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Basic Telescope Designs

The job of a telescope is to collect light, not to magnify an image (the eyepiece does that job). The larger the objective (the part that collects the light) whether it be a lens, in refractors, or a mirror, in reflectors, the more light the telescope will collect. The more light you can collect, the more detail you will be able to capture, and also important for astrophotography, the shorter your exposures will need to be to capture this detail.

Refractor Telescopes

The type of telescope most people visualize when they hear the word telescope is the 'Refractor'. This is what Galileo used for his break-thru discoveries. A refractor has an objective lens at the front which passes the light straight through to the back of the tube, focusing this light at an eyepiece or for astrophotography a camera.

Advantages:

-No central obstruction (see more in the reflecting scopes), giving higher contrast.

-Due to the simple design they require little maintenance.

-Excellent for planetary and lunar viewing and photography.

-Excellent for wide field viewing and astrophotography especially in shorter focal lengths (more on this later).

-Because the objective is permanently mounted and aligned there is no need for collimation (again more on this in another article).

-Excellent color in apochromatic and ED (Extra Dispersion) designs.

Disadvantages:

-Costlier per inch of aperture (objective) than reflectors and catadioptric telescopes.

-Can become bulky and difficult to manage, especially in larger lens designs.

Newtonian Telescopes

This design was invented by Sir Isaac Newton (he of the apple on the head fame). Instead of a lens at the front of the tube this telescope design uses a concave, parabolic mirror to collect light reflecting it back towards the front of the tube to a flat diagonal mirror which reflects the light out the side of the telescope to the eyepiece or camera for astrophotography.

Advantages:

-Lowest cost per inch of all the telescope designs.

-More light gathering power per dollar because of the lower cost design.

-Absolutely perfect color rendition.

-More compact design compared to a refractor of similar light gathering ability.

-Excellent contrast for planetary and lunar astrophotography and viewing in longer focal lengths.

-Can get excellent wide-field astrophotos and short exposures in shorter focal lengths.

Disadvantages:

-Slight loss of contrast due to the central obstruction (the flat secondary mirror) as compared to a refractor.

-Requires more maintenance, such as collimation (discussed in another article) which is vital for great results in your astrophotography, although you will learn how to do this quickly with practice.

Schmidt-Cassegrain Telescopes

This is a very popular design, with a high tech look. Also known as a CAT (Catadrioptics). They use a combination of lenses and mirrors to collect and focus the light onto the eyepiece or camera. The light enters the telescope through a thin 'lens' called a schmidt corrector plate, goes to the back of the scope to a spherical primary mirror which reflects the light back towards the front. Here the light strikes another mirror, the secondary mirror which is mounted on the corrector plate. This secondary mirror then reflects the light back towards the back where it is focused onto a hole in the primary mirror where the light is collected by an eyepiece or your astrophotography camera.

Advantages:

-Compact and portable.

-Low maintenance although once again collimation is required for top performance.

-Many, many astrophotography accessories available.

-Cheaper per inch of aperture as compared with refractors.

-Excellent all-round telescope, good to very good for both visual and astrophography.

-Very good for planetary and lunar viewing and astrophotography.

-Very good to excellent for DSO (Deep Space Object) astrophotography with a caveat (see the disadvantages).

-Very good to excellent optics, both Meade and Celestron are putting out excellent optics on a consistant basis.

Disadvantages:

-Costlier per inch of aperture as compared with Newtonian telescopes.

-Loss of contrast due to the central obstruction which is even larger than that in the Newtonian scopes.

-Due to their longer focal lengths the field of view is smaller and longer exposures are required for astrophotography, although a lens known as a focal reducer is available which minimizes or removes this problem. The longer focal length is actually an advantage in planetary and lunar photography.

Maksutov-Cassegrain

The Maksutov-Cassegrain telescope design is basically the same as the Schmidt-Cassegrain design except it uses a meniscus lens at the front instead of a Schmidt corrector plate. The main advantage to the Mak telescope design is you will get sharper higher contrast planetary and lunar images when compared with the Schmidt design.

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Fixed Stars, Not Fixed Fates!
Nancy R. Fenn
1dc5 What hogwash! he said, only he used a different word. When you screw up your life, you blame astrology, like you had no choice because you were born at a certain time. Now he was smiling. The reason I do drugs and can't keep my fly zipped isn't because of any stars! Like my old man knocked up my mother when Scorpio was Rising and because of that I'm going to jail? I don't think so! I'm going to jail because I'm bad to the bone!

This is a speech made by Edmund the Bastard in Act I, Scene ii of Shakespeare's King Lear. I brought it up to date.

Edmund plots to turn his father against his half brother, Edward, but the boys' father won't go for it. He excuses Edward's recent strange behavior by these late eclipses in the sun and moon ….

Edmund says he was born under the Dragon's tail, the South Node of the Moon. That could be in any sign. He's making a play on words. To be born under any animal's tale is probably a slur on Edmund's mother who was not married at the time of his conception.

Edmund's nativity or horoscope is under Ursa Major, the constellation where the Big Dipper resides. At the time of this play, most of the stars in Ursa Major were in late degrees of Leo and the first half of Virgo.

