The Universe in Perspective

 

5: The Neighborhood

 

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"In more than one respect, the exploring of the Solar System [...] constitutes the beginning, much more than the end, of history." - Carl Sagan

 

 

Stylized SunThe Neighborhood: Our Solar System


The Solar System has 8 planets (now that Pluto has been, rightly, demoted from planet-status).

From closest to the Sun to the farthest they are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Now that we have the Earth as our "measuring tool", we can just make direct comparisons and we'll be going in size order from smallest to largest.

What we'll be doing is placing the center of the planet under consideration at the center of Earth (remember Earth has a radius of 6,371 km).

(Note: In almost all illustrations below will be links to larger versions, each of these links will open in another window/tab.)

 

Our first comparison is with Mercury, the smallest planet. Were we to place Mercury at Earth's center, we will find the surface of Mercury is 3,931 km under our feet.


Mercury

Closest to the Sun, and with no atmosphere to speak of, it is as pock-marked by craters as is the Moon, which, by the way, is only slightly smaller than Mercury.

A larger version can be seen here.

Photo courtesy of NASA.


Mercury

 

Next is Mars, giving the same treatment to Mars we find its surface 2,982 km under our feet.


Mars

Fourth planet from the Sun. It is not as cratered because it does have a (thin) atmosphere and "weather" which erodes craters, as also happens on Earth.

Photo courtesy of NASA.


Mars

 

Next is Venus, our "sister planet" for reasons that will become clear. When Venus is given this treatment we find its surface only 325 km below our feet.

Venus is almost exactly the same size as Earth and so has similar area and volume and mass. Hence, sister planet. But that is where the similarity ends, it is fatally hot, poisonous, and has a very heavy, crushing, atmosphere.


Venus

Second planet from the Sun. There are two pictures here, one as it is normally seen: Cloudy. Sulphuric acid cloudy.

The other image shows it mapped using a variety of methods allowing us to see under the clouds.

Photos courtesy of NASA.


Venus with Clouds

Venus mapped

 

A quick pause for a selfie. One is the famous "Blue Marble", and the second is a more recent version.


Earth

Third planet from the Sun. No need for long-winded descriptions and you can read about it in Chapter 4. Beautiful isn't it?

Larger versions can be seen here and here.

Photos courtesy of NASA.


Earth Blue Marble

Earth recent


We now need to switch gears. Earth and the above planets are the innermost planets, often called "terrestrial" because they are mostly rock. Earth is the largest of these four.

The four remaining outer planets are called "gas and/or ice giants". Let's see why.

Since the remaining planets are all bigger than the Earth, we'll placing Earth's center at the center of the planet in question.

The smallest "giant" is Neptune. Were Earth placed at its center the surface of Neptune would be 18,367 km above our heads. Keep in mind that Neptune's radius is just shy of 3 times Earth's radius. This means it will have an area almost 9 times that of Earth and a volume about 27 times that of Earth (very roughly).

Earth, big on our personal scale, has just substantially shrunk based on Neptune's scale.


Neptune

Eighth planet and furthest from the Sun. It is mix of gas and "ice", exotic chemical ice. Extremely cold, and perhaps the stormiest planet. Storms whip at an accelerated pace over its "surface".

Photos courtesy of NASA.


Neptune

 

The next biggest is Uranus. Pronunciation is an issue, in English at least. I like to pronounce it as oo-rah-nus. "oo" rhymes with who. "rah" with caw. "nus" with noose.

If Earth is placed at its center Uranus' surface would be 19,157 km above our heads. Not too much more than Neptune and so we see that Neptune and Uranus are also "sister" planets in terms of size.


Uranus

Seventh planet from the Sun. It is also a mix of gas and "ice". Interesting in that it orbits the Sun on its side, meaning the poles take turns pointing at the Sun.

A larger version can be seen here.

Photos courtesy of NASA.


Uranus

 

Next comes Saturn. Give Earth "the center treatment" and we would find Saturn's surface 53,830 km over our heads!


Saturn

Sixth planet from the Sun. This is a true gas giant, as is Jupiter. Interesting in that it has spectacular rings. Well it turns out all the outer planets have rings, but Saturn's are the most visible.

A larger version can be seen here.

Photos courtesy of NASA.


Saturn

 

And last we have Jupiter.

Jupiter's surface would be 65,041 km above our heads.


Jupiter

Fifth planet from the Sun, our system's largest planet.

Interesting in that it is really really big. And beautiful.

A larger version can be seen here.

Photos courtesy of NASA.


Jupiter

 

There is an elephant in the room and that elephant is Jupiter.

Consider all you know about Earth now, just how big it is. Consider the comparisons we've made between Earth and the other planets.

Well, Jupiter is so big that it alone has a mass 2 and a half times greater than all the other planets and moons of our Solar System combined. Jupiter's volume can hold 1,321 Earth volumes, it's mass is 318 times Earth's.

