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The Resolving Power of Telescopes

Resolving power of a telescope refers to the ability of a telescope to detect the small details. This article will explain this term so that you can grasp it easily and provide a lot of photographs and drawings. Firstly, let’s look at a double star.

What is resolving power? It is the ability of a telescope to see really small details. In this article I give you a really good understanding of what the resolving power of a telescope is and I show you lots of pictures and drawings. A good explanation of this would be to look at a double star.

Image by Will Kalif

Fig: View of a double star through a small telescope

If you look through a small telescope and point it to a double star, you will see this fuzzy view. Notice that the stars blend together here. This can be an example of resolving power of telescope. The ability of detecting small details or the. The resolving power of a small telescope is less. That is why the sharpness or resolution of the picture we get from it is less. What is the solution here? You can suggest to use higher magnification and get it sharper.

Image by Will Kalif

Fig 2: View of the same double star with a higher magnification through the same small telescope.

The picture shows you how the same double star looks if you use higher magnification. From the picture, it is clear that higher magnification gives you a bigger image, but not a better resolution. This is why you get the same fuzzy blend look of the double star.

So magnification is not all you need to make the view of the telescope better. While you are using the highest resolution of your telescope, you have to understand that magnifying any view will not make the view better or more clear.

Image by Will Kalif

Fig 3: View of the same double star through a larger telescope.

If you look at the same double star with a larger telescope having larger primary mirror or lens, even if the magnification is like the figure 1, you will be able to see the two separate binary stars at the same distance in the view. It is the higher resolution that made the difference between the views of the same object here. It gave a sharper and more detailed and clear view. 

Higher resolution means it works on more pixels per inch of the image, which allows more detail per inch of the view. If you think about television, you will understand this better. Latest high definition television will give you a clearer picture than the older television with poor resolution.

Image by Will Kalif

Fig 4: View of the same double star through the same larger telescope but with higher magnification same as figure 2

This picture shows you that even if you magnify the view of the larger telescope, you will get the same detail as figure 3, only difference here is the picture is bigger. This view is not clear enough to understand the double star system properly. This is why astronomers always feel the need for larger and larger telescopes. The larger the telescope, the better the resolution and the better the view you will get.

Technical aspects of Resolving power

Image by Will Kalif

Fig 5: Objective Lense (on the top), light wave with larger wavelength (the upper wave), light wave with smaller wavelength (at the bottom)

It is known that light has a spectrum of different colors. And different color lights are different in speed, frequency and wavelength. Wavelengths play an important role in resolution.If the light that falls on a telescope lens is of larger wavelength, the telescope can capture more light which causes the higher resolution i.e you will get a clearer view. If the wavelength of the lightwave that falls on the objective lense is less, the telescope can sample less light and in turn gives you a fuzzy image for less resolution. When the wavelength is more, the telescope can gather more information and create a more accurate image.

In short, the higher the wavelength of the light, the better the resolution of the image.

Other factors affecting resolution

  1. The quality of the telescope – It is the quality of optics on which the quality of the telescope depends. A better optics will be able to gather more information (light) and in turn produce a better picture with more detail.
  2. The Atmosphere – Atmosphere is a very important factor while observing through a telescope. Whatever telescope you use, if the weather is turbulent, it will cause distortion of light and create a fuzzy image.
  • The Formula: The resolution of a telescope is measured as the minimum resolvable angle in arc seconds. The formula is
Image by Will Kalif

Fig 6: Formula of the resolution of telescope.

In this formula you will get two variables and a constant, where the value of the constant is 252,000 and the two variables are the diameter of the telescope (in centimeters) and the wavelength of the light (in centimeters).

The formula describes that the resolution of a telescope is 252,000 times the ratio of the wavelength of the light and the diameter of the telescope. This relation determines that the higher the diameter of the scope, the smaller the arc of the angle that can be resolved. And smaller the arc, the better the resolution. 

Hope that this post helps you a lot to understand the Resolution of Telescope easily.

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