You can see the scattered light by looking in directions away from the source of the light hence the sky appears blue during the day.Įxtinction and reddening of starlight are not caused by just the atmosphere. The light of stars also redden in passing through the atmosphere. By analogy, consider ocean waves - a row boat whose length is close to the wavelength of the waves will bob up and down, whereas a long ocean liner will scarcely notice the waves. In addition, short wavelength blue light is preferentially scattered thus objects look redder (astronomers refer to this as reddening) this occurs because the wavelength of blue light is very close to the size of the particles that cause the scattering. Similarly, stars seen from Earth seem fainter to the viewer than they would if there were no atmosphere. Extinction can be seen in our own Sun when it becomes dimmer as its light passes through more of the dusty atmosphere as it sets. As a consequence, light coming from an object seen behind dust is dimmer than it would be without the dust. When reflection occurs in particle‐particle interactions (for example, colliding billiard balls), it's called scattering - light is scattered (reflected) off molecules and dust particles that have sizes comparable to the wavelengths of the radiation. A common example of reflection is mirrors, and in particular, telescope mirrors that use curved surfaces to redirect light received over a large area into a smaller area for detection and recording. The property of reflection, that light can be reflected from appropriate surfaces, can most easily be understood in terms of a particle property, in the same sense that a ball bounces off a surface. For an otherwise non‐luminous object to be visible, light from a source is reflected off the object into our eye. There are a few natural sources of light, such as the Sun, stars, and a flame other sources are man‐made, such as electrical lights. Most visible objects are seen by reflected light.
A “particle” of light is called a photon, or a discrete packet of electromagnetic energy. Although light is generally thought of as acting like an electric wave oscillating in space accompanied by an oscillating magnetic wave, it can also act like a particle. Light is such a complicated phenomena that no one model can be devised to explain its nature. Visible light is only a small portion of the electromagnetic radiation that can be detected by various instruments.
The term should not be confused with radiation associated with a radioactive source, i.e. Note that the word “radiation” can refer to any phenomena that radiates (moves) outwards from a source, here electromagnetic or light radiation. However, these same properties mean that light interacts with other matter before it reaches the observer and this often complicates our ability to observe other objects in the universe. The properties of light (see the section, “Particle properties of light”) allow us to build devices to observe the universe and to deduce the physical nature of the sources that emit the radiation received during these observations. All of these forms of light have both electrical and magnetic characteristics. However, electromagnetic radiation consists of more than just visible light it also includes (from short wavelength to long wavelength) gamma‐radiation, X‐radiation, ultraviolet, visible, infrared (heat), microwaves, and radio waves (see Figure 1). The colors of the visible spectrum stretch from violet with the shortest wavelength to red with the longest wavelength. Wavelengths are usually measured in units of nanometers (1 nm = 10 −9m) or in units of angstroms (1 Å = 10 −10m). Visible light is the relatively narrow frequency band of electromagnetic waves to which our eyes are sensitive. The second great area of physics necessary to address the universe is the subject of light, or electromagnetic radiation. SETI-The Search for Extraterrestrial Intelligence.Internal Structure Standard Solar Model.Interior Structure: Core, Mantle, Crust.Minor Objects: Asteroids, Comets, and More.
Origin and Evolution of the Solar System.
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