As I said, there is more moving parts in our model of the cosmos.
There are more things that do not remain fixed on the celestial sphere, and just
rotate with it, but yet, rise and set so are off the earth.
And the next most conspicuous one after the sun, is our moon.
like the sun, the moon moves along the celestial
sphere. It's not fixed.
for the same reason, the moon orbits the Earth.
It orbits the Earth in the same sense that the Earth orbits the sun.
And the same sense that, therefore, the sun appears to orbit the Earth,
moving towards the east along the celestial sphere.
But the moon orbits the Earth much faster.
The moon completes a complete orbit around the earth in what is called a
sidereal month which is 27 and a one-third days.
that means that it's right ascension increases by 48 minutes per day.
Compare this to the sun's measly four minutes.
In other words the moon takes a month to orbit the earth.
The sun takes a year to orbit the earth. A month is a twelfth of a year, four
minutes is a twelfth of 48. The mathematics adds up.
Now, as the moon orbits the Earth, it also rotates about its axis.
We'll discuss next week why that is. But this means that we are always seeing
the same side of the Moon as it rotates around us.
there's the same side of the Moon that faces us.
This means that while there is no such thing as the dark side of the Moon, there
certainly is such a thing as the far side of the Moon.
There are parts of the Moon that are never visible from Earth, and, those were
first, Seen, or.
Indirectly seen by human eyes. When the Soviet lunar space craft first
orbited the moon. So this is why.
When we look up at the moon, every time we see it.
It has this familiar, look. We're always seeing the same side of the
moon. Now, the, moon, therefore, moves to the
east along the celestial sphere by 48 minutes a day.
The sun moves to the east along the celestial sphere by four minutes a day,
which means the moon moves faster to the east along the celestial sphere.
The moon moves 44 minutes per day farther than the sun does.
Which means moonrise relative to sunrise is delayed by 44 minutes a day.
because the moon and sun are in this race, it takes the moon a little bit
longer to complete a full rotation of the celestial sphere relative to the sun.
To come to the same relative position as the sun.
that takes what is called a synodic month, which is about 29 and a half days.
This is the time say, from the moon being in alignment with the sun.
And then the moon, running ahead of the sun, and catching up with the sun, 29
one-half days later. As usual this takes a little bit longer
than the 27 days that it takes the moon to complete a sidereal rotation.
For the same reason that a solar day is longer than a sidereal day.
The difference being more significant here because we're talking about a month
rather than a day. now, the position of the moon relative to
the sun controls two things. One is, when during the day it rises and
sets? If the moon is at the same right
ascension as the sun, then it rises at sunrise and sets at sunset because it's
in the same direction in the sky as the sun is.
Whereas, if the moon say is twelve hours away from the sun, it's 180 degrees away
at right ascension, the moon will rise at sunset and set at sunrise.
So, rising and setting times of the moon change throughout the synodic month.
And, in addition to this of course, the moon's appearance in the skies changes.
It goes through phases, and the best way to see this is the following interesting
simulation. The best way to understand, how the
moon's position relative to the sun gives us the phases of the moon is to just do
it. And to just do it, you need a source of
light. You can use a light bulb, or if you
prefer, you can just use, the sun. Just go outside if you can't find a light
bulb. Anything round.
I have a white styrofoam ball here to play the role of the moon.
And your head, to play the role of Earth. the view from your eyes will give you the
view as seen by people on that side of earth facing the moon of what the moon
looks like. And then, you simply turn around to
perform a complete lunation. to give you a sense of what this looks
like in case you're not going to do it yourself, though I strongly recommend it.
what we have here is a, on the left side of the screen you'll see a setup of in
the studio of me holding a moon and turning around in the relative
configuration. Whereas on the right side you'll see the
image of a gopro camera that's mounted to the Moon, so it shows you the image of
the Moon as I see it. When the demonstration begins, the moon
is, in between the sun and the Earth. It's on the line between sun and Earth.
And so, the illuminated side of the moon, as we can see in this beautiful picture,
faces the sun, and therefore, faces away from the Earth.
I see the dark side of the, the moon. And then moon will be nearly invisible.
As turn to my left to the east. slowly, the western side of the moon will
become illuminated. And we'll see a growing crescent, until
after I've turned 90 degrees. We'll see a waxing quarter moon.
Since the moon is now six hours, or 90 degrees to the east of the sun, it will
rise six hours after the sun. In other words, the waxing quarter moon
rises about at noon and sets about at midnight.
