Apparent magnitude (m) is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's light caused by interstellar dust along the line of sight to the observer.
The word magnitude in astronomy, unless stated otherwise, usually refers to a celestial object's apparent magnitude. The magnitude scale dates back to the ancient astronomer Ptolemy, whose star catalog listed stars from 1st magnitude (brightest) to 6th magnitude (dimmest). The modern scale was mathematically defined in a way to closely match this historical system.
The scale is reverse logarithmic: the brighter an object is, the lower its magnitude number. A difference of 1.0 in magnitude corresponds to a brightness ratio of 5√, or about 2.512. For example, a star of magnitude 2.0 is 2.512 times brighter than a star of magnitude 3.0, 6.31 times brighter than a star of magnitude 4.0, and 100 times brighter than one of magnitude 7.0.
The brightest astronomical objects have negative apparent magnitudes: for example, Venus at −4.2 or Sirius at −1.46. The faintest stars visible with the naked eye on the darkest night have apparent magnitudes of about +6.5, though this varies depending on a person's eyesight and with altitude and atmospheric conditions. The apparent magnitudes of known objects range from the Sun at −26.7 to objects in deep Hubble Space Telescope images of magnitude +31.5.
The measurement of apparent magnitude is called photometry. Photometric measurements are made in the ultraviolet, visible, or infrared wavelength bands using standard passband filters belonging to photometric systems such as the UBV system or the Strömgren uvbyβ system.
Absolute magnitude is a measure of the intrinsic luminosity of a celestial object rather than its apparent brightness and is expressed on the same reverse logarithmic scale. Absolute magnitude is defined as the apparent magnitude that a star or object would have if it were observed from a distance of 10 parsecs (3.1×1014 kilometres). Therefore it is of greater use in stellar astrophysics since it refers to a property of a star regardless of how close it is to earth. But in observational astronomy and popular stargazing, unqualified references to "magnitude" are understood to mean apparent magnitude.
This section needs additional citations for verification. (May 2019)
|Number of stars |
(other than Sun)
in the night sky
The scale used to indicate magnitude originates in the Hellenistic practice of dividing stars visible to the naked eye into six magnitudes. The brightest stars in the night sky were said to be of first magnitude (m = 1), whereas the faintest were of sixth magnitude (m = 6), which is the limit of human visual perception (without the aid of a telescope). Each grade of magnitude was considered twice the brightness of the following grade (a logarithmic scale), although that ratio was subjective as no photodetectors existed. This rather crude scale for the brightness of stars was popularized by Ptolemy in his Almagest and is generally believed to have originated with Hipparchus. This cannot be proved or disproved because Hipparchus's original star catalogue is lost. The only preserved text by Hipparchus himself (a commentary to Aratus) clearly documents that he did not have a system to describe brightnesses with numbers: He always uses terms like "big" or "small", "bright" or "faint" or even descriptions like "visible at fullmoon".
In 1856, Norman Robert Pogson formalized the system by defining a first magnitude star as a star that is 100 times as bright as a sixth-magnitude star, thereby establishing the logarithmic scale still in use today. This implies that a star of magnitude m is about 2.512 times as bright as a star of magnitude m + 1. This figure, the fifth root of 100, became known as Pogson's Ratio. The zero point of Pogson's scale was originally defined by assigning Polaris a magnitude of exactly 2. Astronomers later discovered that Polaris is slightly variable, so they switched to Vega as the standard reference star, assigning the brightness of Vega as the definition of zero magnitude at any specified wavelength.
Apart from small corrections, the brightness of Vega still serves as the definition of zero magnitude for visible and near infrared wavelengths, where its spectral energy distribution (SED) closely approximates that of a black body for a temperature of 11000 K. However, with the advent of infrared astronomy it was revealed that Vega's radiation includes an infrared excess presumably due to a circumstellar disk consisting of dust at warm temperatures (but much cooler than the star's surface). At shorter (e.g. visible) wavelengths, there is negligible emission from dust at these temperatures. However, in order to properly extend the magnitude scale further into the infrared, this peculiarity of Vega should not affect the definition of the magnitude scale. Therefore, the magnitude scale was extrapolated to all wavelengths on the basis of the black-body radiation curve for an ideal stellar surface at 11000 K uncontaminated by circumstellar radiation. On this basis the spectral irradiance (usually expressed in janskys) for the zero magnitude point, as a function of wavelength, can be computed. Small deviations are specified between systems using measurement apparatuses developed independently so that data obtained by different astronomers can be properly compared, but of greater practical importance is the definition of magnitude not at a single wavelength but applying to the response of standard spectral filters used in photometry over various wavelength bands.
