Looking at the sky-the Guide to the telescope

Absrtact: Left: 1848-built Cincinnati Observatory refractive Telescope Right: Newton's first 6-inch telescope replica of the telescope. Simply put, other band telescopes outside the radio telescope can be roughly divided into refraction and reflection. Refraction


left: 1848-built Cincinnati Observatory Refractive Telescope Right: A replica of Newton's first 6-inch telescope

Classification of telescopes

Simply put, other bands of telescopes outside the radio telescope can be roughly divided into refraction and reflection.

The refractive telescope uses a convex lens as the objective lens and the eyepiece to converge the light, and the reflective telescope uses a curved mirror to reflect the light. In appearance, refracting telescopes are usually longer and more in line with what the average person looks like in a telescope. and reflective telescopes, because the light in the mirror cylinder reciprocating forward, generally appear coarse short.

Because the lens of different light diopter different, the traditional refraction telescope to see the image will produce chromatic aberration, object edge will appear overlapping color stripes, when the telescope magnification is more obvious. Modern refracting telescopes add several additional lens groups to eliminate chromatic aberration, similar to the way the camera lenses are handled. The reflective telescope does not have a chromatic aberration, but because the traditional spherical reflector does not have a good way to converge the edge of the light on the focus, the reflective telescope will produce spherical aberration Het image, see the object will appear halo-like and comet shape deformation. Modern reflective telescopes have produced many variants on the basis of traditional Newton-style telescopes, producing reflective telescopes. such as the very popular Schmidt-Cassegrain style and improved Maksutov-type telescope. Refractive telescopes and reflective telescopes improve the disadvantages by using aspheric primary mirrors and modified lenses.

To sum up, in my own experience it may not be applicable in all cases at the same time, the refracting telescope is more suitable to observe the celestial bodies in the solar system, and the reflective telescope is more suitable for the observation of Deep space objects. The specific situation needs to be judged by the focal ratio, focal length and aperture of the telescope.

left: fork-type equatorial instrument/Theodolite right: German-style equatorial instrument

Theodolite and Equator Instrument

We know that, because of the Earth's rotation and revolution, celestial bodies on the celestial sphere will be at a uniform speed of the Dongsheng West. If you have the experience of using a common telescope to observe objects on the ground, you will see that the larger the focal length, the narrower the view of the telescope--the faint movement of the target or lens will cause the target to run out of sight. Because the observation baseline is longer, the telescope must not only avoid shaking, but also let the mirror tube slowly move to catch up with the celestial bodies of the revolution.

If only the celestial body is required not to leave the field of vision, then the theodolite can meet the requirements. The theodolite is a simple two-axle frame which can be supported and rotated, and the horizontal and vertical axes are perpendicular to each other. This system is usually used in telescopes, cameras, radio antennas, solar panels.

Now, there are many models of civil telescopes with a theodolite base. The original theodolite could not find celestial bodies through vertical and horizontal calibration positions, but the new models had electric motors built into them, which automatically sought for celestial objects and tracking.

But we know that the orbit of the celestial body is centered on the North Star, and tracking objects with the theodolite only tracks the relative position of the celestial body relative to the vertical two axes of the earth, and the celestial bodies in the field of vision are actually slowly spinning. There is no problem with the naked eye, but using a camera for a long time to take a picture cannot be done, and the celestial body is blurred by rotation. To eliminate this "field rotation" must rely on the equator instrument.

The equator is an axis that rotates parallel to the axis of the Earth's rotation, and can follow a device that rotates in the sky. Telescopes use the Equator instrument base, the red warp axis and the paired red latitude axis are perpendicular to each other. When used, only need to let the equatorial instrument of the red axis of the North Star, the red latitude axis in 23 hours and 56 minutes of the Earth rotation cycle to track a celestial body. Because modern astronomy uses the red warp/red latitude coordinates to locate celestial objects, the equator telescope can find a celestial body directly according to the scale of the two axes.

