It is easy to guess that a telescope is an optical device designed to observe celestial bodies. Indeed, its main task is to collect electromagnetic radiation emitted by a distant object and direct it to the focus, where an enlarged image is formed or an amplified signal is formed. Today, there are many different telescopes - from home ones that anyone can buy, to ultra-precise ones, such as the Hubble, that can look at millions and billions of light years deep into the Universe ...
A bit of history
It is believed that the first two-lens telescope that appeared in 1609 was invented by Galileo Galilei. However, it is not. A year earlier, the Dutchman Johann Lippersgay wanted to patent his device, which consists of lenses inserted into the tube, which he called the “spyglass”, but was refused due to the simplicity of the design.
Even earlier, at the end of the 16th century, astronomer Thomas Digges tried to observe the stars through concave mirrors and lenses. True, the idea was never brought to its logical conclusion. Galileo simply turned out to be “at the right time, in the right place”: pointing the Lippersgue pipe into the sky, he discovered craters and mountains on the surface of the Moon and many other interesting things. That's why he is considered the first astronomer to use a telescope. This gave rise to the era of refractory telescopes.
Types of optical equipment
Optical telescopes can be divided into types based on the main type of element that collects light on mirror, lens, and mirror-lens (combined) devices. Each of these types has its own advantages and disadvantages, therefore, when choosing a suitable system, several factors must be taken into account: the conditions and goals of observations, requirements for dimensions, weight and transportability, price, etc. Let's try to understand in more detail what a telescope is and what basic characteristics its most popular types possess. So what does a telescope look like?
Lens Refractor Telescopes
These telescopes use lenses to approximate, which, due to their curvature, collect light. As in other optical devices (cameras, microscopes, etc.), all lenses are assembled in one device - the lens.
At present, refractor telescopes are used mainly by amateurs, since they are designed for observations only of nearby planets and the Moon.
Advantages:
- Relatively simple design, reliability and ease of use.
- No special maintenance required.
- Excellent color rendering in apochromatic performance and good in achromatic.
- Great for observing binary stars, planets, the moon, especially at large apertures.
- Fast thermal stabilization.
- The lens does not require adjustments, as it is adjusted by the manufacturer during manufacturing.
Disadvantages:
- Compared with catadioptrics and reflectors, they have a higher cost per unit diameter of the lens.
- The practical largest aperture diameter is limited by price and bulkiness.
- Due to aperture limitations, refractors are generally less suitable for observing distant, dim objects.
Reflector telescopes
A reflex telescope is an optical device in which a mirror acts as a light-collecting lens. The main mirror can be of small diameter (spherical) or large (parabolic).
Advantages:
- Compared with catadioptrics and refractors, the cost of a unit of aperture diameter is lower.
- Compact and easy to carry.
- Due to the relatively large aperture, they work wonderfully when observing distant and dim objects: star clusters, nebulae, and galaxies.
- No chromatic aberration. Images are bright with little distortion
Disadvantages:
- Thermal stabilization takes time due to the massive glass mirror.
- The image is slightly distorted due to the open pipe, unprotected from warm air and dust.
- Adjustment of mirrors is periodically required, which may be lost during operation or transportation.
Mirror-lens, or catadioptric
A catadioptric telescope is an optical device in which various kinds of image distortions are minimized due to the use of mirrors in them along with corrective lenses. Due to the fact that the light inside the tube is reflected several times, the focus can be long. Some models are capable of capturing an image. If you use a catadioptric telescope for this purpose, the photos will be of good enough quality.
Advantages:
- Correction of high level aberrations.
- Great for observing both close objects, such as the moon, and objects in deep space.
- The closed pipe protects from dust and warm air currents as much as possible.
- Compared to reflectors and refractors, with equal aperture, the greatest compactness is maintained.
- Compared to a refractor, the cost of large apertures is much lower.
Disadvantages:
- Relatively long thermal stabilization.
- The cost of an equal aperture is greater than that of reflectors.
- Self-alignment is difficult due to the complexity of the design.
Modern space telescopes
Having come a long way (starting with a telescope of the 17th century and ending with automatic space giants), the telescope opened up enormous opportunities in the study of the starry sky. But there are many factors that prevent anyone, even the most powerful ground-based telescope, from conducting research. These may include both flare and turbulence, as well as the most commonplace clouds. Orbiting space stations in this regard have a huge advantage, as they are able to work around the clock, in any weather conditions, transmitting images without the slightest atmospheric distortion. One such station is the Hubble, a space telescope. Photos taken by his optics perfectly display the farthest objects of the universe, billions of kilometers away, allowing astronomers to discover new stars, planets and galaxies.