This is, of course, gigantically big. Planets (probably) don't get much bigger than this. Were they heavier the extra mass would tend to contract the planet through the increased gravity.

Theoretically Jupiter would have to be 70-80 times more massive before it could start Hydrogen fusion in its core (becoming a "brown dwarf"), and so Jupiter is sometimes called a "failed star".


Jupiter moon transits

Here we see two of Jupiter's moons transiting; that is, crossing Jupiter's face. These moons are about the size of our Moon.

A larger version can be seen here.

Photos courtesy of NASA.


Jupiter moon transits

 

Before moving on I'd like to show you a very poignant selfie...


Earth from Saturn

Here you can see some exquisite detail of Saturn's rings.

And the blue dot? Yes, that is Earth.

A larger version can be seen here.

Photos courtesy of NASA.


Earth from Saturn

 

We've neglected something about our "Sol"ar system, until now, and that is that a "Sol"ar system needs a "Sol". A star. A Sun.

I mentioned this in the previous chapter but again: The picture at the top left of this page shows, in approximate scale the Sun, Jupiter (black circle), and Earth (black dot). But this doesn't do the scale justice. See the wonderful illustration below:


Solar System to Scale

This gorgeous illustration shows the objects in our Solar System to scale. Fitting it on this page does not do it justice, I recommend you use one of the links below to see the detail.

A larger version can be seen here. And an even larger version (27 megabytes) here. Depending on your browser you may need to click the image to show full enlargement, and then you will have to scroll.

Illustration courtesy of Roberto Ziche. Used with permission.


Solar System to Scale

 

Were we to place Earth at the Center of the Sun, the Sun's surface would be 689,971 km above our heads. Were we to place the Earth-Moon system at the Sun's center, the Moon's orbit would still be 311,947 km below the Sun's surface.

Put another way, were we at the Sun's center, its surface would be almost twice as far away as the Moon is. Think about that for a moment the next time you gaze at the Moon.

If Jupiter is the elephant in the room, then the Sun is the Mega-Brontosaurus in the room, plus some.

The Sun's volume is equal to just under 1000 Jupiter volumes. And is equal 1,303,533 Earth volumes.

The Sun contains 99.9% of the mass of the entire Solar System. All the planets, moons, asteroids, comets? They make up 0.1%.

Count out 1000 grains of rice on a table. Take one grain away. That single grain represents all the planets, moons, etc. The remaining 999 rice grains are Sun.

The Sun's mass is 2 × 1030 kg.

1030!

That's a quadrillion quadrillions.

Wow.

The Sun has a radius of 696,342 km. Our time tested method of comparison of running a Marathon a day (5 months for an Earth radius) falls down here a bit because the time it would take for a Sun radius is 45 years.


Transit of Mercury

Here is a time lapse photo of the planet Mercury crossing the face of the Sun.

Yes, Mercury is smaller than Earth, but only a few times smaller.

Photo courtesy of NASA.


Transit of Mercury

 

The Sun's area is 6 × 1018 m2 (Earth is 5 × 1014). It's volume is 1.4 × 1027 m3 (Earth is 1 × 1021 m3).

Nothing much more to be said.

Remember your "personal-volume" from the previous chapter? Our beautiful, interesting, LARGE Earth has shrunk to the approximate size-relation of your "personal-volume" of 2.44 m3 (based on your "height" of 1.67 m) compared to the Khufu pyramid (opens in new tab or window). If you've had the opportunity to stand next to Khufu, you have a really good idea of just how massively big the Sun is compared to Earth.


Summary of the linear distances outlined above. If the planet is smaller than Earth then its center is placed at the Earth's center. If larger, then Earth is placed at that planets center.

Negative numbers indicate how many kilometers under our feet the planet would be, and positive numbers indicate how high over our heads the planet's surface would be.


Relative size of planets and Sun to Earth
Body Relative Distance to body's surface

Mercury

-3,931 km

Mars

-2,982 km

Venus

-325 km

Neptune

18,367 km

Uranus

19,157 km

Saturn

53,830 km

Jupiter

65,041 km

Sun

689,971 km

 

Some Sun facts:

The Sun is a giant (exclamation point) ball of gas, 99% of which is Hydrogen and Helium, the lightest gases known. Its gigantic mass comes from the fact that there is so much of it. The Sun's average density is 1.408 g/cm3, compared to Earth's 5.515 g/cm3.

But the Sun is so enormous that it compresses itself simply due to the gravity of the hundreds of thousands of kilometers of gas and the density at the Sun's center is 162 g/cm3.

And the pressure at Sun center? Remember 1 atmosphere (atm) is the pressure of air at Earth's sea level surface. The pressure at Sun center is 2.445 × 1011 atm. More about this in later chapters.


 

We've now characterized the relative sizes of the elements of our Solar System but one thing remains...

...Distances.

