The following table, like the companion file, "If a Millimeter Were a Year/Light-Year", attempts to provide some perspective on cosmological distance and time. This table foreshortens distance by using a logarithmic scale, while "If a Millimeter Were a Year/Light-Year" keeps distance and time to scale. Thus distant objects crowd up in this table but are spread out (over thousands of miles in the model) on the other. In each, distance is somewhat at a disadvantage, since a light year is already a greater distance than is easily comprehended, while a year in time is familar to all. On the other hand, since a year is so commonplace, this puts into perspective both the nearby stellar distances and the greath depths of geological time and cosmological distance.
Clicking on the link to the footnotes will usually open a popup window on the note. This new window can be closed. If it is not, if it is minimized or overlain, the next footnote will appear in a new popup, and all the new popup windows will begin to accumulate. It would thus be better to close the popups as they open. Footnotes with "Return to Text" should only be used if the footnote was only linked from another page, or an index page, where a popup for the note has not opened. All the footnotes are at the bottom of this page.
The "present" in this table is 1993. This dates to my teaching time at Los Angeles Valley College. The "present" could be updated to when I write now, in 2018, but it would not improve the idea or the impression.
A discussion of sources may be found in "If a Millimeter Were a Year/Light-Year".
Philosophy of Science, Geology & Astronomy
Alpha Centauri (or The central double star of Alpha Centauri consists of Alpha Centauri A, or Rigel Kentaurus, which is 1.1 solar masses, and Alpha Centauri B, which is 0.907 solar masses. At closest approach (periastron) they are 11.2 Astronomical Units apart; and when furthest apart (apastron) they are 35.6 AU apart. They revolve around each other with a period of 79.91 years. Their distance from the Sun is now measured at 4.37 light years.
Alpha Centauri C orbits AB with a periastron of 4300 Astronomical Units, an apastron of 13,000 AU, and with a period of about 550,000 years. These extraordinary distances and orbital period left the question open whether C was even part of the Alpha Centauri system. Only in 2017 was it positively shown that C was indeed in orbit around the other two. Meanwhile, C lies between AB and the Earth and is only 4.24 light years away. This makes it the closest star to the Sun, and its slow orbital speed means that it will maintain this status for a multiple of many times the sum of human historical time (only about 5000 years). Alpha Centauri C is a red dwarf star, with only 0.123 solar masses, and is too dim to be seen with the naked eye. Nevertheles, a planet has been identified in orbit around the star.
I was perplexed for many years that Proxima Centauri was said to be both the closest star and in orbit around the other two. Wouldn't it be further away in other parts of its orbit? Well, yes; but we might need to wait half a million years for that. The only time I have seen Alpha Centauri was while living in Hawai'i, especially when that was right across the Kalaniana'ole Highway, looking south out over the dark ocean. Pretty much zero light pollution. Alpha and Beta Centauri, and the Southern Cross, were conspicuous.
A Light Year (LY) is the distance light can travel in a year. The velocity of light (usually symbolized with "c") in a vacuum is 299,792,458 m/s by definition (the length of the meter is then based on this). This means a Light Year is 9,460,528,401,200 km. This Astronomical Almanac for 2018 gives the mean length of the tropical year (from equinox to equinox) as 365d 05h 48m 45.2s. Multiplying that out likely will produce a different length of the Light Year in kilometers, since the previous calculation was done some years ago, with an earlier value for the tropical year. Beyond nine trillion kilometers, however, one might wonder how much difference it would make.
The Parsec is often used in astronomy instead of the Light Year. A Parsec (Parallax Second or PC) is the distance of an object from the sun such that the triangle whose base is the distance from the earth to the sun (called the Astronomical Unit, AU, au, or ua) makes an angle of one second of arc at the object. This means that a Parsec is equal to the cotangent of one arc second, in Astronomical Units = 206264.8 AU.
The Astronomical Unit is now defined as exactly 149,597,870,700 m, which makes a Parsec 30.85677581 x 1012 km (or 30.85677581 Pm or petameters). A Parsec is thus 3.26163 LY.
