Many authors have tried to explain how vast space, and the universe contained within it, really are, usually with less than total success, though with each attempt, some few are reached. This is both something that Sci-Fi GMs need to understand and yet, often hand-wave. I have thought of another approach, one that is strictly game-oriented. It may not work, but it’s worth a shot.

Image by MasterTux from Pixabay

I made the time-out logo from two images in combination: The relaxing man photo is by Frauke Riether and the clock face (which was used as inspiration for the text rendering) Image was provided by OpenClipart-Vectors, both sourced from Pixabay.

This is the latest in my series of time-out posts in between the Trade In Fantasy series.

There are three fundamental principles to my approach, and explaining them would be a good way to start. But I suspect that their meaning won’t be fully understood until we get into actual measurements, at which point hopefully it all becomes blindingly obvious.

1. A Nested Hierarchy Of Distance

Space is subdivided into a nested series of scales. Efficiency in transiting these scales requires new technologies each time the scale changes, though it is usually possible to employ a less-efficient transit technology – there is some overlap in principle.

The difficulties and hazards change as a new scale is reached, and these require navigational skills that match the engineering appropriate to that scale. I’m going to do my best to avoid actually spelling out the technologies concerned, leaving the system to be adapted to whatever sub-genre best fits the individual GM’s setting and campaign. This time around, for this particular GM, it might be some sort of interstellar Jump; next time, it might be Warp Drive; and so on.

2. A Fundamental Unit

The minimum distance of a scale is defined by the limit of the scale preceding it. Mastering the principles of this scale may or may not imply as a prerequisite the mastering of the preceding scale; different game systems will support different approaches to the question. Nor is it necessary or appropriate for this to be consistent; the greater the difference in technology required relative to what has gone before, the less transferable skills will be and the more likely a completely different approach required.

Fundamentally, each scale is measured in a new series of units, and the count of such units within the scale resets at ‘1’ each time.

3. Powers Of Five, or Two, or Three

The distances of a scale, measured in Units, require a technological / navigational improvement at regular intervals. each improvement level is known as a tech level or sub-level within the technology required for that particular scale. Each improvement permits maneuvering and transit at an exponential increase over the number of units.

CORRECTION: The following text, which originally followed the above, now needs to be taken with a grain of salt:

My default is going to be powers of five, because that’s what my instincts are telling me should work – but it may be necessary to employ other exponents along the way. I’ll do so as necessary.

In actual fact, i ended up using powers of 2, 3, and 4 a lot more than I did 5 – so much so that 3-exponent is probably best considered the default.

.

I don’t really want there to be more than a couple of handfuls of tech sub-levels within each scale, to keep the numbers manageable. My preference will be to introduce a new scale before ‘sub-level 21’ is reached – but, at the same time, I want each sub-level to achieve a noteworthy increase in the distances that can be transited.

All clear? I didn’t think so, but getting into the scales themselves should make everything fairly clear.

The Planetary Scale

Space starts at the Karman Line, defined as 100 km (62 miles) above sea level. This altitude defines the point at which aerodynamic lift can no longer be the primary means of flight and orbital mechanics takes over.

Anything short of this distance is a distance (vertically) on the Planetary Scale.

The unit at this scale is the Wright. One Wright is an altitude (powered flight) of 6.4m (21 feet).

Public domain image depicting the first flight by the Wright Brothers, courtesy of Wikimedia Commons.

Aircraft 1 = 1 Wright

The Wright Brother’s first flights were about 0.5 Wrights in altitude. The presumption is made that they stayed relatively flat and level to maintain control of the aircraft and could have actually flown higher – with greater risk of control loss.

Aircraft 2 = 5 Wrights = 32m

Aircraft 3 = 25 Wrights = 160m

Between 1906 and 1908, the altitude record was officially just 4m, or 0.625 Wrights. In the latter year, piloting a biplane, Wilbur Wright dramatically raised the record to 110m (17.2 Wrights), and 7 months later, this record was improved again to 150m (23.5 Wrights). It seems likely that at some point in between, a limit of 5 wrights was reached but no-one actually undertook an attempt.

Aircraft 4 = 125 Wrights = 800m

Late in 1909, another dramatic step forward saw the altitude record for powered flight increased to 920m.

Aircraft 5 = 625 Wrights = 4 km (13000 feet)

In 1910 the record increased multiple times, ending the year at 3497m. The next time it was reset was in 1912, to 5610m, another massive step forward.

It’s at this point that air travel becomes commercially viable for both cargo and passengers. The early steps were halting stumbles, but improvements in the technology followed, notably the DC3 and beyond.

After the heady rush of the early flights, and the steady progression of records being set and broken, this sub-scale would hold sway for many years; the technology was improved and refined, becoming more efficient and successful. It also seems likely that interest in altitude records per se declined in favor of speed records.

Aircraft 6 = 3125 Wrights = 20 km (65, 600 feet)

It wasn’t until 1949 that an aircraft exceeded 3125 Wrights in altitude, when an experimental air-launched rocket plane, the Bell X-1, did so, setting an unofficial record. Two years later, another unofficial record extended the window; it was not until 1953 that this limit was officially breached, when an English Electric Canberra B 2 Turbojet got to 20,079m. By now, the unofficial record (set with rocket power) was 27,570m and before the next non-rocket record was set in 1958, at 23, 451m, the rocket-powered or assisted record stood at 38, 491m.

