Saturn Archives

May 12, 2014December 23, 2015 by Bob King

Saturn Disappears Behind the Full Flower Moon May 14 – Watch it Live

Simulation of the moon closing in on Saturn just prior to occultation. Credit: Gianluca Masi using SkyX software

Funny thing. Skywatchers are often just as excited to watch a celestial object disappear as we are to see it make an appearance. Early Wednesday morning (May 14) the Full Flower Moon will slip in front of Saturn, covering it from view for about an hour for observers in Australia and New Zealand. If you don’t live where the dingoes roam, no worries. You can watch it online.And no matter where you are on the planet, the big moon will accompany the ringed planet across the sky this Tues. night-Weds. morning.

Moon-Saturn occultation from Perth, Australia Feb. 22, 2014 captured by Colin Legg

Occultations of stars happen swiftly. The moon’s limb meets the pinpoint star and bam! it’s gone in a flash. But Saturn is an extended object and the moon needs time to cover one end of the rings to the other. Planetary occultations afford the opportunity to remove yourself from planet Earth and watch a planet ‘set’ and ‘rise’ over the alien lunar landscape. Like seeing a Chesley Bonestell painting in the flesh.

Saturn and the moon tomorrow night just before midnight as viewed from the Midwestern U.S. View faces south-southeast. Stellarium — Saturn and the moon Tuesday night (May 13) just before midnight as viewed from the U.S. Stellarium

As the moon approaches Saturn, the planet first touches the lunar limb and then appears to ‘set’ as it’s covered by degrees. About an hour later, the planet ‘rises’ from the opposite limb. Planetary occultations are infrequent and always worth the effort to see.

Seen from the northern hemisphere and equatorial regions, the nearly full moon will appear several degrees to the right or west of Saturn tomorrow night (May 13). As the night deepens and the moon rolls westward, the two grow closer and closer. They’ll be only a degree apart (two full moon diameters) during Wednesday morning twilight seen from the West Coast. Northern hemisphere viewers will notice that the moon slides to the south of the planet overnight.

Map showing the region where the occultation of Saturn will be visible. Click to get the times of Saturn's disappearance and reappearance for individual cities. Times are given in UT or Universal Time. Add 9.5 hours for Australian Central Standard Time. Credit: IOTA — Map showing the region where the occultation of Saturn will be visible. Click to get times of Saturn’s disappearance and reappearance for individual cities. Times shown are UT or Universal Time. Add 9.5 hours for Australian Central Standard Time. Credit: IOTA

Skywatchers in Australia will see the moon cover Saturn during convenient early evening viewing hours May 14:

* 8:09 p.m. local time from Adelaide

* 9:05 p.m. Brisbane

* 8:50 p.m. Melbourne

* 8:53 p.m. Canberra

* 8:56 p.m. from Sydney (More times and a map – click HERE)

Before the occultation, Saturn will shine close to the moon’s upper right and might be tricky to see with the naked eye because of glare.

Binoculars will easily reveal the planet, but a telescope is the instrument of choice. Even a small scope magnifying at least 30x will show Saturn and its rings hovering above the bright edge of the moon. Stick around. About an hour later, Saturn will re-emerge along the moon’s lower left limb.

Saturn and its moons Tuesday night May 13 around 10 p.m. CDT. Titan's the brightest and easiest. Iapetus ranges from magnitude +10 when it's west of Saturn and we see its bright hemisphere to magnitude +12 when it's west of the planet as it will be this week. Created with Meridian software — Saturn and its moons Tuesday night May 13 around 10 p.m. CDT. Titan’s the brightest and easiest moon to see at magnitude +8.5. Iapetus ranges from magnitude +10 when it’s west of Saturn and we see its bright hemisphere to magnitude +12 when it’s east of the planet. Created with Meridian software

Meanwhile, back in the western hemisphere, we’ll watch the nearly full Flower Moon make a close pass of the planet. If you’ve had difficulty finding the celestial ring bearer, you’ll have no problem Tuesday night. Take a look at Saturn’s wonderful system of rings in your telescope – they’re tipped nearly wide open this year. For even more fun, see how many moons you can spot. And don’t forget, you can watch it online courtesy of astrophysicist Gianluca Masi. His Virtual Telescope website will broadcast the occultation live starting at 10:15 Universal Time May 14 (6:15 a.m. EDT, 5:15 CDT, 4:15 MDT and 3:15 PDT).

