an SI Tour℠

Last revised: 13 May 2017.

Length in
0.000 000 000 016 161 991 5 Planck length
Length in
100 Expected change in the length of one of the 4-kilometer arms of the Hanford Laser Interferometer Gravitational Wave Observatory due to a passing garden-variety gravitational wave.
Length in
Length in
1.06836 ± 0.0014 Diameter of a proton, a new and significantly smaller value reported in 2010. For a discussion of the significance, see http://arxiv.org/abs/1301.0905.

Randolf Pohl, Aldo Antognini, François Nez, Fernando D. Amaro, François Biraben, João M. R. Cardoso, Daniel S. Covita, Andreas Dax, Satish Dhawan, Luis M. P. Fernandes, Adolf Giesen, Thomas Graf, Theodor W. Hänsch, Paul Indelicato, Lucile Julien, Cheng-Yang Kao, Paul Knowles, Eric-Olivier Le Bigot, Yi-Wei Liu, José A. M. Lopes, Livia Ludhova, Cristina M. B. Monteiro, Françoise Mulhauser, Tobias Nebel, Paul Rabinowitz et al.
The size of the proton.
Nature, vol 466, pages 213–216 (8 July 2010)

1.754 Diameter of a proton (to the extent it has a diameter!), earlier accepted value.
2.817 940 325 7 Classical electron radius (not the actual radius of an electron, which is a point)
Length in
1 Change in a 5-gigameter distance detectable by NASA's Laser Interferometer Space Antenna (2010)
Length in
1 Width of cavity on which researchers trapped a dye molecule and photon emitted by the molecule, preventing escape of the photon.

Rohit Chikkaraddy, Bart de Nijs, Felix Benz, Steven J. Barrow, Oren A. Scherman, Edina Rosta, Angela Demetriadou, Peter Fox, Ortwin Hess and Jeremy J. Baumberg.
Single-molecule strong coupling at room temperature in plasmonic nanocavities.
Nature, (online 13 June 2016)

45 Diameter of the thinnest axons in the greenhouse whitefly parasite (Encarsia formosa), which is too small for the usual mechanism of signal transmission.

Reinhold Hustert.
Giant and dwarf axons in a miniature insect, Encarsiaformosa, (Hymenoptera, Calcididae).
Arthropod Structure and Development, (in press 12 Sept 2012)

100 Average distance a molecule of air travels at sea level before hitting another molecule.
200 About the smallest object any light microscope can resolve.
470 Typical wavelength of light emitted by blue LED's (also 430 nm, 466 nm).
565 Typical wavelength of light emitted by green LED's (also 569 nm).
630 Typical wavelength of light emitted by orange-red LED's.
660 Typical wavelength of light emitted by red LED's.
Length in
1.5 Length of Pithovirus sibericum, a giant virus discovered in Siberian permafrost 32,000 years old.

Matthieu Legendre, Julia Bartoli, Lyubov Shmakova, Sandra Jeudy, Karine Labadie, Annie Adrait, Magali Lescot, Olivier Poirot, Lionel Bertaux, Christophe Bruley, Yohann Couté, Elizaveta Rivkina, Chantal Abergel and Jean-Michel Claverie.
Thirty-thousand-year-old distant relative of giant icosahedral DNA viruses with a pandoravirus morphology.
PNAS. Published online before print March 3, 2014
doi: 10.1073/pnas.1320670111

200 Typical length of the adult fairy wasp Megaphragma mymaripenne. Remarkably, 95% of the adult's neurons have no nucleus, presumably contributing to its small size.

Alexey Polilov.
The smallest insects evolve anucleate neurons.
Arthropod Structure & Development, vol 41, issue 1, pages 29-34 (January 2012).

Length in
2.5 Approx. maximum depth of new soil produced in 1 year from bedrock in the western Southern Alps, New Zealand.

Isaac J. Larsen, Peter C. Almond, Andre Eger, John O. Stone, David R. Montgomery and Brendon Malcolm.
Rapid soil production and weathering in the Western Alps, New Zealand.
Science, vol 343, no. 6171, pages 637-640 (7 February 2014)
doi: 10.1126/science. 1244908

~30 Annual slippage along the Alpine fault on the South Island of New Zealand.

Simon Lamb, Euan Smith, Tim Stern and Emily Warren-Smith.
Continent-scale strike-slip on a low-angle fault beneath New Zealand's Southern Alps: Implications for crustal thickening in oblique collision zones.
Geochemistry, Geophysics, Geosystems, vol. 16, issue 9, pages 3076–3096 (18 September 2015).

58 Length of tails of sperm of the fruitfly Drosophila bifurca. The fly itself is only about 2 mm long.

Stefan Lüpold, Mollie K. Manier, Nalini Puniamoorthy, Christopher Schoff, William T. Starmer, Shannon H. Buckley Luepold, John M. Belote and Scott Pitnick.
How sexual selection can drive the evolution of costly sperm ornamentation.
Nature v. 533, page 535–538 (26 May 2016)

62 Width of 5 euro note.
66.29 Width of U.S. dollar notes (all denominations, 2.61 inches).
67 Width of 10 euro note.
72 Width of 20 euro note.
77 Width of 50 euro note.
82 Width of 100, 200 and 500 euro notes.
120 Length of a 5 euro note.
127 Length of a 10 euro note.
133 Length of a 20 euro note.
140 Length of a 50 euro note.
147 Length of a 100 euro note.
153 Length of a 200 euro note.
155.96 Length of U.S. dollar notes (all denominations, 6.14 inches).
160 Length of a 500 euro note.
Length in
2 Approximate maximum distance at which the jet of water shot by archerfish (Toxotes jaculatrix) can knock lizards, insects, etc. from overhanging branches into the water.

Peggy Gerullis and Stefan Schuster.
Archerfish actively control the hydrodynamics of their jets.
Current Biology, (in press, 2014)
doi: 10.1016/j.cub.2014.07.059

A video: https://www.youtube.com/watch?v=f8oV4RBYR9U

2.72 Height of Robert Pershing Wadlow (1918-1940). He was still growing at the time of his death.
6.4 Estimated wingspan of Pelagornis sandersi, extinct bird known only from one specimen.

Daniel T. Ksepka.
Flight performance of the largest volant bird.
PNAS 2014; published ahead of print July 7, 2014.

7.5 Maximum length of the giant crocodile Crocodylus thorbjarnarsoni, sp. nov., estimated from fossils.

Christopher A. Brochua and Glenn W. Storrs.
A giant crocodile from the Plio-Pleistocene of Kenya, the phylogenetic relationships of Neogene African crocodylines, and the antiquity of Crocodylus in Africa.
Journal of Vertebrate Paleontology, vol. 32, no. 3, pages 587-602 (2012)

8.1 Maximum tusk length in narwhals.
5.96 Men's pole vault record, set by Steven Hooker, 2008 Beijing Olympics.
8.90 Men's long jump record set by Bob Beamon, 1968 Mexico Olympics.
21 Longest horizontal distance covered in a glide by a paradise tree snake (Chrysopelea paradisi), starting from a height of 9.62 meters. This was an exceptional best out of hundreds of observations.

John J. Socha, Tony O’Dempsey and Michael LaBarbera.
A 3-D kinematic analysis of gliding in a flying snake, Chrysopelea paradisi.
Journal of Experimental Biology, vol 208, pages 1817-1833 (2005).

And personal communication.

22.41 Women's shot put record set by Ilona Schoknecht-Slupianek, 1980 Moscow Olympics.
22.47 Men's shot put record set by Ulf Timmerman, 1988 Seoul Olympics.
25 Bridgelines across rivers, made by Darwin's Bark Spider.

Matjaž Kuntner and Ingi Agnarsson.
Web gigantism in Darwin's bark spider, a new species from Madagascar (Araneidae: Caerostris).
The Journal of Arachnology, vol 38, no. 2, pages 346–356. (2010)

27.7 Peak to trough distance of ocean wave measured Sept. 15, 2004 in Bay St. Louis, Miss., as Hurricane Ivan passed.

Science News, vol 167, page 382 (11 June 2005).

~50 Longest tentacles of the Portuguese man-of-war (Physalia physalis). A typical tentacle is only 10 meters.
50-60 Vertical migration of zooplankton from the surface of arctic waters in the winter, sinking during the six days of the month the moon is full and high. “In terms of biomass and volume, theirs is the biggest daily migration on the planet.”

Kim S. Last, Laura Hobbs, Jørgen Berge, Andrew S. Brierley and Finlo Cottier.
Moonlight drives ocean-scale mass vertical migration of zooplankton during the Arctic winter.
Current Biology, in press Jan 2016.

68.5 Wingspan of the Boeing 747-8.
69.89 Men's discus record, set by Virgilijus Alekna, 2004 Athens Olympics.
76.3 Length of the Boeing 747-8.
79.75 Wingspan of the Airbus A380-800.
84.5 Width of video boards in NRG Stadium, Houston. There are two, built by Mitsubishi.
88.4 Wingspan of the Antonov An-225, “Mriya.” Only one was built.
91 Length of the HAV 304 hybrid air vehicle, a giant blimp-like aircraft that gets its lift from both helium and its “lifting body” shape.
97.54 Wingspan of the “Spruce Goose,” the Hughes H-4 Hercules. Only one was built.
110.3 Width of videoboards in Everbank Field, Jacksonville.
124 Depth to which William Trubridge dove on 1 May 2016, a world free-diving (no external equipment, bare hands and feet) record. He held his breath for 4 minutes 34 seconds.
~160 Depth of Ligeia Mare on Saturn's moon Titan. It is somewhat larger than Lake Superior, and filled with a clear methane-ethane solution.

Marco Mastrogiuseppe, Valerio Poggiali, Alexander Hayes, Ralph Lorenz, Jonathan Lunine, Giovanni Picardi, Roberto Seu, Enrico Flamini, Giuseppe Mitri, Claudia Notarnicola, Philippe Paillou and Howard Zebker.
The bathymetry of a Titan sea.
Geophysical Research Letters, vol. 41, issue 5, pages 1432–1437 (16 March 2014).
doi: 10.1002/2013GL058618

253.2 Depth to which Herbert Nitsch dove in 2012 at Santorini, in Greece. He thus beat his previous world record, 214 m, set in 2007 in Spetses, Greece. In this class of free-diving a weighted sled is permitted for descent and an air-filled balloon in ascending.
300 Aperture of the Arecibo Observatory radio telescope in Puerto Rico.
355 Length of the container ship COSCO Development. It can carry 13,000 cargo containers.

Photo of telescope.

Photo: Fast.bao.ac.cn

Aperture of the FAST radio telescope in Guizhou, China.
564 Depth to which an emperor penguin dove.

Barbara Wienecke, Graham Robertson, Roger Kirkwood and Kieran Lawton.
Extreme dives by free-ranging emperor penguins.
Polar Biology, vol 30, pages 133-142 (2007)
Page 135.

Length in
1.8 Maximum observed dive depth of narwhals.
1.8+ Maximum observed dive depth of Chilean devil ray (Mobula tarapacana)

Simon R. Thorrold, Pedro Afonso, Jorge Fontes, Camrin D. Braun, Ricardo S. Santos, Gregory B. Skomal and Michael L. Berumen.
Extreme diving behaviour in devil rays links surface waters and the deep ocean.
Nature Communications 5, article number: 4274 (1 July 2014)

1.8+ Maximum observed dive depth of the whale shark (Rhincodon typus)

Mark Erdmann.
Whale shark watch: 4 things we've learned from tracking the world's largest fish.
humanature. Conservation International blog. June 26, 2016.
http://blog.conservation.org/2016/06/ Retrieved 29 June 2016.

4.8 Highest elevation on planet Mercury, measured from the average elevation on the planet. The lowest spot is 5.38 km below average elevation, in the Rachmaninoff Basin.

NASA, 6 May 2016.

10 Mean diameter of Leda, moon of Jupiter.
10+ Diameter of the asteroid whose impact with Earth created the Chicxulub crater, in Yucatan. One, at least, of the causes of the extinction of the dinosaurs.
12.4 Mean diameter of Deimos, moon of Mars.
16 Length of the comet 1P/Halley, measured along its longest axis.
22.2 Mean diameter of Phobos, moon of Mars.
39.045 Distance parachutist Felix Baumgartner dropped on 14 October 2012.
41.422 Distance parachutist Alan Eustace dropped on 24 October 2014. This is the distance ratified by the World Air Sports Federation (FAI.org).
200 Height of geysers of water vapor from Jupiter's moon Europa, observed by the Hubble telescope in December 2012. They were not detected by the Galileo or Cassini probes in earlier years, and have not been seen since (through 2014).

Lorenz Roth, Joachim Saur, Kurt D. Retherford, Darrell F. Strobel, Paul D. Feldman, Melissa A. McGrath, Francis Nimmo.
Transient water vapor at Europa’s South Pole.
Science, vol. 343, no. 6167, pages 171-174 (10 January 2014)

321 Longest recorded lightning flash, measured horizontally over Oklahoma on 20 June 2007. Recognized by the WMO.

Timothy J. Lang, Stéphane Pédeboy, William Rison, Randall S. Cerveny, Joan Montanyà, Serge Chauzy, Donald R. MacGorman, Ronald L. Holle, Eldo E. Ávila, Yijun Zhang, Gregory Carbin, Edward R. Mansell, Yuriy Kuleshov, Thomas C. Peterson, Manola Brunet, Fatima Driouech and Daniel S. Krahenbuh.
WMO World Record Lightning Extremes: Longest Reported Flash Distance and Longest Reported Flash Duration.
Bulletin of the American Meterological Society, online 13 September 2016.
doi: 10.1175/BAMS-D-16-0061.1

~500 Roundtrip length of annual migration by Burchell's zebra (Equus quagga) between Botswana and Namibia. Longest measured migration by any large African mammal.

R. Naidoo, M. J. Chase, P. Beytell, P. Du Preez, K. Landen, G. Stuart-Hill and R. Taylor
A newly discovered wildlife migration in Namibia and Botswana is the longest in Africa.
Oryx, FirstView article, pages 1-9, published online: 27 May 2014.

578 Length of the minor planet Vesta, measured along its longest axis.
974.6 Length of the minor planet Ceres, measured along its longest axis.
Length in
1.066 Mean diameter of Tethys, moon of Saturn.
1.21 Mean diameter of Charon, moon of Pluto.
2.263 Longest measured migration of a banded stilt (Cladorhynchus leucocephalus) in search of water in the Australian desert. Took less than 2.5 days.

R. D. Pedler, R. F. H. Ribot and A. T. D. Bennett.
Extreme nomadism in desert waterbirds: flights of the banded stilt.
Biology Letters, vol 10, issue 10 (October 2014).

2.390 Diameter of Pluto.

P. Kenneth Seidelmann, B. A. Archinal, M. F. A’hearn, A. Conrad, G. J. Consolmagno, D. Hestroffer, J. L. Hilton, G. A. Krasinsky, G. Neumann, J. Oberst, P. Stooke, E. F. Tedesco, D. J. Tholen, P. C. Thomas and I. P. Williams.
Report of the IAU/IAG Working Group on cartographic coordinates and rotational elements: 2006.
Celestial Mechanics and Dynamical Astronomy, vol. 98, issue 3, pages 155-180 (July 2007).
All solar system sizes on this page are from this source.

2.7052 Mean diameter of Triton, moon of Neptune.
3.12418 Mean diameter of Europa, moon of Jupiter.
3.174 Height above the Earth's surface at which time slowing due to the orbital speed needed to remain in orbit, is exactly balanced by time speeding up due to the weaker gravity.
3.4748 Mean diameter of the Moon.
3.64292 Mean diameter of Io, moon of Jupiter.
4.818 Mean diameter of Callisto, moon of Jupiter.
4.8794 Diameter of Mercury at equator.

IAU WG on Cartographic Coordinates and Rotational Elements, 2009.

5.150 Mean diameter of Titan, moon of Saturn.
5.26469 Mean diameter of Ganymede, moon of Jupiter.
6.79238 Diameter of Mars at equator; mean diameter is 6.77900 Mm.

IAU WG on Cartographic Coordinates and Rotational Elements, 2009.

~10 Stationary gravity wave at the top of the atmosphere of Venus, caused by lower atmosphere passing over a mountain range.

Tetsuya Fukuhara,Masahiko Futaguchi, George L. Hashimoto, Takeshi Horinouchi,Takeshi Imamura, Naomoto Iwagaimi, Toru Kouyama, Shin-ya Murakami, Masato Nakamura, Kazunori Ogohara, Mitsuteru Sato, Takao M. Sato, Makoto Suzuki, Makoto Taguchi,Seiko Takagi, Munetaka Ueno, Shigeto Watanabe, Manabu Yamada and Atsushi Yamazaki.
Large stationary gravity wave in the atmosphere of Venus.
Nature Geoscience.
Published online 16 January 2017.
doi: 10.1038/NGEO2873.

11.680 Measured migration (as line of sight) flown by a female bar-tailed godwit (Limosa lapponica baueri). The bird, a female tagged “E7”, departed 30 Aug 2007 from the south Yukon–Kuskokwim Delta, Alaska, and arrived 8.1 days later at the mouth of the Piako River, on the North Island of New Zealand.

Robert E. Gill, T. Lee Tibbitts, David C. Douglas, Colleen M. Handel, Daniel M. Mulcahy, Jon C Gottschalck, Nils Warnock, Brian J. McCaffery, Philip F. Battley and Theunis Piersma.
Extreme endurance flights by landbirds crossing the Pacific Ocean: ecological corridor rather than barrier?
Proceedings of the Royal Society London, Ser. B, vol 276, issue 1656, pages 447–457. (7 February 2009)
doi: 10.1098/rspb.2008.1142

12.1036 Diameter of Venus at equator.

IAU WG on Cartographic Coordinates and Rotational Elements, 2009.

12.75628 Diameter of Earth at equator; mean diameter is 12.7420 Mm.

IAU WG on Cartographic Coordinates and Rotational Elements, 2009.

49.528 Diameter of Neptune at equator, at an imaginary surface corresponding to a pressure of 1 bar. The mean diameter (same assumption) is 49.244 Mm.
51.118 Diameter of Uranus at equator, at an imaginary surface corresponding to a pressure of 1 bar. The mean diameter (same assumption) is 50.724 Mm.

Bird in flight.

Photo:Diego Delso, Wikimedia Commons, License CC-BY-SA 4.0

Distance traveled by a juvenile great frigate bird (Fregata minor) in 185 days.

Henri Weimerskirch, Charles Bishop, Tiphaine Jeanniard-du-Dot, Aurélien Prudor and Gottfried Sachs.
Frigate birds track atmospheric conditions over months-long transoceanic flights
Science, vol. 353, issue 6294, pages 74-78 (1 Jul 2016)
doi: 10.1126/science.aaf4374

120.536 Diameter of Saturn at equator, at an imaginary surface corresponding to a pressure of 1 bar. The mean diameter (same assumption) is 116.464 Mm.
129 Diameter of the sunspot AR12192 in 2014. It produced 10 sizable solar flares but no coronal mass ejections.

This region topped out at 2,750 MH, making it the 33rd largest region out of approximately 32,000 active regions that have been tracked and measured since 1874. It is the largest sunspot seen since AR 6368, which measured 3,080 MH on Nov. 18, 1990.--NASA

142.984 Diameter of Jupiter at equator, at an imaginary surface corresponding to a pressure of 1 bar. The mean diameter (same assumption) is 139.822 Mm.
299.79 Distance light travels in a second in a vacuum.
365.7 Earth-moon distance, moon at perigee.
405.4 Earth-moon distance, moon at apogee.
Length in
1.392 Diameter of sun at its equator.
3.2 Length of the great sunspot group of March, 1947.
147.1 Minimum distance of sun from Earth.
152.1 Maximum distance of sun from Earth.
Length in
15.4 Distance from the sun of the dwarf planet V774104 at the time of its discovery (2015) making it the most distant object yet discovered in the solar system. Science (Nov 2015), doi:10.1126/science.aad7414

1 parsec is about 30.8568 petameters; 1 light year is about 9.4609 petameters.

Length in
40.12 Distance to the star alpha Centauri.
83.32 Distance to the star Sirius.
108.0 Distance to the star Procyon.
157.4 Distance to the star Altair.
216.0 Distance to the star Formalhaut.
246.9 Distance to the star Vega.
339.5 Distance to the star Arcturus.
370.3 Distance to the star Pollux.
378 Width of the Local InterStellar Cloud.
432.0 Distance to the star Capella.
493.8 Distance to the star Aldebaran.
925.8 Distance to the star Canopus.
Length in
1.481 Distance to the Large Magellanic Cloud, a local galaxy.
1.728 Distance to the Small Magellanic Cloud, a local galaxy.
2.469 Distance to the star Spica.
3.703 Distance to the star Antares.
3.703 Distance to the star alpha Crucis.
4.629 Distance to the star Betelgeuse.
4.629 Distance to the star beta Crucis.
7.715 Distance to the star Rigel.
9.258 Roughly, thickness of the disk of the Milky Way galaxy.
13.27 Distance to the star Deneb.
141.016 Across the core of the galaxy Holm 15A.

O. López-Cruz, C. Añorve, M. Birkinshaw, D.M. Worrall, H. J. Ibarra-Medel, W. A. Barkhouse, J. P. Torres-Papaqui and V. Motta.
The Brightest Cluster Galaxy in Abell 85: The Largest Core Known so far.

925.8 Roughly, diameter of the disk of the Milky Way galaxy.
Length in
1.5 Approximate radius of the halo surrounding the Milky Way galaxy.
2.1 Distance to the Andromeda galaxy (M31), the galaxy nearest our own.
24.6 Length of a “bridge” of atomic hydrogen between two galaxies.

R. Taylor, R. F. Minchin, H. Herbst, J. I. Davies, R. Rodriguez and C. Vazquez.
The Arecibo Galaxy Environment Survey VII: A dense filament with extremely long HI streams.
Monthly Notices of the Royal Astronomical Society, vol. 443, pp. 2634-2649, (September 21, 2014).
doi: 10.1093/mnras/stu1305

Length in
1.54 Greatest distance within the Local Supercluster of galaxies, which is essentially flat.
8.64 Approximate diameter of the void known as the “WMAP cold spot”.

Lawrence Rudnick, Shea Brown and Liliya R. Williams.
Extragalactic Sources and the WMAP Cold Spot.
Astrophysical Journal, arXiv:0704.0908v2


Composite photograph.

Credits: X-ray: NASA/CXC/CEA/T. Wang et al; Infrared: ESO/UltraVISTA; Radio: ESO/NAOJ/NRAO/ALMA

Approximate distance of the galaxy cluster CL J1001+0220 (z=2.506)

Tao Wang, David Elbaz, Emanuele Daddi, Alexis Finoguenov, Daizhong Liu, Corentin Schreiber, Sergio Martin, Veronica Strazzullo, Francesco Valentino, Remco van der Burg, Anita Zanella, Laure Ciesla, Raphael Gobat, Amandine Le Brun, Maurilio Pannella, Mark Sargent, Xinwen Shu, Qinghua Tan, Nico Cappelluti and Yanxia Li.
Discovery of a galaxy cluster with a violently starbursting core at z=2.506.
Astrophysical Journal, vol. 828, no. 1, 56 (30 August 2016).
doi: 10.3847/0004-637X/828/1/56

~400 Distance to the ultimate horizon. Greatest distance over which information can be transmitted in this universe. Objects this far from us are receding from us at a speed greater than the speed of light (the space between us and the object is expanding at a rate greater than the speed of light). Consequently, light from the objects can never reach us, and vice versa.

other resources

A nice "powers of ten" visualization: htwins.net/scale2

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