Astronomy Part2

Astronomy An introduction to Astronomy for the BSA Astronomy Badge

Part 2: The outer Solar System

The outer planets of the Solar System are the realm of the gas giants, Jupiter, Saturn, Uranus and Neptune. Each of these worlds has a mini-solar system of there own. Pluto and Eris may be worlds of ice.

Jupiter, is the largest of the planets in the Solar System. In this time-lapse video recorded by the Voyager 1 probe during a period of 60 days, we can see the Great Red Spot, a hurricane that could swallow 3 Earths.

Jupiter is 88,846 miles in diameter and averages 484 million miles from the Sun. Ten Earths would fit across it. Jupiter has over sixty moons. The most famous of these are called the Galilean moons, in honor of Galileo Galilei, who discovered them in the early 1610.

The Galilean moons can be seen with binoculars. These moons are, from left to right, top to bottom: Io, Europa, Ganymede, and Callisto. Io looks like a cheese pizza and has active volcanoes spewing sulfur. Europa is covered with ice and may have an ocean of water beneath the ice. Ganymede and Callisto are as large as the planet Mercury.

This is a photo of Jupiter and it’s rings. All of the gas giant planets in the Solar System have rings. Jupiter’s rings are so faint that they are best seen from behind the planet like in this image.

Saturn is often called the Jewel of the Solar System. It averages 886 million miles from the Sun. Galileo first saw the rings of Saturn in 1610 and thought they where handles or moons. It wasn’t until 1656 that Christiaan Huygens concluded that they where actually rings around the planet and in 1675 Giovanni Cassini discovered what we now call the Cassini Division in the rings.

Saturn’s rings are thought to be only about 33 feet thick. Here we can see that they seem to have grooves very much like an old record album, you know those old things your parent’s have laying around that play music like a CD.

Saturn’s rings shift over time as we can see in these images. The rings cannot be seen from the Earth at times when they are edge-on to us.

No, this is not the “Death Star” from Star Wars. This is Mimas, one of the moons of Saturn. The large impact crater is unusual and must have almost shattered the moon when it was formed.

Here we see the moon Titan. Titan, the size of a terrestrial planet, has a dense atmosphere of nitrogen and methane and a surface covered with organic material. Of Saturn’s moons, Titan and the icy moon Enceladus, like Jupiter’s Europa, are the most likely places to have life outside of the Earth and maybe Mars.

Here we can see just how large Titan and the Galilean moons of Jupiter are compared to our moon and the rocky inner worlds.

In this photo taken by the Cassini probe, we can see Saturn as it eclipses the Sun. If you look just outside the main rings, to the upper left, you will notice what looks like a star. This “star” is the planet Earth.

Uranus, discovered by Sir William Herschel in 1781, is literally a planet that got knocked on it’s side. In this photo we can see it’s ring system, some of it’s moons and storms on the planet.

This is Miranda, one of the moons of Uranus. There are several theories as to why Miranda looks as it does. One being that the moon was nearly ripped apart by a collision or two. Another is that upwelling ice has melted and left the ridges and cliffs we see in this image from Voyager 2.

Neptune is the first planet discovered purely with mathematics. Astronomers used the calculations of French Mathematician Urbain Jean Joseph Leverrier and English Mathematician John Couch Adams to locate Neptune in 1846. In the center of this image is a storm similar to the Great Red Spot on Jupiter.

Pluto and it’s 3 moons. Pluto was discovered in 1930 by Clyde Tombaugh at the Lowell Observatory in Flagstaff, Arizona. Are Pluto and the recently discovered Eris planets? That could be an argument that may not end until 2015 when the New Horizons space probe will be the first to visit Pluto.

Pluto’s orbit, shown in green, is inclined 17° to the rest of the Solar System. Pluto takes nearly 248 Earth years to complete one orbit around the Sun. If you think that is a long time, Eris takes around 557 years. Notice how the orbital plane of the Solar System is almost perpendicular to the plane of our Milky Way galaxy.

What else lies beyond Neptune? Comets, among other icy bodies. In this photo we see Comet Ikeya-Zhang. The other fuzzy object to the right of the comet is the Andromeda Galaxy.

What are comets? Imagine a very large and dirty snow ball and there you have a comet. Comets travel elliptical orbits that take them far out into our Solar System. When they start nearing the Sun they warm up and start out gassing particles which make up the tails that we see. This is a photo of Halley’s Comet. Famous because in 1705 Sir Edmond Halley correctly predicted it’s return in 1758.

What happens when the Earth crosses the trail of particles left behind by a comet? We see meteors or shooting stars as they are sometimes called. Most meteors are not much bigger than a grain of sand and burn up in our atmosphere. But occasionally a larger one will hit the Earth.

This is a photo of Meteor Crater located between Flagstaff and Winslow, Arizona. This crater is 4150 feet in diameter and 570 feet deep. When you drive near it on Highway US 40 you see many of the rocks that where ejected from the ground when it was formed nearly 50,000 years ago from a large nickel-iron meteor.

What about planets outside the Solar system? The Hubble telescope was able to find the first visual proof of a planet outside our solar system. It orbits the star Fomalhaut in the constellation Piscis Australis, the southern fish, 25 light years from Earth. Fomalhaut b is 115 AU from it’s star and it takes approximately 872 years to complete one orbit.

Credits: Graphics of Solar System, Pluto’s orbits, and intro page created with Starry Night software, Simulation Curriculum Corp. Photo of Comet Ikeya-Zhang courtesy of Jimmy Westlake, an Eagle Scout, Colorado, USA. Photo of Meteor Crater courtesy of Charles & Josette Lenars/CORBIS. Fomalhaut b photo courtesy of NASA, ESA, P. Kalas, J. Graham, E. Chiang, and E. Kite (University of California, Berkeley), M. Clampin (NASA Goddard Space Flight Center, Greenbelt, Md.), M. Fitzgerald (Lawrence Livermore National Laboratory, Livermore, Calif.), and K. Stapelfeldt and J. Krist (NASA Jet Propulsion Laboratory, Pasadena, Calif.) Other photos and graphics courtesy of NASA/JPL-Caltech.