Jean Tate, Author at Universe Today

January 20, 2010December 24, 2015 by Jean Tate

Planetary Nebulae

No, planetary nebulae are not nebulae found around planets; nor are they nebulae produced by planets … rather, they got stuck with this name because the first ones to be observed (and written about) look like planets (well, they did through the eyepieces of the telescopes of the time … somewhat).

Charles Messier – yep, the comet hunting guy – listed M27 in his famous catalog; that’s the Dumbbell Nebula, and the first planetary nebula recorded (1764). It was Herschel – the guy who discovered Uranus – who dreamed up the name ‘planetary nebula’; and why? Because, to him, they looked a bit like the gas giants Jupiter, Saturn, and Uranus (Neptune wasn’t discovered then). There are four planetary nebulae in Messier’s list; in addition to M27, there’s M57 (the Ring Nebula), M76 (Little Dumbbell Nebula), and M97 (Owl Nebula). So why did Herschel say planetary nebulae looked like giant planets, including Saturn? Because, in 1781, he discovered one – NGC 7009 – that looked like Saturn! Guess what it’s called? The Saturn Nebula.

When spectroscopes were used to observe planetary nebulae, they caused excitement; unlike stars and (what we today call) galaxies – which have dark absorption lines in their spectra – planetary nebula have bright emission lines (and essentially nothing else, i.e. no continuum emission). Further, the brightest of the lines (actually two, close together), in most planetary nebulae, corresponded to nothing ever seen in any laboratory spectrum … so they were thought to be caused by an as yet undiscovered element, called nebulium.

Today we understand planetary nebulae to be a short-lived phase of (most) stars … after the red giant phase, when the star’s fuel has been exhausted, it shrinks to become a white dwarf. The gas expelled during the red giant phase become heated and ionized by the intense UV radiation of the new white dwarf (these central objects, in most planetary nebulae, are among the hottest stars). The plasma has an extremely low density, which means that certain excited, meta-stable states of ions such as O²⁺ can jump to a lower energy state by emission of ‘forbidden’ radiation (rather than by collision).

Such spectacular objects … no surprise that Universe Today has many stories and articles on planetary nebulae! Here are just a few Found: Planetary Nebula Around Heavy Stars, Planets May Actually Shape Planetary Nebulae, Will We Look Like This in 5 Billion Years?, and Penetrating New View Into The Helix Nebula.

Astronomy Cast’s Nebulae has more on planetary nebulae; the following episodes put planetary nebulae into a broader astronomical context: The End of the Universe Part 1: The End of the Solar System, The Life of the Sun, and The Life of Other Stars.

Source: SEDS

January 20, 2010December 24, 2015 by Jean Tate

What is the Boltzmann Constant?

There are actually two Boltzmann constants, the Boltzmann constant and the Stefan-Boltzmann constant; both play key roles in astrophysics … the first bridges the macroscopic and microscopic worlds, and provides the basis for the zero-th law of thermodynamics; the second is in the equation for blackbody radiation.

The zero-th law of thermodynamics is, in essence, what allows us to define temperature; if you could ‘look inside’ an isolated system (in equilibrium), the proportion of constituents making up the system with energy E is a function of E, and the Boltzmann constant (k or k_B). Specifically, the probability is proportional to:

e^-E/kT

where T is the temperature. In SI units, k is 1.38 x 10^-23 J/K (that’s joules per Kelvin). How Boltzmann’s constant links the macroscopic and microscopic worlds may perhaps be easiest seen like this: k is the gas constant R (remember the ideal gas law, pV = nRT) divided by Avogadro’s number.

Among the many places k appears in physics is in the Maxwell-Boltzmann distribution, which describes the distribution of speeds of molecules in a gas … and thus why the Earth’s (and Venus’) atmosphere has lost all its hydrogen (and only keeps its helium because what is lost gets replaced by helium from radioactive decay, in rocks), and why the gas giants (and stars) can keep theirs.

The Stefan-Boltzmann constant (?), ties the amount of energy radiated by a black body (per unit of area of its surface) to the blackbody temperature (this is the Stefan-Boltzmann law). ? is made up of other constants: pi, a couple of integers, the speed of light, Planck’s constant, … and the Boltzmann constant! As astronomers rely almost entirely on detection of photons (electromagnetic radiation) to observe the universe, it will surely come as no surprise to learn that astrophysics students become very familiar with the Stefan-Boltzmann law, very early in their studies! After all, absolute luminosity (energy radiated per unit of time) is one of the key things astronomers try to estimate.

