What is the difference between spectroscopy, spectrography and spectrometry?

What is the difference between spectroscopy, spectrography and spectrometry?

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Spectroscopy is the study of spectra, spectrography is the writing of the spectra, and spectrometry is the measure of spectra. So from an etymological perspective, there is no real difference between the three. On arXiv, there is for instance an article that uses the term "spectrometry" in the title, but "spectroscopy" in the abstract (several, actually) to designate what seems to be the same thing.

But perhaps are there differences between the use of these terms in astrophysics?

There are certain techniques that are designated with one term rather than the other (e.g I haven't seen any mass spectroscopy, but have seen mass spectrometry), but is there a conceptual difference between spectroscopy and spectrometry?

What is the difference between spectroscopy and spectrometry?

Unless you're truly nitpicky, there's no real difference at least in the way the terms are used these days.

Historically, the endings make reference to slightly different processes -- Photography vs photometry is about collecting the light vs measuring it however spectrometry pretty much had to collect photons from the beginning so the line between the two is blurred.

Outside light-measurements, the -metry ending appears more common in practice (as in "mass-spectrometer") but there, too, usage is not always consistent.

BTW there's a third term, spectrography, which is also used mostly interchangably with the other two these days.

(Note that there are in principle IUPAC norms and any one peer-reviewed journal may just have an editor that is hidebound enough to care about such subtle distinctions -- however using any one of the terms will generally be perfectly understood by any practicioner in any of the various fields and a quick scan of the titles of presentations at the last meeting of the American Physical Society shows a fairly even distributions of the terms even in reference to the same experiment).

What is the Difference Between Spectroscopy and Microscopy?

Most of us have used a microscope at some point during our education, but not everyone has used a spectroscope or spectrometer. While they share similar names, spectroscopy and microscopy are used for different purposes. The main goal of microscopy is to improve the visibility of a structure that is too small for the naked eye to observe. Microscopy uses specific lenses to improve the visibility of very fine particles, such as those from tissues, plants, organisms, or blood.

The primary goal of spectroscopy is to determine how electrons respond to light energy. While microscopy is used to visualize objects, spectroscopy is used to determine the spectral lines and/or energy of a sample. Spectroscopy uses electromagnetic radiation at specific wavelengths to investigate a sample's absorbance or transmittance, which enables us to identify the structure, molecular composition, or arrangement of the sample. Below, you will find a comparison of the two processes. For more information, visit our What is Spectroscopy? information guide or check out our other blog post, "Who Discovered Spectroscopy?"

Microscopes enlarge structures that are too small for the naked eye using special lenses. Microscope images allow us to investigate the structure of small organisms and microscopic processes, such as cell division. Absorbance spectrums are produced after a sample is tested with a spectrophotometer. The spectrum of a sample’s absorbed wavelengths is known as its absorption spectrum, and the quantity of light absorbed by a sample is its absorbance.

Spectroscopy Versus Spectrometry

In practice, the terms spectroscopy and spectrometry are used interchangeably (except for mass spectrometry), but the two words don't mean exactly the same thing. Spectroscopy comes from the Latin word specere, meaning "to look at," and the Greek word skopia, meaning "to see." The ending of spectrometry comes from the Greek word metria, meaning "to measure." Spectroscopy studies the electromagnetic radiation produced by a system or the interaction between the system and light, usually in a nondestructive manner. Spectrometry is the measurement of electromagnetic radiation to obtain information about a system. In other words, spectrometry can be considered a method of studying spectra.

Examples of spectrometry include mass spectrometry, Rutherford scattering spectrometry, ion mobility spectrometry, and neutron triple-axis spectrometry. The spectra produced by spectrometry aren't necessarily intensity versus frequency or wavelength. For example, a mass spectrometry spectrum plots intensity versus particle mass.

Another common term is spectrography, which refers to methods of experimental spectroscopy. Both spectroscopy and spectrography refer to radiation intensity versus wavelength or frequency.