With the modern magnitude systems, brightness over a very wide range is specified according to the logarithmic definition detailed below, using this zero reference. In practice such apparent magnitudes do not exceed 30 (for detectable measurements). The brightness of Vega is exceeded by four stars in the night sky at visible wavelengths (and more at infrared wavelengths) as well as the bright planets Venus, Mars, and Jupiter, and these must be described by negative magnitudes. For example, Sirius, the brightest star of the celestial sphere, has a magnitude of −1.4 in the visible. Negative magnitudes for other very bright astronomical objects can be found in the table below.
Astronomers have developed other photometric zeropoint systems as alternatives to the Vega system. The most widely used is the AB magnitude system, in which photometric zeropoints are based on a hypothetical reference spectrum having constant flux per unit frequency interval, rather than using a stellar spectrum or blackbody curve as the reference. The AB magnitude zeropoint is defined such that an object's AB and Vega-based magnitudes will be approximately equal in the V filter band.
Precision measurement of magnitude (photometry) requires calibration of the photographic or (usually) electronic detection apparatus. This generally involves contemporaneous observation, under identical conditions, of standard stars whose magnitude using that spectral filter is accurately known. Moreover, as the amount of light actually received by a telescope is reduced due to transmission through the Earth's atmosphere, the airmasses of the target and calibration stars must be taken into account. Typically one would observe a few different stars of known magnitude which are sufficiently similar. Calibrator stars close in the sky to the target are favoured (to avoid large differences in the atmospheric paths). If those stars have somewhat different zenith angles (altitudes) then a correction factor as a function of airmass can be derived and applied to the airmass at the target's position. Such calibration obtains the brightnesses as would be observed from above the atmosphere, where apparent magnitude is defined.
The dimmer an object appears, the higher the numerical value given to its magnitude, with a difference of 5 magnitudes corresponding to a brightness factor of exactly 100. Therefore, the magnitude m, in the spectral band x, would be given by
which is more commonly expressed in terms of common (base-10) logarithms as
where Fx is the observed flux density using spectral filter x, and Fx,0 is the reference flux (zero-point) for that photometric filter. Since an increase of 5 magnitudes corresponds to a decrease in brightness by a factor of exactly 100, each magnitude increase implies a decrease in brightness by the factor (Pogson's ratio). Inverting the above formula, a magnitude difference m1 − m2 = Δm implies a brightness factor of
Example: Sun and MoonEdit
Difference in magnitude:
The Sun appears about 400000 times brighter than the full moon.
Sometimes one might wish to add brightnesses. For example, photometry on closely separated double stars may only be able to produce a measurement of their combined light output. How would we reckon the combined magnitude of that double star knowing only the magnitudes of the individual components? This can be done by adding the brightnesses (in linear units) corresponding to each magnitude.
Solving for yields
where mf is the resulting magnitude after adding the brightnesses referred to by m1 and m2.
Apparent bolometric magnitudeEdit
While magnitude generally refers to a measurement in a particular filter band corresponding to some range of wavelengths, the apparent or absolute bolometric magnitude (mbol) is a measure of an object's apparent or absolute brightness integrated over all wavelengths of the electromagnetic spectrum (also known as the object's irradiance or power, respectively). The zeropoint of the apparent bolometric magnitude scale is based on the definition that an apparent bolometric magnitude of 0 mag is equivalent to a received irradiance of 2.518×10−8 watts per square metre (W·m−2).
While apparent magnitude is a measure of the brightness of an object as seen by a particular observer, absolute magnitude is a measure of the intrinsic brightness of an object. Flux decreases with distance according to an inverse-square law, so the apparent magnitude of a star depends on both its absolute brightness and its distance (and any extinction). For example, a star at one distance will have the same apparent magnitude as a star four times brighter at twice that distance. In contrast, the intrinsic brightness of an astronomical object, does not depend on the distance of the observer or any extinction.
The absolute magnitude M, of a star or astronomical object is defined as the apparent magnitude it would have as seen from a distance of 10 parsecs (33 ly). The absolute magnitude of the Sun is 4.83 in the V band (visual), 4.68 in the Gaia satellite's G band (green) and 5.48 in the B band (blue).
In the case of a planet or asteroid, the absolute magnitude H rather means the apparent magnitude it would have if it were 1 astronomical unit (150,000,000 km) from both the observer and the Sun, and fully illuminated at maximum opposition (a configuration that is only theoretically achievable, with the observer situated on the surface of the Sun).