(Aircraft 7 = 15625 Wrights = 100km (62 miles))

Everything in aviation since the early 1950s, in terms of altitude limits, falls into this sub-scale. Records past this time tend to split hairs – horizontal flight, crewed or unmanned, propeller-driven, and so on. What becomes more important at this scale is not the record altitude, but the cruising altitude.



Image by Julian Herzog via Wikimedia Commons. Released under the Creative Commons Attribution 4.0 International license.

The Boeing 747 Jumbo cruised at between 35,000 and 40,000 feet. The 767 added another 1,000 feet to the top of that. These are both Aircraft-5 ratings.

The cruising altitude of an airbus A320 is 31,000 to 37,000 feet. It has a service ceiling of 39,100 feet, the absolute maximum altitude that it can achieve. The A380 cruises at 43,000 feet.

Even Concorde only approaches the limits of Aircraft 5 in this respect, with a cruising altitude of 55,000 to 60,000 feet.

Beyond Aircraft 5, greater altitude requires special designs that are not commercially viable. The SR-71 Blackbird cruises at 85,000 feet (25,908m) and is a true Aircraft 6 design. Getting to Aircraft 7 requires rockets, and they operate even more efficiently at even higher altitudes.

If atmospheric pressure were greater, lift could be increased and greater altitudes might become possible, but wind resistance would also increase, and, honestly, you’re looking at a gimmick or marketing exercise or different technology (non-commercial) for most of Aircraft 6.

Aircraft 7 is the upper limit of this scale, as we transition to the Orbital Scale.

The Orbital Scale

From 100km up, we’re talking about the orbital scale, the unit of which is the Oberth. 1 Oberth = 100 km. Oberths use exponential powers of 4, not 5.

There can be other limits used. The US defines the Orbital Scale as starting at 50m (80km), for example.

Orbital 1 = 100 km – 400 km (1-4 Oberths)

Up until 400 km, significant air resistance will cause rapid orbital decay if unchecked. These altitudes are considered “Transatmospheric“. They are of limited practical value because of the air resistance, but may be used as a stepping-stone to higher orbital types.

This sub-level also includes terms such as “Very Low Earth Orbit” and “Suborbital” flight paths. Anything below 160km is generally considered Suborbital; VLEO orbits (160km-400 km) are used for Earth observation, radar, infrared, weather, telecommunications, and rural internet.



Artwork by Russ Arasmith for NASA depicting Project Gemini spacecraft and astronaut, date unknown. Image courtesy of Wikimedia Commons, public domain.

Orbital 2 = 400 km – 1,600 km (4-16 Oberths)

Low Earth Orbit has a very precise definition in terms of period (128 minutes or less) and eccentricity (less than 0.25). Most satellites are in Low Earth Orbit, peaking at around 800km in altitude – but LEO is considered to extend up to 2000 km, putting the outer reaches of LEO into the Orbital 3 sub-level.

Starlink satellites orbit at approximately 550 km, and are amongst the lowest LEO orbits in use.

The inner Van Allen radiation belt starts at around 1000km (10 Oberths) and extends to about 12000km (well into the Orbital 4 sub-level).

Orbital 3 = 1,600 km – 6,400 km (16-64 Oberths)

2000 km marks the entirely arbitrary dividing line between LEO and Medium Earth Orbit. MEOs extend all the way up to Geostationary Orbit (35,786 km). They are defined as having orbital periods of between 2 hours and 24 hours – and yes, that does create a small overlap with LEOs.

This subcategory falls completely within the Van Allen Radiation Belts. Other names for this type of orbit are Mid-Earth Orbit and Intermediate Circular Orbit.

The primary distinction between LEOs and MEOs is that the dominant cause of non-gravitational perturbations of the orbits is solar radiation pressure in an MEO, while atmospheric traces are dominant in an LEO.

This sub-level describes the lower region of MEOs.

When satellites in this sub-level reach the end of their operational life, it is generally cheaper to de-orbit them, permitting them to burn up in the atmosphere. The expectation of this mission terminus plays a critical role in designing those satellites, forbidding such things as nuclear power supplies.

Orbital 4 = 6,400 km – 25,600 km (64-256 Oberths)

The upper region of MEOs is contained almost completely within this sub-level. As such, it is relatively sparsely populated by satellites in comparison to sub-level 3.

The design restrictions on upper MEO satellites are far less restrictive because these are orbits it which it becomes cheaper to put satellites at their end-of-life into a graveyard orbit rather than letting them fall back to earth after a de-orbital maneuver.

Orbital 5 = 25,600 km – 102,400 km (256-1024 Oberths)

Anything aimed at Geostationary orbit that doesn’t quite get there is in the lowest part of this sub-level. Geostationary orbit itself is roughly Orbital 5.133. No orbit above this is considered stable.

A few hundred km further out is a region designated as a Graveyard orbit for defunct satellites; the thrust required to reach these orbits is a lot less than than that required to completely de-orbit a satellite.

Anything with an orbital period of a day or more is defined as being in High Earth Orbit, which are subdivided into a number of complicated designations: Geostationary (GEO), Geosynchronous (GSO), Geostationary Transfer Orbits (GTO), Highly Elliptical Orbits (HEO), and Near-Rectilinear Halo Orbits (NRHO). You don’t have to know what any of these are, really, aside from the obvious and well-known Geostationary and Geosynchronous.

GEOs remain in orbit above a fixed position on the Earth. GSO orbits do not, but they cycle back around to the same fixed point each day.

Satellites in these orbits are used for communications, navigation, scientific research, and of course, military applications.

