explain xkcd - User contributions [en]

1276: Angular Size

2015-07-22T06:18:54Z

108.162.219.151: /* Explanation */ Adding U.S. customary units.

{{comic
| number = 1276
| date = October 11, 2013
| title = Angular Size
| image = angular size.png
| titletext = If the celestial sphere were mapped to the Earth's surface, astronomy would get a LOT easier; you'd just need a magnifying glass.
}}

==Explanation==
This comic is a comparison of the {{w|angular diameter|angular diameters}} (or apparent diameter) of various celestial objects at the surface of the earth relative to a vertex at the center of the Earth as diagrammed in the opening panel. The objects' scales are compared to actual objects on earth. Each size given is for the object at its closest approach to earth.

London's {{w|M25 motorway}} is around 60 km (35 miles) across, a {{w|soccer field}} is about 100 meters long (109yd.), a {{w|Table tennis table|ping pong table}} is 274 centimeters (9ft.) long, a {{w|laptop}} is about 35 centimeters across (13.75in.), the {{w|tilde}} symbol on a keyboard is about 5 millimeters (197 mils) long, and a cell of ''{{w|Escherichia coli|E. coli}}'' is about 2 microns long (78.75 millionths of an inch).

A simple {{w|Intercept theorem|formula}} can be used to find the size on earth of a celestial object when the size of or distance to the object is known. This is done by taking the radius of the earth, multiplying by the diameter of the object, and dividing by the distance to the object from the center of the earth.

The space objects referenced in the panels are:

*The {{w|Sun}} and the {{w|Moon}}, and also the open cluster {{w|Messier 25}}, have approximately the same size (around 0.5 degrees of arc) when seen from the Earth.

*{{w|Mercury (planet)|Mercury}}, {{w|Venus}}, {{w|Mars}}, {{w|Jupiter}}, {{w|Saturn}}, {{w|Uranus}}, and {{w|Neptune}} are the other planets of the {{w|Solar System}}.

*{{w|Io (moon)|Io}}, {{w|Europa (moon)|Europa}}, {{w|Ganymede (moon)|Ganymede}}, and {{w|Callisto (moon)|Callisto}} are the main moons of Jupiter; {{w|Titan (moon)|Titan}} is the largest moon of Saturn; and {{w|Triton (moon)|Triton}} is the largest moon of Neptune. {{w|Ceres (dwarf planet)|Ceres}} and {{w|Pluto}} are {{w|dwarf planet}}s.

*{{w|Phobos (moon)|Phobos}} and {{w|Deimos (moon)|Deimos}} are the moons of Mars. {{w|Eris (dwarf planet)|Eris}} is another dwarf planet. {{w|R Doradus}} and {{w|Betelgeuse}} are giant stars, respectively around 180 and 640 light-years away. R Doradus is the star with the largest apparent diameter (other than the sun, of course).

*{{w|4942 Munroe}} is an asteroid [http://blog.xkcd.com/2013/09/30/asteroid-4942-munroe/ named] after xkcd author [[Randall]] Munroe. {{w|Proxima Centauri}}, {{W|Alpha Centauri|Alpha Centauri AB}}, {{w|Barnard's star}} and {{w|Sirius}} are nearby stars (all within 10 light-years from the Sun).

*{{w|HD 189733 b}}, {{w|Gliese 581 g}}, {{w|Gliese 667 Cc}}, {{w|82 G. Eridani#Planetary_system|HD 20794 c}}, {{w|Tau Ceti#Planets|Tau Ceti c}}, and {{w|KOI-1686.01}} are {{w|extrasolar planet}}s; the parenthetical names are references to the comic [[1253: Exoplanet Names]]. However, some of the planets' parenthetical names do not match the table in the previous comic. For example, HD 20794 c is called "Legoland" rather than "Moonchild" in [[1253: Exoplanet Names]]. The {{w|black hole}} at the center of our Galaxy is {{w|Sagittarius A*}}, a massive object containing a mass more than 4 million times of our Sun.

*{{w|Voyager 1}} and {{w|Voyager 2|2}} are space probes launched in 1977, and currently around 125 and 100 {{w|astronomical unit}}s away, respectively.

The title text states that astronomy would be much easier if the celestial sphere were mapped to the earth - like a giant {{w|globe}}. Due to the distance of the stars you would just need magnifying glass to see the areas representing distant stars instead of an expensive powerful telescope to see huge distances.

