Chapter 2: Stars and the Moon (RQs)

how many total constellations are there

88

the celestial sphere

-An imaginary sphere surrounding Earth to which the stars and are attached -You can only see half of the celestial sphere from where you're standing because the ground blocks the other half. -Appears to move from east to west

Why do we have seasons?

-Earth's axis points in the same direction (to Polaris) all year round, so its orientation relative to the Sun changes as Earth orbits the Sun. -Summer occurs in your hemisphere when sunlight hits it more directly; winter occurs when the sunlight is less direct. -AXIS TILT is the key to the seasons; without it, we would not have seasons on Earth.

zodiac

-The stars and constellations that lie across the ecliptic -There are 12 constellations along the zodiac. -We see different parts of the zodiac at different times in the year b/c of the sun's location along the ecliptic.

how do galaxies move within the universe relative to us?

All galaxies beyond the Local Group are moving away from us with expansion of the universe: the more distant they are, the faster they're moving.

Why don't we see an eclipse at every new and full moon? Describe the conditions needed for a solar or lunar eclipse.

An eclipse occurs when the Sun, Earth, and Moon align when the Moon is a new or full moon. However, we do not see an eclipse at every new and full moon because the Moon's orbit is about 5 degrees inclined to the ecliptic plane. Therefore, the Moon is usually either above or below this plane. An eclipse occurs when the Moon crosses through this plane (at a position called a node) at the same time the Sun and Earth are at that position. Eclipses can only occur during the periods where the nodes lie along a nearly straight line with the Sun and Earth.

how are the star trails above the north and south pole different?

At the north pole, the stars circle Polaris, but in the south pole there is not a distinct star that they circle

What is precession? How does it affect what we see in our sky?

Precession is the gradual wobble that changes the orientation of Earth's axis, and each precession cycle takes about 26,000 years to complete. Precession changes the points in Earth's orbit where solstices and equinoxes occur, leading to changes in the constellations that we see at different times of the year across centuries.

Stars and constellations rise about 4 minutes _____ then they did the previous night. Therefore, if you compare the location in the night sky of a particular constellation tonight with its position one month ago, that constellation will appear farther _____ tonight than it did one month ago.

Stars and constellations rise about 4 minutes earlier than they did the previous night. Therefore, if you compare the location in the night sky of a particular constellation tonight with its position one month ago, that constellation will appear farther west tonight than it did one month ago.

Stars appear to rise in the _____ and set in the _____. When observing the sky from the northern hemisphere, the stars that spend the longest amount of time above the horizon are those in the _____ part of the sky, and the stars that spend the shortest amount of time above the horizon are those in the ______ part of the sky. CHECK THIS**

Stars appear to rise in the east and set in the west. (Just like the sun and moon). When observing the sky from the northern hemisphere, the stars that spend the longest amount of time above the horizon are those in the northern part of the sky, and the stars that spend the shortest amount of time above the horizon are those in the southern part of the sky.

Equinoxes (March ~21 and September ~22)

Sun rises precisely due east and sets precisely due west.

The Sun and stars appear to move ____ across the sky from ____ over the course of a day. This motion occurs because Earth ____ on its axis once per ____. CHECK THIS**

The Sun and stars appear to move together across the sky from east to west over the course of a day. This motion occurs because Earth rotation on its axis once per day.

The line that traces out the Sun's path through the sky over the course of one year is called the ____. Along this path, there are 12 ____. This path and this motion are consequences of Earth's ____.

The line that traces out the Sun's path through the sky over the course of one year is called the ecliptic. Along this path, there are 12 constellations. This path and this motion are consequences of Earth's revolution.

Briefly describe the Moon's cycle of phases. Can you ever see a full moon at noon? Explain.

The lunar phases of the Moon are completed in about 29.5 days, and the phases change as the Moon's position relative to the Sun changes. Half of the moon is always illuminated by the sun, but due to the Moon's position in its orbit, we are sometimes only able to see the fully illuminated part of the moon. You cannot see a full moon at noon because a full moon can only be seen at sunset, when the Moon is opposite the Sun. Although, you could see a first-quarter moon would rise around noon since that is when the Moon is 90 degrees east of the Sun.

celestial equator

The projection of the earth's equator onto the celestial sphere

What is stellar parallax? How did an inability to detect it support the ancient belief in an Earth-centered universe?

The stellar parallax is the concept where as we view stars from different places in our orbit around the Sun at different times of the year, the stars we see appear to move back and forth in the sky. The Greeks believed that all stars lie on the same celestial sphere, and that if the Earth were to orbit the Sun, we would see different parts of the celestial sphere and changes in the separation of the stars. They did not ever observe any shifts or changes, so they concluded the Earth was still the center of the universe.

Why do we always see the same face of the Moon?

We always see the same face of the Moon because of the Moon's synchronous rotation. The Moon rotates on its axis in the same amount of time it takes to orbit Earth. Therefore, when you see the moon you will always see it at the same moment during its rotation.

When the Sun is "in" a particular constellation, that constellation ___ visible at night. Six months later, that same constellation ____ be visible at night.

When the Sun is "in" a particular constellation, that constellation is not visible at night. Six months later, that same constellation will be visible at night.

When you are observing the sky from the Northern Hemisphere and facing to the north, stars appear to move in _____ circles around ______. Each star completes this circle around the sky in _____.

When you are observing the sky from the Northern Hemisphere and facing to the north, stars appear to move in counter-clockwise circles around North Star. (due to the rotation of the earth) Each star completes this circle around the sky in 24 hours.

constellation

a region of the sky with well-defined borders (just like states in the US)

meridian

an imaginary half-circle from the horizon due south, through the zenith, and to the horizon due north

why is Polaris the north star? CHECK**

because it is above our axis of rotation not because it is the brightest star

full circle, arcminute, arcsecond- what are these measurements

full circle- 360 degrees 1 degree is 60' (arcminutes) 1' (arcminute) is 60" (arcseconds)

summer solstice (june 21)

highest path; rise and set at most extreme north of due east longest day of the year, receives the most sunlight

winter solstice (dec. 21)

lowest path; rise and set at most extreme south of due east

the brightest stars in a constellation

may actually be quite far away from each other

If the earth's axis didn't tilt would we have seasons?

no because the amount of sunlight in every region of Earth would never change

sky dome/ local horizon

our view of the earth and sky to us

circumpolar stars

stars near the north celestial pole that never set, they are always above the horizon and always within our view

ecliptic

the Sun's apparent path through the celestial sphere -23.5 degrees angled from the celestial equator due to the tilt of earth

how does latitude affect how you see Polaris?

the altitude of Polaris depends on your latitude if Polaris is at a 90 degree altitude, you are standing at the north pole

Latitude

the fundamental characteristic that determines the night sky constellations that you see -longitude does not do anything -someone with a more similar latitude sees a more similar night sky to you (as long as its not daytime where they are)

horizon

the line that forms the boundary between earth and sky

if you see Polaris, what hemisphere are you in?

the northern hemisphere, you cannot see Polaris from the southern hemisphere.

north celestial pole

the point directly over Earth's North Pole

south celestial pole

the point directly over Earth's South Pole

zenith

the point directly over head from out point of view

which direction does the earth rotate

west to east (counterclockwise)

what would happen to days and years if the earth was further from the sun?

years would be longer, and days would be shorter

do galaxies appear to rise and set in the sky? CHECK THIS**

yes, just as all other objects in the sky do