All Orbits above 357.68 Oberths are eccentric to some degree. That means that they have a significant difference between perihelion and aphelion, the lowest and highest points of their orbit. Which means that periodically, the sun and moon will exert more gravitational force on them at other times because the orbital path will align with those bodies; this creates the instability referred to.

The maximum altitude of High Earth Orbit is another purely-arbitrary number. As the peak aphelion increases, so does the instability – with exceptions resulting from the mass of the orbiting object. There’s no danger of the Moon suddenly wandering off.

Local Interplanetary Scale

I define one unit on this scale as what would be Orbital 6, if such a thing existed, i.e. 102,400 km. I have named the units Lunars.

This scale also uses 4-exponential scale (actually, ideally, it would use exponential-3.5, but that’s too messy and complicated). The midpoint of gravitational attraction between earth and the moon depends on the relative masses – about 80-to-1 in the Earth’s favor, so the midpoint is roughly 1/80th of the distance.

The moon’s orbit has a minimum distance of 363,300 km; 79/80ths of this is 358,758.75 km. And that’s almost exactly 3.5 Lunars.

Oh well.

Local Interplanetary 1: 1 Lunar (102.4 Kkm) – 4 Lunars (409.6 Kkm)

The minimum distance from the earth at which a gravitational field other than that of the planet becomes dominant is, as stated, 358,758.75 km. That happens at 3.5 Lunars.

The moon has a maximum distance from Earth of 405,696 km (3.96 Lunars); the average is 384,400, which is often rounded down to 384,000 or up to 385,000 (because 600km difference at this scale is almost trivial). Call it 3.754 Lunars.

This scale is all about traveling from one planetary body to another, and the entire history of manned spaceflight (so far) is 4 Lunars or less.



Footprint of Buzz Aldrin on the moon. Public domain courtesy of Wikimedia Commons.

Local Interplanetary 2: 4 Lunars (409.6 Kkm) – 16 Lunars (1638.4 Kkm)

Earth-grazing asteroids and dangerous comets.

Local Interplanetary 3: 16 Lunars (1638.4 Kkms) – 64 Lunars (6.5536×10^6 km)

Not very much at all.

Local Interplanetary 4: 64 Lunars (6.5536×10^6 km) – 256 Lunars (2.62144×10^7 km)

Not very much at all.



Image by Wikipedia user Brian0918, Public Domain, courtesy of Wikimedia Commons, rotated & reoriented by Mike

Local Interplanetary 5: 256 Lunars (2.62144×10^7 km) – 1024 Lunars (1.05×10^9 km)

Venus, at its closest to earth, is 390.6 Lunars away.
Mars, at its closest, is 537.1 Lunars away.
Mercury is, at best, 752 Lunars away.

Local Interplanetary 6: 1024 Lunars (1.05×10^9 km) – 4096 Lunars (4.2×10^9 km)

The sun is 1362.3 Lunars away (=1 AU).

The Asteroid Belt sort of fades in and then fades out, without clearly-defined limits. The Core of the belt starts about 2.06 AU out and ends 3.27 AU out, so it straddles the change of scale. 2.06 AU is about 2812.6 Lunars away.

The 4096 Lunars limit of this sub-level is equivalent to 3.0068 AU – call it 3AU.

That’s long enough to reach a counter-earth (if there really was one) without cooking ourselves along the way.

Outer Interplanetary Scale

The boundary between inner and outer solar system is generally considered to be Jupiter. But that doesn’t quite fit our scale, so 1 unit of this scale is 3 AU. I have named these units Bouvards after the mathematician who predicted the planet Neptune from orbital irregularities of Uranus – because I don’t think he gets enough credit for his role in exploring the outer solar system.

From this point on, it becomes less relevant to think of the distance from Earth to an object and more relevant to consider the distance from the sun; by definition, this adds an error rate of ±1 AU, or 0.33 Bouvards, to the measurements.

I have chosen to use 3-exponential for this scale.

Outer Interplanetary 1: 1 Bouvard (3 AU) – 3 Bouvards (9 AU)

The outer edge of the core of the asteroid belt is 3.27 AU from the Sun, or 1.09 Bouvards.



This is an excerpt from a public domain image showing the relative sizes of the planets. Image courtesy Wikimedia Commons.

Outer Interplanetary 2: 3 Bouvards (9 AU) – 9 Bouvards (27 AU)

At its most distant, Jupiter is 3.957 AU or 1.33 Bouvards away from the Earth.

Saturn’s most extreme position is 10.27 AU or 3.42 Bouvards from the Earth.

Uranus is about 20.5 AU, or 6.83 Bouvards away.

That’s three of the four gas giants.

Outer Interplanetary 3: 9 Bouvards (27 AU) – 27 Bouvards (81 AU)

Neptune is about 30.06 AU out, or 10.02 Bouvards.



Image of the Kuiper Belt by the European Southern Observatory released into the Public domain, courtesy Wikimedia Commons.

From that distance and out to 50 AU (16.7 Bouvards) is the Kuiper Belt, and home to comets and dwarf planets like Pluto.

Outer Interplanetary 4: 27 Bouvards (81 AU) – 81 Bouvards (243 AU)

Nothing known.

Outer Interplanetary 5: 81 Bouvards (243 AU) – 243 Bouvards (729 AU)

Nothing known.

Outer Interplanetary 6: 243 Bouvards (729 AU) – 729 Bouvards (2,187 AU)

The inner edge of the Oort Cloud is just barely inside this range at 667 Bouvards.

