How far telescopes can see?

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Telescopes are powerful tools that allow us to observe distant objects in the universe. The distance that a telescope can see is determined by several factors, including the size of the telescope, the quality of its optics, and the location of the telescope. Let’s look more in details about these factors affecting how far telescopes can see, and let’s conclude about asking ourselves if this is a good question.

Telescope size

The aperture size of a telescope is a measure of the diameter of the primary mirror or lens that is used to collect light. The aperture size is one of the most important factors in determining how far a telescope can see, as it directly affects the amount of light that the telescope can collect.

A larger aperture size means that the telescope can collect more light, which in turn allows it to see farther into the universe. This is because more light means that the telescope can detect fainter objects that are farther away. Larger aperture telescopes are also able to produce clearer images of distant objects because they can collect more light, reducing the amount of distortion in the image.

For example, a small telescope with an aperture size of 100mm (4 inches) will be able to see objects very bright and then relatively close. A larger telescope with an aperture size of 1000mm (40 inches) will be able to see much more distant objects that a 100mm telescope cannot see, such as galaxies and nebulae that are millions or even billions of light-years away. For example, the Keck Observatory in Hawaii has two 10-meter telescopes, which are currently the largest in the world. These telescopes can see objects that are billions of light-years away.

Telescope quality

The quality of the optics in a telescope refers to the mirrors or lenses used to focus the light and can have a significant impact on how far a telescope can see.

High-quality optics are essential for producing clear and accurate images of distant objects. The surface of the mirrors or lenses in the telescope should be smooth and free of defects, such as scratches or distortions, to minimize the amount of light that is scattered or lost. The optics should also be coated with a special material to reduce glare and increase the transmission of light. These high-quality optics can help to produce sharper images, which can allow the telescope to see farther into the universe.

Low-quality optics, on the other hand, can produce distorted or blurry images that make it difficult to see distant objects. This can be caused by a variety of factors such as poor quality mirrors or lenses, incorrect alignment of the optics, or poor maintenance of the telescope.

Another important aspect of optics quality is the “diffraction-limited” performance, this means that the telescope can focus light to the best possible resolution limit set by the wave nature of light. The diffraction limit is determined by the aperture size of the telescope and the wavelength of the light being observed. A telescope with high-quality optics that is diffraction-limited will be able to produce images that are as sharp as possible, which can allow it to see farther into the universe. So, a good optical design is also essential on how fat telescopes can see and be able to reach the diffraction limit.

Telescope location

The location of a telescope can play a significant role in determining how far it can see. This is because certain locations have better atmospheric conditions and less light pollution than others, which can affect the quality of the images produced by the telescope.

Atmospheric conditions can greatly affect how far a telescope can see. For example, telescopes located in areas with high altitude and dry climates, such as the Atacama Desert in Chile, have clearer and more stable atmospheres, which can allow them to see farther into the universe than telescopes located in more humid or polluted areas. The stability of the atmosphere, which is usually measured by the seeing conditions, is important to minimize the distortion caused by the air movement, specially when observing at short wavelengths like ultraviolet or near infrared.

Light pollution is another important factor. Urban areas, where there is a lot of artificial light, can cause glare and reduce the contrast of the images produced by a telescope. This makes it difficult for the telescope to see faint objects that are far away. On the other hand, telescopes located in remote areas with little or no light pollution can see farther into the universe because they can detect fainter objects that are farther away.

For example, the Atacama Large Millimeter Array (ALMA) in Chile is located in one of the driest and highest regions on Earth, which allows it to see some of the most distant and faint objects in the universe.

Is “How far telescopes can see?” a good question?

It is definitively not! Even if size, quality and location play a role, it’s not about how far you can see, it is rather how well you can see something that is far away. For example, with my eyes, I can see a galaxy, but it will appear a small blurry point. With a small 4″ telescope, I will start to see some details as the object will start to be resolved. If I use a large telescope, let’s say a 16″ telescope, I will clearly see the galaxy shape and its arms. So, in all these cases, I look at the same distance, but what matters is quality and resolution of the image, and not how far telescopes can see.

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