Approximate values for the mappings to the Earth sphere (based on mean Earth radius at 6,371.0 km or 3,958.8mi.):
{| class="wikitable sortable"
|-
! Panel
! Object
! Distance
! Diameter
! Size at Earth sphere
|-
| rowspan="4"| Panel 1
|| Sun
|| 149,600,000 km (9.296×10^7mi.)
|| 1,392,684 km (865,373.7mi.)
|| 59.3 km (36.8mi.)
|-
|| Moon Semi-major axis
|| 384,399 km (238,854mi.)
|| 3,476.28 km (2,160.06mi.)
|| 57.6 km (35.8mi.)
|-
|| Moon Perigee
|| 363,295 km (225,741mi.)
|| 3,476.28 km (2160.06mi.)
|| 60.9 km (37.8mi.)
|-
|| Messier 25
|| 2,100 light-years 19.867 × 10^15 km (12.158×10^15mi.)
|| 19 light-years 179.753 × 10^12 km (111.693×10^12mi.)
|| 57.6 km (35.8mi.)
|-
| rowspan="7"| Panel 2
|| Mercury closest approach
|| 92 million km (57 million mi.)
|| 4,879.4 km (3,031.9mi.)
|| 0.34 km (370yd.)
|-
|| Venus closest approach
|| 41 million km (25 million mi.)
|| 12,103.6 km (7,520.83mi.)
|| 1.9 km (1.2mi.)
|-
|| Mars closest approach
|| 56 million km (35 million mi.)
|| 6,792.4 km (4,220.6mi.)
|| 0.77 km (840yd.)
|-
|| Jupiter
|| 778,547,200 km (4.8377×10^8mi.)
|| 139,822 km (86,881.4mi.)
|| 1.14 km (1,250yd.)
|-
|| Saturn
|| 1,433,449,370 km (1.5676×10^12mi.)
|| 120,536 km (74,897.6mi.)
|| 0.54 km (590yd.)
|-
|| Uranus
|| 2,876,679,082 km (1.7875×10^9mi.)
|| 51,118 km (31,763mi.)
|| 0.11 km (120yd.)
|-
|| Neptune
|| 4,503,443,661 km (2.7983×10^9mi.)
|| 49,528 km (30,775mi.)
|| 0.07 km (230ft.)
|-
| rowspan="8"| Panel 3
|| Io
|| 778,547,200 km (483.77×10^6mi.)
|| 3,643 km (2,264mi.)
|| 29.8 m (74.8ft.)
|-
|| Europa
|| 778,547,200 km (483.77×10^6mi.)
|| 3,122 km (1,940mi.)
|| 25.5 m (83.7ft.)
|-
|| Ganymede
|| 778,547,200 km (483.77×10^6mi.)
|| 5,262 km (3,270mi.)
|| 43.1 m (141ft.)
|-
|| Callisto
|| 778,547,200 km (483.77×10^6mi.)
|| 4,821 km (2,996mi.)
|| 39.5 m (130ft.)
|-
|| Titan
|| 1,433,449,370 km (890.7×10^6mi.)
|| 5,150 km (3,200mi.)
|| 22.9 m (75.1ft.)
|-
|| Triton
|| 4,503,443,661 km (2.7983×10^9mi.)
|| 2,705.2 km (1,680.9mi.)
|| 3.8 m (12ft.)
|-
|| Ceres Perihelion
|| 380,995,855 km (236.74×10^6mi.)
|| 974.6 km (605.6mi.)
|| 16.3 m (53.5ft.)
|-
|| Pluto Perihelion
|| 4,437,000,000 km (2.757×10^9mi.)
|| 2,306 km (1,433mi.)
|| 3.3 m (11ft.)
|-
| rowspan="6"| Panel 4
|| Phobos
|| 56 million km (35 million mi.)
|| 26.8 × 22.4 × 18.4 km (16.7 × 13.9 × 11.4 mi.)
|| 3.05 m (10.0ft.)
|-
|| Deimos
|| 56 million km (35 million mi.)
|| 15 × 12.2 × 10.4 km (9.3 × 7.58 × 6.46 mi.)
|| 1.71 m (5ft.7in.)
|-
|| Eris Perihelion
|| 5.723 × 10^9 km (3.556×10^9mi.)
|| 2,326 km (1,445mi.)
|| 2.59 m )8ft.6in.)
|-
|| Eris Aphelion
|| 14.602 × 10^9 km (9.0733×10^9mi.)
|| 2,326 km (1,445mi.)
|| 1.01 m (3ft.3.8in.)
|-
|| Betelguse
|| 643 ± 146 light-years max. 7.464 × 10^15 km (4.638×10^15mi.)
|| 950–1,200 solar radii max. 1.671 × 10^9 km (1.038×10^9mi.)
|| 1.43 m (4ft.8.3in.)
|-
|| R Doradus
|| 178 ± 10 light-years max. 1.778 × 10^15 km (1.105×10^15mi.)
|| 370 ± 50 solar radii max. 0.515 × 10^9 km (320×10^6mi.)
|| 1.85 m (6ft.0.8in.)
|-
| rowspan="6"| Panel 5
|| 4942 Munroe
|| 2.2 AU (1.2 AU closest to earth, 179.4 × 10^6 km or 111.5×10^6mi.)
|| 9–10 km (5.6-6.2mi.)
|| 35.5 cm (14.0in.)
|-
|| Proxima Centauri
|| 4.243 light-years 40.142 × 10^12 km (24.943×10^12mi.)
|| 0.141 solar radii 0.196 × 10^6 km (122×10^3mi.)
|| 3.11 cm (1.22in.)
|-
|| Barnard's Star
|| 5.980 light-years 56.574 × 10^12 km (32.668×10^12)
|| 0.196 solar radii 0.272 × 10^6 km (169×10^3)
|| 3.06 cm (1.20in.)
|-
|| Alpha Centauri B
|| 4.366 light-years 41.305 × 10^12 km (25.666×10^12mi.)
|| 0.865 solar radii 1.204 × 10^6 km (748×10^3mi.)
|| 18.6 cm (7.32in.)
|-
|| Sirius
|| 8.6 light-years 81.362 × 10^12 km (50.556×10^12mi.)
|| 1.711 solar radii 2.382 × 10^6 km (1.480×10^6mi.)
|| 18.7 cm (7.36in.)
|-
|| Alpha Centauri A
|| 4.366 light-years 41.305 × 10^12 km (25.666×10^12mi.)
|| 1.227 solar radii 1.708 × 10^6 km (1.061×10^6mi.)
|| 26.3 cm (10.4in.)
|-
| rowspan="9"| Panel 6
|| HD 189733 b
|| 63 light-years 596.024 × 10^12 km (370.352×10^12mi.)
|| 1.138 Jupiter radii 159,117 km (98,870.7mi.)
|| 1.7 mm (67 mils)
|-
|| Gliese 581 g
|| 20.3 light-years 192.052 × 10^12 km (119.336×10^12mi.)
|| 1.3 to 2.0 Earth radii max. 25,484 km (15,835mi.)
|| 0.85 mm (33 mils)
|-
|| Gliese 581 (Parent star)
|| 20.3 light-years 192.052 × 10^12 km (119.336×10^12mi.)
|| 0.29 solar radii 201,695 km (125,411mi.)
|| 1.34 cm (528 mils)
|-
|| Black Hole at the center of our Galaxy
|| 25,900 light-years 245.032 × 10^15 km (152,260×10^15mi.)
|| Mass 4.31 × 10^6: 12.684 × 10^6 km (7.8815×10^6mi.)
|| 0.33 mm (13 mils)
|-
|| Gliese 667 Cc
|| 22.7 light-years 214.757 × 10^12 km (133.444×10^12mi.)
|| 2.0 Earth radii 25,484 km (15,835mi.)
|| 0.76 mm (30 mils)
|-
|| Gliese 667 (Parent star)
|| 22.7 light-years 214.757 × 10^12 km (133.444×10^12mi.)
|| 0.42 solar radii 584,927 km (363,457mi.)
|| 1.74 cm (685 mils)
|-
|| HD 20794 c (Parent star)
|| 20 light-years 189.214 × 10^12 km (117.572×10^12)
|| 0.92 solar radii 1,281,269 km (796,143.6mi.)
|| 4.31 cm (1.70in.)
|-
|| Tau Ceti C (Parent star)
|| 11.905 light-years 112.629 × 10^12 km (69.9844×10^12mi.)
|| 0.793 solar radii 1,104,398 km (686,241.1mi.)
|| 6.25 cm (2.46in.)
|-
|| Koi-1686.01 (Parent star)
|| 1033.8 light-years 9.780 × 10^15 km (6.077×10^15mi.)
|| 0.52 solar radii 724,195 km (449,994mi.)
|| 0.47 mm (19 mils)
|-
| Panel 7
|| Voyager probes
|| (Voyager 1 at 126.10 AU) 18.86×10^9 km (11.72×10^9mi.)
|| 20 meters (66ft.) (with antennas)
|| 6.76 µm (266 millionths of an in.)
|}

==Transcript==
:The size of the part of Earth's surface directly under various space objects
:[Several images are shown, of space objects of differing size and at different distances from Earth, illustrating the differing sizes of their "shadows" as mapped onto Earth's surface viewed from the center of the Earth.]

:[The first image merely sets the stage: Earth is a full circle, with two figures — Cueball and Megan — standing on it; a small space object casts a "shadow" on Megan, while a slightly larger object, though proportionally farther away, casts just about the same size shadow next to Cueball.]

:[The second image is a map showing London, with the Thames running through it, and a ring highway running around it labeled "London's M25 Orbital Freeway". A grey circle is overlaid, just about the diameter of the M25; it is labeled "The Sun and The Moon (about the same size)".]

:[The third image has a small grey rectangle in one corner labeled "Soccer field" for comparison. The image is dominated by four large, grey circles, considerably larger than the soccer field, labeled "Saturn", "Mars", "Jupiter", and "Venus", with Mars slightly larger than Saturn, Jupiter approximately twice the diameter of Saturn, and Venus approximately three times the diameter of Saturn. Smaller circles are labeled "Mercury", "Uranus", and "Neptune", with Mercury still somewhat larger than the soccer field, Uranus about its size, and Neptune slightly smaller.]

:[The fourth image has the soccer field blown up to take up much of the view; its center circle, goal areas, and corner kick areas are visible. Labeled grey circles of various circles are again overlain: Callisto and Ganymede are about as large as one half of the field; Io, Titan, and Europa are somewhat smaller than half the field; and Ceres, Triton, and Pluto are much smaller (all three together would probably fit into the soccer field's center circle).]

:[In the fifth image, there is a different grey rectangle, this one labeled "Ping Pong table", with a few balls and paddles visible. An irregular ovoid labeled "Phobos" is about the size of the table, as is a circle labeled "R. Doradus". An irregular circular shape labeled "Deimos" is about the size of half the table; a circle labeled "Betelgeuse" is a little smaller, and a circle labeled "Eris" is a little smaller, though still comfortably filling most of half of the table.]

:[In the sixth image, a light grey image of laptop computer keyboard and screen is shown, viewed from directly above. An irregular shape labeled "4942 Munroe" is slightly larger than the laptop, while circles labeled "Alpha Centauri A", "Sirius", and "Alpha Centauri B" form a descending series somewhat smaller than it. Circles labeled "Proxima Centauri" and "Barnard's Star" are considerably smaller than the laptop: Proxima Centauri would fit on the trackpad, while Barnard's Star covers perhaps four keys on the keyboard.]

