Arecibo message
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2008-07-15T02:31:08Z
Bensin
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[[Image:Arecibo message.svg|200px|right|thumb|This is the message with color added to highlight its separate parts. The actual binary transmission carried no color information.]]
The '''Arecibo message''' is a radio message that was beamed into space at a ceremony to mark the remodeling of the [[Arecibo Observatory|Arecibo radio telescope]] on [[16 November]] [[1974]].<ref name="phoneet">{{cite web|url=http://www.news.cornell.edu/releases/Nov99/Arecibo.message.ws.html |title=Cornell News: It's the 25th anniversary of Earth's first (and only) attempt to phone E.T., FOR RELEASE: Nov. 12, 1999|accessdate=2008-03-29}}</ref> It was aimed at the [[Great Globular Cluster in Hercules|globular star cluster M13]] some 25,000 [[light year]]s away because it was a large and close collection of stars that was available in the sky at the time and place of the ceremony.<ref>{{cite web|url=http://www.zwire.com/site/news.cfm?newsid=15663534|title=Larry Klaes. Ithaca Times - Making Contact|accessdate=2007-07-27}}</ref> The message consisted of 1679 [[bit|binary digits]] (equivalent to nearly 210 bytes, since 1679 / 8 = 209.87 [8 bits in 1 byte]) transmitted at a frequency of 2380 MHz and modulated by shifting the frequency by 10 Hz, with a power of 1000[[kilowatt|kW]].<ref name="phoneet" /> The beam was extremely narrow (giving a [[effective radiated power|power equivalent]] to 20[[terawatt|TW]] if it were omnidirectional) making it the strongest man-made signal ever sent. The entire transmission lasted 1679 seconds and was not repeated.<ref>{{cite web|author=Jay M. Pasachoff|title=Chapter 20: Life in the Universe|work=[http://www.williams.edu/Astronomy/jay/ETU5/updates.html Astronomy: From the Earth to the Universe, Updates by Chapter, 5th Ed.]|url=http://www.williams.edu/Astronomy/jay/ETU5/chapter20_5th.html| accessdate=2007-05-05}}</ref> The number 1679 was chosen because it is a [[semiprime]] (the product of two [[prime number]]s) and therefore can only be broken down into 23 rows and 73 columns, or 73 rows and 23 columns. This assumes that those who read it will choose to arrange it as a rectangular [[raster scan]]. The information arranged the first way (23 rows, 73 columns) produces jumbled nonsense, but if arranged the second way (73 rows, 23 columns) it forms the image shown on the right (assuming the bits are arranged from left to right and the rows are arranged from top to bottom; otherwise a flipped image is formed), which is assumed to be recognizable as data.<ref>{{cite web|url=http://www.physics.utah.edu/~cassiday/p1080/lec06.html|title=The Arecibo Message]. This also touches upon the confusion regarding arranging the bits from left to right and vice versa|last=Cassiday|first=George|accessdate=2007-07-27}}</ref>
[[Image:Arecibo_shifted.png|The Arecibo message if it were decoded as 23 rows and 73 columns.|thumb|right|300px]]
Reading the image from top to bottom and left to right, it can be divided into 7 parts that state (or show) the following:
#the numbers one (1) through ten (10)
#the [[atomic numbers]] of the elements [[hydrogen]], [[carbon]], [[nitrogen]], [[oxygen]], and [[phosphorus]], which make up [[deoxyribonucleic acid]] (DNA)
#the [[formula]]s for the [[sugar]]s and [[Base (chemistry)|bases]] in the [[nucleotides]] of DNA
#the number of nucleotides in DNA, and a graphic of the double helix structure of DNA
#a graphic figure of a man, the dimension (physical height) of an average man, and the human population of Earth
#a graphic of Earth's [[solar system]]
#a graphic of the [[Arecibo Observatory|Arecibo radio telescope]] and the dimension (the physical diameter) of the transmitting antenna dish
Because it will take 25,000 years for the message to reach its intended destination of stars (and an additional 25,000 years for any reply), the Arecibo message was more a demonstration of human technological achievement than a real attempt to enter into a conversation with extraterrestrials. In fact, the stars that the message was aimed at will no longer be there when it arrives.<ref name="phoneet" /> According to the Cornell News press release of Nov. 12, 1999, the real purpose of the message was not to make contact, but to demonstrate the capabilities of newly installed equipment.<ref name="phoneet" />
Dr. [[Frank Drake]], then at [[Cornell University]] and creator of the famous [[Drake equation]], wrote the message, with help from [[Carl Sagan]], among others.<ref name="phoneet" /> Whether or not this message has any ostensible effects, it has nevertheless forced humanity to consider how it might communicate with extrasolar beings, and what the contents of any such communications might be.
