Ch01 Lecture part2 video
Summary
TLDRThis astronomy lecture explores the concept of Earth's axial tilt and its impact on the seasons. Contrary to common misconceptions, seasons are not due to Earth's proximity to the Sun but rather its 23.5-degree tilt. The tilt results in varying sunlight distribution, causing summer in the Northern Hemisphere when it's tilted towards the Sun and winter when tilted away. Equinoxes, with equal day and night, occur when Earth is perpendicular to the Sun, while solstices mark the extremes of tilt, resulting in the longest and shortest days. The celestial equator and ecliptic, the Sun's apparent path in the sky, further explain seasonal variations and the Sun's position relative to Earth's equator.
Takeaways
- đ The Earth orbits the Sun in an almost perfect circle, which affects what we see in the night sky as the Earth's position changes.
- đ Seasons are not due to the Earth being closer to or farther from the Sun, but rather because of the Earth's axial tilt relative to its orbit.
- đ The axial tilt of the Earth is 23.5 degrees, which causes different hemispheres to receive varying amounts of sunlight throughout the year.
- âïž In the Northern Hemisphere winter, the Earth's axis is tilted away from the Sun, resulting in less direct sunlight and colder temperatures.
- âïž Conversely, during the Northern Hemisphere summer, the Earth is tilted towards the Sun, receiving more direct sunlight and experiencing warmer weather.
- đĄïž The tropics, located between 23.5 degrees north and south of the equator, can have the Sun directly overhead due to the Earth's axial tilt.
- đ The Earth's equator is the center of the sphere, and the ecliptic is the path the Sun appears to take across the sky, which is tilted relative to the equator.
- đ The position of the Sun at sunrise and sunset changes throughout the year, indicating the Earth's tilt and its position in its orbit.
- đ Equinoxes occur when the Earth is perpendicular to the Sun, resulting in equal day and night lengths for both hemispheres.
- đ Solstices happen when the Earth's tilt is at its maximum towards or away from the Sun, leading to the longest and shortest days of the year.
- đ The celestial equator is the projection of the Earth's equator into space, while the ecliptic is the path of the Earth's orbit around the Sun.
Q & A
What is the primary reason for the change of seasons as explained in the script?
-The primary reason for the change of seasons is the axial tilt of the Earth relative to its orbit around the Sun, not because the Earth is closer to or farther from the Sun.
What is the significance of the Earth's axial tilt in relation to the Sun?
-The Earth's axial tilt of 23.5 degrees causes different hemispheres to receive varying amounts of direct sunlight at different times of the year, leading to the seasons.
Why is it not summer all year round on Earth?
-It is not summer all year round because the Earth's axial tilt changes its orientation towards the Sun throughout the year, causing variations in the amount of direct sunlight received by each hemisphere.
What happens during the equinoxes in terms of sunlight distribution?
-During the equinoxes, both the northern and southern hemispheres receive equal amounts of sunlight, resulting in approximately equal day and night lengths.
What is the term used to describe the position of the Earth when it is tilted neither towards nor away from the Sun?
-This position is known as an equinox, which results in equal day and night lengths for both hemispheres.
What causes the Sun to appear higher or lower in the sky throughout the year?
-The Earth's axial tilt and its position in the orbit around the Sun cause the Sun to appear higher in the sky during summer (more direct sunlight) and lower during winter (less direct sunlight).
What is the term for the time of year when the Earth is tilted most towards or away from the Sun?
-This time of year is called a solstice, during which one hemisphere experiences the most direct sunlight (summer solstice) and the other experiences the least (winter solstice).
Why don't we see the same seasons on the equator as we do in other parts of the Earth?
-The equator does not experience significant seasonal changes because the Sun is always relatively close to being directly overhead, resulting in a more consistent climate throughout the year.
How does the Earth's position in its orbit and its axial tilt affect the Sun's position in the sky?
-The Earth's position in its orbit combined with its axial tilt determines the Sun's position in the sky, causing it to rise and set in different directions throughout the year.
What is the ecliptic and how does it relate to the Sun's path in the sky?
-The ecliptic is the path the Sun appears to follow in the sky over the course of a year. It is defined by the Earth's orbit around the Sun and is tilted relative to the celestial equator due to the Earth's axial tilt.