May 4, 2014May 5, 2014 by Fraser Cain

Virtual Star Party – May 4, 2014: It’s Galaxy Season!

Hosts: Fraser Cain and Scott Lewis
Astronomers: Gary Gonella, Andrew Dumbleton, Stuart Foreman, David Dickinson, Shahrin Ahmad and special guest Henna Khan from Bombay, India

Tonight’s Views:
the Moon’s surface
M44 Beehive Cluster
Neutron Star B224 from HST
All-Sky View
Mars with ice caps and Hellas Basin visible
Comet C/2012 K1 PanSTARRS
Stuart demonstrating how to work with software to process images
M51a Whirlpool Galaxy
M53 Globular Cluster
Rosette Nebula – NGC 2237, 2238, 2239 and 2246
Saturn
Horsehead Nebula (Barnard 33 in emission nebula IC 434) and Flame Nebula (NGC 2024) with a satellite trail
NGC 5139 Omega Centauri
M42 Orion Nebula
M63 Sunflower Galaxy
NGC 7635 Bubble Nebula
Large and Small Magellanic Clouds

We hold the Virtual Star Party every Sunday night as a live Google+ Hangout on Air. We begin the show when it gets dark on the West Coast. If you want to get a notification, make sure you circle the Virtual Star Party on Google+. You can watch on our YouTube channel or here on Universe Today.

May 1, 2014December 23, 2015 by Jason Major

Cassini’s View of Another Pale Blue Dot

Uranus as seen by Cassini on July 19, 2013 (NASA/JPL-Caltech/SSI)

When you hear the words “pale blue dot” you’re probably reminded of the famous quote by Carl Sagan inspired by an image of Earth as a soberingly tiny speck, as imaged by Voyager 1 on Feb. 14, 1990 from beyond the orbit of Pluto. But there’s another pale blue world in our Solar System: the ice giant Uranus, and its picture was captured much more recently by the Cassini spacecraft from orbit around Saturn on April 11, 2014.

Released today by the Cassini Imaging Team, the image above shows Uranus as a tiny blue orb shining far beyond the bright hazy bands of Saturn’s F ring.

“Do you relish the notion of being a Saturnian, and gazing out from the lofty heights of Saturn at the same planets we see here from the Earth?”
– Carolyn Porco, Cassini Imaging Team Leader

Uranus’ coloration is a result of methane high in its frigid atmosphere. According to the description on the CICLOPS site, “methane on Uranus — and its sapphire-colored sibling, Neptune — absorbs red wavelengths of incoming sunlight, but allows blue wavelengths to escape back into space, resulting in the predominantly bluish color seen here.”

This was also the first time Uranus had been imaged by the Cassini spacecraft, which has been in orbit around Saturn since 2004. In fact its ten-year orbital anniversary will come on July 1.

This image adds one more planet to the list of worlds captured on Camera by Cassini, which made headlines last fall when a glorious mosaic was released that featured a backlit Saturn in eclipse surrounded by its luminous rings, the specks of several of its moons, and the distant dots of Venus, Mars, and the Earth and Moon. Made from 141 separate exposures, the mosaic was captured on July 19, 2013 — known by many space aficionados as “the day the Earth smiled” as it was the first time the world’s population was alerted beforehand that its picture would be taken from over 900 million miles away.

Saturn — with its terrestrial spacecraft in tow — was about 28.6 AU away from Uranus when the image was acquired. That’s about 4.28 billion kilometers (2.66 billion miles). From that distance the glow of the 51,118-kilometer (31,763-mile) -wide Uranus is reduced to a mere few pixels (which required digital brightening by about 4.5x, as well.)

