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  • Daniella Morrone

Snack-Sized Astronomy

The Earth, The Moon, and The Sun

As we start the new school term, some of you will have to teach astronomy and even introduce it to students who have never thought about the cosmos. You might be thinking “How can I possibly teach *everything* about astronomy in one single unit?” Well, worry not: Discover the Universe is here to give you snack-sized information about key astronomy topics to discuss with your students. These topics will range from small-scale motions of our Solar System to large-scale wonders of the cosmos.


Let’s start locally and introduce a very interesting feature of our Solar System that is near and dear to all of us: the Earth-Moon-Sun system. Each of these three celestial bodies have an impact on our day to day lives… but what is a “day”? What is a “year”? How does the Earth-Moon-Sun system play a role in our understanding of time itself? Let’s get into it…


Introducing: The Sun

The Sun is our daytime star. It is the central feature of our Solar System and has such a powerful impact on both the movement of all the planets around it and the actual formation and composition of those planets. Because of how massive the Sun is (1.99 x1030 kg, to be precise) its gravity pulls all the planets and rocks of our Solar System into orbit around it.


Each of the planets takes a different amount of time to orbit the Sun that depends on how far away it is from the Sun. The Earth takes 365 days to orbit once around the Sun, which we call a year. But what is a day? Let’s investigate the Earth a little more…


Investigating: The Earth

The Earth is our home, where we have lived our entire lives and where everyone we know and love is. This familiar planet holds a wealth of information that we continue to explore every day. But what is a day?

As we explained above, our world orbits every 365 days around the Sun, elapsing one year. Each of these days however is explained by an entirely different phenomenon. As we orbit around the Sun, the Earth also rotates around an axis that passes directly through the North and South poles of the planet. Each of these individual rotations about our axis is what we call one day!


While to us here on the surface, Earth’s axis is visualized as a line from the top to the bottom of our planet, this axis is in fact tilted (23.5° from vertical) compared to our orbit around the Sun. This tilted axis in combination with the orbit of Earth around the Sun grants us seasons!


So, the Earth and the Sun work together to give us days, seasons and years. But what does the Moon give us?


Inspecting: The Moon

The Moon has a rich history both physically and culturally. From causing the tides to influencing animal migration, our cosmic companion is responsible for a wide range of earthly phenomena. As we on Earth spin on our axis and go around the Sun, the Moon orbits around us and spins on its own axis. The amount of time it takes for the Moon to rotate on its axis and orbit around us once is the same: 27.3 days, which is approximately one month!

Over the course of a month, you can look at the sky and inspect the Moon and how it changes over its one revolution. You will notice that the shape of the Moon in the sky shrinks and grows throughout the month, but the Moon itself does not actually change size or shape! When we observe the Moon glowing in our night sky or faintly sitting in the blue of our daytime sky, we are only seeing the part of the Moon that is illuminated by sunlight, where it is daytime on the Moon. The part that we can’t see is still there but just hidden; this is where it is nighttime on the Moon. As the Moon follows its orbit around the Earth, different parts of it are illuminated; this is what we call the lunar phases, a characteristic of our Earth-Moon-Sun system.


What is the Earth-Moon-Sun System?

The Earth-Moon-Sun system is the interaction between all three of these celestial bodies and how they impact each other. As mentioned above, the three have impacts on humanity from our culture to our concept of time. But there are other fascinating phenomena around this system that beg our attention. Namely: eclipses, where the Earth, Moon, and Sun line up in just the right way to cause a spectacular event. There are two types of eclipses, lunar and solar eclipses, with subtypes in each (like partial and total). Let’s get into what these entail…

A lunar eclipse occurs when the Sun, Earth, and Moon line up in that order, and the subtype depends on where the Moon is located behind the Earth and from where you observe it. With the system in this order, the Earth blocks the light from the Sun from reaching the Moon, causing it to darken in the night sky and, in the case of a total lunar eclipse, appear red.


A solar eclipse occurs when the Moon is lined up between the Sun and the Earth, and the subtype depends on where the Moon is located in front of the Earth and from where you observe it. In the solar eclipses, the Moon blocks the sunlight from reaching Earth, causing the sky to darken during the daytime and, in the case of a total solar eclipse, causing the Sun to be completely blocked out.



Solar Eclipses: Coming to a City Near You!


As you teach this topic, you might be pondering various ways to get your students more interested in astronomy and the Earth-Sun-Moon system. As we discussed above, eclipses are a common and engaging way to pique the interest of newcomers to astronomy, and we’re here to tell you how you and your students can see a solar eclipse in the next 8 months.


Whether you’re on the West Coast of Canada or you’re in the Atlantic Provinces, a solar eclipse is coming your way…


On October 14, 2023, an annular solar eclipse is sweeping across the Americas. While over here in Canada we won’t see annularity, a partial eclipse will still be visible across the provinces and territories. As you venture out west, the view of the eclipse will get better. With 17% of the Sun covered in Montreal and 76% in Vancouver, this is a Canada-wide event that you won’t want to miss!


On April 8, 2024, a total solar eclipse hits Canada. As this eclipse passes over North America, the path of totality (a.k.a., the path in which the eclipse will appear as total) intersects with towns and cities in several of the eastern canadian provinces, including Ontario, Quebec, New Brunswick, PEI, and Newfoundland & Labrador. But if you’re observing outside one of these cities, don’t fret: you can still see a partial eclipse!


When all is said and done, we can observe eclipses multiple times a year, so what makes either of these special? Well… the October 14 annular eclipse is the last one with annularity hitting North America until 2039! And the April 8 2024 total solar eclipse is the last one with totality hitting Canada until 2044, and until 2079 for Eastern Canada!


Want to learn more about eclipses? Here’s some good resources…


Want to explore the Sun, Earth and Moon some more?

Check these out our resources page: Discover the Universe/Resources. From that page:

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