Why does the Boltzmann constant pop up so often? Because the large-scale behavior of systems follows from what’s happening to the individual components of those systems, and the study of how to get from the small to the big (in classical physics) is statistical mechanics … which Boltzmann did most of the original heavy lifting in (along with Maxwell, Planck, and others); indeed, it was Planck who gave k its name, after Boltzmann’s death (and Planck who had Boltzmann’s entropy equation – with k – engraved on his tombstone).

Want to learn more? Here are some resources, at different levels: Ideal Gas Law (from Hyperphysics), Radiation Laws (from an introductory astronomy course), and University of Texas (Austin)’s Richard Fitzpatrick’s course (intended for upper level undergrad students) Thermodynamics & Statistical Mechanics.

Sources:
Hyperphysics
Wikipedia

January 20, 2010April 26, 2016 by Jean Tate

Big Bang Timeline

A fraction of a second after the big bang, the universe underwent inflation - but what does that mean? credit: NASA/WMAP — Time line of the Universe (Credit: NASA/WMAP Science Team)

The Big Bang timeline is basically just a list of relative times at which the major events in the history of the universe occurred, per the collection of theories, models, and hypotheses which together form what is called the Big Bang theory.

The start – when time began, when t = 0 – is not actually part of the Big Bang timeline (!), contrary to popular belief. That’s because the two theories of physics which are at the heart of the Big Bang theory – General Relativity (GR) and the Standard Model (of particle physics; SM for short) – are mutually incompatible, and that incompatibility becomes so intolerable that saying anything about what happened in the first Planck second (approx 10^-43 second) is meaningless.

In fact, the closer to the Planck regime – when GR and the SM are utterly incompatible – the less reliable are our descriptions … but the relative times are nonetheless pretty good.

Actually, that’s not quite true … what is relatively certain are temperatures; forces, matter, and radiation interact in very distinct ways, depending on the temperature (and pressure, or density), but converting from temperature back to time depends on various parameters which are not so well pinned down. However, once the average mass-energy density of the universe, today, is estimated, the clock can be wound back with some confidence (it’s ~six hydrogen atoms per cubic meter, or about 7 x 10^-27 kg/m³).

Around 10^-35 seconds leptons and baryons were created (the strong force became a distinct force), and inflation caused the universe to expand so much that the part which later became our observable universe was both flat (no curvature, in the GR sense) and incredibly smooth (with only tiny variations in density due to quantum effects).

At around 10^-11 seconds the electromagnetic and weak force became distinct.

And by about a microsecond the universe underwent another phase change … it was no longer a quark-gluon plasma, but hadrons formed (protons and neutrons).

When t = 1 second (more or less), nuclear reactions produced light nuclides, such as deuterium and helium-3 (before this time the universe was too hot for them to form) – Big Bang nucleosynthesis.

The earliest part of the universe we can still see, directly, happened when the electrons and protons (and other nuclei) combined to form hydrogen atoms; this is the recombination era, and we see it today as the cosmic microwave background … and gravity took over as the dominant force (before this it was electromagnetism – the universe was ‘radiation dominated’ – and before that, at the time of nucleosynthesis, the strong and weak forces ruled).

The rest, as they say, is history … the Dark Ages (during which the first stars were formed), the era of recombination (when stars and quasars ionized the diffuse hydrogen), galaxy formation, … and then about 13.4 billion years later we observed the skies and worked out the timeline!

There’s a lot of good material on the web on the Big Bang timeline; here are some: John Baez (who’s always worth reading) has a brief timeline, in terms of temperature; there’s a more extensive one from the University of Wisconsin-Madison, and perhaps the best, A Brief History of the Universe (University of Cambridge).

Want to explore more? Here are some of the many Universe Today articles on the Big Bang timeline: Cosmologists Look Back to Cosmic Dawn, A Star as Old as the Universe, and Book Review: The Mystery of the Mission Antimatter.

Astronomy Cast has several episodes for you to explore, to learn more about the Big Bang timeline; here are a few: The Big Bang and Cosmic Microwave Background, Inflation, and this 2009 Questions Show.