In the original Star Wars the Parsec was used as though it was a unit of time rather than distance. Carl Sagan complained about this on the Tonight Show, telling Johnny Carson that all they needed was an "impecunious graduate student" from astronomy to prevent them from making those kinds of mistakes. Unfortunately, when it comes to the history of science, even people with Ph.D.'s in astronomy or physics often introduce or perpetuate falsehoods -- for instance about the existence of external galaxies or the experimental refutation of Aristotle's theory of falling bodies. And although Hollywood often hires experts to advise them on movies, their advice is not always taken.
In the old days of shows like The Twilight Zone, very little care was taken with distances, and expressions like "billions of miles" were sometimes used with the implication of encompassing interstellar distances, when that might only barely get us out of the solar system. More recently, a movie in the Alien series, Prometheus [2012], begins with a ship that is said to be 3.27 x 1014 km from Earth. This would give us the equivalent of 35 Light Years, which is about the distance to the star Arcturus. This would be a credible distance if the technology ever develops to allow exploration of nearby areas in the galaxy, although the technology for this kind of space travel, which would require faster-than-light cruising, is never discussed in the movies of this series, and we are also never given any kind of idea about the proximity of this location to the Earth in relation to the size and structure of the galaxy. Of course, as George Lucas realized, it is better to leave these details unaddressed if they would not be in the internal natural discourse of the science fiction world.
Philosophy of Science, Geology and Astronomy
Barnard's Star is the next closest star after Alpha Centauri, but too dim to be seen with the naked eye. It also has the largest proper motion of any star, i.e. the rate at which it moves against the background of the others stars, at 10.34 seconds of arc per year.
Sirius is the brightest star in the sky.
Open Clusters are young stars that have recently blown away the dust and gas from the nebula in which they condensed. In time the stars scatter and become isolated, like the sun. The Hyades take up a large part of the constellation Taurus and are close enough that they do not look conspicuously cluster-like to the naked eye. The Hyades are also just within the radius of the Local Bubble: the spherical void space, probably cleared by an ancient supernova, surrounded by denser dust and gas, within which the sun and other local stars move. Counting down no further than magnitude 8 in brightness, the Local Bubble contains no less than 5000 stars. Other voids within the Orion Arm of the Galaxy abut on the Local Bubble.
Many kinds of non-stellar objects have Messier numbers (M #), from a list compiled by Charles Messier (1730-1817), who wanted to identify objects that might be confused with comets. Messier's list of 103 objects was published in 1781.
The Great Orion Nebula, covering about one degree of arc, is part of one the principal areas of star formation in the Orion (or Local) Arm of the Galaxy. Diffuse nebulae are large bodies of dust and gas. Bright diffuse nebulae scatter blue starlight or are excited by starlight to glow red. Dark nebulae can be identified by the way they block light from background stars, or bright nebulae, behind them. New stars condense within these nebulae. Some nebulae, although invisible to the naked eye, cover relatively large parts of the sky. The North America Nebula stretches across 2.5 degrees of arc, which is five times the diameter of the sun or the moon.
k is the abreviation for the metric or SI (Système International) prefix kilo, which means 1000. M abreviates Mega for a million, and G, Giga for a billion. MLY is thus millions of light years. M$ is a Megabuck, G$ a Gigabuck.
Deneb is the most distant of the bright stars visible to the naked eye.
M 29 is in the Sagittarius Arm of the Galaxy, the next arm in from the Orion Arm.
At right is the Messier object 80 (M 80), in Scorpio, found in 1781 by Charles Messier (1730-1817). It is 32,600 light years distance. Globular Clusters tend to be old, which means their stars are reddish. The physics of the orbits of the stars in the Clusters would be fiendish. How they formed like this is a good question. Return to the Mystery of Order
NGC 869 are 884 are the "Double Cluster" in Perseus. One of the first objects to be recognized as belonging to a distinct spiral arm of the Galaxy, in this case the Perseus Arm, the next one out from the Orion Arm. NGC numbers refer to the New General Catalogue of non-stellar objects. This was J.L.E. Dreyer's 1888 update of John Herschel's 1864 General Catalogue and contains 7840 objects.
