An Introduction to the Planets & their

moons

Hahnenberg Observatory Presents

The word “Planet” comes from the Greek word πλανήτοs, which means

“wanderer.” “Moon” comes from the old German language and is

related to the Latin mensis (month).

Disclaimer: In the preparation of this presentation, most of the information comes from Wikipedia, supplemented by pictures from NASA, other websites, and those of the author Edward J. Hahnenberg. It is

made available for educational use only, and no violation of copyright law is intended.

Our Planets & Their Moons

There are 4 planets close to the Sun.

The next two planets, farther away, are:

Jupiter, with its huge red spot.

Saturn, with its famous rings.

The picture above was taken at our Observatory. Jupiter takes 12 years to orbit the Sun and has 63 moons. It’s the largest planet and has a gaseous surface.

Above picture taken at our Observatory. Saturn has 59 moons. Its winds reach 1100 mph. It is the 2nd largest planet with no solid surface.

The planets farthest from the Sun

Uranus Neptune

Uranus takes some 84 years to orbit the Sun. It has 27 moons. It’s -350 degrees F there, and is 1.7 billion miles from the Sun. It also has rings, but are hard to see.

Neptune has a Dark Spot. It is 2.7 billion miles from the Sun. It takes 165 years to go around the Sun. It’s as cold as on Uranus. Neptune has 13 moons.

The Moon is about 238,857 miles away from earth.Our Moon – The Tycho Crater The Full Moon

Recent close-up lunar picturesApollo 14 landing site

Footprints on the moon

Can you see the landing site of Apollo 14? It’s called LM Antares. The astronauts walked to set up an instrumentation site called ALSEP. Notice the astronauts footprints. Image taken July, 2009.

Phases of the MoonThe Sun and the Moon A lunar monthOne half of the moon’s

surface is always illuminated by the Sun and hence is bright, but the portion of the illuminated hemisphere that is visible to an observer can vary from 100% (full moon) to 0% (new moon). 

The time between two full moons (and between successive occurrences of the same phase) is about 29.53 days (29 days, 12 hours, 44 minutes) on average. 

The side of the Moon we don’t seeWe always see only one side of the moon.

The “other side” of the moon we don’t see

We all know that the Earth rotates on its own axis, so theoretically, the Moon should also do the same, allowing us to get a full picture of the planetoid. Why are we limited to seeing only 50 percent? It turns out that the speed at which the Moon rotates has lead to this particular phenomenon. Millions of years ago, the Moon spun at a much faster pace than it does now. However, the gravitational influence of the Earth has gradually acted upon the Moon to slow its rotation down, in the same way that the much smaller gravitational influence of the Moon acts upon the Earth to create tides. This influence slowed the rotational period of the Moon to match that of its orbit – about 29.5 days – and it is now "locked in" to this period. 

Jupiter’s Four Big Moons –  Io,  Europa, Ganymede, and Callisto.

My image of three of the moons of Jupiter. The 4th is behind Jupiter.

Io – Moon closest to JupiterIo is the 

fourth-largest moon in theSolar System.

With over 400 active volcanoes, Io is the most geologically active object in the Solar System.

Most of Io's surface is coated with sulfur and sulfur dioxide frost.

Europa – Next closest to JupiterEuropa is slightly smaller than

Earth's Moon and is the sixth-largest moon in the Solar System.

 Its surface is composed of ice and is one of the smoothest in the Solar System. This young surface has cracks and streaks, while craters are relatively infrequent. The apparent youth and smoothness of the surface have led to the hypothesis that a water ocean exists beneath it, which could conceivably serve as an abode for life.

Ganymede – Third closest to JupiterIt is larger than the

planet Mercury and is the largest moon in the Solar System.

Ganymede is composed primarily of silicate rock and water ice.

A saltwater ocean is believed to exist its surface, sandwiched between layers of ice.

Callisto – Farthest from Jupiter It is the third-largest moon

 in the Solar System – almost as big as Mercury. 

Compounds detected spectrally on the surface include water ice, carbon dioxide, and silicates.

The surface of Callisto is heavily cratered and extremely old.

The likely presence of an ocean within Callisto indicates that it can or could harbor life. 