:[In the seventh image we see a greatly zoomed-in shape which is identified as the "Tilde on laptop keyboard". A circle labeled "HD 189733 b (permadeath)" is almost as large as the tilde is wide; a circle labeled "Tau Ceti C (giant dog planet)" is somewhat smaller. Circles labeled "Gleise 581 g (jelly-filled planet)", "Gleise 667 C c (PILF)", and "HD 20794 c (moonchild)" are all 1/2 to 1/3 as wide as the tilde is wide. A smaller circle labeled "Event horizon of the black hole at the center of our galaxy" fits comfortably within the tilde's stroke width. A very small dot off in one corner (much smaller than the tilde or anything else in the image) is labeled "KOI-1686.01 (emergency backup earth)".]

:[Finally, in the eighth image, the size comparison is to the grey outlines of four bacilliform bacteria labeled "E. coli". The outlines of two interstellar probes are shown, with circular main housings and protruding instruments and antennae. They are labeled "Voyager 1" and "Voyager 2".]

{{comic discussion}}
[[Category:Math]]
[[Category:Astronomy]]
[[Category:Exoplanets]]
[[Category:Soccer]]

1276: Angular Size

2015-07-22T06:14:46Z

108.162.219.151: /* Explanation */

{{comic
| number = 1276
| date = October 11, 2013
| title = Angular Size
| image = angular size.png
| titletext = If the celestial sphere were mapped to the Earth's surface, astronomy would get a LOT easier; you'd just need a magnifying glass.
}}

==Explanation==
This comic is a comparison of the {{w|angular diameter|angular diameters}} (or apparent diameter) of various celestial objects at the surface of the earth relative to a vertex at the center of the Earth as diagrammed in the opening panel. The objects' scales are compared to actual objects on earth. Each size given is for the object at its closest approach to earth.

London's {{w|M25 motorway}} is around 60 km (35 miles) across, a {{w|soccer field}} is about 100 meters long (109yd.), a {{w|Table tennis table|ping pong table}} is 274 centimeters (9ft.) long, a {{w|laptop}} is about 35 centimeters across (13.75in.), the {{w|tilde}} symbol on a keyboard is about 5 millimeters (197 mils) long, and a cell of ''{{w|Escherichia coli|E. coli}}'' is about 2 microns long (78.75 millionths of an inch).

A simple {{w|Intercept theorem|formula}} can be used to find the size on earth of a celestial object when the size of or distance to the object is known. This is done by taking the radius of the earth, multiplying by the diameter of the object, and dividing by the distance to the object from the center of the earth.

The space objects referenced in the panels are:

*The {{w|Sun}} and the {{w|Moon}}, and also the open cluster {{w|Messier 25}}, have approximately the same size (around 0.5 degrees of arc) when seen from the Earth.

*{{w|Mercury (planet)|Mercury}}, {{w|Venus}}, {{w|Mars}}, {{w|Jupiter}}, {{w|Saturn}}, {{w|Uranus}}, and {{w|Neptune}} are the other planets of the {{w|Solar System}}.

*{{w|Io (moon)|Io}}, {{w|Europa (moon)|Europa}}, {{w|Ganymede (moon)|Ganymede}}, and {{w|Callisto (moon)|Callisto}} are the main moons of Jupiter; {{w|Titan (moon)|Titan}} is the largest moon of Saturn; and {{w|Triton (moon)|Triton}} is the largest moon of Neptune. {{w|Ceres (dwarf planet)|Ceres}} and {{w|Pluto}} are {{w|dwarf planet}}s.

*{{w|Phobos (moon)|Phobos}} and {{w|Deimos (moon)|Deimos}} are the moons of Mars. {{w|Eris (dwarf planet)|Eris}} is another dwarf planet. {{w|R Doradus}} and {{w|Betelgeuse}} are giant stars, respectively around 180 and 640 light-years away. R Doradus is the star with the largest apparent diameter (other than the sun, of course).

*{{w|4942 Munroe}} is an asteroid [http://blog.xkcd.com/2013/09/30/asteroid-4942-munroe/ named] after xkcd author [[Randall]] Munroe. {{w|Proxima Centauri}}, {{W|Alpha Centauri|Alpha Centauri AB}}, {{w|Barnard's star}} and {{w|Sirius}} are nearby stars (all within 10 light-years from the Sun).

*{{w|HD 189733 b}}, {{w|Gliese 581 g}}, {{w|Gliese 667 Cc}}, {{w|82 G. Eridani#Planetary_system|HD 20794 c}}, {{w|Tau Ceti#Planets|Tau Ceti c}}, and {{w|KOI-1686.01}} are {{w|extrasolar planet}}s; the parenthetical names are references to the comic [[1253: Exoplanet Names]]. However, some of the planets' parenthetical names do not match the table in the previous comic. For example, HD 20794 c is called "Legoland" rather than "Moonchild" in [[1253: Exoplanet Names]]. The {{w|black hole}} at the center of our Galaxy is {{w|Sagittarius A*}}, a massive object containing a mass more than 4 million times of our Sun.

*{{w|Voyager 1}} and {{w|Voyager 2|2}} are space probes launched in 1977, and currently around 125 and 100 {{w|astronomical unit}}s away, respectively.

The title text states that astronomy would be much easier if the celestial sphere were mapped to the earth - like a giant {{w|globe}}. Due to the distance of the stars you would just need magnifying glass to see the areas representing distant stars instead of an expensive powerful telescope to see huge distances.