Outer Interplanetary 7: 729 Bouvards (2,187 AU) – 2,187 Bouvards (6,561 AU)

Oort Cloud.

Outer Interplanetary 8: 2,187 Bouvards (6,561 AU) – 6,561 Bouvards (19,683 AU)

More Oort Cloud.

Outer Interplanetary 9: 6,561 Bouvards (19,683 AU) – 19,683 Bouvards (59,049 AU)

Still more Oort Cloud.

Outer Interplanetary 10: 19, 683 Bouvards (59, 049 AU) – 59,049 Bouvards (177, 147 AU)

The outer edge of the Oort Cloud is roughly thought to be 100,000 AU out (33,333 Bouvards) – but some estimates double that. Nevertheless, the outer limit of this scale is big enough to encompass most, if not all, of it.

The inner limit of this sublevel is 0.9337 light-years from Earth, and the outer is 2.8 light-years from Earth. You may also hear or read the term parsec used from time to time; 2.8 light years is 0.858484 parsecs.

This is the outer edge of our solar system, so far as we know. If Alpha Centauri has an Oort Cloud the size of the Earths (and we have no real reason to assume otherwise), it’s outer edge also falls into this sublevel (just barely) at 2.62 light-years or 55,253 Bouvards. Our Oort Clouds would be only 1.04 light years apart.

Unless the 200,000 AU people are right, in which case our Oort cloud would be partially inside theirs and vice-versa….

Local Interstellar Scale

2.8 light-years is one Romer, named for the first person to calculate the Speed Of Light in a Vacuum; Romer’s value stood for 54 years as the best that science could do. Sub-levels on this scale are 2-exponent.

Local Interstellar 1: 1 Romer (2.8 ly) – 2 Romer (5.6 ly)

Alpha Centauri, the closest significant star to Earth, is 4.2 light years away, right in the sweet spot for this range.

Local Interstellar 2: 2 Romer (5.6 ly) – 4 Romer (11.2 ly)

Barnard’s Star, the second-closest star to Earth, is in this sub-level. But so are 13 other stars, including Wolf 359 (well-known to Star Trek fans), Epsilon Eridani, and Sirius, the brightest star in the night sky. Between them, those 13 stars have 14 known or possible planets – so far.

Local Interstellar 3: 4 Romer (11.2 ly) – 8 Romer (22.4 ly)



A spatial representation of every star within 14 light-years of Sol. Image by Inductiveload, released into the public domain, courtesy Wikimedia Commons.

Alpha Canis Minoris (aka Procyon) – 11.4 ly.
61 Cygni – 11.4 ly.
Epsilon Indi – 11.9 ly.
Tau Ceti – 11.9 ly.
70 Ophiuchi – 16.7 ly.
Altair – 16.7 ly.
Alsafi (Sigma Draconis) – 18.8 ly.
Eta Cassiopeiae – 19.33 ly.
G Eridani – 19.7 ly.
Delta Pavronis – 19.893 ly.

Plus another 68 solar systems within 20 ly of Earth. And another 34 beyond that, the most significant of which are HD219134 and Xi Bootis, at 21.3 and 22 ly, respectively..

Local Interstellar 4: 8 Romer (22.4 ly) – 16 Romer (44.8 ly)

Vega – 25 ly.
Fomalhaut – 25.1 ly.
Pollux – 33.7 ly.
Arcturus – 36.7 ly.
Capella 42.9 ly.
And hundreds more.

Local Interstellar 5: 16 Romer (44.8 ly) – 32 Romer (89.6 ly)

Castor – 51 ly.
Aldebaran – 65 ly.
Regulus – 79 ly.
Mizar – 83 ly.
And thousands more.

Local Interstellar 6: 32 Romer (89.6 ly) – 64 Romer (179.2 ly)

Algol – 93 ly.
K2-18b -120 ly
Markab – 140 ly.
And thousands more.

Radio was invented in 1896, but the power was quite until part of the 1936 Olympics in Berlin were transmitted using an early TV transmitter. That signal has now traveled some 89 light years and has just entered this sub-level. If the earlier signals were detectable (not impossible), they are now 129 light years away and approaching the mid-point of the sub-level.



This is an artist’s impression of the Milky Way Galaxy according to the latest information we have, which I have edited to (a) drop in an enlargement, and (b) mark on that enlargement just how minuscule 129 light years is. Original image by NASA (public domain) courtesy Wikimedia Commons. If you can’t find it, I assure you that it’s there – but that rather proves my point, don’t you think?

K2-18b is significant because, from earth, we have been able to detect gasses in its atmosphere that so far as we know are only produced by simple life forms. That means that from that far away, our equivalents could detect life on earth through its chemistry. They would currently be looking at the earth as it was 120 years ago, in 2025-120=1905, by which time significant pollution would be in the atmosphere; sometime over the next 50 years or so, it would become completely clear that the place was either (a) extraordinarily unlikely, or (b) home to a technological civilization.

And that’s what this scale is all about. I’ve erred on the side of caution by suggesting that the signs of intelligent life might be detectable from even further out – the limits of the scale below are 358.4 ly, which would mean anyone observing earth would now be looking at the year 1666. I think that would be pushing credibility beyond breaking point, but somewhere between that and the 32 Romer lower limit of this sub-level, it becomes possible.

Local Interstellar 7: 64 Romer (179.2 ly) – 128 Romer (358.4 ly)

Izar – 202 ly.
Spica – 250 ly.
Bellatrix – 250 ly.
Canopus – 310 ly.
Acrux – 320 ly.

