The summer solstice is quickly approaching, and many know this as the longest day of the year,
but why do we even notice the summer solstice? Why have humans been recording this over the
thousands of years throughout human history in many different parts of the world? In this video
we're going to explore these questions, and get an understanding for what the summer solstice means
and why it happens in the first place. Welcome to Learn the Sky! My name is Janine, and I'll be your
guide as we explore the sky one constellation at a time. The word solstice is derived from the
latin word soul, which means sun, and sistere, which means to stand still, because at the solstices the
sun's declination appears to stand still. That is the seasonal movement of the sun's daily
path across the sky, it pauses at the northern or southern limit before it starts to reverse
direction, but today we know the equinoxes and the solstices as an astronomical event,
and these are really caused by the Earth's tilt on an axis, in its orbit around the Sun.
If we take a look at a diagram of the Earth in its orbital path around the sun
we can see that there are two points of equinox, we have the spring equinox and the autumn equinox.
Then we also have winter equinox for the northern hemisphere and the opposite for summer hemisphere,
and then here we have the summer solstice, where up at the poles there's the midnight sun,
but at the southern hemisphere they have the polar night. Remember that it flips, the seasons flip when
we have the northern and southern hemisphere. So as we take a look at the path of the sun
through the sky, what we notice is that on the equinox we have equal day and night, but
at the summer solstice you have the sun rising to the highest point in the sky which gives us
the longest day of the year. The opposite of this would be the winter solstice, this is when the sun
hits the lowest point in the sky and therefore we have the shortest days of the year, and the
earliest humans spent more time outside than we do, and they use the sky as both a clock and calendar.
They could easily see that the path sun across the sky would change over the course of the year,
and these positions were recorded in different areas throughout the world. So this is something
that all humanity has been doing in order to have a celestial clock. So also keep in mind that
this happens because of the tilt of the Earth. The axial tilt of the Earth is 23 and a half degrees,
and as the sun's light hits the Earth the Earth is heated unevenly. So during the summer months,
in the northern hemisphere we have more direct sunlight on that portion of the Earth, but in the
southern hemisphere that light is spread out over a greater area, therefore cooling that portion of
the globe. This is truly the reason for the seasons is the axial tilt. If we look at other places
in the solar system, Mars has a similar axial tilt and it also has seasons as well. So when we reach
the spring equinox, which happens in March for the northern hemisphere, we start to see that life
reawakens after a quiet winter. We see that plants and flowers begin to bloom. Often we have lots of
rain, that comes with this part of the season, and then we arrive at the summer solstice, and that's
when you have that longest day of the year, and everybody's biological clock starts to shift a
little bit. For me personally what I notice is that I tend to take naps in the midday so I'm ready to
stargaze at night, it's like my body already knows it. I'm just ready, I'm on summer break as a teacher
and I want to get outside and start to look at the stars. The summer is also a great time that
the milky way starts to appear in fact the heart of the Milky Way appears during the summertime,
and that's when I love to go outside and seek out dark skies, so I can hopefully see
the heart of the Milky Way, the center of our galaxy, that's how the Earth is oriented during
this particular time, and then right in August there is a wonderful meteor shower called the
Perseids Meteor Shower. It's one of the best of the year so we kind of end up that summer season
with this awesome meteor shower, and we start to get into the fall season, where we start to see
things like the Andromeda galaxy start to appear, and then again the Earth changes. We see trees and
plants entering their cycle of growth and it's nature's last blast of energy before winter comes,
and then of course winter arrives, and we have shorter days longer nights, which I enjoy because
that means I get to see more of the night sky, but these cycles continue on and we see many
parts around the world in which the timing of the night sky was recorded and lined up with different
structures that were built. That's something I hope to do in the future in this channel, is
study astro archaeology sites which correlate to you know how our ancient cultures studied the sky.
So I hope this video was really helpful for you to understand the differences
between the equinoxes and the solstices. We are approaching at the time this videos were being
recorded the summer solstice. So as you go outside I hope you enjoy those nights where you can see
gorgeous stars, hopefully you can see the Milky Way. I know for me summer is the greatest time
because I have no obligations as a teacher, so I can just spend lots of time in nature and I hope you get to do the same. Remember as you go outside it takes time, patience, and practice to
view the stars. So keep going outside, take a friend with you and always keep looking up.