Approximate values for the mappings to the Earth sphere (based on mean Earth radius at 6,371.0 km or 3,958.8mi.):
{| class="wikitable sortable"
|-
! Panel
! Object
! Distance
! Diameter
! Size at Earth sphere
|-
| rowspan="4"| Panel 1
|| Sun
|| 149,600,000 km (9.296×10^7mi.)
|| 1,392,684 km (865,373.7mi.)
|| 59.3 km (36.8mi.)
|-
|| Moon Semi-major axis
|| 384,399 km (238,854mi.)
|| 3,476.28 km (2,160.06mi.)
|| 57.6 km (35.8mi.)
|-
|| Moon Perigee
|| 363,295 km (225,741mi.)
|| 3,476.28 km (2160.06mi.)
|| 60.9 km (37.8mi.)
|-
|| Messier 25
|| 2,100 light-years 19.867 × 10^15 km (12.158×10^15mi.)
|| 19 light-years 179.753 × 10^12 km (111.693×10^12mi.)
|| 57.6 km (35.8mi.)
|-
| rowspan="7"| Panel 2
|| Mercury closest approach
|| 92 million km (57 million mi.)
|| 4,879.4 km (3,031.9mi.)
|| 0.34 km (370yd.)
|-
|| Venus closest approach
|| 41 million km (25 million mi.)
|| 12,103.6 km (7,520.83mi.)
|| 1.9 km (1.2mi.)
|-
|| Mars closest approach
|| 56 million km (35 million mi.)
|| 6,792.4 km (4,220.6mi.)
|| 0.77 km (840yd.)
|-
|| Jupiter
|| 778,547,200 km (4.8377×10^8mi.)
|| 139,822 km (86,881.4mi.)
|| 1.14 km (1,250yd.)
|-
|| Saturn
|| 1,433,449,370 km (1.5676×10^12mi.)
|| 120,536 km (74,897.6mi.)
|| 0.54 km (590yd.)
|-
|| Uranus
|| 2,876,679,082 km (1.7875×10^9mi.)
|| 51,118 km (31,763mi.)
|| 0.11 km (120yd.)
|-
|| Neptune
|| 4,503,443,661 km (2.7983×10^9mi.)
|| 49,528 km (30,775mi.)
|| 0.07 km (230ft.)
|-
| rowspan="8"| Panel 3
|| Io
|| 778,547,200 km (483.77×10^6mi.)
|| 3,643 km (2,264mi.)
|| 29.8 m (74.8ft.)
|-
|| Europa
|| 778,547,200 km (483.77×10^6mi.)
|| 3,122 km (1,940mi.)
|| 25.5 m (83.7ft.)
|-
|| Ganymede
|| 778,547,200 km (483.77×10^6mi.)
|| 5,262 km (3,270mi.)
|| 43.1 m (141ft.)
|-
|| Callisto
|| 778,547,200 km (483.77×10^6mi.)
|| 4,821 km (2,996mi.)
|| 39.5 m (130ft.)
|-
|| Titan
|| 1,433,449,370 km (890.7×10^6mi.)
|| 5,150 km (3,200mi.)
|| 22.9 m (75.1ft.)
|-
|| Triton
|| 4,503,443,661 km (2.7983×10^9mi.)
|| 2,705.2 km (1,680.9mi.)
|| 3.8 m (12ft.)
|-
|| Ceres Perihelion
|| 380,995,855 km (236.74×10^6mi.)
|| 974.6 km (605.6mi.)
|| 16.3 m (53.5ft.)
|-
|| Pluto Perihelion
|| 4,437,000,000 km (2.757×10^9mi.)
|| 2,306 km (1,433mi.)
|| 3.3 m (11ft.)
|-
| rowspan="6"| Panel 4
|| Phobos
|| 56 million km (35 million mi.)
|| 26.8 × 22.4 × 18.4 km (16.7 × 13.9 × 11.4 mi.)
|| 3.05 m (10.0ft.)
|-
|| Deimos
|| 56 million km (35 million mi.)
|| 15 × 12.2 × 10.4 km (9.3 × 7.58 × 6.46 mi.)
|| 1.71 m (5ft.7in.)
|-
|| Eris Perihelion
|| 5.723 × 10^9 km (3.556×10^9mi.)
|| 2,326 km (1,445mi.)
|| 2.59 m )8ft.6in.)
|-
|| Eris Aphelion
|| 14.602 × 10^9 km (9.0733×10^9mi.)
|| 2,326 km (1,445mi.)
|| 1.01 m (3ft.3.8in.)
|-
|| Betelguse
|| 643 ± 146 light-years max. 7.464 × 10^15 km (4.638×10^15mi.)
|| 950–1,200 solar radii max. 1.671 × 10^9 km (1.038×10^9mi.)
|| 1.43 m (4ft.8.3in.)
|-
|| R Doradus
|| 178 ± 10 light-years max. 1.778 × 10^15 km (1.105×10^15mi.)
|| 370 ± 50 solar radii max. 0.515 × 10^9 km (320×10^6mi.)
|| 1.85 m (6ft.0.8in.)
|-
| rowspan="6"| Panel 5
|| 4942 Munroe
|| 2.2 AU (1.2 AU closest to earth, 179.4 × 10^6 km or 111.5×10^6mi.)
|| 9–10 km (5.6-6.2mi.)
|| 35.5 cm (14.0in.)
|-
|| Proxima Centauri
|| 4.243 light-years 40.142 × 10^12 km (24.943×10^12mi.)
|| 0.141 solar radii 0.196 × 10^6 km (122×10^3mi.)
|| 3.11 cm (1.22in.)
|-
|| Barnard's Star
|| 5.980 light-years 56.574 × 10^12 km (32.668×10^12)
|| 0.196 solar radii 0.272 × 10^6 km (169×10^3)
|| 3.06 cm (1.20in.)
|-
|| Alpha Centauri B
|| 4.366 light-years 41.305 × 10^12 km (25.666×10^12mi.)
|| 0.865 solar radii 1.204 × 10^6 km (748×10^3mi.)
|| 18.6 cm (7.32in.)
|-
|| Sirius
|| 8.6 light-years 81.362 × 10^12 km (50.556×10^12mi.)
|| 1.711 solar radii 2.382 × 10^6 km (1.480×10^6mi.)
|| 18.7 cm (7.36in.)
|-
|| Alpha Centauri A
|| 4.366 light-years 41.305 × 10^12 km (25.666×10^12mi.)
|| 1.227 solar radii 1.708 × 10^6 km (1.061×10^6mi.)
|| 26.3 cm (10.4in.)
|-
| rowspan="9"| Panel 6
|| HD 189733 b
|| 63 light-years 596.024 × 10^12 km (370.352×10^12mi.)
|| 1.138 Jupiter radii 159,117 km (98,870.7mi.)
|| 1.7 mm (67 mils)
|-
|| Gliese 581 g
|| 20.3 light-years 192.052 × 10^12 km (119.336×10^12mi.)
|| 1.3 to 2.0 Earth radii max. 25,484 km (15,835mi.)
|| 0.85 mm (33 mils)
|-
|| Gliese 581 (Parent star)
|| 20.3 light-years 192.052 × 10^12 km (119.336×10^12mi.)
|| 0.29 solar radii 201,695 km (125,411mi.)
|| 1.34 cm (528 mils)
|-
|| Black Hole at the center of our Galaxy
|| 25,900 light-years 245.032 × 10^15 km (152,260×10^15mi.)
|| Mass 4.31 × 10^6: 12.684 × 10^6 km (shouldn't it be tonnes?)
|| 0.33 mm (13 mils)
|-
|| Gliese 667 Cc
|| 22.7 light-years 214.757 × 10^12 km (133.444×10^12mi.)
|| 2.0 Earth radii 25,484 km (15,835mi.)
|| 0.76 mm (30 mils)
|-
|| Gliese 667 (Parent star)
|| 22.7 light-years 214.757 × 10^12 km (133.444×10^12mi.)
|| 0.42 solar radii 584,927 km (363,457mi.)
|| 1.74 cm (685 mils)
|-
|| HD 20794 c (Parent star)
|| 20 light-years 189.214 × 10^12 km (117.572×10^12)
|| 0.92 solar radii 1,281,269 km (796,143.6
|| 4.31 cm (1.70in.)
|-
|| Tau Ceti C (Parent star)
|| 11.905 light-years 112.629 × 10^12 km (69.9844×10^12mi.)
|| 0.793 solar radii 1,104,398 km (686,241.1mi.)
|| 6.25 cm (2.46in.)
|-
|| Koi-1686.01 (Parent star)
|| 1033.8 light-years 9.780 × 10^15 km (6.077×10^15mi.)
|| 0.52 solar radii 724,195 km (449,994mi.)
|| 0.47 mm (19 mils)
|-
| Panel 7
|| Voyager probes
|| (Voyager 1 at 126.10 AU) 18.86×10^9 km (11.72×10^9mi.)
|| 20 meters (66ft.) (with antennas)
|| 6.76 µm (266 millionths of an in.)
|}

==Transcript==
:The size of the part of Earth's surface directly under various space objects
:[Several images are shown, of space objects of differing size and at different distances from Earth, illustrating the differing sizes of their "shadows" as mapped onto Earth's surface viewed from the center of the Earth.]

:[The first image merely sets the stage: Earth is a full circle, with two figures — Cueball and Megan — standing on it; a small space object casts a "shadow" on Megan, while a slightly larger object, though proportionally farther away, casts just about the same size shadow next to Cueball.]

:[The second image is a map showing London, with the Thames running through it, and a ring highway running around it labeled "London's M25 Orbital Freeway". A grey circle is overlaid, just about the diameter of the M25; it is labeled "The Sun and The Moon (about the same size)".]

:[The third image has a small grey rectangle in one corner labeled "Soccer field" for comparison. The image is dominated by four large, grey circles, considerably larger than the soccer field, labeled "Saturn", "Mars", "Jupiter", and "Venus", with Mars slightly larger than Saturn, Jupiter approximately twice the diameter of Saturn, and Venus approximately three times the diameter of Saturn. Smaller circles are labeled "Mercury", "Uranus", and "Neptune", with Mercury still somewhat larger than the soccer field, Uranus about its size, and Neptune slightly smaller.]

:[The fourth image has the soccer field blown up to take up much of the view; its center circle, goal areas, and corner kick areas are visible. Labeled grey circles of various circles are again overlain: Callisto and Ganymede are about as large as one half of the field; Io, Titan, and Europa are somewhat smaller than half the field; and Ceres, Triton, and Pluto are much smaller (all three together would probably fit into the soccer field's center circle).]