And probably tens of thousands more.

Regional Interstellar Scale

358.4 light years is one Herschel, named after the astronomer who did more to establish the shape of the galaxy than any other (even if he did get some details wrong).

The major difference between Regional Interstellar distances and Local Interstellar Distances is that we are more interested in noteworthy and unusual stellar phenomena and not so much in ordinary stars.

For the RI scale, I’m going back to 2-exponential because the distances involved here grow really big really fast, but anything larger is too coarse a measurement at low levels..

Regional Interstellar 1: 1 Herschel (358.4 ly) – 2 Herschels (716.8 ly)

The closest known Pulsar to Earth is 398 ly away – a mere 1.11 Herschels. The next closest is just outside this sub-level.

Betelgeuse is 408-548 or maybe 640 light years away. Everything in that distance is securely in this sub-level.

The Pleiades, one of the closest star clusters to Earth, is only 444 light years away.

Polaris is at a distance of 430 light years, while Antares is 550 light years.

At a distance of 610 light years is another cluster, the Beehive Cluster, which contains an astonishing 1000 or so stars, far more than is usual. Other sources place it even closer at 520 light years, but the consensus is currently moving closer to 600 or so.. It’s only about 23 light years in diameter.

Regional Interstellar 2: 2 Herschels (716.8 ly) – 4 Herschels (1,443.6 ly)

At 727 ly from Earth, the second closest pulsar can be found. It is also the most massive discovered to date. Two more pulsars and a Neutron Star also lie within this sub-level.

Rigel is 848±65 light years from Earth. 860 is the usual approximation.

Mintaka, the third of the stars in Orion’s Belt, is a six-star system 1200 light years from Earth. In combination, it’s six stars are around 250,000 times as bright as the sun.

Alnitak, one of the systems that make up Orion’s Belt, is 1260 light years away. It is a triple-star with the more distant member orbiting the other pair once every 1500 years.



Image by Zegery, released under the Creative Commons Attribution 4.0 International license, courtesy Wikimedia Commons.

The Orion Nebula, a well-known interstellar nursery, is 1344 light years from Earth. It’s actually an astonishingly small object, only about 25 light-years across.

Regional Interstellar 3: 4 Herschels (1,443.6 ly) – 8 Herschels (2,867.2 ly)

The closest known Black Hole is 1560 light years away, part of a binary star system. Another such pair is 1840 light years from us.

Alnilam, the second star of Orion’s Belt, is 2000 light years away. It’s the 29th brightest star in the Earth sky despite being much farther away than the others in the Belt.

There are two known pulsars in this sub-level, at 2055 and 2316 ly respectively. The latter is also named Lich after the Undead monster.



Image of the Ring Nebula by NASA’s Hubble Space Telescope (public domain), courtesy Wikimedia Commons.

The Ring Nebula in the constellation of Lyra is 2567 light years away.

Deneb, one of the most distant stars visible to the naked eye, is not much further at 2600 light years.

Regional Interstellar 4: 8 Herschels (2,867.2 ly) – 16 Herschels (5,734.4 ly)

3400 light years away is a supernova remnant; the explosion was reported by the Chinese in 393 CE and the remnant is now known as the Wei Asterism – there doesn’t seem to be a great deal left.

There is another pulsar 1060 parsecs (3457 ly) away. Three others also lie within this sub-level, and one more – the black widow pulsar – that might be.

The width of the galactic arm containing the sun, the Orion Arm, is 3500 light-years across. However, the Sun is quite close to the inner rim of the arm. Unfortunately, I couldn’t find an estimate for how close the nearer edge was. Still, since 1 Herschel is only 10.24% of the greater distance, it seems likely that it is one Herschel or less to that near boundary.

3800 light years finds another binary-star black hole, as does 4700 light years. At 5150 light years, there is an isolated black hole, and at 5400 light years, another binary pairing. Right on the edge of this sub-level is one more binary pair which includes a black hole, 5720 light years away..

The distance to the next nearest galactic arm (Carina-Sagittarius) is estimated to be 1400 parsecs or 4566.2 light years.

Some of the closest super-massive stars to Earth can also be found in this sub-level. There’s HD229059 (69 Suns) at 3,000 light years, Trumpler 27-27 (81 Suns) at 3900, Trumpler 27-23 (64 suns) also at 3900, HR6187A (63 suns) at 4300, and 5 more. The most distant of them is 5400 light-years away, and it is considered a Runaway Star from Cygnus OB2, a very young star cluster that is one of the largest known (ten times more massive than the Orion Nebula), which at 5120 light years, is also to be found in this sub-level.

Regional Interstellar 5: 16 Herschels (5,734.4 ly) – 32 Herschels (11,470 ly)

At 5900, 6500, and 7500 light years, there are another 11 supermassive stars. There’s also HD190429A at 7800 ly, HD93160 at 8,000, WR22A at 8300, HD303308 at 9200, two more at 10,000, one at 10,400, and no less than four at 11,000 light-years.



A mosaic of multiple images taken by the Hubble Space Telescope (NASA, public domain) of the Crab Nebula. Image courtesy of Wikimedia Commons.

This sub-level also contains five more Pulsars, including the Crab Nebula Pulsar and Cosmic Cannonball, which is moving away from the supernova remnant at 672±115 km per second, making it one of the fastest-moving stars every found – though initial estimates of its speed were an even higher 1500 km/s. At the moment, our theories don’t explain how it’s possible for a supernova to induce such speed.