Outlines
đ Earth's Orbit and Seasons
This paragraph explains the concept of Earth's orbit around the Sun and the resulting seasonal changes. Contrary to a common misconception, seasons are not due to Earth's proximity to the Sun but rather its axial tilt of 23.5 degrees. When the Earth's axis is tilted towards the Sun, it's summer in the respective hemisphere, and winter when it's tilted away. The tropics experience direct sunlight due to their location relative to the equator, leading to less pronounced seasons. The axial tilt causes variations in the angle at which sunlight hits the Earth, affecting the amount of energy received and thus the temperature.
đ Sunlight and Seasonal Variations
The second paragraph delves into how the directness of sunlight influences the seasons. It describes how the Earth's axial tilt affects the distribution of sunlight across the hemispheres. During summer in the northern hemisphere, the direct light is concentrated, leading to warmer temperatures, while in winter, the same light is spread over a larger area, resulting in less heat per unit area. The equator consistently receives direct sunlight, avoiding pronounced seasonal changes. The paragraph also introduces the concepts of the eclipticâthe path of the Sun in the skyâas being related to the tilt of Earth's rotational axis, which is key to understanding the seasonal variations.
đĄ Equinoxes and Solstices Explained
This paragraph clarifies the astronomical events of equinoxes and solstices, which are directly related to the Earth's axial tilt. An equinox occurs when the Earth is positioned such that it is perpendicular to the Sun, resulting in equal day and night lengths across the globe. Conversely, solstices occur when the Earth's tilt is maximized towards or away from the Sun, leading to the longest and shortest days of the year, respectively. The paragraph also encourages observing the Sun's position at sunset to discern the season, with the Sun setting directly west during equinoxes and deviating north or south of west depending on the season.
đ Geographical Impact on Sun's Position
The final paragraph discusses how the Earth's position in its orbit, combined with its axial tilt, affects the Sun's position in the sky relative to an observer's location on Earth. It explains that the Sun's path, or ecliptic, is always overhead at the equator but shifts north or south of the zenith as one moves away from the equator. The paragraph emphasizes that the Sun's position in the sky changes throughout the year due to Earth's orbit and tilt, and these changes are consistent at different latitudes across the globe, such as in Tokyo and the Bay Area, despite the time difference.
Mindmap
Keywords
đĄAxial Tilt
đĄOrbit
đĄSeasons
đĄEquinox
đĄSolstice
đĄEcliptic
đĄCelestial Equator
đĄDirect Sunlight
đĄTropics
đĄNorthern Hemisphere
đĄSouthern Hemisphere
Highlights
Introduction to the second part of the first astronomy lecture.
Explanation of Earth's orbit around the Sun and its effect on the night sky.
Clarification that the Earth's proximity to the Sun is not the cause of seasons.
Introduction of Earth's axial tilt as the primary reason for seasonal changes.
Description of the Earth's axis orientation during different seasons.
Explanation of the Northern Hemisphere winter due to the Earth's axis pointing away from the Sun.
Details on the axial tilt of 23.5 degrees and its significance in seasonal variations.
Differentiation between the tropics, where the Sun can be directly overhead, and other regions.
Explanation of how the Earth's axial tilt affects the distribution and intensity of sunlight.
Discussion on the equatorial region's lack of distinct seasons due to consistent sunlight.
Introduction of the ecliptic as the path of the Sun in the sky and its relation to seasons.
Clarification of the difference between the celestial equator and the ecliptic.
Description of equinoxes as times of equal day and night due to the Earth's axis being perpendicular to the Sun.
Explanation of solstices as points in Earth's orbit where the tilt is maximized towards or away from the Sun.
Observational tips for determining the season based on the Sun's position during sunset.
Discussion on the impact of Earth's tilt on the Sun's position in the sky relative to an observer's location.
Connection between latitude and the Sun's position in the sky, affecting the observer's experience of seasons.
Conclusion of the lecture with a teaser for the third part.