:[In the fifth image, there is a different grey rectangle, this one labeled "Ping Pong table", with a few balls and paddles visible. An irregular ovoid labeled "Phobos" is about the size of the table, as is a circle labeled "R. Doradus". An irregular circular shape labeled "Deimos" is about the size of half the table; a circle labeled "Betelgeuse" is a little smaller, and a circle labeled "Eris" is a little smaller, though still comfortably filling most of half of the table.]

:[In the sixth image, a light grey image of laptop computer keyboard and screen is shown, viewed from directly above. An irregular shape labeled "4942 Munroe" is slightly larger than the laptop, while circles labeled "Alpha Centauri A", "Sirius", and "Alpha Centauri B" form a descending series somewhat smaller than it. Circles labeled "Proxima Centauri" and "Barnard's Star" are considerably smaller than the laptop: Proxima Centauri would fit on the trackpad, while Barnard's Star covers perhaps four keys on the keyboard.]

:[In the seventh image we see a greatly zoomed-in shape which is identified as the "Tilde on laptop keyboard". A circle labeled "HD 189733 b (permadeath)" is almost as large as the tilde is wide; a circle labeled "Tau Ceti C (giant dog planet)" is somewhat smaller. Circles labeled "Gleise 581 g (jelly-filled planet)", "Gleise 667 C c (PILF)", and "HD 20794 c (moonchild)" are all 1/2 to 1/3 as wide as the tilde is wide. A smaller circle labeled "Event horizon of the black hole at the center of our galaxy" fits comfortably within the tilde's stroke width. A very small dot off in one corner (much smaller than the tilde or anything else in the image) is labeled "KOI-1686.01 (emergency backup earth)".]

:[Finally, in the eighth image, the size comparison is to the grey outlines of four bacilliform bacteria labeled "E. coli". The outlines of two interstellar probes are shown, with circular main housings and protruding instruments and antennae. They are labeled "Voyager 1" and "Voyager 2".]

{{comic discussion}}
[[Category:Math]]
[[Category:Astronomy]]
[[Category:Exoplanets]]
[[Category:Soccer]]

what if?

2015-05-05T16:48:34Z

108.162.219.151:

:''Not to be confused with [[17: What If]].''
[[File:whatifbanner.jpg]]

'''''[http://what-if.xkcd.com/ what if?]''''' is a blog hosted on the [[xkcd]].com domain and written by [[Randall Munroe]] with entries posted every week. On the blog, Randall uses his degree in physics and strong scientific background to discuss hypothetical physics questions apparently submitted by readers.
Since 2014 , there's also a book of the blog.

Unlike other sites which answer readers' questions, ''what if?'' typically takes the question beyond the original scope likely intended by the reader and takes it to some extreme for humorous effect. For example, in [http://what-if.xkcd.com/1/ the first article], he discusses what would happen if a baseball were pitched at 90% of the speed of light. After effectively describing what would occur as a nuclear explosion, leveling the stadium and the surrounding mile radius, he concludes with the note ''"A careful reading of official Major League Baseball Rule 6.08(b) suggests that in this situation, the batter would be considered 'hit by pitch', and would be eligible to advance to first base."''

The questions Randall tackles range from realistic possibilities (e.g. the probability of achieving a [http://what-if.xkcd.com/2/ perfect SAT score by guessing]) to completely fictional questions (e.g. [http://what-if.xkcd.com/3/ How much Force power] can {{w|Yoda}} output?). In his explanations, Randall, often uses diagrams in an ''xkcd'' style. Regardless of the context, Randall tends to take the questions extremely literally and responds seriously to them, even if they are whimsical (such as the Yoda question). This is clear from his response to the question of what would happen if everybody on Earth stood together and [http://what-if.xkcd.com/8/ jumped at the same time]. After acknowledging that the question has been answered elsewhere, he recaps the result, but then focuses more intently on the unasked resulting issue of the aftermath of everyone on Earth being magically transported to one location as they all try to return home.

This site is not under [http://creativecommons.org/licenses/by-nc/2.5/ Creative Commons Attribution-NonCommercial 2.5 License] like [[xkcd]] is.

The page currently has a note that "What If updates are temporarily on hold, and will resume on July 14th, 2015 at 7:49:59 AM EDT." This is the date and time that the New Horizons probe will achieve its closest approach to Pluto.

==The book==
{{Incomplete|Maybe give the most (popular) articles their own link. That would be nice. A full list of all articles can be viewed [https://what-if.xkcd.com/archive/ here]}}
Randall announced his ''what if?'' book on 12 March 2014 in [http://blog.xkcd.com/2014/03/12/what-if-i-wrote-a-book/ the blag]. It was published on September 2, 2014.
[[Image:What_If?.jpeg|frame|The general cover of the book]]
It is just like 'xkcd:volume 0' a compilation of questions from the website.
====Summary====
The summary on the back of the book reads:

''Randall Munroe left NASA in 2005 to start up his hugely popular site XKCD 'a web comic of romance, sarcasm, math and language' which offers a witty take on the world of science and geeks. It now has 600,000 to a million page hits daily. Every now and then, Munroe would get emails asking him to arbitrate a science debate. 'My friend and I were arguing about what would happen if a bullet got struck by lightning, and we agreed that you should resolve it . . . ' He liked these questions so much that he started up What If.

*If your cells suddenly lost the power to divide, how long would you survive?
*How dangerous is it, really, to be in a swimming pool in a thunderstorm?
*If we hooked turbines to people exercising in gyms, how much power could we produce?
*What if everyone only had one soulmate?
*When (if ever) did the sun go down on the British empire?
*How fast can you hit a speed bump while driving and live?
*What would happen if the moon went away?

''In pursuit of answers, Munroe runs computer simulations, pores over stacks of declassified military research memos, solves differential equations, and consults with nuclear reactor operators. His responses are masterpieces of clarity and hilarity, studded with memorable cartoons and infographics. They often predict the complete annihilation of humankind, or at least a really big explosion. Far more than a book for geeks, WHAT IF: Serious Scientific Answers to Absurd Hypothetical Questions explains the laws of science in operation in a way that every intelligent reader will enjoy and feel much the smarter for having read.''