As I continue to turn to the, the east, the illuminated part of the moon will
grow and become gibbous until at last, when I am twelve hours away from the sun.
I will see a full round moon illuminated. we're going to have to switch cameras at
some point, to give you the full view, because of studio limitations.
Don't get confused by that. Twelve hours to the east to the sun, the
full moon rises as sunset and sets at sunrise.
And so the full moon is the only moon that is really up all night and only
during the night and you'll note that to give us a view of the full moon, I had to
tilt the moon's orbit I'm holding way above my head, we'll get back to that in
a second. As I continue to turn to the east now the
western part of the moon is losing the sunlight.
I see the eastern part of the moon illuminated.
It is a waning gibbous moon. And then when I reach 90 degrees to the
sun again I have a waning quarter moon. The waning quarter moon which is six
hours to the west of the sun will therefore rise six hours before the sun.
In other words rise about at midnight, set about noon.
This is the moon we see in the morning. Finally, as I continue turning to the
east, the moon becomes closer to the sun in the sky.
only the eastern edge of the moon is illuminated.
I find a waning crescent moon. And after a full synodic orbit is passed,
the moon is back in line with the sun. And again, I see only the dark side of
the moon. And we're back to new moon.
So what I hope you saw and I do encourage you to do it yourself.
It's really fun and you can show it to your
friends and family, is that over the course of a senotic
month as the Moon orbits the Earth relative to the Sun the shape of the
visible part of the Moon changes in the sky,
as well as because of the relative position of Moon and Sun the rise time.
So the New Moon when the Sun and the Moon are roughly at the same right ascension
and the Moon is completely dark in the sky rises at sunrise and sets at sunset.
the waxing quarter moon, when the moon is about six hours of right ascension to the
east of the sun, rises six hours after the sun.
So the waxing quarter moon rises at noon and sets around midnight, and is visible
all afternoon. The full moon, where the moon is twelve
hours of right ascension ahead of the sun,
in other words on the opposite side of the sky.
The full moon is the only time that the moon rises at sunset and sets at sunrise.
And the waning quarter moon, where the moon is
six hours to the west of the sun, or eighteen hours to the east, the moon
being six hours to the west of the sun, rises six hours before the sun.
In other words, rises about at midnight and sets about at noon.
And the waning moon is visible all morning.
So when you see the moon in the daytime, you should not be surprised.
But should you ever see a full moon at noon, something has gone terribly wrong,
so. Both the phases and the periodic change
in moon rise and set times are completely understood in terms of this model where
the moon reflects sunlight and what we see depends on the angle between the
moon, the sun and the earth. You can stimulate this, you can go to the
stimulation page of the University of Nebraska Lincoln and get less freedom
version but I encourage you to construct take a light pall and a.
Ball of some sort and make yourself a moon.
So, this describes the moon's motion and the changes in the phase.
you notice that at new moon and at full moon, I had to sort of adjust the moon.
I was moon, orbiting the moon about my head, not in a horizontal orbit but in a
tilted orbit, so that it went below the sun at new moon, and way high above the
sun at full moon. So, this brings up the question of, what
is the moon's declination? Indeed, the moon roughly orbits the Earth
along the ecliptic. But it deviates from the ecliptic by five
degrees. for comparison, the sun and the moon are
about the same size in the sky. And both of them are about half a degree,
so that the moon is, distant from the sun by up to ten times
their radius. And so typically the moon passes well
below or above the sun when its for example a new moon
And so we have these two circles, now the ecliptic and the orbit of the moon around
the Earth, the tilt between them is five degrees.
The analog of the equinoxes, the hinges at which these two circles are hinged, is
now called the nodes and the line connecting them, the line of nodes.
And so the moon is at most five degrees away from the sun, which means among
other things that as the sun moves north and south along the ecliptic, the by 23.5
degrees in the summer. North and 23.5 degrees south in the
northern winter. the moon, which is at most five degrees
away from the sun pretty much follows the ecliptic.
So the moon too, is higher in the sky in the summer, and lower in the sky in the
winter. But.
It generically is not exactly the same as the sun.
It is only at exactly the same declination of the sun when it is along
the line of nodes, just as the sun is on the celestial equator at the equinoxes.
So twice in each of it's rotations about the Earth, the Moon lies along the lines
of nodes. And in that case the Earth, the Sun and
the Moon are in the same plane. Interesting things happen, of course,
when the moon is in the line of nodes. And, it is either full or new.
