Lec 3

Question 1

constellation

Answer 1

a region of the sky with well-defined borders

-the patterns of stars help us locate constellations

Question 2

north celestial pole

Answer 2

point directly over Earth’s North Pole

Question 3

south celestial pole

Answer 3

point directly over earth’s south pole

Question 4

celestial equator

Answer 4

projection of earths equator into space, makes a complete circle around celestial sphere

Question 5

ecliptic

Answer 5

the path that the Sun follows as it appears to circle around the celestial sphere once each year

-crosses the celestial equator at 23.5 deg (tilt of earth’s axis)

Question 6

local sky

Answer 6

the sky as seen from where you are standing, appears to take the shape of a hemisphere or dome

(explains why ppl of ancient cultures imagined we live on a flat earth)

Question 7

horizon

Answer 7

boundary between Earth and sky

Question 8

zenith

Answer 8

point directly overhead

Question 9

meridian

Answer 9

imaginary half circle stretching from the horizon due south, thru zenith, to the horizon due north

Question 10

azimuth

Answer 10

direction

-helps to pinpoint the position of any object in the local sky by stating its direction along the horizon, which’s degrees cw from due north and its ALTITUDE above horizon

Question 11

angular size

Answer 11

the angle an object appears to span in your field of view

e.g. moon and sun are 0.5deg

-also depends on distance

Question 12

angular distance

Answer 12

b/w a pair of objects in the sky is the angle that appears to separate them

Question 13

circumpolar

Answer 13

when stars near the north celestial pole remain perpetually above the horizon, circling (ccw) around the north celestial pole each day

when a stars daily circle is entirely above your horizon

Question 14

stars near the south celestial pole…

Answer 14

never rise above the horizon at all

Question 15

latitude

Answer 15

measure north-south position

0 deg at the equator, increases to 90degN at North pole and 90degS at south pole

affects the constellations we see because it affects the locations of the horizon and zenith relative to celestial sphere

Question 16

longitude

Answer 16

measures east-west position

-passes through prime meridian

Question 17

the altitude of the celestial pole in your sky is equal to..

Answer 17

your latitude

Question 18

zodiac

Answer 18

made up by constellations along the ecliptic

Question 19

what determines how we can see constellations at night?

Answer 19

the sun’s apparent location

Question 20

what causes seasons?

Answer 20

the tilt of Earth’s axis causes sunlight to fall differently on
Earth at different times of year

Step 1
–tilt of Earth’s axis, which remains pointed in same direction in space (toward Polaris) throughout yr

–as a result, the orientation of the axis relative to the Sun
changes over the course of each orbit: The Northern Hemisphere is tipped toward the Sun in June and away from the Sun in December, while the reverse is true for the Southern Hemisphere.

That is why the two hemispheres experience opposite seasons

the changing angle
of sunlight on the two hemispheres leads directly to seasons

Question 21

how does the tilt of the sunlight affect the seasons?

Answer 21

the axis tilt causes sunlight to strike the Northern Hemisphere at a steeper
angle and the Southern Hemisphere at a shallower angle

the steeper sunlight angle makes it summer in the N hemisphere for 2 reasons

1) steeper angle means more concentrated sunlight, which tends to make it warmer

2) as Earth rotates each day, you’ll see that the steeper angle also means the Sun follows a longer and higher path through the sky, giving the Northern Hemisphere more hours of daylight during which it is warmed by the Sun

Question 22

how does the angle tilt of the sun cause winter?

Answer 22

The shallower sunlight angle makes it winter there because sunlight is less concentrated and the Sun follows a shorter, lower path through the sky

Question 23

june solstice

Answer 23

called the summer solstice in the Northern Hemisphere, occurs around June 21 and is the moment when the Northern Hemisphere is tipped most directly
toward the Sun and receives the most direct sunlight

Question 24

december solstice

Answer 24

called the winter solstice in the Northern Hemisphere, occurs around December 21 and is the moment when the Northern Hemisphere receives the least direct sunlight

Question 25

march equinox

Answer 25

called the spring (or vernal) equinox in the Northern Hemisphere, occurs around March 21 and is the moment when the Northern Hemisphere goes from being tipped slightly away from the Sun to being tipped slightly toward the Sun

Question 26

september equinox

Answer 26

called the fall (or autumnal) equinox in the Northern Hemisphere, occurs around September 22 and is the moment when the Northern Hemisphere first starts to be tipped away from the Sun

