# Why do we need telescopes/ binoculars/ etc? [closed]

Why do we need to use magnifying objects to see things that are far from us? Why isn't the light coming from those objects enough for us to see without special aid? Is it because light loses energy on its path? If that is the case, I do not see how a telescope would help, because said light still has to hit the lens of the telescope, right?

## closed as off-topic by stafusa, Jon Custer, Anders Sandberg, JMac, David WhiteJul 25 '18 at 17:38

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• This question shows no research effort at all. – my2cts Jul 22 '18 at 16:34

Astronomers use telescopes because they're much better than our eyes. Here are a few reasons:

1. Telescopes see lots of colors - telescopes can collect light that our eyes are unable to: radio, microwave, infrared, ultraviolet, x-rays and gamma rays.

2. Telescopes collect lots of light - our pupils are only a few millimeters across, so we can only collect photons over a tiny area whereas telescopes can collect photons of huge areas (football fields worth for radio telescopes)

3. Telescopes see fine details - Because of the wave nature of light and the nerves in our eyes, we can only see details about the same angular size as Jupiter's width. Telescopes can allow us to resolve fine details - like Jupiter's Great Red Spot.

4. Telescopes can record observations with cameras - You can see things with your eye and draw them, but telescopes can share observations with the world! This is especially important for convincing skeptics what you saw was real!

For binoculars, it makes good sense when you think about how much you're spending on your holiday and though not every animal you see on safari will be a great distance away, you'd be amazed at how much you'll gain from having a really good close up look at, say, the eye of an elephant standing 20 yards away; you'll see little hairs, cracks and creases that you couldn't have hoped to notice with the naked eye.

• Telescopes see fine details - Because of the wave nature of light and the nerves in our eyes, we can only see details about the same angular size as Jupiter's width. Telescopes can allow us to resolve fine details - like Jupiter's Great Red Spot. Could you please elaborate a bit on this? I think this is the part I was most interested in. – rickle_pickk Jul 22 '18 at 15:19
• Point #1 is probably the biggest key: our eyes see just a narrow sliver of the EM spectrum and all sorts of physical events occur outside that sliver. – Kyle Kanos Jul 22 '18 at 15:34

## We need telescopes for higher angular resolution

While @RoshanLeyangi already pointed the reasons, the one you are looking for is the angular resolution. What looks like making objects bigger when looking through a telescope is actually amplyfying the angle under which the light rays from different points of this object fall into our eye. The eyes angular resolution is limited, so an amplification over this threshold can enable us to see more detail. The graphic (with the light coming from far away nearly parallel from the left and falling into the eye on the right.) shows how a magnifying lens as used in telescopes increases the angular resolution.

Even if light emitted by a star was not losing energy at all, the light energy passing through a unit area or a pupil of an eye (energy or power density) would be decreasing as a square of the distance from the star.

The area of the objective lens of a telescope is much greater than the area of a pupil, so, at any given distance, it can capture much greater light energy and, with proper focusing, most of this energy will be passing through the pupil of an eye.

Besides the energy aspect, telescopes and binoculars, through the action of the lenses, magnify an object. The angle subtended by a magnified image of an object is much greater than the angle subtended by the object observed directly, which increases the angular resolution and allows us to see more details. According to Wikipedia, the angular resolution of human eye is limited to about $0.02^\circ$.