Let's see what happens then. In our first limation, I kept the moon
way north, or up in this image from the sun when it was full and way south of the
sun when it was new. what we're going to do now is see what
happens to the full moon when the line of nodes is aligned with the direction to
the sun. In other words the moon when it is twelve
hours away in right ascension from the sun, is it exactly the sun's declination.
And we start our demonstration with the waxing gibbous moon.
And it waxes until it, is becoming full. And then, what we see is that, from the
eastern side of the moon, a fuzzy shadow covers the surface of the moon.
Of course, this is the shadow of my head. it would not be as shaggy were it the
real Earth. But this is exactly the geometry for a
total lunar eclipse. The Moon enters the shadow from.
The west moving east and therefore it moves out of the shadow starting with its
eastern edge first so when you see a lunar eclipse take place and then the
moon uncover you're literally watch the moon orbit around the earth.
About two weeks later or two weeks earlier, the Moon is now at the Sun's
right ascension, we're getting a new Moon and the Moon is still at the same
declination as the Sun and we'll see what happens.
We pick up the story with a waning crescent Moon.
The Moon moves in front of the Sun. When it is at the Sun's right ascension
and declination the Moon in fact is obscuring the Sun.
And remember we are on the day time side of the Earth.
This is mid-day because it is a new Moon, we shouldn't be able to see it at all.
In fact we don't. But then we don't see the sun either, we
get complete darkness, in the middle of the day, and as the moon continues to
move to the east, then we see this weird glow on the moon.
This is an artifact of a shiny Gopro camera but even this is instructed.
The lens of the camera is still eclipsed. But the bits of the camera on the right
hand side are already shining in the light.
And they're, you can see their reflection of that off the moon.
This is what would happen if people living a few thousand kilometers to the
west of you. Erected a huge shiny tower on earth,
during a total solar eclipse, you might see the reflections from that shiny tower
on the surface of the moon. And then, as the moon continues to move
east, the sun is again revealed and it's bright mid-day.
What did the model show us? Well, the moon's orbit is tilted five
degrees with respect to the sun's orbit, the ecliptic.
And so there are two points along the moon's orbit at which it is on the
ecliptic. Now, as the sun orbits the earth or the
earth orbits the sun there's going to be two times a year where the direction of
this line of nodes coincides with the direction of the sun because the sun
makes a complete circle and, at two antipodal points along the circle it
coincides with the line of nodes. This gives us twice during an average
year something called and eclipse season. And, the alignment is, need not be
absolutely perfect because neither the sun nor the moon are point like objects.
But there are two sort of one, one and a halve month periods,
during each year. And in those one, one and a half month
periods, eclipses may occur. May occur that is, when the moon is
either full or new. So that it is at the correct part of its
orbit, at the right ascension, either of the sun
or opposite that of the sun, and now at the right declination.
So twice a year we have an eclipse season.
And during an eclipse season, you have usually between two or three eclipses.
One of one kind and flanking it two weeks on either side.
Two of the other kind. So you could can have a solar eclipse
flanked by two lunar eclipses. Or a lunar eclipse flanked by two solar
eclipses by the time, the next eclipse of either type would have occurred the next
new moon for example. the sun is now to far from the line of
nodes and you no longer get an eclipse. So typically no more than three per
season and this should happen twice per year.
In fact like everything else that is tilted the line of nodes wobbles.
In other words the tilt between. The moons orbit and the ecliptic is
always five degrees but its orientation wobbles and as is with the case with the
earth it actually wobbles to the west Because it is orbiting to the east and so
the two persesses to the west very slowly to the west once every eighteen point six
years or so and this just means the eclipse year the year during which two
eclipse seasons happen. is a little bit shorter than the full
orbital year of the Earth. Only 346.6 days.
And so, during each of those two eclipse seasons a newer full Moon might lead to a
solar or a lunar eclipse. so new moon during eclipse season means
the moon is in front of the Sun and at the right declination so you can have a
solar eclipse. A full moon means the.
Earth is between the moon and the sun, and the Earth's shadow will obscure the
moon, just as my shaggy head obscured the moon in our model.
Now, we need to get a handle on the relative sizes and distances of things to
understand the difference of the two phenomena.
So, the moon and the sun are almost precisely the same size, in angular
terms, in the sky. If you think about it, the sun is much
larger than the moon. From our small angular proximation, we
know that it is much farther. The ratio of their sizes is almost
precisely the ratio of their distances. So that both the moon and the sun appear
in the sky to be about the same size. An interesting coincidence.
What this allows is, when you have perfect alignment during new moon, the
moon is able to completely obscure the sun.