==Articles==
*[http://www.what-if.xkcd.com/1/ Relativistic baseball]
*[http://www.what-if.xkcd.com/2/ SAT guessing]
*[http://www.what-if.xkcd.com/3/ Yoda]
*[http://www.what-if.xkcd.com/4/ A mole of moles]
*[http://www.what-if.xkcd.com/5/ Robot apocalypse]
*[http://www.what-if.xkcd.com/6/ Glass half empty]
*[http://www.what-if.xkcd.com/7/ Everybody out]
*[http://www.what-if.xkcd.com/8 Everybody jump]
*[http://www.what-if.xkcd.com/9 Soul mates]
*[http://www.what-if.xkcd.com/10 Cassini]
*[http://www.what-if.xkcd.com/11 Droppings]
*[http://www.what-if.xkcd.com/12 Rain drop]
*[http://www.what-if.xkcd.com/13 Laser pointer]
*[http://www.what-if.xkcd.com/14 Short answer section]
*[http://www.what-if.xkcd.com/15 Mariana trench explosion]
*[http://www.what-if.xkcd.com/16 Today's topic: Lightning]
*[http://www.what-if.xkcd.com/17 Green cows]
*[http://www.what-if.xkcd.com/18 BB gun]
*[http://www.what-if.xkcd.com/19 Tie vote]
*[http://www.what-if.xkcd.com/20 Diamond]
*[http://www.what-if.xkcd.com/21 Machine gun jetpack]
*[http://www.what-if.xkcd.com/22 Cost of pennies]
*Short answer section II
*Model rockets
*Three wise men
*Leap seconds
*Death rate
*Steak drop
*Spent fuel pool
*Interplanetary Cessna
*FedEx bandwidth
*Hubble
*Ships
*Twitter
*Hairdryer
*Cornstarch
*Supersonic stereo
*Voyager
*Hockey puck
*Pressure cooker
*Go west
*Longest sunset
*Train loop
*High throw
*ISS music video
*Bowling ball
*Alien astronomers
*Sunset on the British Empire
*Sunless Earth
*Extreme boating
*Free fall
*Bouncy balls
*Drain the oceans
*Drain the oceans: Part II
*Random sneeze call
*Restraining an airplane
*Dropping a mountain
*Orbital speed
*Updating a printed Wikipedia
*Signs of life
*Speed bump
*Falling with helium
*Google datacenters on punchcards
*Rising steadily
*Twitter timeline height
*500MPH
*Expanding earth
*Little planet
*Facebook of the dead
*The constant groundskeeper
*Stirring tea
*Loneliest human
*Lethal neutrinos
*Soda planet
*Phone keypad
*Reading every book
*Growth rate
*T-rex calories
*Lake tea
*Pile of viruses
*Catch!
*Hitting a comet
*Star sand
*Paint the Earth
*Rocket golf
*Far-travelling objects
*Enforced by radar
*Soda sequestration
*Tungsten countertop
*Great tree, great axe
*Faucet power
*One-second day
*Windshield raindrops
*Billion-story building
*Pyramid energy
*$2 undecillion lawsuit
*Burning pollen
*Blood alcohol
*Starlings
*WWII films
*Plastic dinosaurs
*Keyboard power
*Vanishing water
*Global snow
*Cannibalism
*Ink molecules
*Letter to mom
*Expensive shoebox
*Into the blue
*Walking New York
*All the money
*Balloon car
*Visit every state
*Antimatter
*Into the Sun
*No-rules NASCAR
*Distant death
*Physical salary
*Laser umbrella
*Alternate universe what ifs
*Frozen rivers
*Lava lamp
*Fairy demographics
*Lunar swimming
*Bowling ball
*Stairs
*Tug of war
*Zippo phone
*Black hole moon
*Snow removal
*Microwaves
*Hotter than average
*Flagpole
*Space burial
*Digging downward
*Spiders vs. the Sun

[[Category:Meta]]

what if?

2015-05-05T16:47:23Z

108.162.219.151:

:''Not to be confused with [[17: What If]].''
[[File:whatifbanner.jpg]]

'''''[http://what-if.xkcd.com/ what if?]''''' is a blog hosted on the [[xkcd]].com domain and written by [[Randall Munroe]] with entries posted every week. On the blog, Randall uses his degree in physics and strong scientific background to discuss hypothetical physics questions apparently submitted by readers.
Since 2014 , there's also a book of the blog.

Unlike other sites which answer readers' questions, ''what if?'' typically takes the question beyond the original scope likely intended by the reader and takes it to some extreme for humorous effect. For example, in [http://what-if.xkcd.com/1/ the first article], he discusses what would happen if a baseball were pitched at 90% of the speed of light. After effectively describing what would occur as a nuclear explosion, leveling the stadium and the surrounding mile radius, he concludes with the note ''"A careful reading of official Major League Baseball Rule 6.08(b) suggests that in this situation, the batter would be considered 'hit by pitch', and would be eligible to advance to first base."''

The questions Randall tackles range from realistic possibilities (e.g. the probability of achieving a [http://what-if.xkcd.com/2/ perfect SAT score by guessing]) to completely fictional questions (e.g. [http://what-if.xkcd.com/3/ How much Force power] can {{w|Yoda}} output?). In his explanations, Randall, often uses diagrams in an ''xkcd'' style. Regardless of the context, Randall tends to take the questions extremely literally and responds seriously to them, even if they are whimsical (such as the Yoda question). This is clear from his response to the question of what would happen if everybody on Earth stood together and [http://what-if.xkcd.com/8/ jumped at the same time]. After acknowledging that the question has been answered elsewhere, he recaps the result, but then focuses more intently on the unasked resulting issue of the aftermath of everyone on Earth being magically transported to one location as they all try to return home.

This site is not under [http://creativecommons.org/licenses/by-nc/2.5/ Creative Commons Attribution-NonCommercial 2.5 License] like [[xkcd]] is.

==The book==
{{Incomplete|Maybe give the most (popular) articles their own link. That would be nice. A full list of all articles can be viewed [https://what-if.xkcd.com/archive/ here]}}
Randall announced his ''what if?'' book on 12 March 2014 in [http://blog.xkcd.com/2014/03/12/what-if-i-wrote-a-book/ the blag]. It was published on September 2, 2014.
[[Image:What_If?.jpeg|frame|The general cover of the book]]
It is just like 'xkcd:volume 0' a compilation of questions from the website.
====Summary====
The summary on the back of the book reads:

''Randall Munroe left NASA in 2005 to start up his hugely popular site XKCD 'a web comic of romance, sarcasm, math and language' which offers a witty take on the world of science and geeks. It now has 600,000 to a million page hits daily. Every now and then, Munroe would get emails asking him to arbitrate a science debate. 'My friend and I were arguing about what would happen if a bullet got struck by lightning, and we agreed that you should resolve it . . . ' He liked these questions so much that he started up What If.

*If your cells suddenly lost the power to divide, how long would you survive?
*How dangerous is it, really, to be in a swimming pool in a thunderstorm?
*If we hooked turbines to people exercising in gyms, how much power could we produce?
*What if everyone only had one soulmate?
*When (if ever) did the sun go down on the British empire?
*How fast can you hit a speed bump while driving and live?
*What would happen if the moon went away?

''In pursuit of answers, Munroe runs computer simulations, pores over stacks of declassified military research memos, solves differential equations, and consults with nuclear reactor operators. His responses are masterpieces of clarity and hilarity, studded with memorable cartoons and infographics. They often predict the complete annihilation of humankind, or at least a really big explosion. Far more than a book for geeks, WHAT IF: Serious Scientific Answers to Absurd Hypothetical Questions explains the laws of science in operation in a way that every intelligent reader will enjoy and feel much the smarter for having read.''

''The page currently has a note that "What If updates are temporarily on hold, and will resume on July 14th, 2015 at 7:49:59 AM EDT." This is the date and time that the New Horizons probe will achieve its closest approach to Pluto.''

==Articles==
*[http://www.what-if.xkcd.com/1/ Relativistic baseball]
*[http://www.what-if.xkcd.com/2/ SAT guessing]
*[http://www.what-if.xkcd.com/3/ Yoda]
*[http://www.what-if.xkcd.com/4/ A mole of moles]
*[http://www.what-if.xkcd.com/5/ Robot apocalypse]
*[http://www.what-if.xkcd.com/6/ Glass half empty]
*[http://www.what-if.xkcd.com/7/ Everybody out]
*[http://www.what-if.xkcd.com/8 Everybody jump]
*[http://www.what-if.xkcd.com/9 Soul mates]
*[http://www.what-if.xkcd.com/10 Cassini]
*[http://www.what-if.xkcd.com/11 Droppings]
*[http://www.what-if.xkcd.com/12 Rain drop]
*[http://www.what-if.xkcd.com/13 Laser pointer]
*[http://www.what-if.xkcd.com/14 Short answer section]
*[http://www.what-if.xkcd.com/15 Mariana trench explosion]
*[http://www.what-if.xkcd.com/16 Today's topic: Lightning]
*[http://www.what-if.xkcd.com/17 Green cows]
*[http://www.what-if.xkcd.com/18 BB gun]
*[http://www.what-if.xkcd.com/19 Tie vote]
*[http://www.what-if.xkcd.com/20 Diamond]
*[http://www.what-if.xkcd.com/21 Machine gun jetpack]
*[http://www.what-if.xkcd.com/22 Cost of pennies]
*Short answer section II
*Model rockets
*Three wise men
*Leap seconds
*Death rate
*Steak drop
*Spent fuel pool
*Interplanetary Cessna
*FedEx bandwidth
*Hubble
*Ships
*Twitter
*Hairdryer
*Cornstarch
*Supersonic stereo
*Voyager
*Hockey puck
*Pressure cooker
*Go west
*Longest sunset
*Train loop
*High throw
*ISS music video
*Bowling ball
*Alien astronomers
*Sunset on the British Empire
*Sunless Earth
*Extreme boating
*Free fall
*Bouncy balls
*Drain the oceans
*Drain the oceans: Part II
*Random sneeze call
*Restraining an airplane
*Dropping a mountain
*Orbital speed
*Updating a printed Wikipedia
*Signs of life
*Speed bump
*Falling with helium
*Google datacenters on punchcards
*Rising steadily
*Twitter timeline height
*500MPH
*Expanding earth
*Little planet
*Facebook of the dead
*The constant groundskeeper
*Stirring tea
*Loneliest human
*Lethal neutrinos
*Soda planet
*Phone keypad
*Reading every book
*Growth rate
*T-rex calories
*Lake tea
*Pile of viruses
*Catch!
*Hitting a comet
*Star sand
*Paint the Earth
*Rocket golf
*Far-travelling objects
*Enforced by radar
*Soda sequestration
*Tungsten countertop
*Great tree, great axe
*Faucet power
*One-second day
*Windshield raindrops
*Billion-story building
*Pyramid energy
*$2 undecillion lawsuit
*Burning pollen
*Blood alcohol
*Starlings
*WWII films
*Plastic dinosaurs
*Keyboard power
*Vanishing water
*Global snow
*Cannibalism
*Ink molecules
*Letter to mom
*Expensive shoebox
*Into the blue
*Walking New York
*All the money
*Balloon car
*Visit every state
*Antimatter
*Into the Sun
*No-rules NASCAR
*Distant death
*Physical salary
*Laser umbrella
*Alternate universe what ifs
*Frozen rivers
*Lava lamp
*Fairy demographics
*Lunar swimming
*Bowling ball
*Stairs
*Tug of war
*Zippo phone
*Black hole moon
*Snow removal
*Microwaves
*Hotter than average
*Flagpole
*Space burial
*Digging downward
*Spiders vs. the Sun