The closest galactic arm on the other side of the Orion arm (the Perseus Arm) is about 6400 light years away, down from older estimates of 13,000 light years.

At 7,300 light years, 7,800 light years, 8100 light years, 8800 light years, and 11000 light years there are binary systems with black holes. At 8150 and 9260 light years are isolated Black Holes. The 7,300 light-year system is perhaps the most famous of these, Cygnus X-1.

Regional Interstellar 6: 32 Herschels (11,470 ly) – 64 Herschels (22,940 ly)

The Orion Arm is relatively short at 20,000 light years in length. This distance is enough to go from one end of it to the other.

There are 5 known pulsars and neutron stars within this sub-level.

V762 is the most distant individual star that can be seen from Earth with the naked eye at 16000 light years removed. It’s an absolutely massive variable star that is about 100,000 times as luminous as the sun.

Intergalactic Scale

Even a galaxy or galactic object that is not so far away (as galaxies go) is a LONG way away from Earth. This scale encompasses the entirety of the Milky Way and the nearest such collections of objects. I have decided to name this unit the Messier. Once again, I’ve found it more useful to use 3-exponential for this scale.

I also think it worth quoting the caveats given on the Wikipedia page, List of Nearest Galaxies:

“….aims to reflect current knowledge: not all galaxies within the 3.8 Mpc radius have been discovered. Nearby dwarf galaxies are still being discovered, and galaxies located behind the central plane of the Milky Way are extremely difficult to discern. It is possible for any galaxy to mask another located beyond it. Intergalactic distance measurements are subject to large uncertainties. Figures listed are composites of many measurements, some of which may have had their individual error bars tightened to the point of no longer overlapping with each other.”

In other words, this is the best information we currently have but a lot of it remains uncertain and subject to change. Some galaxies currently thought to be part of the local group may be de-listed, others now thought to be part of a neighboring group may be welcomed to the neighborhood, and distances can be radically altered as better information comes in.

Most of all, the number of galactic objects at a given distance is subject to massive revision. Right now, we haven’t even identified all the phenomena that we should be listing!

It is also worth remembering when perusing the lists that follow that only four galaxies are visible to the naked eye from Earth. Four.

Intergalactic 1: 1 Messier (23K ly) – 3 Messiers (69K ly)

The Galactic Core is 26,000 light years from Earth.

The outer edge of the Milky Way is about 27,000 light years from Earth on the closer side.

Intergalactic 2: 3 Messiers (69K ly) – 9 Messiers (207K ly)

70,100 light years gets you to Draco II, one of the closest and dimmest known galaxies.

75,000 light years away is another close neighbor galaxy, Segue 1.

The outer edge of the far side of the Milky Way is about 77,000 light years away.

The Sagittarius Dwarf Spheroidal Galaxy is 78,000 light years from us.

The Dwarf Galaxy Hydrus I, is 90,000 light-years away. 90,700 light years in a different direction will take you to either the Carina III dwarf.

Travel 98,000 light years and you reach the Ursa Major II Dwarf Galaxy. Or the Triangulum II Dwarf Galaxy, if you go in that direction instead.

102,000 light years away is the Reticulum II Dwarf Galaxy.

The entire Milky Way galaxy is 106,000 light years across.

Between 107,000 light years and 157,000 light years are 9 other galaxies, of which the most notable is Willnan 1 at 124,000 light years, which is an ultra low0-luminosity galaxy – in other words, it’s much darker and dimmer than usual.



Image of the Tarantula Nebula taken by the James Webb Space Telescope (NASA, public domain) courtesy Wikimedia Commons.

The Large Magellanic Cloud is 163,000 light years away. The Tarantula Nebula forms the Southeastern corner of the cloud (from our perspective), and is home to a huge number of supermassive stars, including the largest single star ever discovered at 196 Suns.

Two more galaxies are located at 179K and 186K light years respectively. At 197K light years, you will find Bootes I, which used to be a dwarf galaxy but which appears to have been torn apart – “disrupted” is the official term – by the Milky Way. Intergalactic Road-kill.

The Small Magellanic Cloud is 205,000 light years away, as is the Ursa Minor Dwarf Galaxy.

Intergalactic 3: 9 Messiers (207K ly) – 27 Messiers (621K ly)

At distances ranging from 235K to 258K light years are 7 minor galaxies.

The Pisces Overdensity is a clump of stars of uncertain history – possibly a disrupted dwarf Galaxy, perhaps not. It’s 260,000 light years away.

Between 267K light years and 326 light years are 9 minor galaxies. 330,000 light years takes you to the Carina Dwarf Galaxy.

Between 333 and 466 light years distance are 10 more minor galaxies.

490,000 light years away from us is the Cenes Venatici II Dwarf Galaxy.

You find another 6 minor galaxies between 492K light years and 597K distance from Earth.

Intergalactic 4: 27 Messiers (621K ly) – 81 Messiers (1.863×10^6 ly)

From 682K light years to 820K light years are another 6 minor galaxies.

The Milky Way is surrounded by a dark matter halo at a distance from the galactic center of 952,000 light years.

Beyond that, another 7 minor galaxies can be located within this sub-level.

Intergalactic 5: 81 Messiers (1.863×10^6 ly) – 243 Messiers (5.59×10^6 ly)

This sub-level takes us into the more remote parts of the local group, and a few galaxies which are not part of that group. It was the latter that signaled that it was time to change scales once again.

The nearest such galaxy is Cassiopeia 1, an isolated galaxy located 5.19 M light years from earth. Between us and that distance are 58 other galaxies, including two of the three largest in the local group – the Andromeda Galaxy at 2.5 M light years and the Triangulum at 3.2 M light years.



Everyone’s seen pictures of the Andromeda Galaxy, so I thought I’d do something different. This is an image of the Triangulum Galaxy by Nielander and released to Wikimedia Commons under the Creative Commons CC0 1.0 Universal Public Domain Dedication.

Beyond Cassiopeia 1 but within this sub-level is one more galaxy, Leo P, a small star-forming irregular galaxy first discovered as an ultra-compact high velocity cloud of Hydrogen Gas.

Transgalactic Scale

While there are still some of the more distant members of the local group in the early sub-levels, increasingly this scale is about larger structures within the universe, which we are only just beginning to understand.

At this distance, we don’t yet know what’s interesting and what’s routine. Rather than populate the individual sub-levels with irrelevancies, I’ll just pop in a few landmarks.

For this scale, the units have been named Hubbles (one Hubble = 5.6 M ly) and 5-exponential is the progression.

Transgalactic 1: 1 Hubble (5.6 M ly) – 5 Hubbles (28 M ly)

97 galaxies lie between 1 and 2.2 Hubbles, which is as far as Wikipedia’s table took me. The most distant member of the Local Group is either Leo P (see above) or possibly IC5152 at 5.68 M light years.

This sub-level therefore contains the entire Local Group, less than 1.0143 Hubbles wide.

For the first time ever, I’m delberately overflowing the screen real estate permitted by the site theme – this image simply wasn’t legible otherwise. Image by Richard Powell, courtesy Wikimedia Commons and used under the Creative Commons Attribution-Share Alike 2.5 Generic license.

Transgalactic 2: 5 Hubbles (28 M ly) – 25 Hubbles (140 M ly)

53.8 M ly takes you to the center of the Virgo Cluster. The Cluster contains 1300+ galaxies, possibly as many as 2000. It is

“…an aggregate of at least three separate subclumps: Virgo A, centered on M87, a second centered on the galaxy M86, and Virgo B, centered on M49, with some authors including a Virgo C subcluster, centered on the galaxy M60 as well as a Low Velocity Cloud (LVC) subclump, centered on the large spiral galaxy NGC 4216.

M87 is a giant elliptical galaxy which contains a supermassive black hole. It’s subclump is the dominant one of the entire Cluster, and it is about ten times the mass of the others. The three subgroups are in the process of merging into a single cluster, and are surrounded by isolated galaxies and galactic groups that are gravitationally bound to (and therefore part of) the Cluster, and which are likely to be absorbed at some point in the future.

Our Local group is neighbors to the Virgo Cluster but not a part of it (and it took a lot of research to discover that, for reasons that will become obvious).

The Formax Cluster is 62 M ly from earth; the Antilia Cluster is 133 ly away.

75 M ly from earth is the possible center of the Local Void, a region that starts at the edge of the Local Group and extends for another 150 M or 490 M or 980 M light years (the far edge is a bit fuzzy in definition)! This region has significantly fewer galaxies than normal.

The Virgo Supercluster, which contains more than 100 galaxy groups including the Virgo Cluster and Earth’s Local Group, has a diameter of 110 M ly. This Supercluster is one of about 10 million in the observable universe.

Transgalactic 3: 25 Hubbles (140 M ly) – 125 Hubbles (700 M ly)

A 2014 study found that the Virgo Supercluster is itself a component of a still larger group, Laniakea, which is centered on the Great Attractor. Laniakea contains about 100,000 galaxies. The lowest estimate for the distance to the Great Attractor is 150 M ly, and the highest is 250, so it is definitely a feature of this sub-level.

In fact, the span of the Laniakea Supercluster is about 500 M ly along it’s longest axis, so it also fits comfortably, in it’s entirety, within this sub-level.

Laniakea is in turn part of a larger structure, the Pisces-Cetus Supercluster Complex, also known as a Galaxy Filament. It is adjacent to the Perseus-Pegasus Filament. The PC Supercluster Complex is about 150 M ly wide.

The Centaurus Cluster is 171 M light years away.

The Hydra Cluster is 190 M light years away.

Transgalactic 4: 125 Hubbles (700 M ly) – 625 Hubbles (3.5 B ly)

The PC Supercluster is long and thin in shape – so much so that you have to go to this entirely new sub-level to contain it. It has an estimated length of 1 B ly, making it one of the largest structures in the observable universe.

The Sloan Great Wall is 1.3 B ly in size and is basically a wall of galaxies. If you think of the universe as a whole heap of soap bubbles (voids) connecting to each other, walls and filaments are the soap of the bubble.

Clowes-Campusano LQG is 2 B ly in size – it’s a group of 34 quasars.

U1-11 LQG, another group of quasars is 2.5 B ly.

Only two structures in the observable universe are known to be larger than these.

Transgalactic 5: 625 Hubbles (3.5 B ly) – 3125 Hubbles (17.5 B ly)

The first of those larger structures is the Huge-LQG, a 4 B ly -across quasar group, with 73 quasars.

But the winner (at least at the moment) is the Hercules-Corona Borealis Great Wall, a Galaxy Filament that is 10 B ly in length, and 9.6-10.5 B light years away.

Transgalactic 6: 3125 Hubbles (17.5 B ly) – 15625 Hubbles (87.5 B ly)

Or maybe it’s 15-17.675 B light years – if you factor out the expansion of the universe.