Question 27

equinox

Answer 27

-occur on the only 2 days of the yr on which the sun rises due east and sets west -also the only 2 days when the sun is above and below the horizon for equal times of 12 hrs equinox = equal night

Question 28

solstice

Answer 28

June solstice -occurs on day on which the Sun follows its longest and highest path through N Hemisphere sky (and its shortest and lowest path through the Southern Hemisphere sky). -the day on which the Sun rises and sets farthest to the north of due east and due west; it is also the day on which the Northern Hemisphere has its longest hours of daylight and the Sun rises highest in the midday sky The opposite is true on the day of the December solstice, when the Sun rises and sets farthest to the south and the Northern Hemisphere has its shortest hours of daylight and lowest midday Sun

Question 29

why is the solstice considered the beginning rather than the midpoint of summer?

Answer 29

1) it was much easier for ancient people to identify the days on which the Sun reached extreme positions in the sky—such as when it reached its highest point on the summer solstice—than other days in between. 2) we usually think of the seasons in terms of weather, and the warmest summer weather tends to come 1 to 2 months after the solstice

Question 30

how does the orientation of Earth's axis change with time?

Answer 30

The reason is precession, a gradual wobble that alters the orientation of Earth’s axis in space -precession occurs with many rotating objects Earth’s axis precesses (spins) in much the same way, but far more slowly -each cycle of Earth’s precession takes about 26,000 years -this gradually changes the direction in which the axis points in space -changes the points in Earth’s orbit at which the solstices and equinoxes occur, and therefore changes the constellations that we see --(does NOT affect pattern of seasons)

Question 31

tropic of cancer

Answer 31

The latitude at which the Sun is directly overhead on the June solstice 23.5°N is called the Tropic of Cancer, telling us that it was named back when the Sun appeared in Cancer on this solstice

Question 32

what is precession caused by?

Answer 32

Precession is caused by gravity’s effect on a tilted, rotating object if you spin the top rapidly, it does not fall over so easily -the spinning top stays upright because rotating objects tend to keep spinning around the same rotation axis (a consequence of the law of conservation of angular momentum -this tendency prevents gravity from immediately pulling the spinning top over, since falling over would mean a change in the spin axis from near-vertical to horizontal Instead, gravity succeeds only in making the axis trace circles of precession

Question 33

tenet of astrology

Answer 33

the apparent positions of the sun, moon and planets among the stars in our sky influence human events - position of the Sun in the sky certainly influences our lives, since it determines the seasons and the times of daylight and darkness, and the Moon’s position determines the tides

Question 34

astrology vs astronomy

Answer 34

Astronomy is a modern science that has taught us much about the universe Astrology is a search for hidden influences on human lives based on the apparent positions of planets and stars in the sky; it does not exhibit the hallmarks of science

Question 35

does astrology have any scientific validity?

Answer 35

Scientific tests have shown that astrological predictions do not prove to be accurate more than we can expect by pure chance, showing that the predictions have no scientific validity

Question 36

Summer

Answer 36

Daylight is longer and darkness is shorter Sun gets “higher” in the sky

Question 37

winter

Answer 37

Daylight is shorter and darkness is longer Sun does not get as “high” in the sky

Question 38

constellations

Answer 38

Western: patterns in the stars and originated in ancient Greece Chinese: different patterns that were defined independently from Western Babylonian: ancient patterns

Question 39

northern SUMMER/southern WINTER

Answer 39

in June, sunlight falls more directly on the Northern hemisphere, which makes it more summer there because solar energy is MORE concentrated and the sun follows a longer and higher path through the sky = june SOLSTICE the southern hemisphere receives LESS direct sunlight, making it winter

Question 40

spring/fall

Answer 40

spring and fall begin when sunlight falls EQUALLY on both hemispheres, which happens twice a yr in March, when spring begins in the northern hemisphere and fall in the southern hemisphere; and in september, when fall begins in the northern hemisphere and spring in the southern hemisphere EQUINOXES

Question 41

northern WINTER/southern SUMMER

Answer 41

in december, sunlight falls LESS directly on the northern hemisphere, which makes it winter because solar energy is LESS concentrated and the sun follows a SHORTER and lower path thru the sky = december SOLSTICE southern hemisphere receives more direct sunlight, making it summer

Question 42

celestial sphere

Answer 42

Celestial Sphere: An imaginary sphere around Earth on which stars appear to lie. Useful for mapping positions in the sky.