When you superpose two discs of the exact same size in the sky.
But this requires perfect alignment. So perfect, that in fact, it will only
obtain for a small region on Earth, if you move a little bit away from that
region on Earth. Then the alignment is no longer perfect.
The alignment is only perfect at one point on Earth.
And when I say one point, I mean, a region on Earth,
whose size is up to about 250 kilometers, that's a very small part of a planet with
a radius of 6400 kilometers. And in that region where the moon's
shadow completely obscures the sun, you get what is called a total eclipse.
And we have here a beautiful time series of a a total eclipse.
Notice that as time progresses in this, the moon seems to obscure the sun from
the left. Whereas in mine, and then leave the sun
to the right, whereas in my model, this was happening the other way around.
The reason is that this eclipse in 2001 was observed near Zimbabwe, and, near
Zimbabwe, you're in the southern hemisphere, which means, east and west
are still the same, but looking, since the sun is, now to your north,
The, the moon entering the sun from the west moving to the east is now from the
left to the right. So north to the southern hemisphere
viewers this time it makes sense to you. The moon is coming from the west to the
east across the surface of the sun, it obscures the sun completely for a few
minutes and then. Is seen to move away and what we're
watching again is the moon orbiting the earth although also this place Zimbabwe
is being moved along the surface of the earth by the earth's west to east
rotation and moves out of the shadow as we'll see in a moment and
noteworthy, when the moon completely obscures the sun,
a region around the sun that appeared completely dark before, is suddenly seen
to be brilliantly luminous.
This is called the corona, the crown of the sun.
It is not visible when, we see the, the, the, the sun itself, or the sun's disc,
because the sun's disc is so bright that it blinds us to the, brilliants of the
corona. But once you obscure the sun's disc, you
can see that the region around the sun's disk is illuminated when we talk about
the sun, we'll try to understand what this glowing crown is and how to observe
it away from eclipses. A more common phenomenon than this
beautiful totality is when the new moon occurs, the line of nodes are not exactly
aligned with the sun and so the moon is a little bit south or a little bit north of
the sun, and then the moon would have passed below or above the sun.
Above if it were south since we're in the southern hemisphere, and below, if north,
or the other way in the northern hemisphere.
And then you will find a partial eclipse where not the full surface of the sun is
obscured. But only, some fraction thereof.
And this is far more common, because it requires a less sensitive alignment to
give you a sense of, what the, the shadow of the moon on the
earth looks like. here's a beautiful image taken from the
Mir spacecraft on August eleventh, 1999. And, this is an image of earth,
and what we're seeing on Earth is the moons shadow.
So, the moon's shadow as I said, obscures the, the moon can obscure the entire sun
in this inner circle of a radius of about 250 kilometers, up away, we see this
partial shadow. These are regions where if you look up,
you can see part of the sun, but, some fraction of the sun is obscured by the
moon. You can see around it a little bit, and,
so, this is called the Penumbra or Partial Shadow.
People here see a total eclipse, people here see a partial eclipse.
And, now remember, that underneath. This, shadow.
This earth is rotating so that this shadow is effectively moving along the
earth at some 1000 kilometers per hour and so each, individual location only
gets a short period of totality. Now.
This is what happens if alignment is perfect and if the moon and the sun are
indeed exactly the same size in the sky. How can they change?
Does the moon shrink? No, but the moon's orbit around the earth
is not completely circular. The moon is sometimes a little closer to
earth, and sometimes a little farther, when.
Complete alignment occurs and the moon is on the.
Farther part of its orbit, it's just a bit farther from Earth.
Since its size didn't change, its apparent size in the sky is a little bit
smaller. it's then smaller than the sun in the
sky. And we get what is called an annular,
annular eclipse. because you seen an annulus of sun, a
ring of sun surrounding the moon. This shadow here is the moon.
We see some of the, corona, and even some of the chromosphere
around the sun but what we also see here is a little bit of a disc of the sun, the
photosphere as it's called and the moon not completely obscuring it in this
beautiful image of an annular solar eclipse.
This is what happens when alignment, during eclipse season occurs at new moon.
During full moon, what happens is that the earths shadow prevents sunlight from
hitting the moon and the moon becomes dark.
The moon as I said, is moving to the east, it enters earth's shadow from the
west. Again, the eclipse can be total or
partial and Depending on the quality of the
alignment. And, you can get a penumbral eclipse,
where the moon is only in partial shadow. In other words, where, from the moon, you
can see some part of the sun. But, some of the sunlight is blocked by
the Earth. Just as pieces of the Earth were in
partial moonshadow. then the moon just slightly dims.
