![]() The two encoders provide numeric displays (or electronic signals if connected to a computer). DSCs employ an electronic rotary encoder, which is placed on each axis of the mount. All commercial DSCs work on alt-azimuth telescopes such as Dobsonians as well as on equatorially mounted scopes. ![]() Some Dobsonian mounts have been upgraded with digital setting circles (DSCs), available from many astronomy vendors. Just push the telescope up or down to change altitude and push it left or right to change azimuth. It is a simple dual-pivot mount almost always combined with a Newtonian telescope optical tube assembly. The alt-azimuth mount he invented has revolutionized amateur astronomy. The proliferation of large telescopes is due to one thing: Most large reflecting telescopes now are placed on a type of mount called a Dobsonian mount, named for renowned telescope maker John Dobson. Personally, if a 24-inch telescope is available, I don’t mind climbing a few steps to look through it. I know many observers who chose the size of their telescope based on whether or not they could stand on the ground and view an object at the zenith. Some observers consider having to use an observing ladder or stand (to allow you to look through the eyepiece of a large telescope) a disadvantage. This doesn’t mean an observatory is a must (although it’s the best option), but some sort of protective, insulated, reflective cover for your telescope is required. If you can leave the scope outside so it’s protected from Sun, dust, and rain, you’ll begin your evening observing sessions ahead of the game. Of course, this is easier said than done. Small whisper fans can speed up the cool-down time, but the best way to cool down a telescope is never to let it warm up in the first place. The “tube” is constructed out of lightweight aluminum poles, which are attached to a light secondary mirror assembly.īecause large telescopes generally have thick mirrors, they take longer than smaller telescopes to adjust to ambient temperature. Such a scope’s heaviest components are the mirror and rocker box assemblies. New Dobsonian reflectors often are designed as “truss-tube” telescopes. An observing partner can help in such cases, but then you are dependent on your partner’s availability. A 14-inch Schmidt-Cassegrain telescope is a wonderful instrument, but if you can’t lift it from its storage case to the top of its tripod, it’s useless to you. Purchase a large scope only after you compare what it weighs to what you can lift and carry easily (whether it be from your house to your yard or from your vehicle to your observing site). Large telescopes can be unwieldy and heavy to transport. This quantity doesn’t go up as much as light-gathering power, but it’s still important. The limiting magnitude is the faintest magnitude that can be detected by an instrument. When stars (which are point sources) are viewed, the larger scope will have a higher limiting magnitude. Second, you’ll be able to see fainter objects through the larger telescope. And, as discussed in the previous paragraph, you’ll also see more detail. This advantage is evident in two practical ways: First, if you compare two telescopes of different sizes, a celestial object will look brighter through the larger one. ![]() ![]() The other major advantage of a large telescope is light-gathering power. It’s much easier to resolve small storms in Jupiter’s atmosphere, bright knots in distant galaxies, or tiny lunar craterlets through a large telescope than through a small one. Quality telescopes under an excellent sky often surpass the number given by Dawes Limit, but you get the idea. Compare this with the resolution of a 12-inch telescope: 0.38″. According to an optical law called Dawes Limit, a 4-inch telescope can resolve two double stars with an angular separation of 1.14″. You only can control one of these factors. Resolution depends on two things: the stability of the atmosphere and the aperture of your telescope. Large telescopes have several advantages over their smaller counterparts, and “resolution” - how much detail we see in a celestial object - is the first.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |