It is easy to guess that a telescope is an optical instrument designed to observe celestial bodies. Indeed, its main task is to collect electromagnetic radiation emitted by a distant object and direct it to a focus, where an enlarged image is formed or an amplified signal is formed. To date, there are many different telescopes - from home, which anyone can purchase, to ultra-precise ones, such as the Hubble, capable of looking millions and billions of light years deep into the Universe …
A bit of history
It is generally accepted 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 Lippershey wanted to patent his device, which consisted of lenses inserted into a tube, to which he gave the name "spyglass", butwas rejected 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 just happened to be "at the right time, in the right place": pointing the Lippershey tube at the sky, he discovered craters and mountains on the surface of the moon and many other interesting things. That is why he is considered the first astronomer to use a telescope. This gave rise to the era of refracting 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 objectives of observations, requirements for dimensions, weight and transportability, price, and so on. Let's try to understand in more detail what a telescope is, and what are the main characteristics of its most popular types. So what does a telescope look like?
Refractor lens telescopes
These telescopes use lenses to zoom in, which collect light due to their curvature. Just like in other optical devices (cameras, microscopes, etc.), all lenses are assembled into one device - a lens.
Currently, refracting telescopes are mainly used by amateurs, as they are designed for observationsonly for nearby planets and the Moon.
Dignity:
- Relatively simple design, reliable and easy to use.
- No special maintenance required.
- Excellent color reproduction in apochromatic and good in achromatic.
- Great for observing binary stars, planets, the Moon, especially at large apertures.
- Quick thermal stabilization.
- The lens does not require adjustments, as it is adjusted by the manufacturer during manufacture.
Flaws:
- Compared to catadioptrics and reflectors, they have a higher cost per unit of lens diameter.
- The practical largest aperture diameter is limited by cost and bulkiness.
- Due to aperture limitations, refractors are generally less suitable for observing distant, faint objects.
Mirror reflecting telescopes
A reflecting telescope is an optical device in which a mirror performs the function of a light-collecting lens. The main mirror can be small (spherical) or large (parabolic).
Dignity:
- Compared to catadioptrics and refractors, the cost per unit aperture diameter is lower.
- Compact and easy to transport.
- Due to the relatively large aperture, they work great when observing distant and dim objects: star clusters, nebulae, galaxies.
- No chromatic aberration. Images are bright with little distortion
Flaws:
- Thermal stabilization takes time due to the massive glass mirror.
- The image is slightly distorted due to the open pipe, unprotected from warm air currents and dust.
- Periodic mirror alignment is 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 together 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 turn out to be of fairly good quality.
Dignity:
- High level aberration correction.
- Great for observing both close objects like the Moon and objects in deep space.
- Closed pipe provides maximum protection from dust and warm air currents.
- 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.
Flaws:
- Relatively long thermal stabilization.
- Equal aperture costs more than reflectors.
- Self-adjustment is difficult due to the complexity of the design.
Modern space telescopes
Having come a long way (from the spyglass of the 17th century to the automatic space giants), the telescope has opened up great opportunities in the study of the starry sky. But there are many factors that prevent any, even the most powerful ground-based telescope, from conducting research. These can include both flare and turbulence, as well as the most banal clouds. Orbital space stations in this regard have a huge advantage, as they are able to work around the clock, in all weather conditions, transmitting images without the slightest atmospheric distortion. One such station is Hubble, the space telescope. The photographs taken by its optics flawlessly depict the most distant objects in the universe, billions of kilometers away, allowing astronomers to discover new stars, planets and galaxies.