It's kind of hard to even notice it. But when you get a total eclipse,
when some part of the moon's surface is completely obscured from the sun,
then this is the beautiful image you see. Now this, I'm not sure, surprise you.
I mean, perhaps some sunlight is reaching over here.
Maybe I didn't time this photo to precise totality.
But where is the light coming from that allows us to see the moon this side of
the moon at all. This side of the moon is, in fact, in
total Earth shadow, you cannot see sun, the sun, from this area of the moon.
What you can see in the sky is a bright, glowing Earth.
Remember, the Earth is bigger than the moon, so it, handily obscures the sun.
It's much easier to arrange a total lunar eclipse than a total solar eclipse.
And also, a solar eclipse, a lunar eclipse, when it occurs, is visible,
since the moon is dark, to anybody on Earth who can see the moon.
So whenever it occurs during your nighttime, you can see the moon eclipse.
It's a far less delicate arrangement than the solar eclipse which only blocks out
the sun for a small fraction of the earth.
but the source of this red illumination of the moon.
the answer is here on the slide. Comes from light defracting through
Earth's atmosphere. Why light defracting through the Earth's
atmosphere would give the moon this famous wine red color is something we'll
have to investigate. This is a picture actually taken at our
observatory, in the, solstice eclipse of, December 2010.
And so, this is Pretty image and lunar eclipses are
easier to find and observe. I encourage you to enjoy them.
A few more fun facts about the moon, while we're discussing the moon.
So two well known things that people appear to observe.
One is that when you see the moon rising or setting, it's near the horizon, it
appears larger. This, it turns out, is a psychological
illusion. Taking pictures of the moon with a
camera, you can measure its angular size. And in fact, if anything, the strange
optical effects make it appear a little bit smaller in the sky near the horizon.
But there are various psychological theories, near, the comparison to other
objects nearby, angular corrections. I'm not an expert on the psychology.
But, it does appear to us that the rising full moon seems huge when it's on the
horizon, and small when it's high in the sky.
But, this is completely in our heads. On the other hand, there is this other
famous illusion, where, which is called seeing the old moon in the new moon's
arms. Which is, that when you see a crescent
moon, where only a fraction of the moon is
illuminated, then you can sometimes imagine to yourself that your mind
completes the full disk of the moon, and you can see the part of the moon that is
not illuminated by sunlight. And,
this one is a physical effect. Here's a camera capturing it.
Here's the illuminated side of the moon, so the sun is down that way.
This side of the moon is dark, sunlight cannot reach it, and yet I see it, so
there's sunlight hitting it, and there is a reason, of course, is that when the
moon is a crescent, if you are on the moon,
set up the configuration in your head, you would see that there would be a full
Earth in the sky. And viewing the, the full Earth in the
lunar sky means that there is bright Earth light illuminating the moon.
So the light that is hitting the moon, by which we are seeing this moon is Earth
light, in other words light that was emitted by the sun, reflected by the
earth, hit the moon, reflected off the moon and
came in the appeture of this camera. So the fact that you can see the dark
part of the moon as a crescent is not psychological, it is true.
You can only see this when the moon is a crescent basically because once the moon
becomes too bright, it blinds us, it dazzles us and we can't see this.
Also, the larger the illuminated part of the
moon, the less of the face of the Earth is illuminated.
Of course, when we have a full moon, then people on the moon would see a new Earth.
The phases are complementary. And so for both of those reasons, we only
see this when the moon is a crescent. So we've made some progress in
understanding astronomical phenomenon. The way they change periodically.
We've got the sun, we've got the moon. Let us close this discussion with some
interesting relations between astronomy and time keeping.
I've told you that units of time kept being defined in terms of the Earth's
rotation and orbit. This is not a coincidence.
We want our time to match what's going on.
We want. Six a.m.
On our clock to be solar sunrise, because that's the time we go out and plant,
things, work in our fields. And so, our 24 hour days are adjusted to
be the mean solar day. Are months that, twelve months into which
we traditionally divide the year, are approximately lunar.
the synodic lunar month is 29 and a half days.
Our months are a bit longer than that. But, and this allows for the rare
phenomenon of two full moons. Falling in the same month, which is what,
colloquially, is called a blue moon. It's a rare phenomenon.
