Astronomical telescopes

Introduction

Have you ever seen big laboratories with huge equipment to observe stars and planets? These equipment are known as telescopes used to keep heavenly bodies and magnification to explore bounds of outer space that the naked eyes cannot reach.

The telescope requires a few lenses to focus on objects and an eyepiece to see a magnified image.

By definition, the telescope is an instrument used to observe distant objects of outer space that our naked eyes cannot see. In general, there are two types of telescopes mainly categorized by:

1. Terrestrial telescope

2. Astronomical telescope

Terrestrial and astronomical telescopes come under the category of refracting telescopes. A refracting telescope comes with two convex lenses, the larger one is known as the objective lens, and the smaller one used for viewing is the eyepiece.

Both these telescopes sound identical, but they are not. They come with a set of differences that make them stand out.

Astronomical Telescope

An astronomical telescope is an instrument that works on the principle of optics used to view the enlarged image of far heavenly bodies like stars and galaxies. The last image formed by an astronomical telescope is always virtual, inverted, and magnified. It is an excellent means for analyzing and collecting radiation from heavenly bodies far from the universe we live in. It helps scientists to observe subjects with a detailed view even if they are an infinitely large distance.

Principle of Astronomical Telescope

The working of telescopes is based on the principle that when an object that is to be magnified is placed at a large distance from the objective lens of an astronomical telescope, magnified, virtual, and inverted images are formed at the least distinct vision when held close to the eyepiece.

Construction of Astronomical Telescope

An astronomical telescope’s construction consists of two convex lenses: An objective lens placed at the position O and an eyepiece placed at the position of E. The focal length of the astronomical telescope is fO, and the eyepiece’s focal length is fE. In this construction, the aperture of the objective lens is taken largely as compared to the eyepiece so that more light can be received by it from distant objects and a brighter image can be formed. The placement of both the objective lens and the eyepiece is done at the free ends of the two sliding tubes placed with some considerable distance in between.

Working Principle of Astronomical Telescope

When a parallel beam of light from distant objects like stars and planets falls on the telescope’s objective lens, a real, inverted, and diminished image is formed  of the object. The image of this kind will now act as an object for the eyepiece E by adjusting a proper position such that the image is formed between the focus  and the optical center of the eyepiece. Now when the image is formed, it is a virtual, inverted, and highly magnified image of the object at infinity, The final image is formed at the infinity and then the telescope is considered to be in ‘normal adjustment.

The final image of the object of heavenly bodies formed by the astronomical telescope is always inverted concerning the thing. However, it does not matter if an inverted image is an astronomical object because most heavenly bodies are generally spherical.

Terrestrial Telescope:

It is an instrument that requires lenses and curved mirrors or even a combination of both to observe distant objects. The last image formed by the terrestrial telescope is non-inverted and erect.

Principle of Terrestrial Telescope:

The working principle of the terrestrial telescope uses three lenses. The first lens, L1, acts as the telescope’s objective lens, while L2 acts as the eyepiece. The third lens is placed between L1 and L2 such that the third length of short focal length is placed permanently. This lens is known as the erecting lens. The image formed by this telescope is reversed even if it is virtual.

Construction of Terrestrial Telescope :

It contains three lenses compared to the astronomical telescope, also called a spyglass. The terrestrial telescope creates an erected final image of the object. The third lens, shorter focal length f, is placed at 2f, which forms an inverted image. The image formed by this focal length serves as the object for the eyepiece. The lens responsible for erecting the image is the erecting lens and is placed at the center of the telescope. The two convex lenses will be coaxially mounted at the extreme of the two tubes such that one slides onto another. The distance between them can be changed by applying a screw arrangement.

Working Principle of the Terrestrial Telescope 

As discussed earlier, a terrestrial telescope consists of one extra lens known as the erecting lens in addition to two lenses. After light passes from the objective lens, a reversed image is formed, which needs to get erect because it is terrestrial objects that we are observing and not astronomical objects, therefore,  a Pitching lens is used for reducing a final erect image.

The equipment consists of an objective, an eyepiece, and an erecting lens. The objective lens produces an image of a distant object. The lens L1 is placed at a distance 2f from the object, which forms an erect image. This image is formed at the eyepiece. And therefore, the final image created is erect and forms at infinity.

A telescope is a device that magnifies views of faraway objects. In astronomy, the telescope is, without a doubt, the most significant investigation tool. It allows for the collection and analysis of radiation from celestial objects, even those at the farthest regions of the cosmos.

Conclusion

It was all about the Terrestrial and Astronomical Telescope and their working principles. Both the telescopes serve the basic purpose of letting you view the magnified image of any distant object that might seem negligible in size concerning a naked eye’s vision. As the name suggests, terrestrial telescopes are known for magnifying images present on earth, and anything within the range of the atmosphere, whereas the astronomical telescope is used for viewing far-distant objects like stars, galaxies, and planets. Telescopes have had a major role in discovering various planets, stars, and galaxies, as well as different elements of the universe that would remain obscured from our vision if we had not looked it up in the sky. They have helped make some remarkable discoveries in science, chemistry, physics, and geography.