Standard reference valuesEdit
|Flux at m = 0, Fx,0|
The magnitude scale is a reverse logarithmic scale. A common misconception is that the logarithmic nature of the scale is because the human eye itself has a logarithmic response. In Pogson's time this was thought to be true (see Weber–Fechner law), but it is now believed that the response is a power law (see Stevens' power law).
Magnitude is complicated by the fact that light is not monochromatic. The sensitivity of a light detector varies according to the wavelength of the light, and the way it varies depends on the type of light detector. For this reason, it is necessary to specify how the magnitude is measured for the value to be meaningful. For this purpose the UBV system is widely used, in which the magnitude is measured in three different wavelength bands: U (centred at about 350 nm, in the near ultraviolet), B (about 435 nm, in the blue region) and V (about 555 nm, in the middle of the human visual range in daylight). The V band was chosen for spectral purposes and gives magnitudes closely corresponding to those seen by the human eye. When an apparent magnitude is discussed without further qualification, the V magnitude is generally understood.
Because cooler stars, such as red giants and red dwarfs, emit little energy in the blue and UV regions of the spectrum, their power is often under-represented by the UBV scale. Indeed, some L and T class stars have an estimated magnitude of well over 100, because they emit extremely little visible light, but are strongest in infrared.
Measures of magnitude need cautious treatment and it is extremely important to measure like with like. On early 20th century and older orthochromatic (blue-sensitive) photographic film, the relative brightnesses of the blue supergiant Rigel and the red supergiant Betelgeuse irregular variable star (at maximum) are reversed compared to what human eyes perceive, because this archaic film is more sensitive to blue light than it is to red light. Magnitudes obtained from this method are known as photographic magnitudes, and are now considered obsolete.
For objects within the Milky Way with a given absolute magnitude, 5 is added to the apparent magnitude for every tenfold increase in the distance to the object. For objects at very great distances (far beyond the Milky Way), this relationship must be adjusted for redshifts and for non-Euclidean distance measures due to general relativity.
List of apparent magnitudesEdit
This section needs additional citations for verification. (September 2019)
|−67.57||gamma-ray burst GRB 080319B||seen from 1 AU away||would be over 2×1016 (20 quadrillion) times as bright as the Sun when seen from the Earth|
|−41.39||star Cygnus OB2-12||seen from 1 AU away|
|−40.67||star M33-013406.63||seen from 1 AU away|
|–40.17||star Eta Carinae A||seen from 1 AU away|
|−40.07||star Zeta1 Scorpii||seen from 1 AU away|
|−39.66||star R136a1||seen from 1 AU away|
|–39.47||star P Cygni||seen from 1 AU away|
|−38.00||star Rigel||seen from 1 AU away||would be seen as a large, very bright bluish disk of 35° apparent diameter|
|−30.30||star Sirius A||seen from 1 AU away|
|−29.30||star Sun||seen from Mercury at perihelion|
|−27.40||star Sun||seen from Venus at perihelion|
|−26.74||star Sun||seen from Earth||about 400,000 times brighter than mean full moon|
|−25.60||star Sun||seen from Mars at aphelion|
|−25.00||Minimum brightness that causes the typical eye slight pain to look at|
|−23.00||star Sun||seen from Jupiter at aphelion|
|−21.70||star Sun||seen from Saturn at aphelion|
|−20.20||star Sun||seen from Uranus at aphelion|
|−19.30||star Sun||seen from Neptune|
|−18.20||star Sun||seen from Pluto at aphelion|
|−16.70||star Sun||seen from Eris at aphelion|
|−14.20||An illumination level of 1 lux|
|−12.90||full moon||seen from Earth at perihelion||maximum brightness of perigee + perihelion + full moon (mean distance value is −12.74, though values are about 0.18 magnitude brighter when including the opposition effect)|
|−12.40||Betelgeuse||seen from Earth when it goes supernova|
|−11.20||star Sun||seen from Sedna at aphelion|
|−10.00||Comet Ikeya–Seki (1965)||seen from Earth||which was the brightest Kreutz Sungrazer of modern times|
|−9.50||Iridium (satellite) flare||seen from Earth||maximum brightness|
|−7.50||supernova of 1006||seen from Earth||the brightest stellar event in recorded history (7200 light-years away)|
