How many telescopes are there

Light is one type of electromagnetic EM radiation , energy that is transmitted through space as a wave. Light travels faster than anything else in the universe. In the almost completely empty vacuum of space, light travels at a speed of approximately ,, meters per second ,, miles per hour. To give you an idea of how fast that is, a beam of light could travel from New York to Los Angeles and back again nearly 40 times in just one second. Even though light travels extremely fast, objects in space are so far away that it takes a significant amount of time for light from those objects to reach us.

For example, light from the Sun takes about 8 minutes to reach Earth. Since astronomical distances are so large, it helps to have a unit of measurement that is good for expressing those large distances. A light-year is a unit of distance that is defined as the distance that light travels in one year. One light-year is approximately equal to 9,,,, 9. Proxima Centauri, the closest star to us after the Sun, is 4. That means the light from Proxima Centauri takes 4.

The galaxy we live in, the Milky Way Galaxy, is about , light-years across. How long does it take light to travel from one side of the galaxy to the other? If an astronomer looks through a telescope at a star that is 1, light years away, is she seeing the star as it is now?

The smallest red-shifted galaxies are among the most distant galaxies we have detected so far at 13 billion light-years away. When we look at astronomical objects such as stars and galaxies, we are not just seeing over great distances—we are also seeing back in time.

Because light takes time to travel, the image we see of a distant galaxy is an image of how the galaxy used to look. For example, the Andromeda Galaxy, shown in Figure below , is about 2. If you look at the Andromeda Galaxy through a telescope, what are you seeing? You are seeing the galaxy as it was 2. If the galaxy ceased to exist 1 million years ago, when would you know that?

If you want to see the galaxy as it is now, you will have to wait and look again 2. This recent picture of the Andromeda Galaxy actually shows the galaxy as it was about 2. Light is one type of EM radiation; light is energy that travels in the form of an electromagnetic wave. Figure below shows a diagram of an electromagnetic wave.

An EM wave has two components: an electric field and a magnetic field. The distance between two adjacent oscillations is called wavelength. A related value is frequency , which measures the number of wavelengths that pass a given point every second.

Wavelength and frequency are reciprocal, which means that as one increases, the other decreases. Visible light — the light that human eyes can see — comes in a variety of colors. The color of visible light is determined by its wavelength. Visible light ranges from wavelengths of nm to nm, corresponding to the colors violet through red. The full range of electromagnetic radiation, or the electromagnetic spectrum , is shown in Figure below.

In the top, only the wavelengths of visible light show. In the bottom, a layer of thick clouds appears in the infrared wavelengths. Like our Sun, every star emits light at a wide range of wavelengths, all across the visible spectrum and even outside the visible spectrum. Astronomers can learn a lot from studying the details of the spectrum of light from a star.

Some very hot stars emit light primarily at ultraviolet UV wavelengths, while some very cool stars emit mostly in the infrared. There are extremely hot objects that emit X-rays and even gamma rays. Light from some of the faintest, most distant objects is in the form of radio waves.

Astronomers use telescopes to detect the faint light from distant objects and to see objects at wavelengths all across the electromagnetic spectrum. People have been making and using lenses for magnification for thousands of years.

However, the first true telescopes were made in Europe in the late 16th century. These telescopes used a combination of two lenses to make distant objects appear both nearer and larger.

The term telescope was coined by the Italian scientist and mathematician Galileo Galilei — Galileo built his first telescope in and subsequently made many improvements to telescope design. Telescopes that rely on the refraction, or bending, of light by lenses are called refracting telescopes , or simply refractors. Many of the small telescopes used by amateur astronomers today are refractors. Create a free Team What is Teams? Learn more.

How many space telescopes are currently active? Ask Question. Asked 7 months ago. Active 7 months ago. Viewed times. Related What are the next planned space telescopes? Improve this question.

Peter Erwin For example, the LORRI imager on the New Horizons spacecraft is now being used to observe distant bodies - does it make it a space telescope? I agree that strictly speaking, the term "space telescope" probably refers to all non-terrestrial observing equipment. I am happy to add the telescopes you mentioned. Add a comment.

Also see the Event Horizon Telescope , radio telescopes , space telescopes , and space ports. There are over professional observatories operating in the United States. Here are the 15 largest telescopes in the U. Alabama observatories Alaska observatories Arizona observatories Arkansas observatories California observatories Colorado observatories Connecticut observatories DC observatories Delaware observatories Florida observatories Georgia observatories Hawaii observatories Idaho observatories Illinois observatories Indiana observatories Iowa observatories Kansas observatories Kentucky observatories Louisiana observatories Maine observatories Maryland observatories Massachusetts observatories Michigan observatories Minnesota observatories Mississippi observatories Missouri observatories Montana observatories.