Sources:
http://en.wikipedia.org/wiki/Timeline_of_the_Big_Bang
http://www.damtp.cam.ac.uk/research/gr/public/bb_history.html

January 20, 2010April 26, 2016 by Jean Tate

Atomic Mass

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The mass of an atom is its atomic mass (duh!).

Actually, it’s worth looking into this a bit more deeply … it’s not as simple as the “duh!” implies …

An atom is made up of protons (at least one), neutrons (except for hydrogen), and electrons (at least one), so its mass is simply the total of the masses of protons, neutrons, and electrons, right? Wrong … the nucleus of any atom (except hydrogen) is held together by the strong nuclear force, and the electrons are bound to the atom by the electromagnetic force; it takes energy to break up a nucleus, and energy to free an electron from an atom … and mass and energy are related (remember E = mc²?); the stronger the binding, the more the mass of an atom differs from the sum of the masses of its individual components!

Also, there’s atomic weight (atomic mass applies to each isotope of an element; atomic weight is an average, for each element, of the atomic masses of the isotopes … weighted by their relative abundance); relative atomic mass (a synonym for atomic weight, and also – confusingly – the small difference between standard atomic weight and the atomic weight of a particular sample!); and … you get the idea.

Atomic mass is usually measured in atomic mass units (no, no “duh!” this time, as you’ll see), which is defined as 1/12th of the mass of an isolated carbon-12 atom, at rest, in its ground state … and this is the unified atomic mass unit (symbol u), to distinguish it from the older atomic mass unit (amu). Why? Why go to all this trouble? Because there are actually two different amu’s! And both are different from u!! Both are based on oxygen (rather than carbon); one on the oxygen-16 isotope, the other on oxygen, the mixture of isotopes.

Tricky.

More on atomic mass: from NASA Atoms, Elements, and Isotopes; The Mass Spectrometer of the Galileo Probe , and this Lawrence Berkeley National Lab webpage.

Are there any Universe Today stories featuring atomic mass? Sure! Mini-Detector Could Find Life on Mars or Anthrax at the Airport, Super-Neutron Stars are Possible, and Learning to Breathe Mars Air, to give just three examples.

Are there any Astronomy Cast episodes on atomic mass? Sure! Inside the Atom, and Energy Levels and Spectra, to give just two examples.

January 18, 2010December 24, 2015 by Jean Tate

Electromagnetism

The short version: electromagnetism is one of the four fundamental forces (the strong force, the weak force, and gravitation are the other three), responsible for all magnetic, electrical, and electromagnetic phenomena.

The long version is a little more complicated.

Start with history … phenomena we today call electrical have been known for millennia (e.g. static electricity), as have their magnetic counterparts (e.g. lodestone). The 17th and 18th centuries saw considerable scientific study of each, as separate forces, with Ørsted and Ampère uniting the two into electromagnetism, around 1820. Maxwell consolidated (in 1864) everything known about electromagnetism into what today we call Maxwell’s equations … and predicted electromagnetic waves (or radiation), a prediction verified by Hertz, two decades later. However, Maxwell’s equations opened a can of worms (to do with the aether, and the speed of light) … which lead to Einstein and special relativity. In parallel, a series of discoveries lead to photons (the quanta of electromagnetic radiation) and quantum mechanics, and these in turn to the recognition that the spectacular success of classical electromagnetism (i.e. Maxwell’s equations) actually depends on quantum field theory (with all its counter-intuitives).

Fast forward to the 1940s, and Quantum Electrodynamics (QED), which has electrically charged particles interacting via exchanges of photons (real or virtual), and describes all electromagnetic phenomena. QED is the most successful theory in physics, period (it has been tested, and found accurate, to one part in 10¹²!).

Here’s a fun fact: QED incorporates special relativity … and an electric charge (with no magnetic field) becomes an electric current (with an associated magnetic field), in relativity, simply by switching to a frame of reference moving with respect to the (stationary) electrical charge.

So, in its classical form, electromagnetism is an instantaneous ‘action at a distance’ type of force; in its quantum form; it’s an exchange of virtual photons, at the speed of light.

Now for more complication.

In 1979 Sheldon L. Glashow, Abdus Salam, and Steven Weinberg shared the Nobel Prize for Physics, for their contributions to the unification of electromagnetism and the weak force … which goes under the name electroweak interaction. So electromagnetism is just one manifestation of something more general, just as electricity and magnetism are two manifestations of one underlying thing, electromagnetism.

