Are all astronomical telescopes expensive? There are some mobile ones that are very cheap

The deep and dark universe seems to hide many secrets, and humans have been curious about it since the moment they gained wisdom.

Fortunately, the universe is not invulnerable. The tiny starlight in the night sky is the key to unlocking the mysteries of the universe, so since ancient times, humans have tried every possible way to observe these tiny lights. Now it is different. We have astronomical telescopes, which have made a qualitative leap in human's ability to observe the universe. So what are the astronomical telescopes you are familiar with?

When it comes to the types of telescopes, there are actually many different classification methods. For example, according to the observation band, they can be divided into radio telescopes, infrared telescopes, optical telescopes, ultraviolet telescopes, x-ray telescopes, gamma-ray telescopes, etc., and according to the installation location, they can be divided into ground-based telescopes and space telescopes. Those installed on the surface are ground-based telescopes, while those installed outside the surface such as Hubble and Webb are space telescopes.

What ordinary astronomy enthusiasts have access to are optical telescopes, such as the ancient refracting telescope and the popular Newtonian reflecting telescope. The "China Sky Eye" that we are extremely proud of is a 500-meter aperture spherical radio telescope.

There are many types of telescopes, and their principles are not exactly the same, but all telescopes have one common feature, that is, "high-end", which means "expensive". For example, the total cost of China's Sky Eye reached 667 million, and the famous Rubin Observatory, its cost is no less than 600 million US dollars. It seems that not everyone can afford a telescope, but there are always exceptions, and there are cheap telescopes.

The cheap telescope we are talking about is very different from the telescope in our common sense. It is not a solid, but a fluid.

There are many types of telescopes, and their principles are different, but almost all of them have a parabola. Why is that? Because the distance between celestial bodies in the universe and us is very far, millions of light years away. At such a distance scale, the light emitted by these stars can be regarded as parallel by us. To converge these parallel lights on one point, a parabola is naturally needed. In other words, if we have a parabola that is large enough and has good reflectivity, we can use it to observe the deep space of the universe.

It usually costs a lot to manufacture such a standard parabola, so the price of the telescope naturally goes up, but if the parabola is not solid but fluid, the situation is different.

Let's imagine that if we have a dish, put water in it, and then start to rotate the dish, what will happen? The water in the dish will rotate and form a parabola with a perfect arc. This parabola formed under the rules of nature does not require us to carve it out meticulously. It is the best component for making telescopes. Wait, this parabola is indeed perfect, but the problem is that the reflectivity of water is not good. It doesn't matter. Just replace the water with mercury. Mercury's reflectivity is awesome. Finally, we just need to place a camera at the focus of this mercury parabola, and an astronomical telescope is born.

This telescope consisting of a rotating disk and mercury is called a "mercury mirror telescope".

Currently, there is such a mercury mirror telescope in northern India, called the International Liquid Mirror Telescope, which was jointly built by India, Belgium and Canada. Compared with other telescopes, the biggest advantage of this liquid telescope is its price. For example, the International Liquid Mirror Telescope has an aperture of about 4 meters, but the total cost is less than 2 million US dollars. But don't think that this thing is cheap and must not be good. "Cheap is not good" does not apply here. The research goal of this liquid telescope is the same as those expensive radio telescope arrays, which is to understand the structure of the universe and the evolution of celestial bodies.

It seems that this liquid telescope has all the advantages. Does it have no disadvantages? Of course it does, and they are obvious.

The key to this liquid telescope is to rotate the mercury to form a perfect parabola, which means that the rotating disk must not be tilted, it must always remain horizontal, otherwise the mercury rotating inside cannot form a perfect parabola, so this telescope can only look up at the sky and cannot rotate at will. This is a disadvantage of the mercury mirror telescope, but there are advantages behind the disadvantage, because it can only look at the same angle, so it is easier to detect changes in the observed target, and analyzing the causes behind the changes in the observed target is a key for humans to uncover the mysteries of the universe.

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