[[Category:Meta]]

1126: Epsilon and Zeta

2014-12-13T19:08:27Z

108.162.219.151: /* Transcript */

{{comic
| number = 1126
| date = October 26, 2012
| title = Epsilon and Zeta
| image = epsilon and zeta.png
| titletext = The average error in the NHC forecasted position of a hurricane three days in the future has shrunk to a third of what it was in 1990--a staggering accomplishment. However, as you may have gathered, forecasts of future storm *strength* have proved more difficult to improve.
}}

==Explanation==
The {{w|Atlantic hurricane season}} ''normally'' runs from June to November. [[Randall]] is imagining the situation in the {{w|National Hurricane Center}} when the {{w|2005 Atlantic hurricane season|2005 season}} was extended more than a month by the appearance of {{w|Hurricane Epsilon}} and {{w|Tropical Storm Zeta}}. He imagines the situation as NOAA meteorologists watch with amazement (and increasing annoyance as they were presumably unable to move off to other things such as post-season analysis) as Hurricane Epsilon and Zeta, far beyond the normal end-of-season (November 30th).

The monospaced text in most of the panels is material taken from actual NHC reports [http://www.nhc.noaa.gov/archive/2005/dis/al292005.discus.026.shtml][http://www.nhc.noaa.gov/archive/2005/dis/al292005.discus.027.shtml][http://www.nhc.noaa.gov/archive/2005/dis/al292005.discus.028.shtml] from that season. The commentary has been edited to fit the comic's format, but it's otherwise faithful to the actual reports. While the only change to Forecaster 1 is when he's celebrating New Year's Eve, Forecaster 2 is visibly losing it after the appearance of Zeta in late December, with unkempt hair and an unshaven beard.

The [http://www.nhc.noaa.gov/archive/2005/dis/al302005.discus.030.shtml last report of the 2005 season] was issued on January 6, 2006.

A full analysis of the 2005 hurricane season can be found [http://www.aoml.noaa.gov/general/lib/lib1/nhclib/mwreviews/2005.pdf here].

NHC reports on Epsilion and Zeta:
*[http://www.nhc.noaa.gov/archive/2005/dis/al292005.discus.001.shtml 10 AM EST TUE NOV 29 2005 (Panel 1)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al292005.discus.007.shtml 10 PM EST WED NOV 30 2005 (Panel 2a)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al292005.discus.010.shtml 4 PM EST THU DEC 01 2005 (Panel 2b)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al292005.discus.012.shtml 4 AM EST FRI DEC 02 2005 (Panel 3a)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al292005.discus.013.shtml 10 AM EST FRI DEC 02 2005 (Panel 3b)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al292005.discus.018.shtml 4 PM EST SAT DEC 03 2005 (Panel 4)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al292005.discus.019.shtml 10 PM EST SAT DEC 03 2005 (Panel 5a)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al292005.discus.020.shtml 4 AM EST SUN DEC 04 2005 (Panel 5b)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al292005.discus.021.shtml 10 AM EST SUN DEC 04 2005 (Panel 6,7)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al292005.discus.026.shtml 4 PM EST MON DEC 05 2005 (Panel 8)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al292005.discus.027.shtml 10 PM EST MON DEC 05 2005 (Panel 9)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al292005.discus.028.shtml 4 AM EST TUE DEC 06 2005 (Panel 10)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al292005.discus.031.shtml 10 PM EST TUE DEC 06 2005 (Panel 11a)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al292005.discus.032.shtml 4 AM EST WED DEC 07 2005 (Panel 11b)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al292005.discus.037.shtml 10 AM EST THU DEC 08 2005 (Panel 12)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al302005.discus.001.shtml NOON EST FRI DEC 30 2005 (Panel 14)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al302005.discus.002.shtml 4 PM EST FRI DEC 30 2005 (Panel 15)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al302005.discus.007.shtml 10 PM EST SAT DEC 31 2005 (Panel 16)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al302005.discus.011.shtml 10 PM EST SUN JAN 01 2006 (Panel 17)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al302005.discus.012.shtml 4 AM EST MON JAN 02 2006 (Panel 18a)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al302005.discus.014.shtml 4 PM EST MON JAN 02 2006 (Panel 18b)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al302005.discus.015.shtml 10 PM EST MON JAN 02 2006 (Panel 19a)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al302005.discus.021.shtml 10 AM EST WED JAN 04 2006 (Panel 19b)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al302005.discus.024.shtml 4 AM EST THU JAN 05 2006 (Panel 20)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al302005.discus.025.shtml 10 AM EST THU JAN 05 2006 (Panel 21)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al302005.discus.027.shtml 10 PM EST THU JAN 05 2006 (Panel 22)]
*[http://www.nhc.noaa.gov/archive/2005/dis/al302005.discus.030.shtml 4 PM EST FRI JAN 06 2006 (Panel 23)]

Randall [[453|has discussed]] the seemingly erratic nature of hurricanes before. This may, however, have been a response to the recent {{w|Hurricane Sandy}}.

The text also seems to be a parody of horror stories/movies, and their theme of writing.

==Transcript==
:'''THE SAGA OF EPSILON AND ZETA'''
:The 2005 Atlantic hurricane season saw devastating storms like Katrina and Rita. But less well-remembered is just how ''strange'' the season got toward the end.
:The forecasters at the National Hurricane Center are the best of the best.
:Their predictions are masterpieces of professional analysis. But in November 2005, out in the center of the Atlantic — far from any land — the atmosphere stopped making sense.
:And the forecasters — who'd expected the season to be long over by now — started to get a little...unhinged.
:This is their story, as seen through the actual 2005 NHC Advisories:

:[Two men, one bald and one not, sit looking at their respective computers, at separate desks, back to back. The advisory is printed above them in caps small-caps Courier type.]
:Tuesday, November 29th, 2005: Tropical Storm Epsilon ... The 26th named storm of the apparently never ending 2005 Atlantic hurricane season.

:[The same scene, different text.]
:10 PM Wed: The window of opportunity for strengthening should close in 12-24 hr. 4 PM Thu: Slow but steady weakening is expected to begin in 12-24 hours.

