Chapter 2: Patterns in the Sky - Motions of Earth and the Moon Flashcards
What is apparent daily motion?
the path each celestial body makes across the sky each day
How long is one Earth rotation with respect to stars? What is it referred to as?
23h56min = sidereal day
How long is one Earth rotation with respect to the sun? What is it referred to as?
24 hours = solar day
Earth rotates ____ and also orbits the Sun in this direction
counterclockwise
The Sun rises in the east and sets in the west.
Which way is Earth rotating?
Toward the east
What is the celestial sphere?
an imaginary sphere upon which all stars remain fixed
What are celestial poles?
projection of North and South poles of Earth onto Celestial Sphere
What is the celestial equator?
midway between the two poles.
What is the ecliptic?
apparent path of the Sun, over the course of a year, inclined 23.5 degrees to Celestial Equator
What is the zenith?
the point in the sky directly above you wherever you are
What is the meridian?
imaginary north-south line
At the North Pole, we would see half of the celestial sphere (all stars ___ of celestial equator). The north celestial pole would be at the ___, the point directly overhead.
north, zenith
What is altitude?
angle above the horizon
What is latitude?
measures how far north or south of the equator you are on the surface of Earth
At the North Pole, stars are always above horizon. These stars are called ____ stars and they never rise or set.
circumpolar
What is the only place on Earth where you can see the entire sky over the course of 24 hours?
the equator
What would the sky look like from a latitude
of 35 degrees N (Flagstaff)?
Some stars would be circumpolar; some would never be visible.
From your position in Flagstaff, you look north and see a star near the horizon. A little later you notice it has shifted its position slightly. Which way did it move?
right (east)
A star on the celestial equator rises due ___ and sets due ___
east, west
Stars located north of the celestial equator rise north of __ and set north of ___. Stars located south of the celestial equator rise ___ of east and set south of ___.
Stars located north of the celestial equator rise north of east and set north of west. Stars located south of the celestial equator rise south of east and set south of west.
An observer can see exactly half of the northern sky and exactly half of the southern sky. Where would the north celestial pole be located?
On the horizon
At the North Pole, stars revolve around what?
the zenith
In the Northern hemisphere, stars rise in the east, set in the west, and revolve counterclockwise around the north celestial pole. In the Southern hemisphere, stars
Rise in the east, set in the west, and revolve clockwise around the south celestial pole.
What is the average distance to the Sun?
-astronomical unit (AU)
1 AU = 150 million km = 8.3 light-min
Six months from now, Earth will be on the other side of the Sun. The stars are overhead at midnight 6 months from now are those that are overhead at ___ today.
noon
The zodiac lies along the _____.
ecliptic
Earth’s axis is tilted at an angle of ___ with respect to the ecliptic plane.
23.5°
What causes the seasons?
Tilt
Describe what happens on the summer solstice and when does it occur?
- Sun is at its highest point above the celestial equator (June 21 - Longest day)
- the sun rises farthest north of east and sets farthest north of west
Describe what happens on the autumnal equinox and when does it occur?
-Sun on the celestial equator (September 22 - Equal hours of day and night)
Describe what happens on the winter solstice and when does it occur?
- Sun is at its lowest point below the celestial equator (December 21 - Shortest day)
- North pole is tilted away from the Sun
Describe what happens on the vernal equinox and when does it occur?
-Sun on the celestial equator (March 20 - Equal hours of day and night)
If the ecliptic were aligned with the celestial equator, what would happen to the seasons?
no seasons
Earth’s axial tilt changes orientation over a period of 26,000 years due to ____.
precession
The location of the poles slowly shifts like a spinning top. Currently the north celestial pole is near what star?.
Polaris
Why do we always see the same face of the moon?
Synchronous rotation: the Moon completes one full rotation in one full revolution around Earth.
What are the 8 phases of the moon?
new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, third quarter, waning crescent
Describe the new moon phase:
Moon between Earth and the Sun.
Describe the crescent phase of the moon:
Less than half of the Moon is lit up from the Earth’s point of view.
Describe the quarter phase of the moon:
Moon at right angles with Earth and the Sun.
Describe the gibbous phase of the moon:
More than half of the Moon is lit up from Earth’s point of view.
Describe the full moon phase:
Moon on opposite side of Earth from the Sun.
Solar eclipses happen at what moon phase?
new moon
When does an eclipse occur?
when the shadow of one astronomical body falls on another
When does a solar eclipse occur?
when the moon passes between the earth and the sun
When does a total solar eclipse occur?
the Moon completely blocks the Sun, it lasts for a few minutes; sky grows dark; brighter stars are visible
When does a partial solar eclipse occur?
only part of Sun is blocked
When does an annular solar eclipse occur?
the Sun appears as a bright ring surrounding the Moon, it occurs due to Moon’s changing distance from Earth
At what phase of the Moon is a lunar eclipse possible?
full moon
When does a total lunar eclipse occur?
- Moon is completely in umbral shadow
- Lasts for a few hours
- Red due to refraction of sunlight through atmosphere
When does a partial lunar eclipse occur?
part of Moon is in umbral shadow
When does a penumbral lunar eclipse occur?
- Moon is in penumbral shadow
- Seen as a dimming rather than a shadow
How often do we have eclipses?
every 6 months
