<< TO DO >>: Notes in ROUGH DRAFT ...

The information in these notes should not duplicate what is found under the specific objects observed during this program ... rather, these notes should supplement the objects' information with regards to the topic of this program... and provide hyperlinks to the object pages that will be used during this program:

These notes are still in DRAFT... edited/reviewed to "TO BE COMPLETED..." below...

Sizing Up Saturn

During this program we will observe the Moon, Saturn and the most distant planet in our solar system, Neptune, as we compare and contrast their different sizes, compositions and features.

Suggested Observing List

  • Moon Craters
  • Moon Mare
  • Saturn
  • Neptune

Sizing Up Saturn Program Information

  • Moon Craters

  • The Moon is 3.6 times smaller than Earth and over 34 times smaller than Saturn.

  • Since the Moon is a piece of rock it is very different from a gas planet like Saturn. The biggest difference is that the moon has a solid surface while gas planets don't.

  • Craters were formed when pieces of rock struck the moon and left large holes. Since gas giant planets don’t have surfaces, you won’t find craters on Saturn.

  • The Moon has no atmosphere, unlike Saturn which has a very thick atmosphere. Thus the Moon has no cloud bands across its face like Saturn does.

  • The size of the typical crater visible on the moon is about 50 miles. The smallest craters that can be seen with the telescope are a few miles across. However, the Apollo astronauts that visited the Moon saw craters as small as a few inches across.

  • Over 500 thousand craters can be seen on the moon with the largest telescope on Earth.

  • If the area you have chosen has two craters which overlap, you may wish to ask which one was formed first and why.

  • If the crater you have chosen has a mountain peak or peaks in the center, you may wish to ask how the mountain peak got there. If you do ask, it is usually best to start by asking how craters are made and if that explanation is consistent with a mountain in the center. Of course the mountain peak is formed when material that originally flowed away from the impact site flows back in to fill up the hole. This is similar to dropping a pebble into a thick mud puddle.

  • Moon Mare

  • The smooth dark areas are the mare. The lighter colored regions with numerous craters are the highlands.

  • People often wonder why the moon map is upside down. While they are looking through the finder, tell them to notice which side of the moon is sunlit and which is dark. Have them do the same with their naked eye and they should realize that telescopes turn images upside down.

  • The maria are the smooth dark areas on the moon. They formed about 3.2 to 4 billion years ago when lava flowed through cracks in the lunar surface and filled in the low lying areas.

  • The Moon is very different from Saturn. It’s made of rock and has a solid surface. Since Saturn doesn’t have a solid surface, it doesn’t have features like maré.

  • Generally speaking, our Moon has more in common with the moons of Saturn than Saturn itself. The Moon has a thick, rocky crust, while the moons of Saturn have thick water ice crusts. These ice crusts behave in similarly to the rock crust of the Moon, folding, faulting, eroding and showing impact cratering.

  • One of Saturn’s moons, Enceladus, has cryovolcanoes. Although these, cryovolcanoes spew liquid water instead of liquid rock or magma it is a similar mechanism to the one that created the maré on our Moon. .

  • Magma or lave on the Moon is much runnier (less viscous) than it is on Earth. As a result, there are no tall volcanic cones on the Moon like the ones we find here on Earth. Instead the Moon’s lava rapidly oozed out onto the surface building up relatively flat 'volcanic plains'

  • The majority of cratering took place early in the moon’s history, covering the entire surface of the moon somewhat evenly with craters. When the maria formed a few hundred million years later they presented new smooth surfaces on which to record subsequent cratering.

SATURN - PLANET

! Saturn will appear as a yellowish ball with a ring around it. A dark line is often visible within the rings and is called Cassini’s division. Four of Saturn’s 62 moons can usually be seen through the telescope.

! Saturn is a large ball of hydrogen and helium gas, the same material that our sun is made of in fact, if Saturn had gathered 300 times more of this gas during its formation, it might have become a star.

! Saturn is 9.4 times larger in diameter than Earth and 34 times larger in diameter than our Moon. It has a solid rocky core that’s two to three times the size of Earth but 10 times its mass.

! Since Saturn is made almost entirely of gas, craters can not form because it has no surface like the Moon. Since the Moon has no atmosphere, we never see different colored cloud bands on it like we see on Saturn.

! Although we can only see three rings from Earth, each one is composed of thousands of small ringlets. The rings are made of particles of ice that range in size from a grain of sand to the size of a car or house. Each of these particles orbits Saturn like a tiny moon.

! Saturn is the second largest planet in the solar system and the farthest planet known to ancient stargazers. .

! It is difficult to see any cloud features on Saturn because the cloud layers are spread out in depth. This means the lower layers are obscured by the upper ones. You should be able to see one band through the telescope.

! Winds in Saturn’s upper atmosphere reach 1,100 miles per hour. (Hurricane force winds on Earth only reach about 240 miles per hour.)

! Saturn is so large for the amount of matter that it’s made of that it would float in water. Compare this to our Moon which is just a great big rock.

! Saturn has at least 62 moons with confirmed orbits, 53 of which have names but only 13 have diameters larger than 50 km (31 mi). There are seven moons big enough to be spherical.

! Saturn’s largest moon, Titan, is larger than the planet Mercury, about 40% the size of Earth. It is one of only two moons in the solar system with a visible atmosphere. Neptune’s moon Triton is the other one.

SATURN - RINGS

! Saturn’s rings are obvious through the telescope.