Transcripts
hello everyone welcome to part two of
our first lecture of astronomy now last
time in part one we talked about how the
earth goes around the Sun and so we have
and the Sun and the earth orbits around
that Sun and that's why we see different
things in the sky at night right because
and sometimes at night we're looking in
this direction sometimes at night we're
looking in that direction now the fact
that the earth goes around the Sun has
other effects that we actually observe
every year one of those effects is the
seasons now the way I've drawn this here
is not very good okay the Sun and the
earth goes around the Sun this drawing
should be almost a perfect circle now
it's not quite a perfect circle we're
gonna talk about that in upcoming
lectures but it's almost a perfect
circle so the reason why we have seasons
well a lot of people will tell you the
reason why it's sour is because the
earth is closer to the Sun so you know
we have the Sun and the earth going
around the Sun some people will tell you
well it's summer because we are closer
to the Sun that is not the case it is
not the case that it's not why it is
summer okay
why is summer has to do with the fact
that the Earth's axis is tilted relative
to its orbit around the Sun which means
that at certain times of the year in
certain times of the year the earth is
actually tilted towards the Sun and
other times the year
from our point of view here in the earth
were tilted away from the Sun that is
the season so what causes seasons well
alright if you look at the earth as it
is right here this would be our in the
northern hemisphere if you're in the
northern hemisphere this would be winter
why well if you look at where the earth
is relative to the Sun and this by the
way is not to scale not to scale at all
the earth is much much smaller than us
honest but if you look at the Earth's
axis okay we spin around this axis and
right now where you see the earth
relative to the Sun the Earth's axis is
tilted such that it points away from the
Sun this would be Northern Hemisphere
winter because sunlight coming from the
Sun okay is going to hit the southern
hemisphere this part of the earth the
southern hemisphere more directly than
the northern hemisphere and when the
southern hemisphere gets more direct
sunlight well it gets more energy
because light is energy and you get more
energy more light in the southern
hemisphere well it's it's summer they're
in the northern hemisphere we're getting
less energy from the Sun it's gonna be
winter and the tilt is 23 and a half
degrees and so 23 and a half degrees the
Sun is going to be 23 and a half degrees
off from being directly overhead if
you're in the northern miss fear or the
southern hemisphere now if you're
actually in what we call the tropics
which is 23 and a half degrees twenty
three and a half degrees above and below
the equator is
at the tropics this little region on the
earth right in the middle of the earth
right there the Sun can be directly
overhead but only if you're in that
region that is twenty three and a half
degrees above and below where the
Equator is that's the tilt of the earth
okay but so that's why we have seasons
it's the axial tilt it's the axial tilt
of the earth so here the tilt is towards
the Sun and in the northern hemisphere
you're gonna have summer the southern
hemisphere tilted away from the Sun
you're gonna have winter whereas over
here in December the northern hemisphere
tilts it away from the Sun the northern
hemisphere winter you're getting less
direct sunlight southern hemisphere
you're gonna have summer you're getting
direct sunlight or more direct sunlight
from the Sun now technically speaking it
only on the equator you get actually
direct sunlight which again in the
equator you don't really have seasons on
the equator it's always warm okay so
it's the axial tilt is why we have
seasons right now another way to look at
this or think about this is how direct
the sunlight gets to us so if you
imagine the Sun is over here okay if the
earth is tilted this way relative to the
Sun so the Earth's orbit going around
the Sun the earth is tilted relative to
that orbit well if you're in the
northern hemisphere this would be like
June direct light it's you and that
direct light is spread out over this
area the southern hemisphere that same
light
cuz the southern hemisphere is tilted
away from the Sun and same light is
spread out over a much larger area so
the same amount of light is spread out
over a larger area which means that each
individual spot is getting less light
the southern hemisphere this would be
winter the northern hemisphere we're
getting all that light concentrated in a
small spot and that's it's summer it's
why it's summer we're getting a more
direct light from the Sun and that's it
it's Oh the reason why we have seasons a
it has to do with the ecliptic ok the
tilt the tilt of the Earth's rotational
axis relative to the eclectic ecliptic
that's why we have seasons and if you're
in the northern miss fear it has to do
with how high the Sun is above the
celestial equator Sun in the summer
sun's high up in the sky well high up in
the sky means we're getting more direct
sunlight if it's a really low in the sky
we're getting less direct sunlight you
can see this day a day right if you know
in the morning the very when the Sun
just first rises it's very low on the
horizon right it's right near the
horizon it's just rising well the Sun is
not nearly it doesn't feel as warm right
then as it does at noon when the Sun is
as high as it gets in the sky right and
at sunset the Sun seems less warm than
it does when the Sun is in the middle of
the sky well this is seasons
hey this is seasons if the Sun gets
higher in the sky and summer that means
we're getting more direct light we are
tilted towards the Sun in the winter and
the sun's not nearly as high in the sky
we're getting less direct light we're
getting less energy and it's cold
