Hello friends of Steemit, continuing with the previous post talking about the basic concepts of astronomy and astrophysics.
Periodic waves
Almost all the information we have about celestial objects has been obtained from the light that comes from them. Therefore, it is very important to know some concepts related to light and that are used in Astronomy.
periodic traveling wave (or wavetrain): is a periodic function of one-dimensional space that moves with constant speed. This is a special type of spatiotemporal oscillation that is a periodic function of both space and time.
Image source [1]: A periodic traveling wave.
The light we see is transmitted as periodic waves. This light, as well as gamma rays, X-rays and radio waves are electromagnetic waves, which are part of the electromagnetic spectrum. The waves and in particular the electromagnetic waves can experience different phenomena within which is the Doppler effect. In order to explain it we are going to see some concepts.
Wavelength: is the distance over which a periodic wave repeats itself. Usually the distance between the maxima of the wave is used to measure its length.
Image source [2]: Wavelength of a sine wave, λ, can be measured between any two points with the same phase, such as between crests (on top), or troughs (on bottom), or corresponding zero crossings as shown.
Frequency: is the number of waves that occur per time interval. To measure the frequency, a time interval of one second is generally used. That is, the frequency is the number of times a wave is repeated in a second.
Image source [3]: These three dots are flashing, or cycling, periodically—from lowest frequency (0.5 hertz) to highest frequency (2.0 hertz), top to bottom. For each flashing dot: "f" is the frequency in hertz, (Hz)—or the number of events per second (i.e., cycles per second)—that the dot flashes; while "T" is the period, or time, in seconds (s) of each cycle, (i.e., the number of seconds per cycle). Note T and f are reciprocal values to each other.
Period: is the time needed for a complete cycle of vibration to pass to given point. As the frequency of a wave increases, the time period of the wave decreases.
Sound waves: The sound waves are generated by a sound source, such as the vibrating diaphragm of a stereo speaker. The sound source creates vibrations in the surrounding medium. As the source continues to vibrate the medium, the vibrations propagate away from the source at the speed of sound, thus forming the sound wave. At a fixed distance from the source, the pressure, velocity, and displacement of the medium vary in time.
Electromagnetic waves: The electric and magnetic fields propagate in space at the speed of light and vary simultaneously and periodically. This form in which electromagnetic energy propagates is called electromagnetic waves, these waves do not require a means to propagate (unlike sound waves). An example of electromagnetic waves is the light that our eyes capture.
Image source [5]: The electromagnetic waves that compose electromagnetic radiation can be imagined as a self-:propagating transverse oscillating wave of electric and magnetic fields. This diagram shows a plane linearly polarized EMR wave propagating from left to right (X axis). The electric field is in a vertical plane (Z axis) and the magnetic field in a horizontal plane (Y axis). The electric and magnetic fields in EMR waves are always in phase and at 90 degrees to each other.
The electromagnetic spectrum: The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies.
Image source [6]: A diagram of the electromagnetic spectrum, showing various properties across the range of frequencies and wavelengths.
Wave properties
The waves can experience different phenomena within which are the following:
Refraction: is the change in direction of wave propagation due to a change in its transmission medium.
Image source [7]: Refraction in a glass of water. The image is flipped.
Dispersion: is the separation of waves of different wavelength when crossing a material.
Diffraction: Diffraction refers to various phenomena that occur when a wave encounters an obstacle or a slit. It is defined as the bending of light around the corners of an obstacle or aperture into the region of geometrical shadow of the obstacle.
Image source [8]: Diffraction pattern of red laser beam made on a plate after passing through a small circular aperture in another plate.
Plate scale: is a parameter used in observational astronomy. It is called a plate scale because, before the use of CCDs and digital cameras, the image captured by the telescopes was recorded on photographic plates.
The angular resolution is the ability to distinguish two nearby stars and not see them as one.