|−6.50||The total integrated magnitude of the night sky||seen from Earth|
|−6.00||Crab Supernova of 1054||seen from Earth||(6500 light-years away)|
|−5.90||International Space Station||seen from Earth||when the ISS is at its perigee and fully lit by the Sun|
|−4.92||planet Venus||seen from Earth||maximum brightness when illuminated as a crescent|
|−4.14||planet Venus||seen from Earth||mean brightness|
|−4||Faintest objects observable during the day with naked eye when Sun is high|
|−3.99||star Epsilon Canis Majoris||seen from Earth||maximum brightness of 4.7 million years ago, the historical brightest star of the last and next five million years|
|−2.98||planet Venus||seen from Earth||minimum brightness when it is on the far side of the Sun|
|−2.94||planet Jupiter||seen from Earth||maximum brightness|
|−2.94||planet Mars||seen from Earth||maximum brightness|
|−2.5||Faintest objects visible during the day with naked eye when Sun is less than 10° above the horizon|
|−2.50||new moon||seen from Earth||minimum brightness|
|−2.48||planet Mercury||seen from Earth||maximum brightness at superior conjunction (unlike Venus, Mercury is at its brightest when on the far side of the Sun, the reason being their different phase curves)|
|−2.20||planet Jupiter||seen from Earth||mean brightness|
|−1.66||planet Jupiter||seen from Earth||minimum brightness|
|−1.47||star system Sirius||seen from Earth||Brightest star except for the Sun at visible wavelengths|
|−0.83||star Eta Carinae||seen from Earth||apparent brightness as a supernova impostor in April 1843|
|−0.72||star Canopus||seen from Earth||2nd brightest star in night sky|
|−0.55||planet Saturn||seen from Earth||maximum brightness near opposition and perihelion when the rings are angled toward Earth|
|−0.3||Halley's comet||seen from Earth||Expected apparent magnitude at 2061 passage|
|−0.27||star system Alpha Centauri AB||seen from Earth||Combined magnitude (3rd brightest star in night sky)|
|−0.04||star Arcturus||seen from Earth||4th brightest star to the naked eye|
|−0.01||star Alpha Centauri A||seen from Earth||4th brightest individual star visible telescopically in the night sky|
|+0.03||star Vega||seen from Earth||which was originally chosen as a definition of the zero point|
|+0.23||planet Mercury||seen from Earth||mean brightness|
|+0.46||star Sun||seen from Alpha Centauri|
|+0.46||planet Saturn||seen from Earth||mean brightness|
|+0.71||planet Mars||seen from Earth||mean brightness|
|+1.17||planet Saturn||seen from Earth||minimum brightness|
|+1.86||planet Mars||seen from Earth||minimum brightness|
|+1.98||star Polaris||seen from Earth||mean brightness|
|+3.03||supernova SN 1987A||seen from Earth||in the Large Magellanic Cloud (160,000 light-years away)|
|+3 to +4||Faintest stars visible in an urban neighborhood with naked eye|
|+3.44||Andromeda Galaxy||seen from Earth||M31|
|+4||Orion Nebula||seen from Earth||M42|
|+4.38||moon Ganymede||seen from Earth||maximum brightness (moon of Jupiter and the largest moon in the Solar System)|
|+4.50||open cluster M41||seen from Earth||an open cluster that may have been seen by Aristotle|
|+4.5||Sagittarius Dwarf Spheroidal Galaxy||seen from Earth|
|+5.20||asteroid Vesta||seen from Earth||maximum brightness|
|+5.38||planet Uranus||seen from Earth||maximum brightness|
|+5.68||planet Uranus||seen from Earth||mean brightness|
|+5.72||spiral galaxy M33||seen from Earth||which is used as a test for naked eye seeing under dark skies|
|+5.8||gamma-ray burst GRB 080319B||seen from Earth||Peak visual magnitude (the "Clarke Event") seen on Earth on 19 March 2008 from a distance of 7.5 billion light-years.|
|+6.03||planet Uranus||seen from Earth||minimum brightness|
|+6.49||asteroid Pallas||seen from Earth||maximum brightness|
|+6.5||Approximate limit of stars observed by a mean naked eye observer under very good conditions. There are about 9,500 stars visible to mag 6.5.|
|+6.64||dwarf planet Ceres||seen from Earth||maximum brightness|
|+6.75||asteroid Iris||seen from Earth||maximum brightness|
|+6.90||spiral galaxy M81||seen from Earth||This is an extreme naked-eyetarget that pushes human eyesight and the Bortle scale to the limit|
|+7.25||planet Mercury||seen from Earth||minimum brightness|
|+7.67||planet Neptune||seen from Earth||maximum brightness|
|+7.78||planet Neptune||seen from Earth||mean brightness|
