Tag Archives: Solar System

Understanding the eclipse by creating a to-scale demonstration of orbits and moon phases

I was recently asked to do a presentation about the upcoming solar eclipse at our library as I am one of a small local group of amateur astronomers. I happily accepted. I always enjoy putting together Keynote presentations for such events. I spent several days last week assembling the 38 slide presentation and did the presentation last night. It seemed to go well. For one part of the presentation I used three volunteers to serve as the sun, moon, and Earth. The idea was to illustrate the phases of the moon as well as the angle of the moon’s orbit with these three people and in truth, after a bit of initial confusion, I think it went pretty well. But it wasn’t to scale as we were crowded into a fairly small room at the library. After the event I got to thinking about how that sort of presentation, in particular the bit involving the volunteers, could be expanded into something really fun but in an outside location so that a sense of scale could be created. It would involve a bit of math so I thought it might be fun to recruit Siri as my helper in preparing this activity.

The idea would be to create a scale model of the Earth in relation to the sun and moon based on a circle of 365 feet in circumference. Each foot represented one day in the Earth’s orbit around the sun. Now, at this scale, I wanted to properly represent the position the sun at the center of our orbit. I needed the radius of my circle. Okay. I asked Siri to calculate the radius of a circle with a circumference of 365 feet. I was given a WolframAlpha calculation screen as a result: 58.1 feet. But I wondered if I could copy/paste the content. It had never occurred to me to tap the WolframAlpha icon, just a bit of text in a square in the corner of that display of results. I’ve done this kind of thing many times but never thought to see what would happen if I tapped. I expected it would do nothing. Instead, it took me to the AppStore for the WolframAlpha app. It never occurred to me that there was such an app but of course there is! I downloaded it and it opened my results into the app. It’s a very nice app that allows further input and new calculations among many other things. But no option to copy/paste the content.

Now, back to working out the activity. I’ll need to get some string but before that, I now know that if my orbit is scaled to 365, feet my radius is 58.1 feet. So, I’ll position my sun with a pole with string tied to it. From there I’ll walk out 58.1 feet and place another pole. I’ll have two strings. One which I’ll keep tied to the center pole (my sun) and which will guide my “orbit”. The second string will be tied to the second pole. Now it’s just a matter of walking the circle around the sun and dropping my string to represent the 365 feet of orbit. The next step is to convert a few other distances. For this I hopped over to this solar system scale model calculator.

Next, I used Siri to do a bit of math. First I asked her for the average circumference of the Earth’s orbit. Then I asked her to convert this from miles into feet. Then I divided that by 365 come up with my model scale of 8,447,618,973. With that number input into the solar system scale calculator I confirmed my Earth orbit radius of 58.1 in the results. Next, I wanted to get the moon’s orbit as well as the size of my three solar system objects at this scale. I made sure to select the Moons option and on the form and I got an orbit radius for the moon of 1.79 inches. TINY!! With that radius the average circumference of the lunar orbit is just 11.25 inches. Whats’ the size of the sun, Earth and moon at this scale? According to this same calculator, at this scale the sun is just 6.49 inches in diameter. Of course, the Earth and moon are very tiny! The Earth is just .06 inches in diameter and the moon is .016. Just a spec.

So, I’ve got the scale though in truth it might be best done at a slightly larger scale given how tiny the Earth and moon are in this model. Regardless of the ultimate scale of the model it is fun to play with and I expect it will be a fun model to explore in the yard. The idea would be to set the scale and then discuss the movement of the moon in it’s orbit of the Earth and the Earth’s orbit around the sun. By positioning volunteers it becomes a bit more obvious why a new moon is invisible to us. By adjusting the position of the volunteer “moon” in orbit around the volunteer “Earth” it become easier to understand how the moon gradually becomes more visible as a crescent then a quarter then a full moon and so on. Further discussion of the 5° elevation of the moon off of the ecliptic helps participants further understand why we do not have solar eclipses with every new moon.

Jupiter in an amazing fly-by video


Wired has a great post about the project.

Jupiter is immense. The fifth planet from the sun has a diameter of 89,000 miles, and could easily envelop every other planet (and Pluto). The gas giant also has 2.5 times the mass of all those planets combined. Even its enormous storms boggle the mind: the Great Red Spot is big enough to contain the Earth.

Photos provide glimpses of Jupiter’s grandeur, but you can’t appreciate its stunning scale without some perspective. Gerald Eichstaedt and Seán Doran provide some with a stunning flyby video made from dozens of still photographs taken by the Juno probe.

Precarious

As is my usual routine I took my dog Cosmo out for our walk to the mailbox yesterday. Along the way I had a thought about the precariousness of our existence on Earth. We live in this sort of illusion as our daily life is wrapped in an assumption of stability. For the most part our human brains encounter the same environment everyday. Most of us wake up in the morning and are active during the day. The light from our sun scatters in our atmosphere, heating and lighting and otherwise presenting a world around us that seems stable. Somedays are cloudy, others sunny, often a mix of the two. As we go about our days we see a mix of human and non-human species, natural and human environments. We eat and breath, work, play, and talk.

But our life on this planet exists on the thinnest of onion skins. The biosphere of our planet, the zone in which all life happens is remarkably thin. While the actual thickness of the biosphere is not easily measured it generally falls within a range of 6.5 miles. At the highest we have birds flying as high as 1.1 mile and at the depth we have fish 5.2 miles below the water. There are examples of higher flying birds and deeper dwelling organisms but they are exceptions to the general. The diameter of the earth is 7,918 miles. The radius is 3,959 miles. Almost all life on our planet lives on the outer 6.5 miles of that.

The image above is to scale for size but not distance in orbits

The image above is to scale for size but not distance in orbits

As an amateur astronomer I've spent a good bit of time viewing and contemplating space and distance. For all of the beauty of the stars in the night sky, space is mostly empty. The space between stars is vast. The space between galaxies even more so. If we just turn our attention to our own solar system and what exists here well, again, it's mostly empty space. Our Sun makes up 99.86% of the matter in our solar system. Our Earth, though it is the densest planet in the solar system, is only the tiniest proportion of the mass of our solar system. It barely registers. On the scale of our solar system our Earth is merely a tiny point separated from the sun and other planets by vast distances. To get a sense of it watch this amazing video by Wylie Overstreet in which three guys drove out to the desert of Nevada with a to-scale model to demonstrate the spacing of our solar system.

Our lived experience, our world, is just a precarious, thin layer on what amounts to a very tiny planet. On a clear, dark night I can lookup and see several thousand stars with my naked eyes. In remote locations such as mine there is little light pollution and the atmosphere disappears. It is in this star-lit darkness that I can begin to experience the Earth as a space ship of sorts. It really is a living space ship. In our orbit around the sun we move through space at 67,000 miles per hour. But remember, our solar system is also moving around the center of the Milky Way galaxy at 490,000 miles per hour. Of course we don't see it or feel it directly but it is happening nonetheless.

Life on Earth is precarious. It's stability is not permanent. Our sense of day-to-day continuity is something we're used to and something we assume will continue. I'd suggest that if more people had a better sense of how it all works, had a better sense of just how thin the envelope of safety is, perhaps they might be more inclined to take seriously the warning of science regarding climate change, habitat loss and other aspects of biosphere stability. It's too late to stop much of what we've set in motion but if we don't make real change very soon we will experience the worst case scenarios.