Want to learn more? Try Stargazers’ Electromagnetism, Math Pages on Maxwell’s equations, Richard Feynman’s excellent non-technical book on QED, and the 1979 Nobel Press Release on the electroweak interaction.

To get a handle on how diverse the roles of electromagnetism are, in astronomy, check out these Universe Today articles (just some of the many): Stellar Jets are Born Knotted,
Magnetic “Ropes” Connect the Northern Lights to the Solar Wind, and Spitzer Spies Ghostly Magnetar.

Astronomy Cast has an episode devoted to electromagnetism, called Electromagnetism. Some others you may also find interesting, on this topic, are The Search for the Theory of Everything, and The Important Numbers in the Universe.

Sources:
Wikipedia
University of Oregon
NASA

January 18, 2010December 24, 2015 by Jean Tate

What is Beta Radiation?

Radiation Belts on Saturn. Image credit: NASA/JPL/SSI

Beta radiation is radiation due to beta particles, which are electrons (or, sometimes, positrons); mostly, when you come across the words ‘beta radiation’, what is meant is what is produced by beta decay (radioactive decay which produces beta particles … either electrons or positrons).

Within a few years of Becquerel’s discovery of radioactivity (in 1896), its heterogeneous nature was discovered … and the three (then) known components given the memorable names alpha radiation, beta radiation, and gamma radiation. And, in 1900, Becquerel showed that beta radiation was composed of particles which have the same charge-to-mass ratio as electrons (which had been discovered only a few years’ earlier). The realization – by Irène and Frédéric Joliot-Curie, in 1934 – that some beta radiation is composed of positrons, rather than electrons, had to wait until positrons themselves were discovered (in 1932).

Some fun facts about beta radiation:

* beta radiation is in between alpha and gamma in terms of its penetrating power; typically it goes a meter or so in air

* like all kinds of radioactive decay, beta decay occurs because the final state of the nucleus (the one decaying) has a lower energy than the initial one (the difference is the energy of the emitted beta particle and neutrino)

* beta decay involves only the weak interaction (or force), unlike alpha and gamma decay

* the key to the specifics of beta decay is the emission of a neutrino (or antineutrino), postulated by Pauli (in 1931) and combined into a model by Fermi, in 1934 (though it wasn’t until 1956 that the neutrino was detected, and the 1960s for the existence of carriers of the weak force – the three bosons W^–, W⁺, and Z⁰ – to be hypothesized).

* beta radiation has the characteristics we observe it to have because key constants in the weak interaction have the values they have (no theory in physics predicts what those values are … yet); had those values been just a teensy bit different in the early universe, we would not be here today (this is part of an idea called the anthropic principle).

Here are some of the Universe Today stories that are related to beta radiation New Insights on Magnetars, Superstrings Could Be Detectable As They Decay, and Don’t ‘Supermassive’ Me: Black Holes Regulate Their Own Mass.

Two Astronomy Cast episodes are well worth a listen, as they provide further insights into beta radiation The Strong and Weak Nuclear Forces, and Nucleosynthesis: Elements from Stars.

Sources: EPA, Wikipedia

January 18, 2010December 24, 2015 by Jean Tate

Beta Particles

Beta particles are electrons (symbol β^–), or positrons (symbol β⁺), emitted in beta decay (a kind of radioactivity); beta radiation in other words. Sometimes ‘beta particles’ refers to high energy electrons, irrespective of their source (e.g. the beta particles in the Van Allen radiation belts around the Earth; very few are produced by beta decay).

Of the three kinds of radioactivity (alpha, beta – both of which are particles – and gamma (which is electromagnetic radiation)), beta particles have intermediate penetrating power.

Beta particles have an important role in medicine … as diagnostic tools, to treat some diseases (notably various cancers, particularly via radionuclide therapy), in biochemical analysis, etc. For example, ¹⁸F (the fluorine-18 isotope) is used as a positron (β⁺) emitter in positron emission tomography (PET).

Beta particles – or rather the weak interaction which is the cause of their emission – were crucial in Big Bang Nucleosynthesis … as the early universe cooled, reactions between the protons, neutrons, electrons, and photons produced many light nuclides, but the balance between many reactions left only hydrogen, deuterium, helium-3, helium-4, and lithium-7 when the universe became too cool for any nuclear reactions to continue (of course, isolated neutrons and unstable nuclides – such as tritium – were also left, but they decayed well before the time of cosmic microwave background).