:[The man with hair now has questions marks above his head.]
:4 AM Fri: Epsilon does not appear weaker. 10 AM Fri: Epsilon has been upgraded to a 65-kt hurricane.

:[The two still sit back-to-back.]
:4 PM Sat: Epsilon has continued to strengthen against all odds ... [but] can not maintain the current intensity much longer since the environment is becoming increasingly unfavorable.

:[Ditto.]
:10 PM Sat: Epsilon might or might not still be a hurricane ... but in any case it likely will not be one on Sunday. 4 AM Sun: Epsilon is downgraded to a tropical storm.

:[Yep.] 10 AM Sun: Morning satellite images indicate that Epsilon has restrengthened.

:[A closer view of just the balding man at his desk.]
:There are no clear reasons ... and I am not going to make one up ... to explain the recent strengthening of Epsilon and I am just describing the facts. However ... I still have to make an intensity forecast and the best bet at this time is to predict weakening ... Epsilon will likely become a remnant low. I heard that before about epsilon ... haven't you?

:[The two men still sit back to back, but the man with hair is now turning his head toward the other man, with his arm resting on the back of his chair. The bald man is leaning forward in his seat, toward his computer while typing.]
:4 PM Mon: The cloud pattern continues to be remarkably well-organized for a hurricane at such high latitude in December.

:[The other man has turned back to his own screen.]
:10 PM Mon: We have said this before ... but Epsilon really does not appear as strong this evening as it did this afternoon.

:[Just the bald guy now.]
:4 AM Tue: I have run out of things to say.

:[The two of them again.]
:10 PM Tue: The end is in sight. It really really is. But in the meantime ... Epsilon continues to maintain hurricane status. 4 AM Wed: The end is in sight ... yes ... but not quiet yet. I thought I was going to find a weakening system and instead I found that Epsilon is still a hurricane.

:[Ditto.]
:10 AM Thu: Convection has vanished and Epsilon is now a tight swirl of low clouds. I hope this is the end of the long lasting 2005 hurricane season.

:[This panel is blank and just reads: Nope.]
:'''NOPE.'''

:[The men are still at their desks. The bald man is leaning back on his chair and staring at his screen, the other man's hair is noticeably disheveled, and he has started growing a five o'clock shadow.]
:Enter Tropical Storm Zeta.
:Friday, December 30th, 2005: An elongated area of low pressure ... which had its origins in an old frontal trough ... began developing organized convection overnight. Advisories are initiated on the 27th tropical storm of 2005.

:[The men are still at their desks, the man with hair is even more bedraggled-looking.]
:Any new storms would be in the 2006 season.
:4PM Fri: Although the atmosphere seems to want to develop tropical storms ad nauseam ... the calendar will shortly put an end to the use of the Greek alphabet to name them.

:[The bald man is now wearing a party hat and there is confetti in the air.]
:But 2005's wouldn't end until Zeta did.
:10 PM Sat: Zeta appeared on the verge of losing all of its deep convection a few hours ago ... but since about 21z the convection has been on somewhat of an increase again.

:[A close view of the man with hair at his desk.]
:10 PM Sun: This is like Epsilon all over again. Most of the conventional guidance suggested that zeta should have been dissipated by now ... well ... zeta is pretty much alive at this time. I have no choice but to forecast weakening again and again.

:[Both of them at their desks.]
:4 AM Mon: By 24-36 hours ... a significant increase in westerly winds ... should act to shear away most of the associated convection ... and finally bring the 2005 Atlantic hurricane season to a merciful ending. 4 PM Mon: It is hard to conceive that a tropical cyclone will be able to survive for very long in such a hostile environment. therefore I have not backed off on the forecast of weakening.

:[And again.]
:10 PM Mon: Zeta is stronger than yesterday. 10 AM Wed: As you can see... I ran out of things to say.

:[And again.]
:4 AM Thu: Satellite intensity estimates have decreased. Zeta is downgraded to a 30 kt tropical depression.

:[And again.]
:10 AM Thu: Shortly after the previous advisory had been issued ... regretfully ... the intensity ... increased to 35 kt and Zeta is a tropical storm once again.

:[And again.]
:10 PM Thu: Although it seems as if Zeta will never die ... the forecast continues to show weakening.

:[Both men are now leaning back in their chairs, exhausted.]
:4 PM, Friday, January 6, 2006: Zeta no longer meets the criteria of a tropical cyclone... which means that both it and the 2005 Atlantic hurricane season have ended. This is the national hurricane center signing off for 2005.

:[The bald man still sits at his desk, the man with hair is no longer in his chair.]

:[Again, we see the bald man at his desk and the other guy's empty desk.]
:Bald guy: Actually, Zeta's cloud pattern is...
:Hair guy: (out of panel) '''''NO'''''.
:Bald guy: Ok.

{{comic discussion}}
[[Category:Hurricanes]]

Talk:1417: Seven

2014-09-05T11:59:11Z

108.162.219.151: Guacamole may refer to Taco Bell's 7 layer burrito

Guacamole = 7-layer dip ingredient
[[Special:Contributions/108.162.215.81|108.162.215.81]] 05:08, 5 September 2014 (UTC)Anonymous XKCD reader

Seventh Seal more likely to be a reference to Book of Revelation (I think he's brought it up before?) or the film? [[Special:Contributions/199.27.133.96|199.27.133.96]] 05:17, 5 September 2014 (UTC)

Arctic Ocean is one of the modern Seven "Seas" of the world.
Green is the 4th color of seven in the Arthur Hamilton song "I Can Sing a Rainbow".

I guess the title text is a play on the fact that the dwarves in the new Snow White (2001) movie are called Monday, Tuesday, ... That is the connection between Snow White dwarves and days of the week. The filmmakers decided to intermix sets of seven in the first place. Sebastian --[[Special:Contributions/108.162.254.90|108.162.254.90]] 06:27, 5 September 2014 (UTC)

There could be a pattern with order.

*Sneezy: 1st dwarf of the seven dwarves in Snow White.
*Phylum: 2nd rank in the Seven Taxonomic Ranks
*Europe: 3rd continent of the world
**The list on the page needs to be fixed to show Europe third. --[[Special:Contributions/141.101.99.213|141.101.99.213]] 11:15, 5 September 2014 (UTC)
*Sloth: 4th sin of the Seven Deadly Sin
*Guacamole: 5th Layer in a 7 Layer Bean Dip
*Data Link: 6th Layer in the OSI Model
*Collosus of Rhodes: 7th Wonder of the Ancient World

*Monday: 1st Day of the Week (American).
*Arctic: 2nd ocean in the modern Seven "Seas" of the world.
*Wellesley: 3rd college of the Seven Sister colleges
*Green: 4th color in the Arthur Hamilton song "I Can Sing a Rainbow".
*Electra: 5th sister of the Pleiades, the Seven Sisters.
*Synergize: 6th Habit in the Stephen R. Covey self-help book "Seven Habits of Highly Effective People".
*Seventh Seal: 7th Seal of the Seven Seals in the Book of Revelations

The Pleiades is Randall's favorite constellation. [[Special:Contributions/108.162.237.161|108.162.237.161]] 08:40, 5 September 2014 (UTC)

It sure is nice seeing the explanation getting more refined and complete every time I visit... [[Special:Contributions/103.22.201.168|103.22.201.168]] 10:37, 5 September 2014 (UTC)

I've always been told there are only six continents. North America and South America are one continent. The seventh continent sometimes refers to this gigantic area filled with plastic rubbish in the Pacific Ocean. [[Special:Contributions/108.162.229.143|108.162.229.143]] 11:47, 5 September 2014 (UTC)

Guacamole may also be a reference to a famous joke which made the rounds about 15 years ago, where somebody had compared the 7 layers of the OSI network model to Taco Bell's 7-layer burrito. Guacamole was the 5th layer, which lends credence to this idea. It's still available on the WayBack Machine: http://web.archive.org/web/19990826193318/http://www.europa.com/~dogman/osi/ [[Special:Contributions/108.162.219.151|108.162.219.151]] 11:59, 5 September 2014 (UTC)