It requires a full moon right at the beginning of the month, but it does
happen. Our definition of a year is designed to
match the orbit. A year is 365 days.
the Earth, orbits the sun once. every 365.2564 days, a little over a
quarter of a day, This is sidereal orbit, in other words,
this is the time that it takes the Earth to return to the same position in the sky
relative to the sun, or the time it takes the sun to return to the same position in
our sky, relative to the stars. Hence, sidereal orbit.
The first thing we observe is, that the year is not, unfortunately, an integral
number of days. This is a problem.
It means that, Since we, our days turn over every 24
hours, that every four years You're timekeeping if you have a 365 day
year. Then every four years, you are off by a
day relative to the Earth's orbit. So who cares?
Well, accumulate those days for 180 intervals of four years.
And now, you are off by 180 days which is half a year which means that now January
corresponds to northern summer. This is very inconvenient if you're
trying to plan agriculture and we have a solution to this, right, this was
discovered by Julius Caesar, or in his time, and it was his legislation that
added leap years. Once every four years we add another day,
making that year 366 days long. The average year is now 365 and a quarter
days long, and now we never drift more than a day off from having our orbit
match our calender. However, this is not completely precise
enough. In fact what we want our calendar to
match is the seasons. The seasons have to do with the relation
between the earth's position relative to the Sun and not the stars, but the
direction of the tilt of the celestial north pole or the terrestrial north pole.
And remember that, that wobbles to the west,
rather than to the east. So a, a complete rotation.
Where, between solstice and solstice, or equinox and equinox, is a little bit
shorter than the sidereal year, rather than longer.
This is called the tropical orbit. The mean time between solstice and
solstice is 365.2422 days. Remember that the precession is very
slow, takes 26,000 years. So it's not a big effect over a year, but it does make
the mean tropical year a bit shorter than 365.25 days.
This was understood in the sixteenth century and led to the correction from
the Julian to the Gregorian calendar, correcting for the deviation between
0.2422 and 0.25 required removing some of the leap years.
That is why on Centuries that are not millennia, in
other words years whose number divides 100 but not 1,000, we do not add a leap
year. We do not add a 29th day to February,
those years are only 365 days long. The average year is a little bit less
than 365 and a quarter days long. In fact it's close enough to this number
on average that it will be a millennium before we have to make another
correction. And so we definitely use astronomical
phenomena to adjust our clocks and our calendars, not for any silly reason but
because astronomical phenomena govern our life,
and we need our, timekeeping to match that.
It's quite an elaborate universe we're starting to build around us.
We have the celestial sphere where the stars are fixed.
we have a solar sphere that rotates relative to the celestial sphere about
this tilted axis. So that the sun can move along the
ecliptic. We have a lunar sphere tilted relative to
the ecliptic around which the moon moves a little bit faster.
Moreover, all these, tilted trajectories are also wobbling to the west, one very
slowly, every 26,000 years. The moon's a little bit faster, every 2.6
years. This is very elaborate, but it does
explain everything we see. The alternations of day and night, the
phases of the moon, eclipses, seasons. Almost everything.
Let's go to Athens and see what we might have been missing.
We're back to our favorite picture of the sky in Athens.
And I've allowed the software to show us the ecliptic and we see the 23.5 degree
tilt, relative to the celestial equator. We the, see the intersection of the
ecliptic and the equator here at the prime meridian in Pisces.
We still live in the age of Pisces and We see that the part of the ecliptic
that's visible at night is mostly the part north of the equator.
That's reasonable because, end of November, the sun is well south of the
equator. The part of the ecliptic that lies south
of the equator is what we see during the day.
So far, so good. the other thing you'll notice.
And I'm sure if you, tried to run your own simulation.
And certainly, if you went outdoors, you will have realized by now that I
fudged. I suppressed some things in the
simulations I've been showing. In particular, the two brightest objects
in the sky were omitted from my discussion up to now.
One of these, the brightest of them is this waning gibbous moon,
which we see here. A waning gibbous moon, remember,
is a moon that is past full.
And so, it rises after sunset, and at 9:00 p.m., we're still seeing it
in the eastern sky, so we expected that. the moon happens to lie very close to the
ecliptic right now. It could have deviated, remember, by as
much as five degrees. we also have, the next brightest object
in the sky is the beautiful planet, Jupiter.
and we have not brought up planets. And once we allow that, we see that
scattered along this ecliptic are a few others, non-star objects,
Neptune, Uranus, and the asteroid, Ceres. And, if we look at this image over time.
We would notice that, like the moon and the sun, the planets move as well,
which means we're going to have to start next week by adding even more moving
parts to our universe, and enriching what we know,
and eventually leading us to a much, much deeper understanding.