! Not as obvious but often visible is Cassini’s division, a dark line within the rings. This division or gap in the rings is actually about 2,900 miles wide. It is named after the Italian-born astronomer Jean Dominique Cassini who first saw the gap in 1675.

! Saturn has seven ring systems, but from Earth only three of them can be clearly seen. However, in 1980 and ‘81, the Voyager missions found that each ring is actually made up of thousands of tiny ringlets. These ringlets could be compared to the grooves on a phonograph album.

TO BE COMPLETED...

SATURN’S MOONS BACKGROUND INFORMATION FOR EXPLAINERS: SATURN - MOONS Moon Distance From Saturn (miles) Compared to Earth / Moon distance Revolution Period (around Saturn) Diameter (miles) Diameter Compared to Earth’s Moon Enceladus 147,900 0.62 1.4 days 310 1/7 Tethys 183,000 0.76 45 hours 658 1/3 Dione 234,000 0.98 2.7 days 700 1/3 Rhea 327,000 1.4 4.5 days 950 0.4 Titan 759,000 3.2 15.9 days 3200 1.5 ! Saturn has at least 62 moons with confirmed orbits, 53 of which have names. Up to five of these moons can be seen with the telescope. ! Titan " Titan is the second largest moon in the solar system, with a diameter of 3,200 miles, a little larger than Mercury (3,029 miles), slightly smaller than Jupiter’s moon Ganymede (3,270 miles) and 40% the size of Earth. " Titan is one of only two moons in our solar system with an atmosphere. The atmosphere is 95% nitrogen and 5% methane. Methane playing the same role on Titan as water does on Earth. There are clouds of methane, lakes of methane, and ice caps of methane on Titan. " The Huygens probe, which descended to Titan surface in January of 2005 found that Titan has rivers and lakes of liquid methane-ethane. ! Tethys is a medium-sized moon (658 miles) that has a density near that of water indicating that it is made almost entirely of water ice with a very small fraction of rock. It has a heavily cratered surface. ! Dione (diameter 670 miles) and Rhea (950 miles) are medium-sized moons that are half ice and half rock. They are also heavily cratered. 118 The following moons can not be seen through our telescope ! Mimas is a small moon, only 250 miles across, that has a 60 mile crater on it. The impact which formed the crater almost split the moon in two. (Mimas can’t be seen through the telescope. It is only 90,000 miles away from Saturn.) ! Iapetus is a strange looking moon: part of it is very dark, the other part is very bright. ! Enceladus was the big surprise of the Cassini mission. This moon is only 310 miles across and is too small to be seen with our telescope. Its small size means it should be geologically inactive and covered with craters. Instead it has a large number of tectonic folds and faults and an active ice volcano was detected at it’s southern pole. Scientists believe Enceladus is still geologically active because of gravitational tidal forces imparted on it by Saturn. 119 120 NEPTUNE Actual Compared to Earth Distance From Sun (average) 2.8 billion miles 30 Revolution Period 165 years -- Rotation Period 16 hours -- Diameter 30,700 miles 3.9 Mass -- 17.2 Surface Gravity -- 1.12 Temperature (Cloud Tops) -162 ºC (-260 ºF) -- Density (gram/cubic cm) 1.8 gm/cm3 0.32 Recommended eyepiece: 26 mm to 40 mm. ! Neptune appears like an out-of-focus bluish star in the telescope. None of its moons or rings can be seen through the telescope. The reason it appears so small is that it is almost 3 billion miles from Earth. ! Neptune is the third largest planet in our solar system, almost 4 times larger in diameter than Earth and 14 times larger in diameter than the our Moon. ! Neptune has a rocky core about the same mass as Earth surrounded by a liquid mantle of water, methane, and ammonia. Its thick atmosphere is made up of hydrogen and helium. ! Since Neptune is a planet almost entirely made up of gas, craters can not form because it has no surface like the Moon and since the Moon has no atmosphere, the beautiful blue clouds we see on Neptune can not exist on the Moon SIZING UP SATURN - PROGRAM INFORMATION: 121 ! Hurricane-like storms similar to those on Jupiter and Saturn are present in Neptune’s atmosphere. The Great Dark Spot, was one such storm. Voyager 2 saw the Great Dark Spot in 1989, but when the Hubble Telescope took pictures of Neptune in November, 1994, the Great Dark Spot had disappeared. ! The Great Dark Spot was about the same size as Earth with winds that were clocked at 1,300 mile per hour, the fastest winds in the solar system! ! Neptune has at least 14 moons (as of July, 2013), none of which can be seen through the telescope. The largest moon, Triton, is the seventh largest moon in the solar system. It is one of only two moons in the solar system that has an atmosphere. Saturn’s moon Titan is the other one. ! Triton is the only large satellite in the solar system with a retrograde orbit around a planet. This “backwards” orbit most likely means the moon formed somewhere else and was captured by Neptune’s gravity. ! Triton is the coldest measured object in the solar system at -396 ºF. ! Neptune was the first planet in our solar system to be found by prediction alone. In the early 1800's astronomers realized Uranus wasn’t moving in its orbit the way it should be. They realized another planetary body was out there affecting its orbit. ! A French mathematician specializing in celestial mechanics and a British mathematician and astronomer independently calculated a theoretical position for the planet later to be named Neptune. On September 23, 1846, Neptune was found within 1 degree of its predicted position. NEPTUNE BACKGROUND INFORMATION FOR EXPLAINERS: