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The Solar System
Transcript of The Solar System
Planets Which is which? Measuring Planetary Distances and Sizes Debris In The Solar System An Inventory of the Solar System Created by Tyler Baxter This content is available for educational purposes only. This presentation will cover four important topics: • General planetary properties What's the difference between the two? Shall we begin? Let's take a closer look at our solar system. As you can see here, our solar system consists of one star and eight planets. While not shown in this picture,
the asteroid belt between Mars
and Jupiter counts as part of the solar
system, too! It doesn't appear that this picture
shows Pluto, either. Despite this, we can still say that Pluto
is a part of our solar system.
A full inventory of our solar system reveals
an additional 5 dwarf planets, 166 moons,
7 asteroids, over 100 Kuiper Belt objects
larger than 200 miles long, tens of thousands
of smaller asteroids, and countless
meteoroids floating around in space
(at this current time). That's a lot of space junk! But hey!
What about the distances between the planets?
The picture we saw earlier made them look like they were pretty close together.. is that right? Well.. not really. While the planets are closely spaced on an astronomical scale.. ... there's a LOT of space between them.
We know each planet's distance from the Sun by using Kepler's laws, as well as utilizing radar ranging.
Let's look at an overhead view. It might be easier to learn a bit more with a different perspective. As we can see in this picture,
the distance between the planets increases
as we go farther from the Sun. While the rocky planets are extremely close together on this scale, the larger, more distant jovian planets are waaaay out there! (Especially Pluto!) From the picture,
we can tell that the solar system is pretty flat on a large scale. All of the planets orbit the Sun
counter-clockwise as seen from
above the Earth's north pole, and
all in the same plane as Earth as
(Mercury being a slight exception.) For classification purposes, the planets are
split into two different categories: The innermost planets, Mercury, Venus, Earth, and Mars are primarily rocky and dense. These are known as 'the terrestrial planets'. The word 'terrestrial' derives
from the Latin word terra,
meaning "land" or "earth". The outer larger planets, Jupiter, Saturn, Uranus, and Neptune all belong to a group known as 'the jovian planets', after Jupiter, the largest member of the group. The word 'jovian' comes from
"Jove", another name for the
Roman god Jupiter. The primary differences between these two categories is more than just mere labeling.
Let's take a look at a chart that compares the two. Terrestrial Planets:
• Close to the Sun
• Closely spaced orbits
• Small masses
• Small radii
• Predominately rocky
• Solid surface
• High density
• Slower rotation
• Weak magnetic fields
• No rings
• Few number of moons Jovian Planets:
• Far from the Sun
• Very widely spaced orbits
• Very large masses
• Large radii
• Predominately gaseous
• No solid surface
• Low density
• Faster rotation
• Very strong magnetic fields
• Many rings
• Many moons Asteroids, meteors, and comets! Why geometry has use
outside the classroom! Earlier, it was mentioned that the sizes of the planets and their distances from the Sun were found using radar and Kepler's laws.
But what about before radar, or before Kepler's laws? Did anyone know the sizes before then? Well, actually... There's a really cool trick we can do using geometry.
If we know the distance to the object we want to know the size of, we can utilize a simple argument first postulated by the Greek geometer, Euclid. For an example, let's try it with the moon. First, we will need to create a visualization.
Let's make a circle that represents the moon's orbit. Orbit of the moon! Next, we'll put the moon
on this line. The line will go
directly through the center of the moon. The moon! In the center of the circle
will be us, the observer. The orange line will represent the
moon's diameter, which we don't know
for this example. This white line will represent the distance from us (the observer) to the moon's orbit. We will define the distance as 384,000 kilometers. Looking at the moon, we see
that it takes up about 31 arc
minutes in the sky (little over half a degree). This measurement of arc seconds
and degrees is what's known as the
"angular diameter". What's interesting is..
If we look at the angular diameter
here (the orange arrow).. .. and if we look
at the actual diameter
of the moon.. There's an interesting ratio going on.
The ratio of the small orange arrow
(the angular diameter) to the moon's orbit
is EXACTLY the same as the ratio as the
moon's actual diameter (the orange line)
to 360° of a full circle! A mathematical representation would
look something like this: diameter
2π x distance angular diameter
360° Using the measurements we provided for the distance and the angular measurement of the moon in the sky, the equation turns into the following: diameter = distance x angular diameter ___________________ 57.3° But is it right? Let's double-check. 384,000 kilometers x (31/60)° / 57.3° = 3,460 kilometers.
Were we close?
According to radar measurements conducted by NASA, a more
precise measurement of the moon's diameter gives 3,476 kilometers.
Cool, huh? All we used was simple geometry, and we were only off by
6 kilometers! Thanks for watching! "In all our searching, the only thing we've found
that makes the emptiness bearable is each other."
- Carl Sagan