okay the tilt the the earth this is what
we call the ecliptic now the ecliptic is
the path of the Sun in the sky so it's a
path the Sun seems to go through our sky
go out during the day look at the Sun
that's the ecliptic period now the
earth's equator the center or if you
imagine the earth as a sphere and the
equator is the center of that sphere
well the earth is actually tilted so if
you imagine a line that goes up and down
well the Sun we orbit around the Sun we
are tilted relative to that so is
actually 23 and 1/2 degrees tilted
that's why we have seasons that is why
we have a different ecliptic than an
equator the celestial equator is just
the earth's equator projected out into
space the ecliptic is the earth Earth's
orbit around the Sun so if you imagine
the Sun earth goes around the Sun a
spherically and the Earth's orbit around
the Sun that is the ecliptic and it's
tilted 23 and 1/2 degrees relative to
the earth's equator now there will be
points when the earth is going around
the Sun so you know the Sun you have the
earth going around the Sun and the earth
again is tilted relative to the Sun now
there will be times in summer
ok the earth is say here and we are
tilted towards the Sun so that's our
summer however what if the earth is here
and we are tilted still like this the
tilt is always the same direction
so the tilt is there well we're not
pointed towards or away from the Sun
right we are perpendicular to the Sun
not towards or away that is known as an
equinox on an equinox you have equal
days and nights both hemispheres of the
earth are getting equal amounts of
sunlight so northern hemisphere and
southern hemisphere are getting equal
amounts of sunlight that's why it's
called an equinox however if you are
here or here well the earth is either
tilted as much as it ever is towards the
Sun or tilt it as much as it ever is
away from the Sun those are called
solstices and in the northern hemisphere
let's say the northern miss fear is
tilted towards the Sun here so this
would be the North hemisphere sorry well
that is as much direct sunlight as this
the earth is going to get in the
northern hemisphere ever that is the
Solstice when we're directly torque
pointed towards the Sun is a solstice
war if the earth is here or directly
pointed away from the Sun that's also a
sources so we either get the most amount
of direct sunlight or the least amount
of direct sunlight during the year now
again the Earth's axis is always pointed
in the same direction so when the earth
is here there's access is pointed in
this direction up and down and that
would be another equinox we're not
pointed towards or away from the Sun now
from our point of view what it's going
to look like is the Sun is going to rise
and set in different directions
if you are looking encourage you to do
this go outside at night or in the early
evening and watch where the Sun sets now
if the Sun is setting
exactly west exactly west well that
means it's an equinox if it's setting a
little bit north of West well that means
we are in the summer seasons if it's
setting south of West we are in the
winter seasons if you are in the
northern hemisphere if you're in the
southern hemisphere it's the opposite
and again this is from our point of view
the Earth's point of view of where the
Sun is rising and setting and it all has
to do with the fact that the earth is
tilted relative to its orbit around the
Sun so we spin on an axis and that axis
is tilted relative to the Sun that's why
we have seasons that's it and again you
can observe this so you go outside you
know at night watch the sunset watch it
day after day after day and you will see
its position when it sets it's gonna
change day after day after day it's
gonna get more and more if this
direction is north it's gonna get more
and more north during the summer and the
winter it's gonna get more and more
south and on the equinoxes it's gonna
set exactly west all right now
it is also the case that where the Sun
is in the sky depends on where you are
on the earth that should make sense
right if you're on the side of this
earth that's facing away from the Sun
it's gonna be night if you're on the
side of the earth face in the Sun it's
gonna be day but because of the Earth's
orbit around the Sun where the Sun is in
the sky also depends on where you are in
the earth so if you're in the Omni
equator the Sun is gonna be pretty much
directly overhead if you're on the
equator the sun's would be directly
overhead but if you're north of the
equator or southeast equator the Sun is
gonna be either north or south of that
directly overhead and so you're gonna
see different paths and the Sun in the
sky but the Sun is always on the
ecliptic always on the ecliptic that is
kind of by definition the ecliptic again
is the Earth's orbit around the Sun and
from our point of view because we're on
the earth the ecliptic is always where
the Sun is how far how high it is above
the horizon is gonna depend on where we
are on the earth and what time of year
it is if you are in the Bay Area in
California
well what you're gonna see above you
that latitude that latitude on the earth
if you imagine the earth ok the equator
is latitude 0 you go up on the earth
that's positive latitude if we go down
on the earth it's negative latitude
you're in the Bay Area it's a brown
right here it's about 40 degrees plus
okay 40 plus now the Bay Area is here if
you look at say Tokyo and Japan took you
in Japan is over here in the earth it's
also at the same latitude so in Tokyo in
the Bay Area you're gonna see the same
things happen
in the sky so you're gonna see the same
stars you're gonna see the Sun rise and
set in the same places they're just
gonna be a bit different in time so you
know Tokyo is like 10 hours apart from
the bay area so it's gonna happen a
little bit later but your to see the
same stuff in this guy alright so that
is the second part of this stay tuned
for part 3
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