Welcome to ON(line)SC's Virtual Learning!
Good evening, Naturalists!
Tonight we will take some time to take a look at astronomy, the study of things beyond the edge of our own planet. Take a couple of minutes to think about some of the things beyond the edge of our atmosphere. How do we know they're there? What do you already know about them?
We'll start with a bit about the closest natural object to our planet, the moon. If you have a clear sky and can see the moon at some point, take a look at it. As the moon revolves (circles around) around our planet, it moves in a pattern across our sky. To find out what time the moon will be in the sky today, it might be helpful to use online resources. We like to use https://www.timeanddate.com/moon to see when the moon will rise and set at ONSC, as well as additional information about the moon. If you enter your town or city's name and scroll down on the site, you'll see something that looks a bit like this.
This chart has lots of interesting information about what the moon is doing on any given day, but let's look at just four parts of that for right now, the parts that we have circled in blue. Two of these, “Rise” and “Set”, tell us when the moon will be rising and setting on April 14, 2020. Take a look and notice these times. When will the moon be in the sky? If the moon has already set, what were you doing while it was in the sky today? Do you notice any patterns in this information if you look at the times throughout the week? It's important to remember that sometimes, the moon will be crossing our portion of the sky during the daytime.
The next thing to notice is the meridian passing. This is when the moon will be at about its highest point in its daily trip across the sky. When is today's meridian passing? This is sometimes (but not always) when it is the easiest to see the moon.
(Bonus info: You may have noticed that there are numbers with the degree symbol (°) underneath these times. In this case, that symbol represents where to look to find the moon. For moonrise and moonset, you can take a compass outside, point it north, and the numbers will tell you what direction to look for it. For the meridian, this tells you how high above the horizon you will need to look for the moon. Numbers closer to 0 will mean that the moon is closer to the horizon, and 90 will be closer to looking straight upwards. In my case, it says 30.1°, meaning it will be about 1/3 of the way up in the sky. See if you can use this information to track where the moon is for you!)
The final thing to notice is the half-filled circle next to the date. This does not appear every day, but it tells us something special about what the moon looks like! Our moon goes through different phases as it orbits the earth. To us the moon appears to be shrinking or growing; we call this either waning (shrinking) or waxing (growing). When the full disk of the moon is completely visible it is called a full moon. When the disk of the moon is completely invisible (even on a clear night) it is called a new moon.
Think about when you've seen a crescent moon, a thin curve of silver light in the sky. You can actually use the direction this curve is making to figure out whether the moon is waxing or waning!
Let's create a guide to help us remember. Find an ordinary piece of paper, and trace a round object (like the bottom of a cup) twice onto this sheet with a colored pencil, crayon, or marker. Next, draw a straight line down the middle of each circle. Bring the top of that line above the top of the circle as well, and then draw mirroring crescent moon shapes onto each half. Leave the crescent blank, and color the rest of the circle black. It should look like this.
Can you see letters in this picture? It probably looks like a lowercase “b” and “d”! To help you remember, go ahead and write “bigger” under the “b”, and “declining” under the “d”. You can then write “waxing” under “bigger”, and “waning” under “declining”
But what happens when the moon is gibbous, meaning that more than half, but not all, of the moon is visible? How do we know then? You simply look to see which side of the middle of the moon has more light and looks more “full”!
Watch over the next few days. Is the moon waxing, or waning? If you want, keep track of this next to the weather on your weather chart from week one. Using these patterns can be a fun way to plan night-time activities with your family!
But why does the Moon go through these phases? Imagine the moon's surface as a giant mirror. The light from the sun bounces off of it, and if you are in the right spot, you can see that reflection. If you have a hand mirror at home, you can test this out for yourself by standing in place with the mirror in your hand and spinning to mimic the moon's revolution around Earth. This diagram helps explain it as well.
Now we'll shift our focus to some of the other bright objects in our sky-the stars! These sparkling points of light in the night sky have been used over thousands of years for many purposes, such as navigation and storytelling. But what are stars?
Stars are large balls of super-hot gases that produce light and heat. Can you think of the closest star to our planet? If you said the sun, you'd be right! Our sun is very close to Earth compared to every other star in the universe. We're close enough that we're trapped in its gravity. We're very lucky, however, because we're at a spot where we orbit the sun, rather than just crashing into its surface like a ball thrown up in the air. If you go outside on a clear night, with no moonlight or city lights to outshine them, you can see about 3,000 other stars. How can we tell that our sun is the closest?
Many stars are much larger than our sun in real life, but their distance makes them appear much smaller. To give you an idea of how far light has to travel, a ray of light can travel around the whole planet about 7.5 times per second. Even with it moving that fast (186,282 miles per second), it takes light from the sun about 8 minutes to reach Earth, and about five hours to reach Pluto. What were you doing eight minutes ago?
The next-closest star, a (“alpha”) Proxima Centauri, takes 4.2 years for its light to reach us. That means that when we look at that star, we're seeing it as it appeared about four years ago! What were you doing when the light left that star?
Bonus fact: The light from the farthest-away visible star from our planet is over 16 THOUSAND years old! That was about one thousand years before the very first people came to North America from Asia, or almost five thousand years before the end of the last ice age! Keep in mind that this star is still part of the Milky Way, our “neighborhood” in the universe, and there are many galaxies that are much, MUCH farther away!
One of the most amazing connections we have to the stars are in our stories. Long before the first television or book, people would look up at the sky and see shapes and patterns in the stars; these are called constellations. Some cultures believed stars to tell the stories of fabled heroes and rulers, powerful gods and goddesses, or monsters they believed existed. Take some time to look up constellation stories-almost every culture on the planet has some! Here's one of our favorites here at ONSC. This is the Greek myth behind the Big Dipper and the Little Dipper, also known as “Ursa Major” and “Ursa Minor”.
For extra fun, go out and make your own constellation! Map out the stars, and write out a story. Feel free to share your created constellations with us!
Enjoy the stars, and we'll see you again tomorrow to look at some amazing ways that animals survive at night!
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