Transgalactic 7: 15625 Hubbles (87.5 B ly) – 78125 Hubbles (437.5 B ly)

The Observable Universe is about 93 B light years (16,607 Hubbles) in diameter. Beyond that, science claims, it’s impossible to know anything about what’s there – it doesn’t exist so far as we’re concerned.

Summary

So there you have it.

• The Planetary Scale: Aircraft 1, 2, 3, 4, 5, and 6 from 1-16525 Wrights.
• The Orbital Scale: Orbital 1, 2, 3, 4, and 5, from 1 to 1024 Oberths.
• The Local Interplanetary Scale: 1, 2, 3, 4, 5, and 6, from 1 to 4096 Lunars.
• The Outer Interplanetary Scale: 1,2 ,3, 4, 5, 6, 7, 8, 9, and 10, from 1 to 59049 Bouvards.
• The Local Interstellar Scale: 1, 2, 3, 4, 5, 6, and 7; from 1 to 128 Romer.
• The Regional Interstellar Scale: 1, 2, 3, 4, 5, and 6; from 1 to 64 Herschels.
• The Intergalactic Scale: 1, 2, 3, 4, and 5, from 1 to 243 Messiers.
• The Transgalactic Scale: 1, 2, 3, 4, 5, 6, and 7; from 1 to 78125 Hubbles.

6(+1)+5(+1)+6(+1)+10(+1)+7(+1)+6(+1)+5(+1)+7 = 59 exponential increases to define the observable universe and the distance to anything and everything within it.

If I had used 2-exponential throughout, that would be 2^59 = 576,460,752,303,423,488 times the original 1 Wright.

If I had used 3-exponential throughout, that would be 3^59 = 14,130,386,091,738,734,504,764,811,067 times 1 Wright.

But, in fact, I used 2 sometimes and 4 or 5 sometimes. Nevertheless, it’s a totally preposterous number that I refuse to have anything more to do with.

59 Skill or Tech levels to define the ability to navigate anywhere in space.

The universe is thought to be 4.35 x 10^17 seconds old. If I divide that by 2^59, the matching precision for time travel would be 0.7546 seconds being the equivalent of 1 wright. But that’s only the past – what about the totality?

27.0 seconds – based on the most pessimistic estimate of the remaining lifetime of the universe. It well could be longer.

Models of Skill

I would contend that navigating at the planetary scale is a completely different problem to navigating in space, and that navigating interstellar distances in any practical way is also a fundamentally different practice. You might disagree, but play along for a minute until you see where I’m going with this.

If your current technology is measured, say, in Romer – which is what I would consider to be the case in Traveler, to name one game system – then you have Interstellar Navigation and Interstellar Engineering as the basic skills. The next smallest scale, Bouvards, is considered a freebie, a simpler subset of the Romer skills.

Local Interplanetary Navigation and Engineering is a separate skill, and gives you the next smaller one – Orbital – as a freebie.

That takes you down to basic aerial navigation at the planetary scale.

Okay, but what if you’re more advanced than that? Let’s talk Star Wars, and Herschel-scale skills.

Regional Interstellar Engineering (better known in this case as Hyperspace Drive Engineering) and Navigation covers Herschels.

You get the next smaller scale, Romers, free. They are considered a subset of the skills already listed.

You have to Buy Bouvard-scale Engineering and Navigation, probably described as Planetary-system Navigation and Sub-light Drive engineering.

That gives you both Inner and Outer system skills, because you get the next smaller scale for free, as usual.

Orbital is the next one that’s not covered, so you have Thrusters Engineering and Orbital Astrogation skills. But they give you the next scale down for free, and that’s the planetary scale, and ordinary Navigation.

This basic methodology means that most campaigns will define two or three engineering skills (to cover the maintenance and repair of wildly differing technologies) and two or three navigational skills to let you plot a course to where you are going.

Throw in the following:

The tech level within a Scale defines how far you can safely transit without incurring systems damage. Experimental systems may permit one additional step or may act to increase the reliability of the existing systems. Navigational skills cannot exceed the tech level; any additional skill levels beyond this limit provide a +1 to skill checks without increasing the skill description that you have. So Warp Drive Engineering (for a Star Trek campaign) 3+3 means that you can navigate up to 8 Herschels, and get +3 on your chances to do so. Smaller trips also add bonuses – so if you’re only going 4 Herschels, you’re only using skill 2, leaving an extra +1 for your rolls.

…and what you have is a universally-adaptable skill subsystem for the maintenance and navigation of any distance throughout the universe. If a trip is longer than you can navigate, you have to break that trip into smaller chunks and plot new courses when you reach the end of each stage of the journey.

The exponential increases in distance mean that it isn’t and should not be easy to go from one tech sub-level to the next. It will take time and technological improvements. Going from one scale to another may involve whole new technologies, even if you’re measuring them on the same old scale – being able to go from Warp Factor 3 to Warp Factor 5 as a top speed, for example.

So let’s end with this: the defined units (not all of which will be used in every campaign).

1 Wright = 6.4 m (21 feet).
1 Oberth = 15625 Wrights= 100km.
1 Lunar = 1024 Oberths = 102,400 km.
1 Bouvard = 4096 Lunars = 3 AU
1 Romer = 59049 Bouvards = 177,147 AU = 2.8 ly.
1 Herschel = 128 Romer = 358.4 ly
1 Messier = 64 Herschels = 22, 940 ly
1 Hubble = 243 Messiers = 5.59 M ly
16,607 Hubbles = the observable universe.

9 units – ten, if you count the meter or the foot – to define reality. My work is done.