It's a funny coincidence (no such thing?) when Edmund speculates, what if he were born under the maidliest star -- because that's exactly when he was born. If under Ursa Major, then the influence of Virgo, the Maiden.

Edmund shows a mistake people sometimes make about astrology. You can't be born under something, you have to be born when the Sun is in something.

Edmund's character is used as a contrast to King Lear's very evil daughters, Goneril and Regan. King Lear is destroyed by their cruelty. While these girls are dark to the core, Edmund is openly, carelessly and light-heartedly villainous. Back then as now, some people are bad but some people are really evil. M. Scott Peck wrote a good book to help with this distinction, The Road Less Traveled.

Edmund actually has a pretty good handle on an important concept in humanistic astrology -- way before Dane Rudhyar (1895-1985) wrote his books. It is our character that determines our fate, not our horoscope.

Thousands of people are born the same hour, day, year and even minute all over the world; yet no two are alike. The energy of the stars is neutral like electricity but there is a Soul lying beneath the horoscope which uses the energy for good or ill.

Charles Darwin was born on February 12, 1809 in Shrewsbury, England. Abraham Lincoln was born on February 12, 1809 in Larue County, Kentucky. It was a good day for men!

There's nothing evil about being born in Virgo. In fact many Virgos are among the most gentle people. But 9 degrees of Virgo is a degree of homicide. Alioth of Ursa Major in Shakespeare's time was at about 7 degrees Virgo while Mizar and Alcor were at 12 degrees Virgo.

I think, too, that Shakespeare refers to the importance Ursa Major has always had in the northern hemisphere. It is one of the first things children learn to pick out in the starry night sky.

Ursa Major isn't part of the zodiac but its stars can be seen vividly at night. There are seven main stars, Alkaid, Mizar, Alioth, Megrez, Phecda, Merak and Dubhe.

The last two are special stars people use to site the North Star (Polaris). Mizar has a fainter companion, Alcor. As everyone knows, if you can see these two stars with your own two eyes, you have good eyesight!

Beginning astronomy students are taught to start from Ursa Major and follow the arc to Arcturus; then spin on to Spica. Arcturus is the second brightest star in the spring sky, a fortunate star of the zodiac, while Spica is considered the luckiest star of all. Are you lucky enough to have a planet at 23 Libra? Email me at parklanenancy@hotmail.com and I'll let you know.

Mizar and Alcor have a love story in American Indian mythology. Not everyone can see Alcor, but she is the 7th sister of the Pleiades, the youngest sister, who fell in love with a mortal man. One night the Windsong lifted him up into the stars for her His name is Mizar and they have been together ever since. All cultures speak of the Seven Pleiades, but that is why you can only see six of them.

Astrologically, the constellation Ursa Major is said to give a quiet, prudent, suspicious, mistrustful, self-controlled patient nature, but an uneasy spirit and great anger when roused. Much like a bear, I suppose. The name Ursa Major (the Big Bear) comes from a myth about Zeus, the king of gods. Zeus raped a young nymph named Callisto. Callisto gave birth to a son named Arcas. Zeus' wife was so angry she turned Callisto into a bear. Callisto roamed the woods for 15 years. One day she ran into her son, who had become a hunter. As he drew his bow to shoot her, of course not recognizing that she was his mother, Zeus took pity on Callisto and turned her son into a bear as well. Then he took them both by the tail and swung them up into the heavens which is why their tails are so long. Zeus' wife became furious again and drug a promise out of the ancient ruler of the sea that these two constellations would never get their paws wet. To this day they do not set below the horizon of the sea as other constellations do.

The constellation has had other meanings. In Arabic, Mizak and Alcor are called the horse and rider. The rest of the constellation is seen as a funeral procession ... perhaps because of the slow and solemn motion of the figure around the pole.

The Babylonians saw a chariot in these stars and the Romans, seven oxen. In Ireland the constellation is called King David's Chariot; in Denmark and Sweden the Stori Vagn or Chariot of Thor. Similarly the Vikings, Poles, Germans and Medieval Christians saw it as a chariot for their gods.

The Plough, as it is called in the UK, is the bucket shaped figure on the back of the Bear, outlined by the stars Merak, Dubhe, Phecda and Megrez. The Three Horses pulling the plough are located in the tail.

Ursa Major has also been called the Wain by the Welsh, short for Charlie Wain or Charlemagne, while Arcturus refers to King Arthur.

The stars do not compel any more than there are chariots, bears and funeral processions in the skies. Most individual stars have Arabic names while the constellations in our northern hemisphere have names derived from Greek and Roman mythology. There was a time 2000 years ago when these worlds were all one -- when shepherds sat alone on hilltops at night and stared into the sky. There was a time when desert caravans followed star maps reliably across the sands and sailors cried “By Jiminy!” to the constellation of the twins to keep them safe at sea. There was a time when astrology and astronomy were twins as well and I'm one astrologer who likes to return to those times every now and then.

About the Author

Nancy R. Fenn has been a professional astrologer in the San Diego area for over 25 years. She's the astrologer who wasn't born yesterday.

2c
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