If you look at the Ziche's illustration above you will see on the right hand side an approximate scale of distances as well, you will need to look at the bigger versions to see it well.

And we'll do some more comparisons right now.

Significant distances, for us, will be "familiar" distances like Earth to Moon, Earth to Sun, and Sun to Neptune (farthest planet out and so the radius of our Solar System).

We'll compare these distances using time.

A jetliner, think Boeing or Airbus, travels around 250 m/s at top speed, it takes 4 seconds to go 1 kilometer, equivalent to 900 km/h.

Taking a jetliner to the Moon would take about 18 days.

Taking a jetliner to the Sun would take 19 years, and out from Sun to Neptune about 570 years.

Our everyday speeds we're familiar with just don't cut it. The distances are just too big. We can cut this time by traveling faster, but what speed to choose?

Here is one with which we are all (sort of) familiar: The speed of the Earth.

Earth lies 1 AU from the Sun (remember AU stands for astronomical unit). The AU's average size in more familiar terms is 149,597,870,700 meters (1.496 × 1011 m). This means the Earth's orbital circumference, the distance Earth travels around the Sun, is about 9.4 × 1011 m, almost a trillion meters.

It takes the Earth one year (365.25 days) to travel that distance which means, by simple division, the Earth is moving around the Sun at 29,780 m/s (29.78 km/s). That's pretty fast. Let's call that E-speed.

Traveling from Earth to Moon at E-speed takes 3.5 hours, from Earth to Sun 58 days. And from Sun to Neptune? 4.8 years.

But wait. What is the fastest anything can go in our Universe? You know that it is light which travels at, ahem, light speed. This is 299,792,450 m/s (3 × 105 km/s).

Please notice it is defined in terms of seconds, not hours.

Using light speed we find Earth to Moon takes 1.28 seconds, and Earth to Sun takes 8.3 minutes. Sun to Neptune takes 4 hours 10 minutes.

Now why bother using the speed of light? How is that familiar to us?

Of course, its not familiar to us, but we will need it and so need to become familiar with it.

Why?

Because the Universe is really big and we'll be leaving our Solar Sytem soon.

We are not, of course, the only Solar System in the Universe, you know that by the twinkling of thousands of other stars at night.

The closest other star to our Solar System is called Alpha Centauri. How does the distance to Alpha Centauri relate to our Solar System distances??

At jetliner speeds it would take 5 million years to get there. At E-speed it would take 42,563 years.

And it takes, at light speed, 4.25 years.

Mind blown, yes?

Our HUGE Solar System can be traversed in a couple of hours at light speed but takes years to get to the next closest star system.

We'll be adding, as we must, a new measure of length called the "light year". It is the distance (length) light travels in one year and equals 9.461 × 1015 meters.

Alpha Centauri is about 4 × 1016 m away. To avoid using numbers like this, using light years (abbreviated ly) is easier to read: Alpha Centauri is 4.25 ly away.


Summary of times needed to traverse the Solar System...

...and beyond...

...to Alpha Centauri.


Interstellar travel times
 

Jetliner
250 m/s

E-speed
29,780 m/s
light speed
3  × 108 m/s
Earth to Moon 18 days 3.5 hr 1.28 s
Earth to Sun 19 yr 58 days 8.3 min
Sun to Neptune 570 yr 4.8 yr 4 hr 10 min
Sun to Alpha Centauri 5 million yr 42,563 yr 4.25 yr

 

Lastly, Looking at these distances another way,...

...Let's imagine that we shrink all these objects by the same amount, shrinking the Sun to have a diameter of only 1 meter.

Then Earth will be about 9 mm in diameter and lie 107 m away from the 1 meter Sun.

Jupiter will be 10.2 cm in diameter and at a distance of 562 m.

Neptune will be 3.5 cm in diameter and be found at 3,231 m from the Sun.

And Alpha Centauri would, on this scale, be found 28,720 kilometers away from our 1 meter wide Sun. 28,700 km is about three quarters of the way around the equator.

This is like placing our 1 m Sun in Indonesia, then going around the equator over the entire pacific ocean, then crossing Ecuador/Colombia/Brazil, then crossing the Atlantic Ocean to Africa, over Gabon and the Congo, and ending up in Kenya to find another 1 m diameter star: Alpha Centauri.

So, re-inflate your blown mind and we'll continue outside of the Solar System in the next chapter.

BTW, all the planets and Sun are really interesting and so many new things have been learned in the past few decades. I encourage you to search internet and read up on all of them, and don't forget the NASA images. Just awesome stuff.

In the next chapter we take on the Universe.

I'll leave you now with a picture of the Sun, the source that makes possible all life on Earth.


Sun in other light

Here is a picture taken of the Sun in other light wavelengths than visible light. Much detail and the krazy kool corona is now visible.

You can see a larger version here.

Photo courtesy of NASA.


Sun in other light

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