Signs like this normally show the distance to places on earth's surface. This sign also has an arrow pointing away from earth and towards "space", with a distance of 62 miles (100 km), due to "astronaut vandalism". The 62 mile distance is the Kármán line, one of the conventional demarcations of the beginning of "outer space".
We think of space as being very far away. This comic puts into perspective that it's really a lot closer to space than to many destinations we're used to getting to by car or airplane. We think of 62 miles as being an easy trip on the ground, but that same 62 miles is incredibly hard when going vertically, against the force of gravity.
Although most authorities use the FAI definition of space - the Kármán line - since the FAI is the international organization of record for aeronautics, there are good scientific reasons for the U.S. Air Force definition. The line is named for Theodore von Kármán, who originally calculated the height at which an vehicle would have to travel faster than orbital velocity to generate lift from wings, therefore making the vehicle an object in orbit rather one using air to generate lift. Von Kármán originally calculated this height as 51.9 miles (83.6 km) - closer to the USAF definition than to what is now called the Kármán line. Additionally, the boundary between the mesosphere and the thermosphere is traditionally taken to be 53 miles (85 km), also close to the Air Force definition. On the other hand, some newer research suggests the mesopause (the line between the mesosphere and thermosphere) may have peaks between 53 and 62 miles (85-100 km). Also the turbopause - the line where gas molecules cease mixing atmospherically and begin stratifying by molecular weight as if they are in orbit - is generally taken to be about 100 kilometers (62 miles).
All of the atmospheric boundaries are variable, however, changing from day to day and season to season with no clear boundary. Additionally, objects cannot reliably orbit below 130-150 km (80-93 miles) due to drag from even the sparse atmosphere in the lower thermosphere. Despite this comic associating "space" with having a definite start the way you might definitely know when you cross the city limits of a town, the reality is that the transition from atmosphere to space takes place gradually over tens of kilometers. Interestingly, since it is too high for aircraft and high altitude balloons, but too low for spacecraft in orbit, this "near space" transition region is one of the least-visited and least-used regions of the larger atmosphere. This comic thus both points out that the limit where space starts is arbitrarily chosen and also that space is often much closer than, for instance, two nearby cities in some randomly chosen location in the US.
The two distances shown on the signpost can occur only at certain points on Earth. One possible location is Grenada, MS, which is about 100 miles from Memphis, TN and about 114 miles from Jackson, MS. Alternatively "Jackson" could mean Jackson, TN, in which case Tupelo, MS or Kenneth, MO are both viable options for the location of the signpost. However, in Tupelo the roads to Jackson and Memphis meet at a right angle, instead of pointing in opposite directions as in the comic.
Is there an actual place that this is referencing? --18.104.22.168 05:14, 30 May 2014 (UTC)
- This seems to be Grenada, MS. 22.214.171.124 (talk) (please sign your comments with ~~~~)
Grenada is possible - but given the NASA connection to Winona, and the fact that the numbers are exact (but reversed), I think it's a better candidate. -- Thesetwoutes (talk) (please sign your comments with ~~~~)
- There is Camp McCain 17 miles north of Winona which would have the correct distances. STEN (talk) 10:20, 30 May 2014 (UTC)
Space is usually indicated by pointing straight up. This sign points a little to one side as well though. Since these places the other pointers reference are in the northern hemisphere, and from the comic's point of view Memphis (North) is on the left and Jackson (south) is on the right, the 'Space' sign is pointing slightly south. Assuming the sign would point straight up at the equator, measuring the angle from the direction the sign is pointing to the vertical axis, and doing some math, would give the latitude of the sign and a better indication of its exact location. 126.96.36.199 06:49, 30 May 2014 (UTC)
There doesn't seem to be anywhere named anything like "space" 53 miles from Jackson along this line. (Approximately Goodman, MS, birthplace of John Lomax.) Is the marker supposed to have been brought in specifically for this purpose? I thought it would make more sense if the arrow had just been turned up. (For the numbers reversed theory, 36 miles from Jackson appears to be completely rural, though features the site of Casey Jones' death.) 188.8.131.52 12:00, 30 May 2014 (UTC)
My first thought that this was a reference to the blues musician Robert Johnson. According to legend, Johnson met the devil at a crossroads in Mississippi to exchange his soul for talent in blues music. There are a few different real crossroads that have been put forth as the legendary location. These include Dockery Plantation, Hazelhurst, Beauregard, Clarksdale, and Rosedale. None of these locations, though, match the distances shown in the comic (Dockery Plantation is probably the closest). 184.108.40.206 (talk) (please sign your comments with ~~~~)
I think Occam's Razor suggests the Robert Johnson Crossroads. Space's distance, unless the numbers have hidden meaning, is irrelevant. So, Randall could have chosen literally any point on Earth -- Istanbul, Port-au-Prince, or Perth. He chose and illustrated a simple crossroads in the Mississippi Delta. We do not know whether the distances indicated are by road or as the crow flies, nor where in Memphis or Jackson are the targets -- Perhaps it's not official center of each, but Beale St. In Memphis, and Hal & Mal's in Jackson ... The important places. Miamiclay (talk) 21:02, 9 July 2014 (UTC)
Here is a map showing the distances from each city (with sPace as Pace.)  -- Jdallman2570 (talk) (please sign your comments with ~~~~)
So we can follow that sign, have a good day and go to space today? 220.127.116.11 13:56, 30 May 2014 (UTC)
I think the point Randall is trying to make here (as he did repetitively in the past) is that space (100 km) is actually not that far away as it "seems", at least closer than the cities on the other two arrows. 18.104.22.168 (talk) (please sign your comments with ~~~~)
He also rather neatly (with the help of the USAF) makes the point that there is no single hard line where space starts. Jim E (talk) 15:45, 30 May 2014 (UTC)
I'm wondering whether Jackson 115 might relate to the Jackson 5. --Dfeuer (talk) 15:05, 31 May 2014 (UTC)
The driving distance from Jackson, Mississippi to Memphis, Tennessee is 210 miles. I figure the extra three miles added was done so as to accommodate the disposal of the bodies in the trunk - or the children in the back - and/or purchase a gun. 22.214.171.124 (talk) (please sign your comments with ~~~~)
I don't want to delete this, but the following statements do not explain the comic and even do not belong to a trivia section.
