If you stand in front of a nebula, can the naked eye see a beautiful scene like a photo?

At the turn of spring and autumn, if the sky is clear, we may have a chance to see the Milky Way? The mica screen has a deep candle shadow, and the long river is gradually falling. Beautiful scenery.

Don't be sorry if you can't see it. The developed Internet still provides us with many colorful images of galaxies or nebulae taken by Hubble telescope.

In fact, the Hubble telescope uses a black-and-white image sensor, and the color is artificially added to the photos by many astronomers according to the spectra corresponding to different wavelengths of light.

under the real galaxy or nebula, can we still see the beautiful scenery in the photo? Today we will explore the answer. What is the essence of color and how does the human eye distinguish it?

In our daily life, we can see an object because our eyes receive that the object can emit or reflect light. Of course, if it does not emit or reflect any light, we will see a completely dark world. The shorter the wavelength? The higher the frequency, the longer the wavelength? The lower the frequency?

whereas light is essentially electromagnetic wave, it exists in various colors because electromagnetic waves with different wavelengths correspond to different colors. In fact, for people, objects can show different colors because of the different components and structures that make up the object, which leads to different frequencies of electromagnetic waves absorbed and reflected by the object, so we can think that the essence of colors is that they reflect different frequencies of electromagnetic waves.

For example, we can see green grass because under the irradiation of sunlight (which is a composite light composed of seven colors of light), the grass absorbs the light with wavelengths other than green, reflects the electromagnetic wave with the corresponding wavelength of green, and finally reflects it to our eyes, so the color of the grass we see is green.

Now let's look at the imaging principle of the naked eye. When the human eye receives visible light, it will first pass through the refractive system of the eye, then image on the retina, and finally be felt by the photosensitive cells.

There are two kinds of photoreceptor cells: cone cells: these cells can distinguish colors, but they can only work in bright environment. Color blindness is caused by the lack of cone cells with corresponding colors. Rod cells: The ability to distinguish colors is poor, but it can work in dim environment, and rod cells account for more, so we can see clearly at night.

The reason why all the scenes we see in the telescope are close to black and white is that the night vision ability of human eyes is poor and it is impossible to distinguish colors better, which leads to the galaxies we see are all glistening. How are brilliant pictures of galaxies taken?

Friends who know astrophotography should be able to do so. If you only observe with the naked eye, the galaxy seen through the telescope will only be a dull black-and-white scene, because the human eye is insensitive to color in low light.

The second is the exposure time. When we take photos of deep space, we simply can't get more details through instant exposure, so we need to increase the exposure time. Those beautiful pictures of galaxies are only taken after exposure for dozens of minutes and dozens of hours.

Hubble telescope is different from ordinary astronomical telescope. As we all know, Hubble telescope is an optical telescope above the earth's atmosphere, and the benefits of doing so are obvious. It will not be affected by bad weather, light pollution and atmospheric turbulence when shooting.

In the universe, the frequency of electromagnetic waves that can be received is far more narrow than that visible to the naked eye (38-76 nanometers). So if you want to get more information from the universe, you must accept a wider range of electromagnetic frequencies.

You know, Hubble's mission is not just to take a picture, it also needs to analyze the composition of distant celestial bodies, what elements they contain, measure the distance between galaxies and other important tasks, and then people can calculate the size and age of the universe and the origin of various celestial bodies through the collected data.

Although Hubble telescope is also an optical telescope, the difference is that it does not directly image the received light, but analyzes the light spectrum through a spectrometer to get more data. So what is the principle of spectral analysis?

from a microscopic point of view, all elements are made up of atoms, and atoms are made up of nuclei and electrons. Electrons outside the nucleus can be divided into different energy levels according to their abilities, the ground state energy level with the lowest energy, and the others are excited states.

under normal circumstances, electrons don't jump, but when atoms receive external energy, they will absorb the energy needed for electron jump and the light with the corresponding characteristic wavelength, so the light that provides energy will lose a light with the characteristic wavelength, which is the absorption spectrum. Similarly, electrons will release energy when they return to the ground state, which is called emission spectrum.

for the received light, by measuring the absorption spectra and emission spectra of different substances, the spectra of different elements will have corresponding color lines or lack corresponding color lines at different positions, but in general, the spectral lines of elements with the same meaning will always have the same color lines at the same position.

That's why the Hubble Space Telescope works with a black-and-white image sensor, because through spectral analysis, we can know the colors and elemental composition of distant galaxies. Back to the topic, what would we see if we had the chance to stand in front of a nebula in person?

At this time, have many sci-fi movies come to your mind? But I regret to tell you that we can't see the colorful photos released by NASA.

First of all, most nebulae in the universe are very dark, and the human eye's ability to distinguish colors is even worse in a dark environment, just like walking on a path without any lights in the middle of the night.

Secondly, many details of Hubble's photos come from invisible light. Only by mapping specific bands to RGB can scientists convert electromagnetic waves in invisible bands into visible light.

Isn't that gorgeous nebula colorless? Obviously not, it's just that what the naked eye sees is different from that in the photo.

Let's take another example: For example, in the moonlight at night, everything we see is close to black and white, because the ambient light is insufficient, so we can't distinguish colors better, but we can't say that they are colorless.

Astronomers just try their best to eliminate the interference, restore their original colors, and convert what is invisible to human eyes into a visible form and present it to our eyes.

And colorful pictures of galaxies can, to a certain extent, stimulate people's interest in science and enthusiasm for exploring the universe, and they also have more illusions about the mysterious starry sky. Having talked so much, let's sum up: the essence of color comes from the different reactions of the naked eye to different wavelengths of light, so richer colors depend on whether we have more kinds of photosensitive cells. Astrophotography relies on high sensitivity and long exposure, which the human eye does not have, which is an important reason why we can't directly see the beautiful starry sky through the telescope. Galaxies are colored, but you can't see some details outside the visible light only by the naked eye, but if you can really stand in front of the nebula, I believe it is enough to shock you.