End of Wisconsin glaciation. Beginning of modern post- or inter-glacial period.
NGC 3603 is a distant nebula in the Sagittarius Arm.
The Wisconsin Glacial was the last glacial advance of the Pleistocene Epoch.
The Magellanic Clouds, although they look like detached pieces of the Milky Way, are irregular galaxies that are the closest separate members of the Local Group of galaxies.
All present mitochondrial DNA in humans appears to decend from one human female who lived at this time. She has been dubbed "Eve." This means that we are related to the other females only through their male descendants.
Homo habilis has been regarded as the first species of genus Homo.
The Andromeda Galaxy, or the Great Spiral Nebula in Andromeda, is a spiral galaxy that is the near twin and companion of the Milky Way in the Local Group. The bright nucleus of the galaxy is the most distant object that can be seen with the naked eye. The whole galaxy stretches across at least 3 degrees of arc in the sky, six times the apparent diameter of the sun or the moon.
Australopithecus is the oldest genus of family Hominidae.
The velocity of light can be used to measure radial distance in the universe because of the velocity the expansion of the universe gives to all distant objects. Here the expansion is up to a thousanth of c.
The conspicuous cluster of galaxies in the constellation Virgo, with the giant elliptical galaxy M 87 at the center, is the heart of the Local (or Virgo) Supercluster. The Coma-Sculptor Cloud, containing the Local Group, the Milky Way, etc., is gravitationally part of the Virgo Supercluster.
In the Cenozoic, dinosaurs have become extinct, the Age of Mammals begins.
Everything up to this point, at a radius of 1% c/H (The Hubble Radius, see page 4), contains only a millionth of the volume of the universe.
At this range clusters of galaxies start becoming more conspicuous than individual galaxies. Several are listed here with George Abell's catalogue numbers.
Many nearby galaxies, including our own, are headed towards a concentration of mass equal to 100,000 Milky Ways, dubbed The Great Attractor. Abell 3627, which matches The Great Attractor in direction and distance, has recently been suggested as a candidate, though its visible mass is only about 10% of what it would need to be.
Triassic Period, beginning of the Age of Dinosaurs.
The Red Shift from the Doppler Effect is how we actually know about the radial velocity of recession, and distance, of galaxies. The Red Shift (z) is the change in a wavelength of radiation (Δλ) from the object divided by what the original wavelength was (Δλ/λ). This can be related to velocity (u) as: (z+1)2=(c+u)/(c-u) or u/c=(z2+2z)/(z2+2z+2), where c=1.
Distance (s) then depends on Hubble's Law: u=sH, where the Hubble Constant (H0) is taken to be 75 km/s/MPC (it is somewhere between 50 and 100 km/s/MPC). 1/H is the Hubble Time, which for the given H is 13.04 Gy. c/H, the Hubble Radius, is thus 13.04 GLY. At low values, z is virtually identical to u/c. This is the point where the two values begin to diverge. u/c cannot be larger than 1, but z can be any number up to infinity (at the speed of light).
The June 2010 edition of Sky & Telescope reported the Hubble Constant to be 70.4 +/- 1.4 km/s/MPC [p.14]. They also report the age of the universe to be 13.75 +/- 0.11 years. It used to be that the Hubble Time would be larger than the age of the universe; but if the expansion of the universe in accelerating, then the Hubble Time is smaller than the age of the universe.
The March 2022 edition of Sky & Telescope, in an article called "The Hubble Constant: Tension and Release," now reports that different methods have produced different estimates of the Hubble Constant, one at 73 km/s/Mpc, andother at 67 km/s/Mpc. This discrepency is being called the "Hubble Tension," and various theories and investigations are being explored to reconcile the values.
Philosophy of Science, Geology and Astronomy
In the Devonian, life appears on land.
Beginning of the Cambrian Era, when multicellular life first becomes abundant.
Cells that have nuclei first appear.
Everything up to this point, at a radius of 10% c/H, contains only a thousanth of the volume of the universe.