- Possible interpretations
There may be an Elvis aspect to this comic. The mileages are approximately consistent with the signs being in Tupelo, Mississippi, birthplace of Elvis Presley. Tupelo is about 100 miles from Graceland (Elvis' home) in Memphis, Tennessee. Tupelo is also a bit over a hundred miles from the International Rock-A-Billy Hall of Fame in Jackson, Tennessee. The mileages given by Google maps, however, don't exactly match the mileages on the sign in the comic. Instead of 98 & 115 (in the comic), Google maps gives 101 & 104.
Another possible explanation is a simple mixup. Winona, Mississippi is the hometown of astronaut Donald H. Peterson, who is a retired Air Force officer and pilot, and served as an astronaut in the early Shuttle program. From Winona, it is 115 miles to Memphis International Airport, and 98 miles to Jackson-Medgar Wiley Evers International Airport (source). Thus, the sign would be reasonably located in Winona, albeit with an error, and Peterson would have vandalized it (and some visiting USAF buddy of his could change it back).
The road from Jackson to Memphis is I-55 (northwards); the distance (according to Google Maps) is 210 miles. That 98+115=213 may indicate that the location is 3 miles off I-55. There is a place called "Pace" near Cleveland which is around 79 miles from Winona. The "astronaut vandalism" may have been to prefix "Pace" with an "s" to form "sPace", and then to rotate the sign. The spacing on the signs in the cartoon is consistent with the idea that the "s" was added; it is a little cramped. The "P" of "space", "M" of "Memphis" and "J" of "Jackson" are perhaps a little larger than the other letters, indicating that those might have been the original initial majuscule letters.
Based purely on the mileages, it is most likely that the sign is located in or near Grenada, MS. This makes the mileages nearly correct when using US-51 as opposed to I-55 to get to Memphis and Jackson, and also is about 62 miles from Pace, MS via Mississippi Route 8. It is unlikely, however, that a sign in Grenada would include the mileage to such a small town as Pace from such a great distance. Cleveland would be a much more useful control city for motorists. Additionally, since the viewer is looking east, Pace would be behind the viewer. Assuming the one doing the vandalism did more than simply turn and add a letter to the sign, it is possible that they also detached it from the southbound-side of the pole (where it could be viewed pointing to the west) and reattached it to the eastbound side, as shown here.
--Dgbrt (talk) 23:06, 2 June 2014 (UTC)
I would like to add another explanation to the air force vandalism part of the comic and explain the two values, 50 miles and 62 miles a bit further (I'm a graduating aerospace engineer for reference). As stated, there are two different definitions of where space begins. The "american" definition used by NASA and US Air Force says space begins at an altitude of 50 miles (80 km), the other definition (used by, for example, Europeans) says space begins at an altitude of 62 miles (100 km).
Roughly at an altitude of 50 miles the control surfaces of an aircraft (rudder, ailerons, elevator) become useless because air pressure is to low and they can't create aerodynamic forces or momenta high enough to control the aircraft. If you want an aircraft/spaceship to go higher, you need to implement other means of control, like thrust vectoring, gyroscopes or a reaction control system (RCS). It is the american definition, because they were the first ones to successfully fly high altitude aircraft (like the X-15) and had to consider this to remain control of the aircraft. The US still designates everyone who travels above 50 miles as an astronaut (according to Wikipedia).
The other definition is, as said, based on the Kármán-line. Its a bit difficult to explain as a non-native English speaker, but I will try to give my best. An aircraft needs to fly at a certain velocity to generate enough lift to keep flying. With lower air pressure at increasing altitudes lift decreases, so the crafts velocity has to increase. At an altitude of 62 miles the speed to generate enough lift is the same as the orbital velocity at the same altitude. Which means, below this altitude an aircraft is slower than orbital velocity (at the aircraft's altitude), while above an aircraft would go faster than orbital velocity, an thus, it would gain altitude, not because of lift, but because of orbital mechanics. You could also say, if you want to go higher than 62 miles, you don't need wings any more, just an engine that's powerful enough to hold the velocity.
Because there is no general consent about which definition is used among space agencies and air-forces, astronauts who went into space with "real" spacecraft and did at least one full orbit might want to be exclusive, while air-force pilots, who only did a small "hop", want to be called astronauts as well and thus altering the number over night. 126.96.36.199 (talk) (please sign your comments with ~~~~)
Too bad, I can't find any confirmation for the "american" definition. A professor of mine explained it that way. So what's best, delete my whole text or add ? 188.8.131.52 (talk) (please sign your comments with ~~~~)