"From the infinitesimal to the infinite . . ."

SCALE OF THE COSMOS

Astronomy grapples with concepts from the infinitesimal to the infinite!  Nuclear particles  which power stellar ob- jects are so tiny, while  galaxies  and the  filaments  com- posed of their  superclusters  are so huge, that they tax our capacity to comprehend their true dimensions!  But let's give it a try, with the aid of  Scale of the Universe 2, Nikon's  Universcale  and  The Size of Space.

Elsewhere on this page we'll also try to give you a sense of the scale of other objects that we all recognize, but which may be larger or smaller than you think!

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SCALE OF THE "OBSERVABLE" UNIVERSE

From the  Hubble eXtreme Deep Field photograph    the observable universe  is now known to contain hundreds of billions—perhaps trillions!—of galaxies!  And it is now calculated to have a diameter of tens of billions of light years, though there is still debate as to its full extent.  To help us appreciate how large the observable universe is and the galaxies it contains, this  awesome video from the Sloan Digital Sky Survey  accurately shows the rela- tive positions of 400,000 galaxies!  Yet this represents only a tiny fraction of the observable universe and all the galaxies in it!  If the latest calculations are correct, then what we "can observe of our universe" must contain mil- lion of times more galaxies than the video displays!  And we mustn't forget that  millions to trillions of stars com- prise each galaxy!  These vast amalgamations of matter and energy, huge in themselves, are arranged in even larger  galaxy clusters    and  superclusters  that make up the immense  galaxy filaments    that stretch across the universe in incredibly complex  3-dimensional webs  and networks!  Millenium Simulation 

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SCALE OF GALAXIES

Galaxies, often described as "island universes", are im- mense collections of star systems, nebulae, interstellar matter and energy bound by gravity.  Often forming clus- ters, galaxies are generally classified by shape  as spiral (which may be barred, as shown just below), elliptical or
irregular, most from a few thousand to half a million light years across.  This sampling of galaxy size comparison charts  #1   #2   #3   #4  begins to give us an idea of how varied the scale of galaxies can be.  Much more on gal- axies is available on our  Deep-Sky Objects  page.

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SCALE OF OUR GALAXY, THE MILKY WAY

Evidence indicates that  our own galaxy the Milky Way is a barred-spiral about 100,000 light-years across  .  This is immense by any earthly standards, and it is interest- ing to note that, even as late as the 1920's, the Milky Way was believed to constitute the entire Universe!

The ground-breaking observations of Edwin Hubble in the 1920's established conclusively that the Universe is far larger than was previously believed.  Moreover, the satellite telescope named after him has shown that hun- dreds of billions—perhaps trillions!—of galaxies exist in the cosmos, whose true extent is so staggering that it is nearly unimaginable!  Compared to a sphere with the di- ameter of the Milky Way, the volume of the known Uni- verse is now believed to be at least 20 quadrillion times larger!  That's a huge number: a 2 followed by sixteen zeroes (20,000,000,000,000,000)!  In fact, this figure is among some of today's more conservative estimates!

Here's a link to the engrossing  100,000 Stars  Chrome Experiment 3-D visualization.  While it does not depict our Solar System's orbital tilts and eccentricities, it does nicely map many  local stars, and reveals the scale of the cosmos from our Sun to the edge of the Milky Way!

This video from NASA shows the  Eventual Collision & Merging of the Milky Way with the Andromeda Galaxy.

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SCALE OF THE CONSTELLATIONS

One interesting aspect of the constellations is that their shapes depend on viewing them from Earth in the pres- ent era.  If we view them from far out in space, say light years from Earth, or view them from far in the past or the future, then  Constellation Shapes Change  enormously!  Viewed from far out in space, the positions of their stars are distorted beyond recognition.  The motions of those same stars over eons has the same effect.

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SCALE OF THE SOLAR SYSTEM

Above we see the scale of the Solar System expressed both in kilometers and in light-time.

And from NASA / JPL-CalTech, here's a fascinating look at a  Logarithmic Scale of our Solar System.  This means that, with the Sun at 0 (zero), beyond 1 AU the distance marked off between any two adjacent numbers is ten times greater than the distance marked off immediately before it!  Though some persons find them confusing, logrithmic-scale diagrams  allow the representation of incredibly vast distances in a limited amount of space.