Devices used to take spectral measurements include spectrometers, spectrophotometers, spectral analyzers, and spectrographs.

Spectroscopy can be used to identify the nature of compounds in a sample. It is used to monitor the progress of chemical processes and to assess the purity of products. It can also be used to measure the effect of electromagnetic radiation on a sample. In some cases, this can be used to determine the intensity or duration of exposure to the radiation source.

What is the difference between spectroscopy, spectrography and spectrometry? - Astronomy

According to the Wikipedia (
Spectroscopy is an equivalent or synonim of Spectrometry. Wikipedia
definition of spectroscopy also enumerates the Physical quantities that are
measured by spectroscopy and the measurement processes and types of

Spectroscopy is the study of spectra, that is, the dependence of physical
quantities on frequency. Spectroscopy is often used in physical and
analytical chemistry for the identification of substances, through the
spectrum emitted or absorbed. A device for recording a spectrum is a
spectrometer. Spectroscopy can be classified according to the physical
quantity which is measured or calculated or the measurement process.

Moreover, according to the website:

Spectroscopy is a technique that uses the interaction of energy with a
sample to perform an analysis.
The data that is obtained from spectroscopy is called a spectrum. A spectrum
is a plot of the intensity of energy detected versus the wavelength (or mass
or momentum or frequency, etc.) of the energy.
A spectrum can be used to obtain information about atomic and molecular
energy levels, molecular geometries, chemical bonds, interactions of
molecules, and related processes. Often, spectra are used to identify the
components of a sample (qualitative analysis). Spectra may also be used to
measure the amount of material in a sample (quantitative analysis).

and they define Mass Spectrometry as one type of spectroscopic method:

Mass Spectrometry
A mass spectrometer source produces ions. Information about a sample may be
obtained by analyzing the dispersion of ions when they interact with the
sample, generally using the mass-to-charge ratio.

So, in general, the name for a spectroscopic method depends upon the type of
energy source one uses for it.

Spectroscopy vs. Spectrophotometry

Spectroscopy is the study of the interaction between matter and electromagnetic radiation. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, by a prism. Later the concept was expanded greatly to include any interaction with radiative energy as a function of its wavelength or frequency. Spectroscopic data are often represented by an emission spectrum, a plot of the response of interest as a function of wavelength or frequency.

In chemistry, spectrophotometry is the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength. It is more specific than the general term electromagnetic spectroscopy in that spectrophotometry deals with visible light, near-ultraviolet, and near-infrared, but does not cover time-resolved spectroscopic techniques.

Spectrophotometry is a tool that hinges on the quantitative analysis of molecules depending on how much light is absorbed by colored compounds. Spectrophotometry uses photometers, known as spectrophotometers, that can measure a light beam's intensity as a function of its color (wavelength). Important features of spectrophotometers are spectral bandwidth (the range of colors it can transmit through the test sample), the percentage of sample-transmission, the logarithmic range of sample-absorption, and sometimes a percentage of reflectance measurement.

A spectrophotometer is commonly used for the measurement of transmittance or reflectance of solutions, transparent or opaque solids, such as polished glass, or gases. Although many biochemicals are colored, as in, they absorb visible light and therefore can be measured by colorimetric procedures, even colorless biochemicals can often be converted to colored compounds suitable for chromogenic color-forming reactions to yield compounds suitable for colorimetric analysis. However, they can also be designed to measure the diffusivity on any of the listed light ranges that usually cover around 200 nm - 2500 nm using different controls and calibrations. Within these ranges of light, calibrations are needed on the machine using standards that vary in type depending on the wavelength of the photometric determination.

An example of an experiment in which spectrophotometry is used is the determination of the equilibrium constant of a solution. A certain chemical reaction within a solution may occur in a forward and reverse direction, where reactants form products and products break down into reactants. At some point, this chemical reaction will reach a point of balance called an equilibrium point. In order to determine the respective concentrations of reactants and products at this point, the light transmittance of the solution can be tested using spectrophotometry. The amount of light that passes through the solution is indicative of the concentration of certain chemicals that do not allow light to pass through.