Fast forward to today … beta (β⁺) particles from the decay of potassium-40 is one source of internal heat for the Earth – giving us plate tectonics, its magnetic field, etc – … the decay of carbon-14 and beryllium-10 (both of which produce beta (β^–) particles) provide us with tools to do radioactive (or radiometric) dating (these are two of the nuclides produced by cosmic ray spallation).

Beta Particle Radiation is a good, introductory webpage (from the University of California, Davis), and Weak Interactions explains how beta particles and the weak (nuclear) force are related (from SLAC’s Virtual Visitor Center)

Universe Today has several stories which cover the role of beta particles in astronomy; for example A Prototype Detector for Dark Matter in the Milky Way, and Fermilab Putting the Squeeze on Higgs Boson.

The Strong and Weak Nuclear Forces, and Nucleosynthesis: Elements from Stars are two Astronomy Cast episodes which will help you understand beta particles better.

January 15, 2010April 26, 2016 by Jean Tate

Atomic Spectra

An example of an atomic spectrum, showing emission lines at particular wavelengths.

The light which atoms give off is made up of specific wavelengths, called lines; observed by a spectroscope, the lines are, collectively, atomic spectra.

In more detail …

In an atom, electrons have specific and discrete energies. There are many more energy states (or levels) in each atom than there are electrons. When an electron transitions (‘jumps’) from one energy level to another, it emits (if going from a higher level to a lower one) or absorbs (vice versa) light – a photon – with a discrete, specific wavelength. In any given set of conditions (pressure, temperature, magnetic field strength, etc), the collection of all those specific wavelengths is the spectrum of the atom … so atomic spectra are the spectra of atoms!

As the atomic electron energy levels are unique to each element, the lines in a spectrum (emission or absorption) can be used to identify the elements present in the source (a star, say) or gas between the source and us (e.g. the interstellar medium). Of course, for an extragalactic object – a quasar, perhaps – you need more than one line to make a certain identification … because the universe is expanding (and so you don’t know how much just one line may have been redshifted).

The light electronic transitions in atoms produces may not be in the visual part of the electromagnetic spectrum, but for atoms that are neutral or have lost only one or two electrons (yes, ‘atomic spectra’ refers to the line spectrum of ions too!), most lines are in the UV, visual, or near infrared. For highly ionized atoms, the lines are found in the extreme UV or x-ray region.

As the relative intensity of the lines in an atomic spectrum varies with temperature, analysis of the lines in the spectrum of a star (say) can give an estimate of the temperature of the star’s surface (photosphere). The width of the lines depends on the pressure of the gas; the structure of the lines depends on the magnetic field strength; the … (you get the idea) – atomic spectra are a wonderful window into the physical conditions of places far, far away!

Looking for more? This University of Oregon webpage has a good, brief, description of atomic spectra; and Physics Lab’s Atomic Models and Spectra covers both the historical context and a bit more of the theory.

As atomic spectra play such a vital role in optical astronomy, no wonder there are so many Universe Today articles involving atomic spectra! Here’s a random selection: New Study Find Fundamental Force Hasn’t Changed Over Time, Spitzer Discovers Early Galaxy Forming Region, and Strange Nebula Around Eta Carinae .

The Astronomy Cast episode Energy Levels and Spectra is all about atomic spectra. Other Astronomy Cast episodes well worth a listen, in regard to atomic spectra, include Optical Astronomy and In Search of Other Worlds.

Sources:
GSU Hyperphysics
NIST

January 14, 2010December 24, 2015 by Jean Tate

States of Matter

Solid, liquid, gas … those are the states of matter we’re thoroughly familiar with, but what makes for a state of matter? And are there other states of matter?

Since people first made distinctions between them, the states of matter were defined by how the matter behaved, in bulk; so a solid had a fixed shape (and volume), a liquid a fixed volume (but changed shape to fit the container it was in), and a gas expanded to fill its container. Once we realized that matter is made up of atoms (and molecules), the states of matter were distinguished by how the molecules (or atoms, in an element) behaved: in solids they are both close by and in a fixed arrangement (e.g. in crystals), in liquids close by but the arrangement is not fixed, and in gases not close by (so no particular arrangement).

But what about plasma? Sorta like a gas – so as it fills any container it’s in, it’s a gas – but not (the ions and electrons interact in completely different ways, in a plasma, than molecules (or atoms) do in a solid, liquid, or gas). Hence, plasma is the fourth state of matter.