Mars – The planet nearest to earthMars is a terrestrial planet

 with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the volcanoes, valleys, deserts and polar ice caps ofEarth.

Of all the planets in the Solar System other than Earth, Mars is the most likely to harbor liquid water, and perhaps life.

The picture on the right is how it looks on Mars

The two tiny moons of Mars Mars has two tiny moons, 

Phobos and  Deimos, which are thought to be

captured asteroids. The picture on the right is that of Phobos.

The motions of Phobos and Deimos would appear very different from that of our own Moon. Speedy Phobos rises in the west, sets in the east, and rises again in just eleven hours, while Deimos, being only just outside synchronous orbit, rises as expected in the east but very slowly. Despite its 30 hour orbit, it takes 2.7 days to set in the west as it slowly falls behind the rotation of Mars, and has long again to rise.  

Deimos – The odd-shaped moon of MarsOnly two geological

features on Deimos have been given names. The craters Swift and Voltaire are named after two writers.

Notice how oddly shaped Deimos is.

The Planet with no Moon - Mercury Mercury is the smallest planet in

our solar system. Mercury is about the same size as our Moon. It is very close to the Sun. Mercury travels around the Sun faster than any other planet. That is how it got its name. It was named after Mercury, the swift messenger of the gods in ancient Roman mythology. Mercury can only be seen from Earth just before sunrise or just after sunset, but not in the middle of the night. That is because Mercury always appears near the Sun when viewed from Earth. Mercury has a very thin atmosphere. Humans would not be able to live there. 

Saturn – The Ringed PlanetSaturn is the sixth 

planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn, Jupiter, Uranus and Neptune, are called “gas giants.”

Saturn has a prominent system of rings, consisting mostly of ice particles.

To the right is my image of Saturn.

Titan – Saturn’s largest moon  Frequently described as a planet-like

moon, Titan has a diameter roughly 50% larger than Earth's moon and is 80% more massive. It is the second-largest moon in the Solar System, after Jupiter's moon Ganymede, and it is larger by volume than the smallest planet, Mercury.

The atmosphere of Titan is largely composed of nitrogen and its climate includes methane andethane clouds. The climate—including wind and rain—creates surface features that are similar to those on Earth, such as sand dunes and shorelines, and, like Earth, is dominated by seasonal weather patterns. 

The picture shows the surface of Titan

Uranus – 1.7 million miles away

Uranus's atmosphere, while similar to Jupiter's and Saturn's in being composed primarily of hydrogen and helium, contains a higher proportion of "ices" such as water, ammonia and methane, along with traces of hydrocarbons. It is the coldest planetary atmosphere in the Solar System, with a minimum temperature of −224 °C

Uranus has 27 known  moons.The five main moons are Miranda, Ariel, Umbriel, Titania and Oberon

Miranda – One of Uranus’ moons

Miranda is about half water ice and half rocky material.

It is actually possible to see Uranus's 4 largest moons with an amateur telescope, but Miranda is a real challenge.

Miranda's surface is all mixed up with heavily cratered terrain intermixed with weird grooves, valleys and cliffs.

Neptune – The farthest planet – 2.7 million miles away. My picture on left.

Triton – Neptune’s largest moon

Neptune has 13 moons. Neptune's largest moon is

named Triton. Triton is much larger than any of the planet's other moons. Triton is a very cold place, so the moon is covered with ice. Even though Triton is cold there is a lot going on there. It has geysers like the ones at Yellowstone Park on Earth. The geysers shoot ice 8 km (5 miles) high into Triton's thin atmosphere! There may be water under the ice at Triton. It is even possible that there might be life in that water. The interior of Triton is probably geologically active.

What about Pluto?Pluto used to be

called a planet. However, it is now called a dwarf planet, because it is so small.

There are other dwarf planets farther than Pluto.

Pluto has a moon, Charon, but it is so close it is almost a dwarf planet itself.

The End – Now, to the ObservatoryI hope you have

enjoyed this slide show on the Planets and their moons.

There are many more suns in our Galaxy…400 billion or so.

These suns have planets too.

Over 300 have been discovered so far.