Don't forget that our page on the  Solar System  offers overhead views of its more central region, where the ma- jor planets orbit the Sun.  This is further explored below.

A CROSS SECTION OF THE SOLAR SYSTEM

Our Solar System is so vast and comprised of so many objects—some "relatively" near one another, yet most separated by great distances—that depicting large parts of it to scale is difficult.  So you will have to look closely just above and to the left.  Able to show only one side of the Solar System out to Neptune, this cut-away displays the 8 major planets' perihelia and aphelia distances  (i.e. when they are closest to and farthest from the Sun), and their orbital inclinations relative to the Ecliptic—all to scale.  Also indicated are regions where  Smaller Worlds  populate the Solar System: the Asteroid Belt, the expan- sive realm of the Centaurs, and the edge of the Kuiper Belt, which stretches from the orbit of Neptune to over 50 au from the Sun!  (Note: when you hover above to reveal the "relative" sizes of the planets, their scale is hugely enlarged compared to that of the cross section!)

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APPARENT SIZE OF THE SUN
FROM THE MAJOR PLANETS

Below and at left, slide the blue pointer left and right "or" click along the Astronomical Unit (au) scale (which also shows light-time) to  inspect the Sun's relative apparent size from from Mercury all the way out to Neptune!  Most browsers (though not Safari) also permit you to use your keyboard Arrow Keys to "fine-tune" your slider position.  Clearly the Sun, which simultaneously scorches Mercury and bakes Venus, is not nearly so prominent in the frigid skies of the Solar System's distant outer planets!

This page opens with the Sun (below) seen from Earth.  The perihelia and aphelia of the major planets are shown

in the cross section just above the zoomable Sun.  Note that Venus's and Earth's orbits are so circluar that their extremes of distance are less than one pixel apart at this scale!  At the Inner Planets in particular you will have to look closely—or zoom your browser—to pinpoint your distance!  Mercury is especially seared by the Sun, and much more at its perihelion than its aphelion!  Mars is close enough to the Sun that  the Martian seasons are affected by the planet's orbital eccentricity!  Uranus has the greatest difference between its nearest and farthest distances from the Sun!  Yet the planet's orbit is so large that  the Sun does not look much different from Uranus's perihelion to its aphelion!  What other intriguing facts will you discover from planet to planet—and in between?

As you examine all this, you should also check out the  Relative Intensity of Sunlight at the Planets.  Since the human eye can adapt so well to varying light levels, you may be surprised by what "daylight looks like" as you venture further out in the Solar System.

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SCALE OF THE SUN-EARTH DISTANCE

Below, the partial cross section of the Ecliptic shows the Sun (tiny, at left) and its distance from Earth in their cor- rect relative dimensions.  However, even here in the in- ner Solar System we are forced to face the broad ranges of sizes and distances that characterize our universe.  At this view's scale Earth's size must be exaggerated.  If it were represented proportionately here, Earth (tiny dot at right) would be less than 1/10 of a pixel in diameter!

By earthly standards, one Astronomical Unit (au) seems very large.  Yet by the standards of the universe, it is ac- tually not quite so impressive.  To the edge of the Oort Cloud is one light year from the Sun, or over 63,000 au!  And the nearest stars are over four times farther away!

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SCALE OF THE SUN

The Sun is so immense that the
Moon's orbit would easily fit inside!

And don't forget to check out our  Sun  page.

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SCALE OF STARS

Stars vary greatly in size, brightness, lifetimes, even in the nuclear reactions that power them.  For example, a neutron star and a quark star would fit in the Grand Can- yon, while the largest supergiants and hypergiants have diameters as large as the orbit of Saturn!  Much on the scale of stars is available on our  Stellar Objects  page.

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SCALE OF MAJOR MOON DISTANCES

The cross sections just below show the distances of the major moons of Earth, Jupiter, Saturn, Uranus and Nep- tune, all in the same scale, confirming that major moons can orbit their parent planets at a range of distances.

However moons cannot orbit too close to their parent planets!  Within a planet's  "Roche Limit", moons will be torn apart by tidal forces!  The rings of the Gas Giants—partly denoted here—are examples of this effect.

