Monday, April 12, 2010

What Can I See with My Telescope: Saturn

Saturn is one of the things in the sky that you can see through a small telescope that is just as impressive as it looks in the photos you see. While many deep sky objects, such as nebulas and galaxies, do not look as impressive as in the books and magazines, Saturn does.

Not only that, there is something special about the way it looks that makes it look different than any photograph or video. When you see it with your eye, it's special. Just like the Grand Canyon, it has to be experienced to be appreciated.

Amateur astrophoto of Saturn by Rochus Hess
Astrophoto of Saturn by amateur Rochus Hess

As I write this, Saturn is a bright star visible in the early evening sky. To find out whether it's visible as you read this, visit one of the free on-line star charts, such as those listed to the right.

What to expect with:

7x35 to 8x65 Binoculars: A bright object that looks somewhat different from a star. It will be steadier than most stars, and a pale yellow in color under most skies. You will also be able to see 2-3 small companions as points of light. One will be brighter than the others. These are satellites of Saturn, the brightest is Titan. Saturn itself will not show a disk with small binoculars, but sometimes it will look misshapen as a result of the rings.

60 to 90mm Telescope: At 50 to 100 powers of magnification, you will have a nice view of Saturn and the area around it. You will probably see 1 to 3 satellites, the brightest of which will be Titan. The rings will be easy to see. At 150 to 200 powers, look for the shadow of the rings on the surface of the planet, under good conditions it will appear as a thin black line. Careful looking with a relaxed eye should show the bands in the atmosphere of Saturn. Some bands will be yellow, others will be white. They will go from side to side across Saturn.

4.5 to 6 inch Telescope: Far more detail will be visible at powers of 150 to 200 times magnification than with a 60-90mm telescope, in most cases. Also, more moons will be visible, as many as five under the best conditions. From brightest to dimmest they will be Titan, Iapetus, Rhea, Dione, and Tethys. Tethys is a difficult find with a 6" scope. Titan will almost always be the brightest when it is seen. Iapetus, Rhea, and Dione are hard to tell apart. There's a Saturn Satellite Finder on Sky and Telescope's site, since you can't tell your moons without a program.

Saturn itself can show a lot of detail. The best way to see it is to stay at moderate magnifications for this scope size (150-200 powers) and look with a relaxed eye. Give yourself time, be seated if possible, and use a scope that tracks the sky with a clock drive or computer if possible. See if you can see the bands within the light bands of Saturn's atmosphere. Enjoy the rings, the break in the rings called the Cassini Division should be obvious with good optics.

7" to 9" Telescope: At this point it's possible for Saturn's features to be washed out by how much light your telescope collects. However, telescopes in this range are excellent for observing Saturn. Start at low powers (50 to 100x) and observe Saturn and its neighborhood, looking for up to 9 moons (see the section on 4.5-6" scopes). Then move up to moderate magnification, about 150 t0 200 powers. At this point you may need to actually block off some of Saturn's light to see fine detail. There are many ways of doing this. My favorite simple methods are to either partially block the light coming in to the telescope with my hand, or do the "hat trick" by blocking some of the light with my hat.

By moving the object you are using to block either more or less light, a little at a time, details can come out for you that would not either without some of the light blocked, or using a light blocker that sits still.

With this size of scope, you can take magnification up to 300 powers or more. Most scopes will give the best views at 350x or less, some can go up to 450x before the image degrades. As the magnification goes higher, the problem of too much light will be less of a problem. However, at higher magnifications you'll need to have some means of tracking the sky, or you won't be able to see much of Saturn before needing to move the scope to follow it across the sky.

Larger Telescopes:

Larger scopes can be used in the same way as 8" telescopes. The only advantage to larger scopes is that they can see more detail within the detail, and can pick more detail out of the rings of Saturn. They are more sensitive to washed-out images of Saturn than scopes in the 7-8" size, but when properly "masked off" they can provide sharp, stunning views. Fine detail that larger scopes can pick up includes "clouds" in the atmosphere of Saturn, streaks in the atmosphere, more detail at the edges of the different bands in the atmosphere, such as swirls, and of course the dimmer inner rings of Saturn. Very well designed scopes of smaller size can pick out these details under excellent viewing conditions, but with a larger scope it's easier to do under less than optimum conditions.
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Friday, April 9, 2010

Meteors, Meteorites, and Meteoroids

Meteors, or falling stars, are a common and wonderful sight in the sky. It doesn't take any special equipment to see them, or any special training to enjoy them. They can be seen anywhere that the sky is dark enough for them to show. In some cases, extremely bright ones have been seen in daylight!

Meteors are small objects falling into the Earth's atmosphere from space. Just as spacecraft returning to Earth are surrounded by brightly ionized air due to the friction of the air with the falling spacecraft, the small object is surrounded by brightly lit air, caused by the friction of its entry into the atmosphere. The light mostly comes from the heating of the air. Little or none of the light comes from burning of the meteor itself, normally, though there are some types of meteor where there can be more burning of the material than the norm.



Meteoroids

The objects in space are called meteoroids, before they encounter the Earth. They are not a special class of objects, it's just a general term for small objects like bits of dust, small rocks, and so on. They can have a number of sources.

Meteors

The term meteor refers to the event of the meteoroid passing through the atmosphere. This is the show we get to enjoy. As an event, it has a name, just like "rainstorm" is a name for an event. It's not a name for a "thing", so to speak.

Meteorites

A meteorite is a thing, on the other hand. It's what we call the material of the meteoroid that reaches the surface of the Earth.

Chondrite

Chondrites (pronounced kon-drites) are the most common meteorites. They are remnants of the earliest material that formed in the solar system around the Sun. The name chondrite refers to the chondrules (kond-rools) that they're made of--little blobs of rock.


Close Up of a Chondrite, Showing Chondrules

Chondrules Rubbed Out of a Chondrite


One type of chondrite is rare among chondrites, this is the Carbonaceous Chondrite. The name refers to the fact that it's got a lot of carbon in it. This gives it a black color. Carbonaceous condrites are the earliest of the chondrites.


Carbonaceous Chondrites


All chondrites come from small bodies that formed in the early solar system that never got large enough to form enough heat to melt down the various materials that they are made of, and separate them. For example, in the Earth the materials it was made of did melt. The iron and nickle and other heavy metals sunk to the center of the Earth for the most part, and the lighter "rocky" materials stayed in the Earth's outer crust.

There are meteorites that come from larger bodies that did melt and separate the materials that are all mixed together in chondrites. The ones that were once in the core of these larger bodies are the iron meteorites.


Campo del Cielo Iron Meteorite, photo courtesy of Meteor Recon

Iron Meteorite

Photo courtesy of Meteorite Recon

Since most iron meteorites formed in a much smaller body than the Earth, the iron in them cooled in an environment where the metal formed large crystals that can only form in a low gravity environment where cooling is very slow. Iron meteorites can be cut, polished, and etched to show these beautiful crystal patterns, known as Widmanst├Ątten or Thomson patterns.


Crystal Patterns in Iron Meteorite


Some meteorites are pieces of larger bodies in space. Pieces of the Moon and Mars have been identified. These meteorites are the result of a meteorite hitting the Moon or Mars hard enough to knock pieces of them off into space!

Some are pieces of asteroids. One type of meteorite, called a Pallasite, are believed to be pieces of the asteroid Vesta. They are especially beautiful, and are often turned into jewelry.

Pallasite

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