The common equatorial instrument has two kinds of structure, German type and fork type. The German-style equator has a very distinctive T-shaped structure, but the disadvantage is that one end of the red warp axis needs to be balanced with the weight of the telescope. The fork-type equatorial instrument, which is improved from the theodolite, does not need counterweight. As long as the theodolite adds a platform to adjust the slope, so that the vertical axis of the theodolite is aimed at the Polaris, the theodolite can be converted into a equator instrument for use. In fact, there are many smart-tracked telescopes that use this structure.

left: Reflective light Way Left: Newton-type Light road on the right: Schmidt-Cassegrain-type lower right: Maksutov-Cassegrain-type

Refraction or reflection? It's a problem.

General Merchandise refraction telescope in the focal length of about 800-1000mm, the mirror tube is very long, looking very cool. To make a joke, maybe such a large, reflective telescope would be more satisfying for a novice. Choosing a refractive telescope is relatively simple, and only needs to look at the aperture of the telescope, focal length, focal ratio, color-resistant lenses, and additional functions. Reflective and reflective telescopes are relatively complex to choose from, and traditional Newton-style telescopes are suitable for deep space observation, but there are problems with the contamination and distortion calibration of open mirror cylinders. In a reflective telescope, you need to select one of the Schmidt-Cassegrain or Maksutov.

However, several well-known telescopes such as the United States star Trump (Celestron), Mead (Meade), Taiwan's Xinda (Sky watcher) and so on have produced a large number of various types of telescopes, and different series of functional demands vary greatly. Star Trump production of a large number of refraction-type entry products, many products are equipped with German-style equatorial instrument, as a child's hobby to cultivate more appropriate. And Mead's midrange products ETX Series Maksutov telescope with the star Trump of the C series is the same as the size of many products, price segmentation is also very comprehensive. In the circle of astronomy enthusiasts, the letter reached a nickname for "Small Black" Newton's telescope because of the low entry price, can be later upgraded very popular.

For the first time you enter amateur astronomical observations, the selection of telescopes follows these principles:

1. Is the target a planet or a deep sky object? Planetary observations require large focal lengths, and deep space celestial observations require relatively large diameters. In terms of caliber, Schmidt-Cassegrain or Maksutov-Cassegrain telescopes have advantages.

2. Do you need to take pictures of celestial bodies? If necessary, you must select a model with an equatorial instrument, plus a camera or an electronic eyepiece interface.

3. Budget.

From the sight of the good shot

The first telescope, the general people will complain, see things really difficult. It is almost impossible to find a star directly with a telescope, and the telescope has its own accessories to search for stars. Whether it is a red dot search mirror or a low magnification telescope search mirror requires the user to adjust their own, so that the search star mirror and the main mirror coaxial. The process is also simple, is the method of infinite approximation. First you need to use the main mirror to find a fixed target, using a low magnification eyepiece to place the recognizable point of the target in the center of the field of vision, and then adjust the screws on the search mirror, transfer the object seen in the main mirror to the center of the Cross of the search mirror, or coincide with the red Then switch to the high magnification eyepiece and repeat the adjustment.

In the formal observation, first use the search star mirror to find the object to see, and then focus on the main mirror to watch directly. To find celestial bodies, you must be familiar with the movement of celestial bodies at different times of the season. Looking for the moon at the end of the lunar calendar is like looking for a Scorpio and looking for Orion as impossible. Of course, you can also use mobile phone software like Skywalk to know the sky.

If you're buying a telescope with a go-to function, it's much easier to find a star. Go-to technology is a technique that appears on new telescopes, using electronic systems to compute the position of celestial bodies and automatically track them, such as the Mead ETX-90 in my hand.

For the go-to telescope, the first step is to calibrate. When you use the horizon, you need to lock the horizontal axis of the telescope so that the lens is pointing north. Then turn on the calibration function, and the telescope will provide you with some bright objects to choose from, such as Vega, Sirius, etc. After selecting an object, the telescope will automatically turn to the direction of the celestial body and automatically follow it, and when the telescope arrives in the direction of the target object, the object is accurately tuned to the center of the field with the handle, and then the next celestial body is calibrated. In general, the calibration of two stars is sufficient. After calibration, just select the object you want to observe in the menu, and press the "Go-to" key, the telescope will automatically turn to that direction and follow.

Skilled to find a star, you can try to shoot. In fact, in astronomical photography, because the light is weak, the exposure time is long, the camera is not a good choice, only in the shooting of the moon such a large and bright celestial body is suitable. All other times you need an electronic eyepiece. Below please enjoy some celestial photography photos, guess what I shot?