Quasars (Quasi-Stellar Objects, or QSO's) are among the most mysterious objects in the universe. Small, distant, and incredibly bright, their energy output (a mass the size of the moon is turned into energy every second) and their absence from nearby space are largely unexplained. Some quasars appear to be in the middle of galaxies, and it is theorized that they all are. Their strangeness leads some astronomers to argue that they are really not so distant and that their red shift is from some other effect, but that theory hasn't work out very well. 3C [the Third Cambridge Catalogue of Radio Sources] 273 is actually one of the intrinsically brightest Quasars, and it is relatively close, as close as many observable galaxies. If we were to bring it merely as close as the star Arcturus, it would appear as bright as the sun in the sky.
The oldest Earth rocks date the beginning of the Archaean aeon.
The Hadaen Aeon begins with the origin of the Earth and the Moon.
Closed universes, which will collapse upon themselves, cannot be older than this.
0.6 Alpha Centauri1 4.24 LY2 Years before present (BP, 1993):
0.7 5y H.W. Bush Elected
Barnard's Star3 5.90 LY
0.8
Wolff 359 7.66 LY 7y Challenger explodes
0.9
Sirius4 8.80 LY
1.0 9y Reagan Re-elected
Procyon 11.4 LY
1.1 12y Reagan Elected
1.2 Altair 16.6 LY 16y John Paul I
1.3 Fomalhaut 21.8 LY 18y Vietnam War ends
1.4 Vega 26.4 LY 24y Landing on Moon
1.5 33y Kennedy Elected
Arcturus 35.8 LY
1.6 [Far Edge of Local Fluff] 36y Korean War ends
Capella 42.4 LY
1.7 48y World War II ends
1.8 Aldebaran 68.5 LY 64y Stock Market Crash
1.9 Achernar 84.8 LY 75y World War I ends
2.0 Algol 94.5 LY 111y Britain Occupies Egypt
2.1 Almach 121 LY 128y Civil War ends
2.2 Hyades Open Cluster5 150 LY 173y George III
[Local Bubble]
2.3 Rasalas 179 LY
2.4 Spica 258 LY 278y Louis XIV
2.5 Betelgeuse 309 LY 344y King Charles I
2.6 Pleiades Open Cluster 408 LY
2.7 Beehive Open Cluster 522 LY 447y Martin Luther
2.8 M 7 Open Cluster6 783 LY
2.9 Rigel 913 LY 766y Chingiz Khan
3.0 M 42 Great Orion Nebula7 1000 LY 968y Basil II Bulgaroctonus
3.1 Canopus 1.17 kLY8 1179y Charlemagne
3.2 1428y Justinian
Deneb9 1.83 kLY
3.3 1979y Augustus
3.4 M 67 Open Cluster 2.61 kLY 2314y Alexander the Great
3.5 M 50 Open Cluster [Orion Arm] 2.97 kLY 3224y Ramesses II
3.6 M 29 Open Cluster10 4.08 kLY
3.7 M 8 Lagoon Nebula [Sagittarius Arm] 5.22 kLY 4654y Khufu
3.8 M 4 Globular Cluster11 6.85 kLY 5754y Jewish Creation
3.9 NGC 869 & 884 Open Clusters12 7.34 kLY 7502y Byzantine Creation
4.0 M 24 Open Cluster [Sagittarius Arm] 9.39 kLY 10ky Holocene Epoch13
4.1 NGC 6440 Globular Cluster 12.1 kLY
4.2
M 12 Globular Cluster 17.9 kLY
4.3 18ky height of glaciation
NGC 3603 Nebula14 25.0 kLY
4.4
[Center of the Milky Way Galaxy] 27.7 kLY
4.5 35ky Homo sapiens sapiens
M 2 Globular Cluster 36.9 kLY
4.6
NGC 1261 Globular Cluster 43.7 kLY
4.7
M 53 Globular Cluster 56.1 kLY
4.8
M 54 Globular Cluster 70.1 kLY
4.9 85ky Wisconsin Glacial15
[far edge of the Milky Way Galaxy] 75 kLY
5.0
NGC 7006 Globular Cluster 113 kLY
5.1 125ky Homo sapiens
neanderthalenis
5.2 Large Magellanic Cloud16 163 kLY
5.3 Small Magellanic Cloud 196 kLY 200ky "Eve"17
5.4 Draco Galaxy (Local Group) 261 kLY
