent path of our sun across the sky day by day throughout the year is known as the...

ecliptic

How much of the overall sky is north of the celestial equator (the Northern hemisphere)?

exactly one half

The phrase "diurnal motion" refers to the...

graudual motion of the constellations from E to W across the sky each night resulting in different constellations being visible at 4am than 10pm on any given night.

If you point toward the Zenith today and point there again 45 days later, you will have pointed twice in the same direction relative to the...

horizon

The ecliptic is defined as the...

line traced in our sky by the Sun over one year against the background stars.

Two opposite sides of the Egyptian pyramid are aligned with what direction(s) on the horizon?

north-south

The declination of a star is a measure its

position north or south of the celestial equator along a great circle passing through the north and south celestial poles

The nightly motion of objects across our sky is caused by the...

revolution of earth on its own axis

The celestial coordinates that together describe a star's position precisely unambiguously are...

right ascension and declination

The two angles used by astronomers to define a particular position in the sky and define a coordinate system applicable everywhere on Earth are

right ascension and declination

The most easily observed motion in the sky is produced by the...

rotation of Earth on its axis.

Over the course of one night, the observer from any given location on the Earth sees the constellations gradually move E to W across the sky. This is caused by primarily by the...

rotation of the Earth around its own axis.

The most readily observed E to W motion of objects in the night sky is caused by the...

rotation of the Earth on its axis

When we watch the nighttime sky, we find that...

stars and constellations slowly rise in the east, pass overhead, and set in the west

What is the ecliptic plane? What is the ecliptic?

the apparent path of the Sun on the celestial sphere the path of the Earth's orbit around the sun

As the Earth rotates, the Zenith of a person standing on the equator sweeps out the...

the celestial equator.

The celestial equator is defined as the...

the line in the sky perpendicular to Earth's spin axis

A given star in the sky will reach its highest point to a particular observer in the northern hemisphere when it passes through...

the region of the sky due south.

Diurnal motion of objects in the sky is caused by...

the rotation of Earth on its axis.

The pattern of stars that is visible from one position on the Earth gradually shifts from E to W across the sky over one night. This is caused by the...

the rotation of the Earth on its own N-S axis.

The ecliptic crosses the celestial equator at the...

two points, known as equinoxes

Compared to its appearance to a person in mid-latitude northern-latitudes, how will the constellation Orion appear to an observer in Australia?

upside-down with the same orientation of stars

If you were standing on the equator, which of the following positions in the sky would pass through your Zenith at some time in the 24 hour period?

vernal equinox, or 0 hours right ascension, 0 degree declination

The Zenith defines a direction...

vertically above the equator