Read more on the Cassini Imaging Central Laboratory for Operations (CICLOPS) page here and in a news release from NASA’s JPL here.

Image credit: NASA/JPL-Caltech/SSI. Source: Carolyn Porco, CICLOPS Director

April 29, 2014April 29, 2014 by Fraser Cain

Virtual Star Party – April 26, 2014- Hangoutathon Special Edition!

This week’s Virtual Star Party was a special 2-hour Saturday night version recorded as part of the Cosmoquest Hangoutathon. The Star Party at this link starts at 1 hour in – we’ll get an edited version up soon!
Continue reading “Virtual Star Party – April 26, 2014- Hangoutathon Special Edition!”

April 25, 2014February 9, 2021 by Fraser Cain

Weekly Space Hangout – April 25, 2014: Asteroids, ISS Repairs & an Annular Eclipse

Host: Fraser Cain
Guests: Morgan Rehnberg, Brian Koberlein, David Dickinson, Jason Major

This Week’s Stories:
Morgan Rehnberg (cosmicchatter.org / @cosmic_chatter):
EVA
Cosmos
SpaceX announcements

Brian Koberlein (@briankoberlein, briankoberlein.com):
Meteors are not more likely to hit Earth

Dave Dickinson (@astroguyz, www.astroguyz.com):
Saturn at Opposition
Bizarre Annular Eclipse

Jason Major (@JPMajor, LightsInTheDark.com):
B612 Foundation asteroid announcement

We record the Weekly Space Hangout every Friday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch us live on Google+, Universe Today, or the Universe Today YouTube page.

April 24, 2014December 23, 2015 by Ken Kremer

Curiosity Captures First Ever Asteroid Images from Mars Surface

NASA's Curiosity Mars rover has caught the first image of asteroids taken from the surface of Mars. The image includes two asteroids, Ceres and Vesta. This version includes Mars' moon Deimos in a circular, exposure-adjusted inset and square insets at left from other observations the same night. Credit: NASA/JPL-Caltech/MSSS/Texas A&M

NASA’s Curiosity Mars rover has caught the first image of asteroids taken from the surface of Mars on April 20, 2014. The image includes two asteroids, Ceres and Vesta. This version includes Mars’ moon Deimos in a circular, exposure-adjusted inset and square insets at left from other observations the same night. Credit: NASA/JPL-Caltech/MSSS/Texas A&M
More night sky views and surface mosaics below[/caption]

The Curiosity rover has captured the first images of asteroids even taken by a Human probe from the alien surface of the Red Planet during night sky imaging.

And it’s not just one asteroid, but two asteroids caught in the same night time pointing on the Red Planet. Namely, asteroids Ceres and Vesta.

The stupendous image – seen above – was snapped by Curiosity’s high resolution Mastcam camera earlier this week on Sunday, April 20, 2014, Sol 606, whilst she was scanning about during daylight for her next drilling target at “The Kimberley” waypoint she pulled into at the start of this month.

Ceres and Vesta appear as streaks since the Mastcam image was taken as a 12 second time exposure.

“This imaging was part of an experiment checking the opacity of the atmosphere at night in Curiosity’s location on Mars, where water-ice clouds and hazes develop during this season,” said camera team member Mark Lemmon of Texas A&M University, College Station, in a statement.

“The two Martian moons were the main targets that night, but we chose a time when one of the moons was near Ceres and Vesta in the sky.”

View our “Kimberley” region photo mosiacs below to see exactly from where the six wheeled robot took the asteroid image shown above, while driving around the base of “Mount Remarkable”.

And those two asteroids are extra special because not only are they the two most massive objects in the Main asteroid belt between Mars and Jupiter, but they are also the destinations of another superlative NASA unmanned mission – Dawn.