Things got a bit more complicated as scientists studied matter more carefully.

For example, if you heat water in a strong, but transparent, container, above a certain temperature (and pressure) – called the critical temperature (critical pressure) – the liquid and gas states become one … the water is now a supercritical fluid (you may have seen this demonstrated, in a chemistry class perhaps, though likely not with water!).

Then there’s the distinction between crystals (crystalline state) and glasses (glassy state); both seem very solid, but the arrangement of molecules in a glass is more like that of molecules in a liquid than those in a crystal … and glasses can flow, just like liquids, if left for a long enough time.

Is there a ‘fifth state of matter’? Yes! A Bose-Einstein condensate (BEC) … which is like a gas, except that the constituent atoms are all (or mostly) in the lowest possible quantum state … so a BEC has bulk properties quite unlike those of any other state of matter (quantum behavior become macroscopic).

In astrophysics, there are quite a few exotic states of matter; for example, in white dwarf stars matter is prevented from further (gravitational) collapse by electron degeneracy pressure; the same sort of thing happens in neutron stars, except that its neutron degeneracy pressure (there may also be an even more extreme state of matter, held up by quark degeneracy pressure!). There’s also a counterpart to ordinary plasmas: quark-gluon plasma (in an ordinary plasma made of hydrogen the atoms are broken into electrons and protons; in a quark-gluon plasma protons and neutrons ‘melt’ into their constituent quarks and gluons).

States of matter, including some exotic ones, is something you’ll find discussed in Astronomy Cast; for example this Questions Show.

Sources:
Wikipedia
Purdue University
New York University
Wikipedia: Bose-Einstein Condensate

January 14, 2010December 24, 2015 by Jean Tate

Light Spectrum

LCROSS UV/Visible spectrum. Credit: NASA

Light spectrum can mean the visible spectrum, the range of wavelengths of electromagnetic radiation which our eyes are sensitive to … or it can mean a plot (or chart or graph) of the intensity of light vs its wavelength (or, sometimes, its frequency). More possible ambiguity: ‘light’ … which can refer to what we see, or to the part of the electromagnetic spectrum that optical telescopes (especially the ones down here on the ground) work in (and sometimes, just occasionally, it means the whole of the electromagnetic spectrum, or any electromagnetic radiation). Good news: the context makes it clear!

The realization that visible light is made up of colors is most often attributed to Isaac Newton (though a strong case can be made that it was known well before him), who used a prism to create a spectrum (rainbow of colors) from a beam of white light, and another to recombine them back into white light. And what’s it called when you spread light into a spectrum, for the purpose of studying it (in astronomy, chemistry, …)? Spectroscopy. And is there a different word if it’s infrared, ultraviolet, x-rays, … which are spread into a spectrum (rather than visible light)? Nope, it’s still spectroscopy.

Visible light ranges from about 380 nanometers (nm) to about 750 nm (or, as is still common in astronomy, ~3800 angstroms (Å) to ~7500 Å); the window in the Earth’s atmosphere which allows us to do astronomy from down here on its surface (and lets the light of the Sun through, so we can see!) is a bit wider than the visible spectrum; it goes from about 300 nm to about 1100 nm (or 1.1 µ).

To an astronomer, a light spectrum has two main components, the continuum and the lines (sometimes bands as well). The lines are discrete wavelengths (well, they do have some ‘width’, hence ‘narrow lines’ and ‘broad lines’), either emission or absorption, and correspond to a particular atomic transition (an electron jumps between one allowed energy level in an atom, or ion, and another; bands are the same thing, except for molecules … and the allowed states are either vibrational or rotational). And the continuum? Well, it’s the part that isn’t lines! It varies smoothly, and generally slowly, across the spectrum.

Spectroscopy – analysis of the light spectrum – is one of the most powerful tools astronomers use to work out what’s going on, and what it’s like, way out there where the light from the sky originates. Do you know why? If not, then these two NASA webpages will help! Visible Light Waves , and Electromagnetic Spectrum.

It’s such a broad topic, light spectrum, no wonder Universe Today has so many articles on it! For example, Amateur Spectroscopy, Atmosphere of an Extrasolar Planet Measured, and Oops, the Universe is Beige.

Astronomy Cast has several good episodes on the spectrum of light; here’s two to get you started Energy Levels and Spectra, and Detectors.