The absorption of light is due to the interaction of light with the electronic and vibrational modes of molecules. Each type of molecule has an individual set of energy levels associated with the makeup of its chemical bonds and nuclei, and thus will absorb light of specific wavelengths, or energies, resulting in unique spectral properties. This is based upon its specific and distinct makeup.

The use of spectrophotometers spans various scientific fields, such as physics, materials science, chemistry, biochemistry, and molecular biology. They are widely used in many industries including semiconductors, laser and optical manufacturing, printing and forensic examination, as well in laboratories for the study of chemical substances. Spectrophotometry is often used in measurements of enzyme activities, determinations of protein concentrations, determinations of enzymatic kinetic constants, and measurements of ligand binding reactions. Ultimately, a spectrophotometer is able to determine, depending on the control or calibration, what substances are present in a target and exactly how much through calculations of observed wavelengths.

In astronomy, the term spectrophotometry refers to the measurement of the spectrum of a celestial object in which the flux scale of the spectrum is calibrated as a function of wavelength, usually by comparison with an observation of a spectrophotometric standard star, and corrected for the absorption of light by the Earth's atmosphere.

What is the difference between spectroscopy, spectrography and spectrometry? - Astronomy

The term spectra is defined as the entire electro-magnetic wavelength.

Spectroscopy began in 1666 when Sir Isaac Newton discovered that white light passing through a glass prism split the light into a rainbow. To confirm this, Newton passed the rainbow through another prism and it recombined into white light.

Spectroscopy took off in the 19th century when Joseph Fraunhofer took a spectra of the Sun and noticed dark lines in the spectra

In 1857, Gustav Kirchhoff and Robert Bunsen experimented with laboratory chemical spectra and determined that each chemical element has its own unique spectral signature - called spectral lines. Furthermore, Kirchhoff summarized the three important elements of spectra, called Kirchhoff's Laws. To understand the laws, it is important to understand the concept of a "blackbody." This is not an object that is black or dark, instead a blackbody is a theoretical object that emits all light and radiation that is directed to it. If 100% of light were to illuminate a blackbody, 100% of that light will be emanated.

Kirchhoffs Laws (three of them):

1. A blackbody process a continuous spectrum, free of any spectral lines.

2. A hot, transparent gas will produce emission lines - a series of bright lines against a dark background.

3. A cool transparent gas in front of a blackbody will produce absorption lines - dark lines on a spectra that would appear in the same place as a hot gas cloud comprised of the same elements.

A diffraction grating is nothing more than a special cut glass plate with small lines etched into the glass. The more accurate and more numerous the cuts, the more accurate the spectra. The reason gratings are used instead of prisms is that the grating can be adjusted and the prism cannot. The prism of a spectroscope must have 60 degree angles and cannot be rotated.

The image above is from the group of amateur astronomers using this style of spectroscope to capture the radial velocity of a stars wobble as a result of an exoplanet.

The image below shows the Fraunhofer spectra, complete with the brightest Fraunhofer lines (shown by letters of the alphabet). This image also shows the frequencies of each color.

Image Credit - and additional information.

Difference between spectroscopy and spectrometry

Gold Book

IUPAC. Compendium of Chemical Terminology, 2nd ed. (the Gold Book). Compiled by A. D. McNaught and A.Wilkinson. Blackwell Scientific Publications, Oxford (1997).

Also contains definition of: spectrometry

The study of physical systems<ref>Representative parts of the system (for example, serum) may be treated (for example, diluted) before measurement. In analytical chemistry, the instrumentation or parts of it may also be considered as systems</ref> by the electromagnetic radiation with which they interact or that they produce. Spectrometry is the measurement of such radiations as a means of obtaining information about the systems and their components. In certain types of optical spectroscopy, the radiation originates from an external source and is modified by the system, whereas in other types, the radiation originates within the system itself.