ELEMENTS OF URANUS'S
MAJOR MOON ORBITS

	Period (Earth Days)	Orbital Inclin- ation	Radius (103 km)	Eccen- tricity
Mir	1.413	4.34°	129.90	0.0013
Ari	2.520	0.04°	190.90	0.0012
Umb	4.144	0.13°	266.00	0.0039
Tit	8.706	0.08°	436.30	0.0011
Obe	13.46	0.07°	583.50	0.0014

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SCALE OF THE EARTH-MOON DISTANCE

Probably because they are addressing a different issue than size, most depictions of Earth, the Moon and the distance between them do not show them at their proper relative scale.  In the partial cross section directly below they are represented accurately—including the extremes of perigee and apogee of the lunar orbit!  For reference, you may also view the time required to send a photon to the Moon and bounce it back to Earth!  Clicking as noted at left will confirm that—due to the Scale of the Cosmos —even light-speed communication with our nearest ce- lestial neighbor is not instantaneous!  (See below left.)

Moon Distances (in Earth equatorial diameters):
Min Perigee = 27.9, Average = 30.1, Max Apogee = 31.9

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SCALE OF THE MAJOR PLANETS

Here's an interesting way of viewing the relative sizes of the planets.  Note how small the Inner Planets (Mercury, Venus, Earth & Mars) are compared to the Outer Planets (Jupiter, Saturn, Uranus & Neptune.)

Here's an older but effective interactive for a side-by-side  Planet Size Comparison.  Select planets and click on "COMPARE".  Or use the  NASA/JPL "Eyes" Orrery  to compare them in 3-D!

Axial Tilts of the Planets 

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SCALE OF EARTH AND THE MOON

Even the two worlds that we consider the most familiar, Earth and the Moon, can surprise us when shown in the same relative scale!  Our video  How Big Is Our Moon?  will help clear things up!  And Earth and our Moon are shown in the correct relative scale just below—enlarged in the foreground of their view with the lunar orbit.  (P.S. Don't forget to check out our  Moon  page.)  As a bonus here is the Moon's Velocity around Earth!

      Mean:    3,680 km/hr
                    (about as fast
                    as an SR-71)
      Min:    3,480 km/hr
      Max:    3,950 km/hr

You'll get a good sense of the true relative sizes of Earth, the Moon and the lunar orbit at 3:27 into  this video,  as Earth and the Moon accurately orbit their barycenter.

COMPARE MOON TO EARTH'S CONTINENTS

The Moon's surface area is a bit less than
the area of Asia, Earth's largest continent,
and a bit greater than the area of Africa,
Earth's second largest continent!

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SCALE OF COMMON
EARTH-SATELLITE ORBITS

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SCALE OF THE ISS
The International Space Station

This enlightening image from NASA shows the scale of the ISS, the International Space Station.  Is it larger or smaller than you thought?  This is the largest structure ever assembled in space by humankind.  To view in high resolution and save the high-res PDF,  click here.  And from ESA here is a  high-res exploded view of the ISS.

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SCALE OF THE HUBBLE AND THE
JAMES WEBB SPACE TELESCOPES

This comparison really has us excited!  Why?  Because the  James Webb Space Telescope (JWST)    will be able to peer deeper into the cosmos and therefore fur- ther back in time than Hubble.  In fact, it will peer back over 275 million years closer to the Big Bang than Hubble can!  Where is Webb?  Orbit

Hubble was about the size of an average school bus.  In contrast, the James Webb Space Telescope will be more on the order of the size of a tennis court!

Scroll the image below to see how much further into space and time the JWST will peer, thereby increasing our understanding of the scale of the cosmos.

Scroll the image below to compare the electromagnetic wavelengths used by Hubble, the JWST and other satellites and observatories to study the cosmos.

Interactive Electromagnetic Spectrum  Drag white bar.

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SCALE OF THE JUNO SPACECRAFT

Compare to Other Spacecraft

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SCALE OF THE MARS CURIOSITY ROVER

Though the Mars rovers have come in a variety of sizes, the Curiosity Rover is roughly the size of a small SUV.