The electromagnetic spectrum is a range of wavelengths of electromagnetic radiation. From long to short wavelength, the EM spectrum includes radio waves, microwaves, infrared, visible light, ultraviolet, x-rays and gamma rays. Show Energy is propagated through space in the form of electromagnetic (EM) waves, which are composed of oscillating electric and magnetic fields. EM waves do not require a substance (like air or water) to travel through, meaning that — unlike sound — they can travel through empty space. In a vacuum, all EM waves travel at the same speed: the speed of light (which is itself an EM wave). Like all waves, an EM wave is characterised by its wavelength, and the range of wavelengths we observe, from very long to very short, is what we refer to as the EM spectrum. We divide up the EM spectrum roughly according to how the waves behave when they interact with matter and each division has a name. So we have: radio waves, which have the longest wavelengths; microwaves; infrared; visible light; ultraviolet; x-rays; and finally gamma rays, which have the shortest wavelengths. Celestial objects such as stars, planets and galaxies all emit EM waves at various wavelengths and so different telescopes are designed to be sensitive to different parts of the EM spectrum. EM radiation in and around the visible part of the spectrum is often referred to broadly as ‘light’, with shorter wavelengths referred to as ‘bluer’ and longer wavelengths referred to as ‘redder’. By combining observations at different wavelengths, we can develop a more complete picture of the structure, composition and behaviour of an object than the visible wavelengths alone can show. For more than three decades, Hubble has studied the Universe using its 2.4-metre primary mirror and its five science instruments. They observe primarily in the ultraviolet and visible parts of the spectrum, but also have some near-infrared capabilities. Hubble observes in different wavelength bands, one band at a time, each providing different information on the object under study. Each of these wavelengths is reproduced in a different colour and these are combined to form a composite image that well resembles the true emission from that celestial object. By exploring this image, you can see how astronomers have used a set of single-colour images to construct the colour picture of a ring of star clusters surrounding the core of the galaxy NGC 1512. Each image represents a specific colour or wavelength region of the spectrum, from ultraviolet to near infrared, and shows the wide wavelength range covered by Hubble. Astronomers chose to study NGC 1512 in these colours to emphasise important details in the ring of young star clusters surrounding the core. Astronomers use multi-wavelength imagery to study details that might not otherwise be present in visible images. For example, a new multiwavelength observation of Jupiter released in 2020 by Hubble in ultraviolet/visible/near-infrared light of Jupiter gave researchers an entirely new view of the giant planet. These observations provided insights into the altitude and distribution of the planet’s haze and particles and showed Jupiter’s ever-changing cloud patterns. The planet’s aurorae are only visible in the ultraviolet; however, the structure of the red spot is well studied at visible wavelengths. To celebrate the telescope’s 25th anniversary in 2015, Hubble unveiled two new beautiful portraits of the popular Pillars of Creation, revealing how different details can be studied in visible and near-infrared observations. While the visible light captures the multi-coloured glow of gas clouds, the infrared image penetrates much of the obscuring dust and gas to uncover countless newborn stars. We invite you to watch this Hubblecast that explores how Hubble’s observations differ across different wavelengths of the electromagnetic spectrum, and how these observations will be complemented by those of the James Webb Space Telescope. Electromagnetic waves are categorized according to their frequency f or, equivalently, according to their wavelength λ = c/f. Visible light has a wavelength range from ~400 nm to ~700 nm. Violet light has a wavelength of ~400 nm, and a frequency of ~7.5*1014 Hz. Red light has a wavelength of ~700 nm, and a frequency of ~4.3*1014 Hz.  Visible light makes up just a small part of the full electromagnetic spectrum. Electromagnetic waves with shorter wavelengths and higher frequencies include ultraviolet light, X-rays, and gamma rays. Electromagnetic waves with longer wavelengths and lower frequencies include infrared light, microwaves, and radio and television waves.
Problem:Two microwave frequencies are authorized for use in microwave ovens, 900 and 2560 MHz. Calculate the wavelength of each. Solution:
Problem:Distances in space are often quoted in units of light years, the distance light travels in one year. Solution:
Spectroscopy:What can we learn by analyzing the EM spectrum emitted by a source? The velocities of particles with thermal energy are changing almost all the time. The particles are accelerating. Accelerating charged particles produce electromagnetic radiation. The power radiated is proportional to the square of the acceleration. Higher rates of velocity change result in higher frequency (shorter wavelength) radiation. The observed intensity of thermal radiation emitted by as a function of wavelength can be described by the Planck Radiation Law (Physics 221). When light passes through or reflects or scatters of matter, it interacts with the atoms and molecules. Atoms and molecules have characteristic resonance frequencies. The preferentially interact with light waves of exactly those frequencies. When excited in collisions, atoms and molecules emit light with a set of characteristic frequencies. This results in a line spectrum. Only light with a discrete set of wavelengths is produced and the spectrum is not continuous, but consist of a set of emission lines. That set characterizes the atoms and molecules which produced it and can be used to identify those atoms and molecules and their environment. When light with a continuous distribution of wavelengths passes through a low-density material, the atoms and molecules of the material absorb light waves with the same set of characteristic frequencies that appear in their emission spectrum. This produces an absorption spectrum, a nearly continuous spectrum with missing lines. The
absorption spectrum can also be used to identify those atoms and molecules and their environment. Embedded Question 3Please explore this simple simulations of various molecules interacting with electromagnetic radiation of different wavelength. Discuss this with your fellow students in the discussion forum! Is all electromagnetic radiation considered light?The light we can see, made up of the individual colors of the rainbow, represents only a very small portion of the electromagnetic spectrum. Other types of light include radio waves, microwaves, infrared radiation, ultraviolet rays, X-rays and gamma rays — all of which are imperceptible to human eyes.
Are all electromagnetic waves invisible?Electromagnetic waves are invisible forms of energy that travel though the universe. However, you can "see" some of the results of this energy. The light that our eyes can see is actually part of the electromagnetic spectrum.
What does electromagnetic radiation include?Examples of EM radiation include radio waves and microwaves, as well as infrared, ultraviolet, gamma, and x-rays. Some sources of EM radiation include sources in the cosmos (e.g., the sun and stars), radioactive elements, and manufactured devices. EM exhibits a dual wave and particle nature.
What type of electromagnetic radiation is visible light?Visible light falls in the range of the EM spectrum between infrared (IR) and ultraviolet (UV).
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Electromagnetic radiation includes only visible light waves
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