Difference Between Photometry and Spectrophotometry

Photometry and spectrophotometry are two important applications of light measurements. These two methods have various applications in fields such as chemistry, physics, optics and astronomy. It is vital to have a solid understanding in these concepts in order to excel in such fields. This article presents the definitions, applications, examples, similarities and finally the differences between photometry and spectrophotometry.

What is Spectrophotometry?

To understand spectrophotometry, one must first understand the concept of spectrum, especially the absorption spectrum. The light is a form of electromagnetic waves. There are other forms of EM waves such as X-Rays, Microwaves, Radio waves, Infrared and Ultraviolet rays. The energy of these waves is dependent on the wavelength or the frequency of the wave. High frequency waves have high amounts of energies, and low frequency waves have low amounts of energies. The light waves are made up of small packets of waves or energy known as photons. For a monochromatic ray, the energy of a photon is fixed. The electromagnetic spectrum is the plot of the intensity versus the frequency of the photons. When a beam of waves having a whole range of wavelengths is passed through liquid or gas, the bonds or electrons in these materials absorb certain photons from the beam. It is due to the quantum mechanical effect that only photons with certain energies get absorbed. This can be understood using the energy level diagrams of atoms and molecules. Spectrophotometry is the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength. For the visible region, the perfect white light contains all the wavelengths within the region. Assume white light is sent through a solution absorbing photons with a wavelength of 570 nm. This means the red photons of the spectrum is now reduced. This will cause a blank or reduced intensity at the 570 nm mark of the plot of intensity versus wavelength. The intensity of the passed light as a proportion to the projected light can be plotted for some known concentrations, and the resultant intensity from the unknown sample can be used to determine the concentration of the solution.

What is Photometry?

The term “photo” means light and the term “metry” refers to measurement. Photometry is the science of the measurement of light, in terms of its perceived brightness to the human eye. In photometry, the standard is the human eye. The sensitivity of the human eye to different colors is different. This has to be considered in photometry. Therefore, amplification methods are used so that the effect from each color would be same as that of the eye. Since the human eye is only sensitive to visible light, photometry only falls in that range.

What is the difference between photometry and spectrophotometry?

• Spectrophotometry is applied to the whole electromagnetic spectrum, but photometry is only applicable to the visible light.

• Photometry measures the total brightness as seen by the human eye, but spectrophotometry measures the intensity at each wavelength on the whole range of the electromagnetic spectrum for which the measurements are necessary.

What is difference between spectrophotometry and spectroscopy?

You can think of Spectrometry as general study of interaction of matter with electromagnetic waves (the whole spectra). While Spectrophotometry is the quantitative measurement of light spectra reflection and transmission properties of materials as function of the wavelength. Note from first principle perspective you need to have the former for the latter. Think of the former as the foundational component (the physics),and the latter an application of the former for a specific subject of measurement.


Spectroscopy is the study of the interaction between matter and radiated energy (electro magnetic waves). This can be interpreted as the science of studying the interactions of matter and radiation. To understand spectroscopy, one must first understand the electromagnetic spectrum that stretch from Microwaves, Radio waves, Infrared and Ultraviolet rays, X-Rays and Gamma rays . The energy of these waves is dependent on the wavelength or the frequency of the wave. High frequency waves have high amounts of energies, and low frequency waves have low amounts of energies.

If you look at NIST definition of spectrophotometry is states that
" Spectrophotometry is the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength. While relatively simple in concept, determining the reflectance or transmittance involves careful consideration of the geometrical and spectral conditions of the measurement ."

A spectrophotometer consists of two instruments, namely a spectrometer for producing light of any selected color (wavelength), and a photometer for measuring the intensity of light. The instruments are arranged so that liquid in a cuvette can be placed between the spectrometer beam and the photometer. The amount of light passing through the tube is measured by the photometer. The photometer delivers a voltage signal to a display device, normally a galvanometer. The signal changes as the amount of light absorbed by the liquid changes.

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