Curiosity Mars rover captured this panoramic view of a butte called "Mount Remarkable" and surrounding outcrops at “The Kimberley " waypoint on April 11, 2014, Sol 597. Colorized navcam photomosaic was stitched by Marco Di Lorenzo and Ken Kremer. Credit: NASA/JPL-Caltech/Marco Di Lorenzo/Ken Kremer - kenkremer.com — Curiosity Mars rover captured this panoramic view of a butte called “Mount Remarkable” and surrounding outcrops at “The Kimberley ” waypoint on April 11, 2014, Sol 597. Colorized navcam photomosaic was stitched by Marco Di Lorenzo and Ken Kremer. Credit: NASA/JPL-Caltech/Marco Di Lorenzo/Ken Kremer – kenkremer.com

The exotic Dawn probe, propelled by a stream of ions, orbited Vesta for a year in 2011 and is now approaching Ceres for an exciting orbital mission in 2015.

Ceres, the largest asteroid, is about 590 miles (950 kilometers) in diameter. Vesta is the third-largest object in the main belt and measures about 350 miles (563 kilometers) wide.

And as if Curiosity’s mouthwatering and heavenly double asteroid gaze wasn’t already spectacular enough, the tinier of Mars’ moons, Deimos, was also caught in that same image.

A trio of star trails is also seen, again due to the 12 second time exposure time.

Furthermore, Mars largest moon Phobos as well as massive planets Jupiter and Saturn were also visible that same Martian evening, albeit in a different pointing.

These celestial objects are all combined in the composite image above.

“The background is detector noise, limiting what we can see to magnitude 6 or 7, much like normal human eyesight. The two asteroids and three stars would be visible to someone of normal eyesight standing on Mars. Specks are effects of cosmic rays striking the camera’s light detector,” says NASA.

An unannotated image is seen below.

Curiosity’s makers back on Earth are nowhere to be seen. But check out the Curiosity’s earlier photo below of the Earth and Moon from my prior article – here.

To date, Curiosity’s odometer totals 3.8 miles (6.1 kilometers) since landing inside Gale Crater on Mars in August 2012. She has taken over 143,000 images.

The sedimentary foothills of Mount Sharp, which reaches 3.4 miles (5.5 km) into the Martian sky, is the 1 ton robots ultimate destination inside Gale Crater because it holds caches of water altered minerals. Such minerals could possibly indicate locations that sustained potential Martian life forms, past or present, if they ever existed.

Martian landscape with rows of curved rock outcrops at ‘Kimberly’ in the foreground and spectacular Mount Sharp on the horizon. NASA’s Curiosity Mars rover pulled into Kimberly waypoint dominated by layered rock outcrops as likely drilling site. This colorized navcam camera photomosaic was assembled from imagery taken on Sol 576 (Mar. 20, 2014). Credit: NASA/JPL-Caltech/Marco Di Lorenzo/Ken Kremer-kenkremer.com

Curiosity has some 4 kilometers to go to reach the base of Mount Sharp sometime later this year.

Stay tuned here for Ken’s continuing Curiosity, Opportunity, Chang’e-3, SpaceX, Orbital Sciences, LADEE, MAVEN, MOM, Mars and more planetary and human spaceflight news.

Ken Kremer

You are here! – As an Evening Star in the Martian Sky. This evening-sky view taken by NASA’s Mars rover Curiosity shows the Earth and Earth’s moon as seen on Jan. 31, 2014, or Sol 529 shortly after sunset at the Dingo Gap inside Gale Crater. Credit: NASA/JPL-Caltech/MSSS/TAMU — You are here! – As an Evening Star in the Martian Sky
This evening-sky view taken by NASA’s Mars rover Curiosity shows the Earth and Earth’s moon as seen on Jan. 31, 2014, or Sol 529 shortly after sunset at the Dingo Gap inside Gale Crater. Credit: NASA/JPL-Caltech/MSSS/TAMU