Question 43

angles

Answer 43

1 degree = 60 arcminutes = 3600 arcseconds Angular Size Formula: (angular size= physical size/ (2pi x distance)) x 360deg

Question 44

daily motion

Answer 44

Daily Motion (1 Day): Earth rotates once every 24 hours on its axis, spinning from west to east. This rotation makes the Sun, Moon, and stars appear to rise in the east and set in the west. The sky appears to rotate around Polaris, the North Star, in the Northern Hemisphere. Stars move in circular paths around the celestial poles, with some being circumpolar (never setting).

Question 45

annual motion

Answer 45

Annual Motion (1 Year): Earth orbits the Sun once per year along a flat path called the ecliptic plane. As Earth moves, the Sun appears to shift eastward through the background stars and constellations along the zodiac. This changing position causes different constellations to be visible at night during different times of the year. Axis tilt (23.5°) causes the seasons, as the Northern and Southern Hemispheres receive different amounts of sunlight throughout the year.

Question 46

ecliptic plane

Answer 46

Ecliptic Plane: The flat plane of Earth’s orbit around the Sun; the Sun appears to follow this path through the sky over the year.

Question 47

axis tilt

Answer 47

Axis Tilt: Earth’s axis is tilted 23.5° from perpendicular to the ecliptic plane, causing seasonal changes in sunlight.

Question 48

Explain why we can see different fractions of the celestial sphere from different locations on Earth

Answer 48

Depends on our latitude, because the horizon and zenith (the point directly overhead) shift relative to the celestial sphere as you move north or south on Earth At the North Pole, only the northern half of the celestial sphere is visible, and all visible stars are circumpolar (they never rise or set) At the equator, you can see both hemispheres of the celestial sphere throughout the year, with the celestial equator passing directly overhead. At mid-latitudes, you see a combination of circumpolar stars and stars that rise and set. Your longitude does not affect which stars you see—only your latitude does

Question 49

how does the celestial sphere affect telescope placement

Answer 49

Because different latitudes give access to different parts of the sky, astronomers place research telescopes in specific locations based on what parts of the celestial sphere they need to observe: Telescopes in the Southern Hemisphere (e.g. Chile or Australia) are essential for studying southern sky objects like the Magellanic Clouds. Equatorial sites are ideal for observing stars from both hemispheres, making them useful for comprehensive sky surveys. Observatories are also placed at high altitudes and in dry, dark locations to reduce atmospheric distortion and light pollution. So, Earth’s curvature and tilt mean that latitude determines your sky view, and telescope locations are chosen to maximize visibility of the desired celestial targets.

Question 50

Describe the cause of seasons

Answer 50

What Causes the Seasons? The seasons are caused by the tilt of Earth’s axis (about 23.5°) as it orbits the Sun—not by changes in Earth’s distance from the Sun Throughout the year, Earth’s axis remains pointed in the same direction in space (toward Polaris), so as Earth moves around the Sun: In June, the Northern Hemisphere is tilted toward the Sun. Sunlight hits it at a steeper angle, making it warmer with longer days—summer in the north and winter in the south. In December, the Northern Hemisphere is tilted away from the Sun. Sunlight is less direct and days are shorter—winter in the north and summer in the south. During the equinoxes (March and September), both hemispheres receive equal sunlight, marking spring or fall, depending on the direction of tilt change

Question 51

What If a Planet Had a Different Axis Tilt?

Answer 51

The greater the axis tilt, the more extreme the seasons: A planet with no tilt (0°) would have no seasons—each location would receive the same sunlight all year. A planet with a larger tilt (e.g., 45° or more) would experience more extreme seasonal changes—hotter summers and colder winters—because the Sun would be much higher in the sky during summer and much lower in winter. So, axial tilt directly controls how much sunlight each hemisphere gets during the year, shaping the intensity and timing of seasonal change

Question 52

Understand the difference between astronomy and astrology

Answer 52

Astronomy is a science It is the study of the universe and the objects within it—such as stars, planets, and galaxies—using observation, experimentation, and mathematical modeling Astronomy is based on empirical evidence and the scientific method. Astrology, in contrast, is a belief system It originated thousands of years ago and is based on the idea that the positions of celestial bodies (like the Sun, Moon, and planets) at the time of your birth influence your personality and future However, this is not supported by scientific evidence Astrological “Sun signs” were determined using star positions from nearly 2,000 years ago Because Earth’s axis slowly changes direction (a motion called precession), those positions have since shifted As a result, most people’s actual Sun sign today does not match the one listed in astrology charts In short: astronomy is a science, while astrology is a pseudoscience based on outdated celestial positions and lacks empirical support