Why is electromagnetic radiation important to astronomers

Likewise, we commonly see red on faucet or air conditioning controls to indicate hot temperatures and blue to indicate cold temperatures. We can develop a more precise star thermometer by measuring how much energy a star gives off at each wavelength and by constructing diagrams like Figure 3.

The location of the peak or maximum in the power curve of each star can tell us its temperature. The average temperature at the surface of the Sun, which is where the radiation that we see is emitted, turns out to be K.

Throughout this text, we use the kelvin or absolute temperature scale. On this scale, water freezes at K and boils at K. All molecular motion ceases at 0 K. The various temperature scales are described in Units Used in Science.

There are stars cooler than the Sun and stars hotter than the Sun. For the Sun, the wavelength at which the maximum energy is emitted is nanometers, which is near the middle of that portion of the electromagnetic spectrum called visible light. Characteristic temperatures of other astronomical objects, and the wavelengths at which they emit most of their power, are listed in Table 1. If the emitted radiation from a red dwarf star has a wavelength of maximum power at nm, what is the temperature of this star, assuming it is a blackbody?

We can also describe our observation that hotter objects radiate more power at all wavelengths in a mathematical form. If we sum up the contributions from all parts of the electromagnetic spectrum, we obtain the total energy emitted by a blackbody. What we usually measure from a large object like a star is the energy flux , the power emitted per square meter. It turns out that the energy flux from a blackbody at temperature T is proportional to the fourth power of its absolute temperature.

This relationship is known as the Stefan-Boltzmann law and can be written in the form of an equation as. Notice how impressive this result is. Increasing the temperature of a star would have a tremendous effect on the power it radiates. If the Sun, for example, were twice as hot—that is, if it had a temperature of 11, K—it would radiate 2 4 , or 16 times more power than it does now.

Tripling the temperature would raise the power output 81 times. Hot stars really shine away a tremendous amount of energy. While energy flux tells us how much power a star emits per square meter, we would often like to know how much total power is emitted by the star. We can determine that by multiplying the energy flux by the number of square meters on the surface of the star.

Two stars have the same size and are the same distance from us. Star A has a surface temperature of K, and star B has a surface temperature twice as high, 12, K.

How much more luminous is star B compared to star A? Two stars with identical diameters are the same distance away. One has a temperature of K and the other has a temperature of K. Which is brighter? How much brighter is it? The electromagnetic spectrum consists of gamma rays, X-rays, ultraviolet radiation, visible light, infrared, and radio radiation. The emission of electromagnetic radiation is intimately connected to the temperature of the source. The higher the temperature of an idealized emitter of electromagnetic radiation, the shorter is the wavelength at which the maximum amount of radiation is emitted.

The total power emitted per square meter increases with increasing temperature. X-rays: electromagnetic radiation with wavelengths between 0. Skip to main content. Radiation and Spectra. Search for:. Example 2: Calculating the Power of a Star While energy flux tells us how much power a star emits per square meter, we would often like to know how much total power is emitted by the star.

Key Concepts and Summary The electromagnetic spectrum consists of gamma rays, X-rays, ultraviolet radiation, visible light, infrared, and radio radiation. Licenses and Attributions. This light is given different names, depending on its wavelength and energy — radio waves long wavelength, low energy , microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays short wavelength, high energy. Scientists call the whole range of light types the electromagnetic spectrum.

Get used to using the scientific term electromagnetic spectrum when talking about light. Our eyes only see a very small part of the electromagnetic spectrum, so we need special instruments to detect the rest. Even though you may not be able to see certain wavelengths, you will have experienced them in one way or the other:. Most objects in space give off several types of electromagnetic radiation at the same time. What they radiate depends on many things, such as how hot they are and what they are made of.

Astronomers collect information about the radiation from space objects to find out about such things as the births and deaths of stars, how hot objects are, how far away they are, even how the universe was formed. Astronomers use telescopes that detect different parts of the electromagnetic spectrum. Each type of telescope can only detect one part of the electromagnetic spectrum.

There are radio telescopes, infrared telescopes, optical visible light telescopes and so on. There are radio waves, microwaves, infrared light, visible light, ultraviolet light, X-rays and gamma rays, all of which form what is known as the 'electromagnetic spectrum'. Oddly enough, visible light — to which human eyes are sensitive - is the smallest band of radiation. To our eyes, what we see seems like the entire Universe; yet there is much more out there.

Different types of objects in the Universe emit different types of radiation. Our Sun is a rather obvious source of visible light. But it also glows in radio waves, infrared, ultraviolet light and X-rays. Some objects emit only radio waves or only X-rays.