Mars rock rows and Mount Sharp. Martian landscape scene with rows of striated rocks in the foreground and Mount Sharp on the horizon. NASA's Curiosity Mars rover paused mid drive at the Junda outcrop to snap the component images for this navcam camera photomosaic on Sol 548 (Feb. 19, 2014) and then continued traveling southwards towards mountain base. UHF Antenna at right. Credit: NASA/JPL-Caltech/Marco Di Lorenzo/Ken Kremer-kenkremer.com — Mars rock rows and Mount Sharp. Martian landscape scene with rows of striated rocks in the foreground and Mount Sharp on the horizon. NASA’s Curiosity Mars rover paused mid drive at the Junda outcrop to snap the component images for this navcam camera photomosaic on Sol 548 (Feb. 19, 2014) and then continued traveling southwards towards mountain base. UHF Antenna at right. Credit: NASA/JPL-Caltech/Marco Di Lorenzo/Ken Kremer-kenkremer.com

April 23, 2014May 12, 2018 by Elizabeth Howell

The Inner and Outer Planets in Our Solar System

The Solar System. Credit: spaceplace.nasa.gov

In our Solar System, astronomers often divide the planets into two groups — the inner planets and the outer planets. The inner planets are closer to the Sun and are smaller and rockier. The outer planets are further away, larger and made up mostly of gas.

The inner planets (in order of distance from the sun, closest to furthest) are Mercury, Venus, Earth and Mars. After an asteroid belt comes the outer planets, Jupiter, Saturn, Uranus and Neptune. The interesting thing is, in some other planetary systems discovered, the gas giants are actually quite close to the sun.

This makes predicting how our Solar System formed an interesting exercise for astronomers. Conventional wisdom is that the young Sun blew the gases into the outer fringes of the Solar System and that is why there are such large gas giants there. However, some extrasolar systems have “hot Jupiters” that orbit close to their Sun.

The Inner Planets:

The four inner planets are called terrestrial planets because their surfaces are solid (and, as the name implies, somewhat similar to Earth — although the term can be misleading because each of the four has vastly different environments). They’re made up mostly of heavy metals such as iron and nickel, and have either no moons or few moons. Below are brief descriptions of each of these planets based on this information from NASA.

Mercury: Mercury is the smallest planet in our Solar System and also the closest. It rotates slowly (59 Earth days) relative to the time it takes to rotate around the sun (88 days). The planet has no moons, but has a tenuous atmosphere (exosphere) containing oxygen, sodium, hydrogen, helium and potassium. The NASA MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft is currently orbiting the planet.

The terrestrial planets of our Solar System at approximately relative sizes. From left, Mercury, Venus, Earth and Mars. Credit: Lunar and Planetary Institute

Venus: Venus was once considered a twin planet to Earth, until astronomers discovered its surface is at a lead-melting temperature of 900 degrees Fahrenheit (480 degrees Celsius). The planet is also a slow rotator, with a 243-day long Venusian day and an orbit around the sun at 225 days. Its atmosphere is thick and contains carbon dioxide and nitrogen. The planet has no rings or moons and is currently being visited by the European Space Agency’s Venus Express spacecraft.

Earth: Earth is the only planet with life as we know it, but astronomers have found some nearly Earth-sized planets outside of our solar system in what could be habitable regions of their respective stars. It contains an atmosphere of nitrogen and oxygen, and has one moon and no rings. Many spacecraft circle our planet to provide telecommunications, weather information and other services.

Mars: Mars is a planet under intense study because it shows signs of liquid water flowing on its surface in the ancient past. Today, however, its atmosphere is a wispy mix of carbon dioxide, nitrogen and argon. It has two tiny moons (Phobos and Deimos) and no rings. A Mars day is slightly longer than 24 Earth hours and it takes the planet about 687 Earth days to circle the Sun. There’s a small fleet of orbiters and rovers at Mars right now, including the large NASA Curiosity rover that landed in 2012.