5.5 NGC 2419 Globular Cluster 304 kLY 300ky Homo sapiens
5.6
450ky Hawaii Island
5.7
Carina Galaxy (Local Group) 555 kLY
5.8 1.6My-300ky Homo erectus
5.9 Leo I Galaxy (Local Group) 750 kLY
860ky East Maui Island
6.0
6.1 2-1.5My Homo habilis18
6.2 NGC 6822 Galaxy (Local Group) 1.70 MLY 1.63My West Maui Island
6.3 2My Pleistocene Epoch
M 31 Great Andromeda Galaxy19 2.38 MLY
6.4
M 33 Galaxy (Local Group) 2.94 MLY 4-1.2My Australopithecus20
6.5
[edge of the Local Group] <3.26 MLY 3.65My Oahu Island
6.6
6.7 NGC 1569 Galaxy (M 81 Group) 5.22 MLY 5My Pliocene Epoch
6.8 5.72My Kauai Island
6.9 NGC 404 Galaxy (Local Outlier) 7.83 MLY 7.5My Nihoa Island
7.0 NGC 253 Galaxy (Sculptor Group) 9.78 MLY
11.3My Necker Island
7.1
M 94 (Canes Venatici I Group) 14.0 MLY .001c21
7.2
7.3 20My Midway Atoll
M 106 (Canes Venatici II Group) 22.2 MLY .002c
7.4 25My Miocene Epoch
7.5 NGC 4274 Galaxy (Coma I Cluster) 31.6 MLY .003c
7.6 [end of the Coma-Sculptor Cloud] 37My Oligocene Epoch
7.7 M 87 Galaxy (Virgo Cluster)22 54.8 MLY .004c
7.8 NGC 157 Galaxy (Tele'-Grus Cloud) 68.2 MLY .006c 65My Cenozoic Era23
7.9
NGC 2577 Galaxy (Cancer-Leo Cloud) 89.3 MLY .007c
8.0 100My Gulfian Age
NGC 474 Galaxy (Cetus-Aries Cloud) 106 MLY .009c
8.1 _______1% c/H______24
Abell 1060 (Hydra I) Cluster25 149 MLY .011c
8.2 144My Cretaceous Period
NGC 145 Galaxy 186 MLY .014c
8.3 208My Jurassic Period
Abell 3627 (The Great Attractor?)26 209 MLY .016c
8.4 Abell 426 (Perseus) Cluster 239 MLY .018c
248My Mesozoic Era27
8.5 Ab. 1656 (Coma Berenices) Cluster 303 MLY .023c .02328
8.6 Abell 2506 Cluster 432 MLY .033c .034 408My Devonian Period29
8.7 Abell 76 Cluster 542 MLY .042c .043 505My Ordovician Period
8.8 Abell 1377 (Ursa Major I) Cluster 670 MLY .051c .053 590My Phanerozoic Aeon30
8.9 Abell 1452 Cluster 823 MLY .063c .065
1.0-0.8Gy Grenville Orogeny
9.0 Ab. 2065 (Corona Borealis) Cluster 940 MLY .072c .075
9.1 Abell 1346 Cluster 1.26 GLY .097c .102 1.4Gy Eukaryotic Cells31
9.2 _____10% c/H_____32
3C 273 Quasar33 1.90 GLY .146c .158 1.9-1.6Gy Penokean Orogeny
9.3
Hydra II Cluster 2.65 GLY .203c .229
9.4 2.6Gy Proterozoic Aeon
3C 79 Radio Galaxy 2.92 GLY .224c .256
9.5 3.3-3.2Gy Oldest Fossils
9.6 3C 48 Quasar 3.95 GLY .303c .367 3.9Gy Archaean Aeon34
9.7 3C 147 Quasar 5.34 GLY .410c .545 4.6-5Gy Hadean Aeon35
9.8
3C 309.1 Quasar 7.40 GLY .568c .905
9.9 8.69Gy Limit of Closure36
4C 41.17 Galaxy37 11.96 GLY .917c 3.80
10.0
Q0000-26 Quasar 12.08 GLY .926c 4.11
10.1
Hubble Radius, c/H38 13.04 GLY 1.00c 13.04Gy Hubble Time, 1/H
10.2
Distance Velocity Shift
(s) (u) (z)
If a Millimeter Were a Year/Light-YearCopyright (c) 1996, 1998, 2000, 2003, 2008, 2010, 2013, 2018, 2020, 2022 Kelley L. Ross, Ph.D. All Rights Reserved
Comparison of Cosmological Distances
with Historical, Paleontological, and Geological Time, FootnotesComparison of Cosmological Distances with Historical and Geological Time, Note 1;
Alpha Centauri
Cen) is the closest star to the Sun, and the third brightest star in the sky (after Sirius and Canopus), but it is too far south in the sky to be seen from the continental United States. It is a system of three stars. The dimmest of those, Alpha Centauri C, or Proxima Centauri, in orbit around the other two, is presently the closest to the sun.
Comparison of Cosmological Distances with Historical and Geological Time, Note 2;
Light Years and Parsecs
Comparison of Cosmological Distances with Historical and Geological Time, Note 3
Comparison of Cosmological Distances with Historical and Geological Time, Note 4
Comparison of Cosmological Distances with Historical and Geological Time, Note 5
Comparison of Cosmological Distances with Historical and Geological Time, Note 6
Comparison of Cosmological Distances with Historical and Geological Time, Note 7
Comparison of Cosmological Distances with Historical and Geological Time, Note 8
Comparison of Cosmological Distances with Historical and Geological Time, Note 9
Comparison of Cosmological Distances with Historical and Geological Time, Note 10
Comparison of Cosmological Distances with Historical and Geological Time, Note 11
Globular Clusters are great, permanent, compact balls of stars, much larger (they can contain a million stars or more), older, and denser than Open Clusters, and are in orbit around the Galaxy. The distribution of Globular Clusters in the sky was the first solid evidence that the sun was not at the center of the Milky Way Galaxy; for there are more in the sky around the constellation Saggitarius, which is actually the direction of the center of the galaxy, around which they were orbiting.
Comparison of Cosmological Distances with Historical and Geological Time, Note 12
Comparison of Cosmological Distances with Historical and Geological Time, Note 13
Comparison of Cosmological Distances with Historical and Geological Time, Note 14
Comparison of Cosmological Distances with Historical and Geological Time, Note 15
Comparison of Cosmological Distances with Historical and Geological Time, Note 16
Comparison of Cosmological Distances with Historical and Geological Time, Note 17
Comparison of Cosmological Distances with Historical and Geological Time, Note 18
Comparison of Cosmological Distances with Historical and Geological Time, Note 19
Comparison of Cosmological Distances with Historical and Geological Time, Note 20
Comparison of Cosmological Distances with Historical and Geological Time, Note 21
Comparison of Cosmological Distances with Historical and Geological Time, Note 22
Comparison of Cosmological Distances with Historical and Geological Time, Note 23
Comparison of Cosmological Distances with Historical and Geological Time, Note 24
Comparison of Cosmological Distances with Historical and Geological Time, Note 25
Comparison of Cosmological Distances with Historical and Geological Time, Note 26
Comparison of Cosmological Distances with Historical and Geological Time, Note 27
Comparison of Cosmological Distances with Historical and Geological Time, Note 28;
The Red Shift & the Hubble ConstantComparison of Cosmological Distances with Historical and Geological Time, Note 29
Comparison of Cosmological Distances with Historical and Geological Time, Note 30
Comparison of Cosmological Distances with Historical and Geological Time, Note 31
Comparison of Cosmological Distances with Historical and Geological Time, Note 32
Comparison of Cosmological Distances with Historical and Geological Time, Note 33
Comparison of Cosmological Distances with Historical and Geological Time, Note 34
Comparison of Cosmological Distances with Historical and Geological Time, Note 35
Comparison of Cosmological Distances with Historical and Geological Time, Note 36