|+8.00||planet Neptune||seen from Earth||minimum brightness|
|+8||Extreme naked-eye limit, Class 1 on Bortle scale, the darkest skies available on Earth.|
|+8.10||moon Titan||seen from Earth||maximum brightness; largest moon of Saturn; mean opposition magnitude 8.4|
|+8.29||star UY Scuti||seen from Earth||Maximum brightness; one of largest known stars by radius|
|+8.94||asteroid 10 Hygiea||seen from Earth||maximum brightness|
|+9.50||Faintest objects visible using common 7×50 binoculars under typical conditions|
|+10.20||moon Iapetus||seen from Earth||maximum brightness, brightest when west of Saturn and takes 40 days to switch sides|
|+11.05||star Proxima Centauri||seen from Earth||2nd closest star|
|+11.8||moon Phobos||seen from Earth||Maximum brightness; brightest moon of Mars|
|+12.23||star R136a1||seen from Earth||Most luminous and massive star known|
|+12.89||moon Deimos||seen from Earth||Maximum brightness|
|+12.91||quasar 3C 273||seen from Earth||brightest (luminosity distance of 2.4 billion light-years)|
|+13.42||moon Triton||seen from Earth||Maximum brightness|
|+13.65||dwarf planet Pluto||seen from Earth||maximum brightness, 725 times fainter than magnitude 6.5 naked eye skies|
|+13.9||moon Titania||seen from Earth||Maximum brightness; brightest moon of Uranus|
|+14.1||star WR 102||seen from Earth||Hottest known star|
|+15.4||centaur Chiron||seen from Earth||maximum brightness|
|+15.55||moon Charon||seen from Earth||maximum brightness (the largest moon of Pluto)|
|+16.8||dwarf planet Makemake||seen from Earth||Current opposition brightness|
|+17.27||dwarf planet Haumea||seen from Earth||Current opposition brightness|
|+18.7||dwarf planet Eris||seen from Earth||Current opposition brightness|
|+19.5||Faintest objects observable with the Catalina Sky Survey 0.7-meter telescope using a 30-second exposure and also the approximate limiting magnitude of Asteroid Terrestrial-impact Last Alert System (ATLAS)|
|+20.7||moon Callirrhoe||seen from Earth||(small ≈8 km satellite of Jupiter)|
|+22||Faintest objects observable in visible light with a 600 mm (24″) Ritchey-Chrétien telescope with 30 minutes of stacked images (6 subframes at 5 minutes each) using a CCD detector|
|+22.8||Luhman 16||seen from Earth||Closest brown dwarfs (Luhman 16A=23.25, Luhman 16B=24.07)|
|+22.91||moon Hydra||seen from Earth||maximum brightness of Pluto's moon|
|+23.38||moon Nix||seen from Earth||maximum brightness of Pluto's moon|
|+24||Faintest objects observable with the Pan-STARRS 1.8-meter telescope using a 60-second exposure This is currently the limiting magnitude of automated allsky astronomical surveys.|
|+25.0||moon Fenrir||seen from Earth||(small ≈4 km satellite of Saturn)|
|+25.3||Trans-Neptunian object 2018 AG37||seen from Earth||Furthest known observable object in the Solar System about 132 AU (19.7 billion km) from the Sun|
|+26.2||Trans-Neptunian object 2015 TH367||seen from Earth||200 km sized object about 90 AU (13 billion km) from the Sun and about 75 million times fainter than what can be seen with the naked eye.|
|+27.7||Faintest objects observable with a single 8-meter class ground-based telescope such as the Subaru Telescope in a 10-hour image|
|+28.2||Halley's Comet||seen from Earth (2003)||in 2003 when it was 28 AU (4.2 billion km) from the Sun, imaged using 3 of 4 synchronised individual scopes in the ESO's Very Large Telescope array using a total exposure time of about 9 hours|
|+28.4||asteroid 2003 BH91||seen from Earth orbit||observed magnitude of ≈15-kilometer Kuiper belt object Seen by the Hubble Space Telescope (HST) in 2003, dimmest known directly observed asteroid.|
|+31.5||Faintest objects observable in visible light with Hubble Space Telescope via the EXtreme Deep Field with ~23 days of exposure time collected over 10 years|
|+34||Faintest objects observable in visible light with James Webb Space Telescope|
|+35||unnamed asteroid||seen from Earth orbit||expected magnitude of dimmest known asteroid, a 950-meter Kuiper belt object discovered by the HST passing in front of a star in 2009.|
|+35||star LBV 1806-20||seen from Earth||a luminous blue variable star, expected magnitude at visible wavelengths due to interstellar extinction|
- Curtis, Heber Doust (1903) [1901-03-27]. "On the Limits of Unaided Vision". Lick Observatory Bulletin. University of California. 2 (38): 67–69. Bibcode:1903LicOB...2...67C. doi:10.5479/ADS/bib/1903LicOB.2.67C.
- Matthew, Templeton (21 October 2011). "Magnitudes: Measuring the Brightness of Stars". American Association of Variable Stars (AAVSO). Archived from the original on 18 May 2019. Retrieved 19 May 2019.
- "Vmag<6.5". SIMBAD Astronomical Database. Archived from the original on 22 February 2015. Retrieved 25 June 2010.
- "Magnitude". National Solar Observatory—Sacramento Peak. Archived from the original on 6 February 2008. Retrieved 23 August 2006.
- Bright Star Catalogue
- Hoffmann, S., Hipparchs Himmelsglobus, Springer, Wiesbaden/ New York, 2017
- Pogson, N. (1856). "Magnitudes of Thirty-six of the Minor Planets for the first day of each month of the year 1857". MNRAS. 17: 12. Bibcode:1856MNRAS..17...12P. doi:10.1093/mnras/17.1.12. Archived from the original on 3 July 2007. Retrieved 16 June 2006.
- See .
- North, Gerald; James, Nick (2014). Observing Variable Stars, Novae and Supernovae. Cambridge University Press. p. 24. ISBN 9781107636125.
- Oke, J. B.; Gunn, J. E. (15 March 1983). "Secondary standard stars for absolute spectrophotometry". The Astrophysical Journal. 266: 713–717. Bibcode:1983ApJ...266..713O. doi:10.1086/160817.
- Williams, David R. (1 September 2004). "Sun Fact Sheet". NASA (National Space Science Data Center). Archived from the original on 15 July 2010. Retrieved 3 July 2010.
- Williams, David R. (2 February 2010). "Moon Fact Sheet". NASA (National Space Science Data Center). Archived from the original on 23 March 2010. Retrieved 9 April 2010.
- "Magnitude Arithmetic". Weekly Topic. Caglow. Archived from the original on 1 February 2012. Retrieved 30 January 2012.
- IAU Inter-Division A-G Working Group on Nominal Units for Stellar & Planetary Astronomy (13 August 2015). "IAU 2015 Resolution B2 on Recommended Zero Points for the Absolute and Apparent Bolometric Magnitude Scales" (PDF). Resolutions Adopted at the General Assemblies. arXiv:1510.06262. Bibcode:2015arXiv151006262M. Archived (PDF) from the original on 28 January 2016. Retrieved 19 May 2019.
- Evans, Aaron. "Some Useful Astronomical Definitions" (PDF). Stony Brook Astronomy Program. Archived (PDF) from the original on 20 July 2011. Retrieved 12 July 2009.
- Čotar, Klemen; Zwitter, Tomaž; et al. (21 May 2019). "The GALAH survey: unresolved triple Sun-like stars discovered by the Gaia mission". Monthly Notices of the Royal Astronomical Society. Oxford University Press (OUP). 487 (2): 2474–2490. doi:10.1093/mnras/stz1397. ISSN 0035-8711.
- Bessell, Michael S. (September 2005). "Standard Photometric Systems" (PDF). Annual Review of Astronomy and Astrophysics. 43 (1): 293–336. Bibcode:2005ARA&A..43..293B. doi:10.1146/annurev.astro.41.082801.100251. ISSN 0066-4146.
- Luciuk, M., Astronomical Magnitudes (PDF), p. 8, retrieved 11 January 2019
- Huchra, John. "Astronomical Magnitude Systems". Harvard-Smithsonian Center for Astrophysics. Archived from the original on 21 July 2018. Retrieved 18 July 2017.
- Schulman, E.; Cox, C. V. (1997). "Misconceptions About Astronomical Magnitudes". American Journal of Physics. 65 (10): 1003. Bibcode:1997AmJPh..65.1003S. doi:10.1119/1.18714.
- Umeh, Obinna; Clarkson, Chris; Maartens, Roy (2014). "Nonlinear relativistic corrections to cosmological distances, redshift and gravitational lensing magnification: II. Derivation". Classical and Quantum Gravity. 31 (20): 205001. arXiv:1402.1933. Bibcode:2014CQGra..31t5001U. doi:10.1088/0264-9381/31/20/205001. S2CID 54527784.
- Hogg, David W.; Baldry, Ivan K.; Blanton, Michael R.; Eisenstein, Daniel J. (2002). "The K correction". arXiv:astro-ph/0210394.
- Dufay, Jean (17 October 2012). Introduction to Astrophysics: The Stars. p. 3. ISBN 9780486607719. Archived from the original on 24 March 2017. Retrieved 28 February 2016.
- McLean, Ian S. (2008). Electronic Imaging in Astronomy: Detectors and Instrumentation. Springer. p. 529. ISBN 978-3-540-76582-0.
- Dolan, Michelle M.; Mathews, Grant J.; Lam, Doan Duc; Lan, Nguyen Quynh; Herczeg, Gregory J.; Dearborn, David S. P. (2017). "Evolutionary Tracks for Betelgeuse". The Astrophysical Journal. 819 (1): 7. arXiv:1406.3143. Bibcode:2016ApJ...819....7D. doi:10.3847/0004-637X/819/1/7. S2CID 37913442.
- "Brightest comets seen since 1935". International Comet Quarterly. Archived from the original on 28 December 2011. Retrieved 18 December 2011.
- Winkler, P. Frank; Gupta, Gaurav; Long, Knox S. (2003). "The SN 1006 Remnant: Optical Proper Motions, Deep Imaging, Distance, and Brightness at Maximum". The Astrophysical Journal. 585 (1): 324–335. arXiv:astro-ph/0208415. Bibcode:2003ApJ...585..324W. doi:10.1086/345985. S2CID 1626564.
- "Supernova 1054 – Creation of the Crab Nebula". SEDS. Archived from the original on 28 May 2014. Retrieved 29 July 2014.
- "Heavens-above.com". Heavens-above. Archived from the original on 5 July 2009. Retrieved 22 December 2007.
- Mallama, A.; Hilton, J.L. (2018). "Computing Apparent Planetary Magnitudes for The Astronomical Almanac". Astronomy and Computing. 25: 10–24. arXiv:1808.01973. Bibcode:2018A&C....25...10M. doi:10.1016/j.ascom.2018.08.002. S2CID 69912809.
- "Sirius". SIMBAD Astronomical Database. Archived from the original on 24 June 2013. Retrieved 26 June 2010.
- "Canopus". SIMBAD Astronomical Database. Archived from the original on 14 July 2014. Retrieved 26 June 2010.
- "Arcturus". SIMBAD Astronomical Database. Archived from the original on 14 January 2014. Retrieved 26 June 2010.
- "Vega". SIMBAD Astronomical Database. Archived from the original on 7 July 2015. Retrieved 14 April 2010.
- Evans, N. R.; Schaefer, G. H.; Bond, H. E.; Bono, G.; Karovska, M.; Nelan, E.; Sasselov, D.; Mason, B. D. (2008). "Direct Detection of the Close Companion of Polaris with The Hubble Space Telescope". The Astronomical Journal. 136 (3): 1137. arXiv:0806.4904. Bibcode:2008AJ....136.1137E. doi:10.1088/0004-6256/136/3/1137. S2CID 16966094.
- "SIMBAD-M31". SIMBAD Astronomical Database. Archived from the original on 19 May 2014. Retrieved 29 November 2009.
- Yeomans; Chamberlin. "Horizon Online Ephemeris System for Ganymede (Major Body 503)". California Institute of Technology, Jet Propulsion Laboratory. Archived from the original on 2 February 2014. Retrieved 14 April 2010. (4.38 on 1951-Oct-03)
- "M41 possibly recorded by Aristotle". SEDS (Students for the Exploration and Development of Space). 28 July 2006. Archived from the original on 18 April 2017. Retrieved 29 November 2009.
- "Uranus Fact Sheet". nssdc.gsfc.nasa.gov. Archived from the original on 22 January 2019. Retrieved 8 November 2018.
- "SIMBAD-M33". SIMBAD Astronomical Database. Archived from the original on 13 September 2014. Retrieved 28 November 2009.
- Lodriguss, Jerry (1993). "M33 (Triangulum Galaxy)". Archived from the original on 15 January 2010. Retrieved 27 November 2009. (Shows bolometric magnitude not visual magnitude.)
- "Messier 81". SEDS (Students for the Exploration and Development of Space). 2 September 2007. Archived from the original on 14 July 2017. Retrieved 28 November 2009.
- "Neptune Fact Sheet". nssdc.gsfc.nasa.gov. Archived from the original on 10 January 2019. Retrieved 8 November 2018.
- John E. Bortle (February 2001). "The Bortle Dark-Sky Scale". Sky & Telescope. Archived from the original on 23 March 2009. Retrieved 18 November 2009.
- Yeomans; Chamberlin. "Horizon Online Ephemeris System for Titan (Major Body 606)". California Institute of Technology, Jet Propulsion Laboratory. Archived from the original on 13 November 2012. Retrieved 28 June 2010. (8.10 on 2003-Dec-30)
- "Classic Satellites of the Solar System". Observatorio ARVAL. Archived from the original on 31 July 2010. Retrieved 25 June 2010.
- "Planetary Satellite Physical Parameters". JPL (Solar System Dynamics). 3 April 2009. Archived from the original on 23 July 2009. Retrieved 25 July 2009.
- "AstDys (10) Hygiea Ephemerides". Department of Mathematics, University of Pisa, Italy. Archived from the original on 8 July 2013. Retrieved 26 June 2010.
- Zarenski, Ed (2004). "Limiting Magnitude in Binoculars" (PDF). Cloudy Nights. Archived (PDF) from the original on 21 July 2011. Retrieved 6 May 2011.
- "What Is the Most Massive Star?". Space.com. Archived from the original on 11 January 2019. Retrieved 5 November 2018.
- Williams, David R. (7 September 2006). "Pluto Fact Sheet". National Space Science Data Center. NASA. Archived from the original on 1 July 2010. Retrieved 26 June 2010.
- "AstDys (2060) Chiron Ephemerides". Department of Mathematics, University of Pisa, Italy. Archived from the original on 29 June 2011. Retrieved 26 June 2010.
- "AstDys (136472) Makemake Ephemerides". Department of Mathematics, University of Pisa, Italy. Archived from the original on 29 June 2011. Retrieved 26 June 2010.
- "AstDys (136108) Haumea Ephemerides". Department of Mathematics, University of Pisa, Italy. Archived from the original on 29 June 2011. Retrieved 26 June 2010.
- "Catalina Sky Survey (CSS) Facilities". Archived from the original on 3 November 2019. Retrieved 3 November 2019.
- Steve Cullen (sgcullen) (5 October 2009). "17 New Asteroids Found by LightBuckets". LightBuckets. Archived from the original on 31 January 2010. Retrieved 15 November 2009.
- Boffin, H.M.J.; Pourbaix, D. (2014). "Possible astrometric discovery of a substellar companion to the closest binary brown dwarf system WISE J104915.57–531906.1". Astronomy and Astrophysics. 561: 5. arXiv:1312.1303. Bibcode:2014A&A...561L...4B. doi:10.1051/0004-6361/201322975. S2CID 33043358.
- Pan-STARRS limiting magnitude
- Sheppard, Scott S. "Saturn's Known Satellites". Carnegie Institution (Department of Terrestrial Magnetism). Archived from the original on 15 May 2011. Retrieved 28 June 2010.
- What is the faintest object imaged by ground-based telescopes? Archived 2016-02-02 at the Wayback Machine, by: The Editors of Sky Telescope, 24 July 2006
- "New Image of Comet Halley in the Cold". ESO. 1 September 2003. Archived from the original on 1 March 2009. Retrieved 22 February 2009.
- Illingworth, G. D.; Magee, D.; Oesch, P. A.; Bouwens, R. J.; Labbé, I.; Stiavelli, M.; van Dokkum, P. G.; Franx, M.; Trenti, M.; Carollo, C. M.; Gonzalez, V. (21 October 2013). "The HST eXtreme Deep Field XDF: Combining all ACS and WFC3/IR Data on the HUDF Region into the Deepest Field Ever". The Astrophysical Journal Supplement Series. 209 (1): 6. arXiv:1305.1931. Bibcode:2013ApJS..209....6I. doi:10.1088/0067-0049/209/1/6. S2CID 55052332.
- http://www.jaymaron.com/telescopes/telescopes.html Archived 2017-08-01 at the Wayback Machine (retrieved Sep 14 2017)
- "Hubble Finds Smallest Kuiper Belt Object Ever Seen". NASA. Archived from the original on 9 June 2017. Retrieved 16 March 2018.
- "The astronomical magnitude scale". International Comet Quarterly.