The Outer Planets:

The outer planets (sometimes called Jovian planets or gas giants) are huge planets swaddled in gas. They all have rings and all of plenty of moons each. Despite their size, only two of them are visible without telescopes: Jupiter and Saturn. Uranus and Neptune were the first planets discovered since antiquity, and showed astronomers the solar system was bigger than previously thought. Below are brief descriptions of each of these planets based on this information from NASA.

Jupiter: Jupiter is the largest planet in our Solar System and spins very rapidly (10 Earth hours) relative to its orbit of the sun (12 Earth years). Its thick atmosphere is mostly made up of hydrogen and helium, perhaps surrounding a terrestrial core that is about Earth’s size. The planet has dozens of moons, some faint rings and a Great Red Spot — a raging storm happening for the past 400 years at least (since we were able to view it through telescopes). NASA’s Juno spacecraft is en route and will visit there in 2016.

Saturn: Saturn is best known for its prominent ring system — seven known rings with well-defined divisions and gaps between them. How the rings got there is one subject under investigation. It also has dozens of moons. Its atmosphere is mostly hydrogen and helium, and it also rotates quickly (10.7 Earth hours) relative to its time to circle the Sun (29 Earth years). Saturn is currently being visited by the Cassini spacecraft, which will fly closer to the planet’s rings in the coming years.

Near-infrared views of Uranus reveal its otherwise faint ring system, highlighting the extent to which it is tilted. Credit: Lawrence Sromovsky, (Univ. Wisconsin-Madison), Keck Observatory.

Uranus: Uranus was first discovered by William Herschel in 1781. The planet’s day takes about 17 Earth hours and one orbit around the Sun takes 84 Earth years. Its mass contains water, methane, ammonia, hydrogen and helium surrounding a rocky core. It has dozens of moons and a faint ring system. There are no spacecraft slated to visit Uranus right now; the last visitor was Voyager 2 in 1986.

Neptune: Neptune is a distant planet that contains water, ammmonia, methane, hydrogen and helium and a possible Earth-sized core. It has more than a dozen moons and six rings. The only spacecraft to ever visit it was NASA’s Voyager 2 in 1989.

To learn more about the planets and missions, check out these links:

Solar System Exploration: Planets (NASA)
NASA Photojournal (NASA)
Missions (NASA)
Space Science (European Space Agency)
USGS Astrogeology (U.S. Geological Survey)
The Solar System And Its Planets (European Space Agency)

April 21, 2014July 26, 2016 by Elizabeth Howell

How Far Are The Planets From The Sun?

Artist's impression of the planets in our solar system, along with the Sun (at bottom). Credit: NASA

The eight planets in our solar system each occupy their own orbits around the Sun. They orbit the star in ellipses, which means their distance to the sun varies depending on where they are in their orbits. When they get closest to the Sun, it’s called perihelion, and when it’s farthest away, it’s called aphelion.

So to talk about how far the planets are from the sun is a difficult question, not only because their distances constantly change, but also because the spans are so immense — making it hard for a human to grasp. For this reason, astronomers often use a term called astronomical unit, representing the distance from the Earth to the Sun.

The table below (first created by Universe Today founder Fraser Cain in 2008) shows all the planets and their distance to the Sun, as well as how close these planets get to Earth.

Mercury:

Closest: 46 million km / 29 million miles (.307 AU)
Farthest: 70 million km / 43 million miles (.466 AU)
Average: 57 million km / 35 million miles (.387 AU)
Closest to Mercury from Earth: 77.3 million km / 48 million miles

Venus:

Closest: 107 million km / 66 million miles (.718 AU)
Farthest: 109 million km / 68 million miles (.728 AU)
Average: 108 million km / 67 million miles (.722 AU)
Closest to Venus from Earth: 40 million km / 25 million miles

Earth:

Closest: 147 million km / 91 million miles (.98 AU)
Farthest: 152 million km / 94 million miles (1.01 AU)
Average: 150 million km / 93 million miles (1 AU)

Mars:

Closest: 205 million km / 127 million miles (1.38 AU)
Farthest: 249 million km / 155 million miles (1.66 AU)
Average: 228 million km / 142 million miles (1.52 AU)
Closest to Mars from Earth: 55 million km / 34 million miles

Jupiter:

Closest: 741 million km /460 million miles (4.95 AU)
Farthest: 817 million km / 508 million miles (5.46 AU)
Average: 779 million km / 484 million miles (5.20 AU)
Closest to Jupiter from Earth: 588 million km / 346 million miles

Saturn:

Closest: 1.35 billion km / 839 million miles (9.05 AU)
Farthest: 1.51 billion km / 938 million miles (10.12 AU)
Average: 1.43 billion km / 889 million miles (9.58 AU)
Closest to Saturn from Earth: 1.2 billion km /746 million miles

Uranus:

Closest: 2.75 billion km / 1.71 billion miles (18.4 AU)
Farthest: 3.00 billion km / 1.86 billion miles (20.1 AU)
Average: 2.88 billion km / 1.79 billion miles (19.2 AU)
Closest to Uranus from Earth: 2.57 billion km / 1.6 billion miles

Neptune:

Closest: 4.45 billion km /2.77 billion miles (29.8 AU)
Farthest: 4.55 billion km / 2.83 billion miles (30.4 AU)
Average: 4.50 billion km / 2.8 billion miles (30.1 AU)
Closest to Neptune from Earth: 4.3 billion km / 2.7 billion miles

As a special bonus, we’ll include Pluto too, even though Pluto is not a planet anymore.

Uranus and Neptune, the Solar System’s ice giant planets. (Images from Wikipedia.) — *Uranus and Neptune, the Solar System’s ice giant planets. Credit: Wikipedia Commons*

Pluto:

Closest: 4.44 billion km / 2.76 billion miles (29.7 AU)
Farthest: 7.38 billion km / 4.59 billion miles (49.3 AU)
Average: 5.91 billion km / 3.67 billion miles (39.5 AU)
Closest to Pluto from Earth: 4.28 billion km / 2.66 billion miles

To learn more:

Online resources demonstrating the scale of the Solar System:

If The Moon Were Only A Pixel (Josh Worth Art & Design)
Scale Model Of Our Solar System (University of Manitoba)
Build A Solar System (Exploratorium)
Scale Solar System (Josh Wetenkamp)

Many cities and countries have also installed scale models of the Solar System, such as:

Voyage Scale Solar System (Washington, D.C.)
Sagan Planet Walk (Ithaca, N.Y.)
Maine Solar System Model
Sweden Solar System
Planet Walk (Munich, Germany)
The Solar System (Brittany, France; website in French only)
Solar System Drive (Australia)

April 21, 2014December 23, 2015 by Nancy Atkinson

Video: Carolyn Porco Discusses Her Life at Saturn

Planetary scientists Carolyn Porco. Via NASA/JPL.

Space historian Andrew Chaikin sat down with planetary scientist Carolyn Porco, and she discusses how her career has ended up focusing on the Saturn system. I love how Porco relates how even she has been “blown away” by some of the imagery sent back by the missions — just like the rest of us! — saying she’s had to call members of her team several times to verify she wasn’t looking at computer simulations vs. real images.

Enjoy this candid interview of one of the leading planetary scientists of our day.

April 21, 2014May 12, 2018 by Elizabeth Howell

The Planets in Our Solar System in Order of Size

Planets in our Solar system size comparison. Largest to smallest are pictured left to right, top to bottom: Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, Mercury. Via Wikimedia Commons.

If you’re interested in planets, the good news is there’s plenty of variety to choose from in our own Solar System. From the ringed beauty of Saturn, to the massive hulk of Jupiter, to the lead-melting temperatures on Venus, each planet in our solar system is unique — with its own environment and own story to tell about the history of our Solar System.

What also is amazing is the sheer size difference of planets. While humans think of Earth as a large planet, in reality it is dwarfed by the massive gas giants lurking at the outer edges of our Solar System. This article explores the planets in order of size, with a bit of context as to how they got that way.

A Short History of the Solar System:

No human was around 4.5 billion years ago when the Solar System was formed, so what we know about its birth comes from several sources: examining rocks on Earth and other places, looking at other solar systems in formation and doing computer models, among other methods. As more information comes in, some of our theories of the Solar System must change to suit the new evidence.

Today, scientists believe the Solar System began with a spinning gas and dust cloud. Gravitational attraction at its center eventually collapsed to form the Sun. Some theories say that the young Sun’s energy began pushing the lighter particles of gas away, while larger, more solid particles such as dust remained closer in.

Artist's conception of a solar system in formation. Credit: NASA/FUSE/Lynette Cook — Artist’s conception of a solar system in formation. Credit: NASA/FUSE/Lynette Cook

Over millions and millions of years, the gas and dust particles became attracted to each other by their mutual gravities and began to combine or crash. As larger balls of matter formed, they swept the smaller particles away and eventually cleared their orbits. That led to the birth of Earth and the other eight planets in our Solar System. Since much of the gas ended up in the outer parts of the system, this may explain why there are gas giants — although this presumption may not be true for other solar systems discovered in the universe.

Until the 1990s, scientists only knew of planets in our own Solar System and at that point accepted there were nine planets. As telescope technology improved, however, two things happened. Scientists discovered exoplanets, or planets that are outside of our solar system. This began with finding massive planets many times larger than Jupiter, and then eventually finding planets that are rocky — even a few that are close to Earth’s size itself.

The other change was finding worlds similar to Pluto, then considered the Solar System’s furthest planet, far out in our own Solar System. At first astronomers began treating these new worlds like planets, but as more information came in, the International Astronomical Union held a meeting to better figure out the definition.

Hubble image of Pluto and some of its moons, Charon, Nix and Hydra. Image Credit: NASA, ESA, H. Weaver (JHU/APL), A. Stern (SwRI), and the HST Pluto Companion Search Team

The result was redefining Pluto and worlds like it as a dwarf planet. This is the current IAU planet definition:

“A celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit.”

Size of the Eight Planets:

According to NASA, this is the estimated radii of the eight planets in our solar system, in order of size. We also have included the radii sizes relative to Earth to help you picture them better.

Jupiter (69,911 km / 43,441 miles) – 1,120% the size of Earth
Saturn (58,232 km / 36,184 miles) – 945% the size of Earth
Uranus (25,362 km / 15,759 miles) – 400% the size of Earth
Neptune (24,622 km / 15,299 miles) – 388% the size of Earth
Earth (6,371 km / 3,959 miles)
Venus (6,052 km / 3,761 miles) – 95% the size of Earth
Mars (3,390 km / 2,460 miles) – 53% the size of Earth
Mercury (2,440 km / 1,516 miles) – 38% the size of Earth

Eight planets and a dwarf planet in our Solar System, approximately to scale. Pluto is a dwarf planet at far right. At far left is the Sun. The planets are, from left, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Credit: Lunar and Planetary Institute

Jupiter is the behemoth of the Solar System and is believed to be responsible for influencing the path of smaller objects that drift by its massive bulk. Sometimes it will send comets or asteroids into the inner solar system, and sometimes it will divert those away.

Saturn, most famous for its rings, also hosts dozens of moons — including Titan, which has its own atmosphere. Joining it in the outer solar system are Uranus and Neptune, which both have atmospheres of hydrogen, helium and methane. Uranus also rotates opposite to other planets in the solar system.

The inner planets include Venus (once considered Earth’s twin, at least until its hot surface was discovered); Mars (a planet where liquid water could have flowed in the past); Mercury (which despite being close to the sun, has ice at its poles) and Earth, the only planet known so far to have life.

To learn more about the Solar System, check out these resources:

Planets (NASA)
Solar System (USGS)
Exploring the Planets (National Air and Space Museum)
Windows to the Universe (National Earth Science Teachers Association)
Solar System (National Geographic, requires free registration)