== Explanation ==
=== Numbers ===
[[Image:Arecibo message part 1.png|Part 1 — The numbers from 1 to 10|left]]
1 2 3 4 5 6 7 8 9 10
----------------------
0 0 0 1 1 1 1 00 00 00
0 1 1 0 0 1 1 00 00 10
1 0 1 0 1 0 1 01 11 01
X X X X X X X X X X <-least-significant-digit marker
{{clr}}
The numbers from [[1 (number)|1]] to [[10 (number)|10]] appear in [[Binary numeral system|binary]] format (the bottom row marks the beginning of each number).
Even knowing binary, the encoding of the numbers may not be immediately obvious due to the way they have been written. To read the first seven digits, ignore the bottom row, and read them as three binary digits from top to bottom, with the top digit being the most significant.
The readings for 8, 9 and 10 are a little different, as they have been given an additional column next to the first (to the right in the image). This is probably intended to show that numbers too large to fit in a column can be written in several contiguous ones, where the contiguous columns do not have the base marker.
=== DNA elements ===
[[Image:Arecibo message part 2.png|Part 2 — The elements constituting DNA|left]]
H C N O P
1 6 7 8 15
----------
0 0 0 1 1
0 1 1 0 1
0 1 1 0 1
1 0 1 0 1
X X X X X
{{clr}}
The numbers 1, 6, 7, 8 and 15 appear. These are the atomic numbers of [[hydrogen]] (H), [[carbon]] (C), [[nitrogen]] (N), [[oxygen]] (O), and [[phosphorus]] (P), the components of DNA.
The numbers 8 and 15 are written in a logical extension of binary encoding, rather than with the contiguous-columns method shown in the message's number figures at the top:
=== Nucleotides ===
[[Image:Arecibo message part 3.png|Part 3 — The nucleotides of DNA|left]]
[[Deoxyribose]] [[Adenine]] [[Thymine]] Deoxyribose
(C<sub>5</sub>OH<sub>7</sub>) (C<sub>5</sub>H<sub>4</sub>N<sub>5</sub>) (C<sub>5</sub>H<sub>5</sub>N<sub>2</sub>O<sub>2</sub>) (C<sub>5</sub>OH<sub>7</sub>)
[[Phosphate]] Phosphate
(PO<sub>4</sub>) (PO<sub>4</sub>)
Deoxyribose [[Cytosine]] [[Guanine]] Deoxyribose
(C<sub>5</sub>OH<sub>7</sub>) (C<sub>4</sub>H<sub>4</sub>N<sub>3</sub>O) (C<sub>5</sub>H<sub>4</sub>N<sub>5</sub>O) (C<sub>5</sub>OH<sub>7</sub>)
Phosphate Phosphate
(PO<sub>4</sub>) (PO<sub>4</sub>)
{{clr}}
The [[nucleotides]] are described as sequences of the five atoms that appear on the preceding line. Each sequence represents the [[molecular formula]] of the nucleotide as incorporated into DNA (as opposed to the free form of the nucleotide).
For example, deoxyribose (C<sub>5</sub>OH<sub>7</sub> in DNA, C<sub>5</sub>O<sub>4</sub>H<sub>10</sub> when free), the nucleotide in the top left in the image, is read as:
11000
10000
11010
XXXXX
-----
75010
i.e. 7 atoms of hydrogen, 5 atoms of carbon, 0 atoms of nitrogen, 1 atom of oxygen, and 0 atoms of phosphorus.
=== Double helix ===
[[Image:Arecibo message part 4.png|Part 4 — The DNA double helix structure|left]]
11
11
11
11
11
01
11
11
01
11
01
11
10
11
11
01
X
1111111111110111 1111101101011110 (binary)
= 4,294,441,822 (decimal)
{{clr}}
DNA double [[helix]] (the vertical bar represents the number of nucleotides, but the value depicted is around 4.3 billion when in fact there are about 3.2 billion base pairs in the human genome).
=== Humanity ===
[[Image:Arecibo message part 5.png|Part 5 — Human form, the height and population of humans|left]]
X011011
111111
X0111 110111
111011
111111
110000
1110 (binary) = 14 (decimal)
000011 111111 110111 111011 111111 110110 (binary)
= 4,292,853,750 (decimal)
{{clr}}
The element in the center represents a human. The element on the left (in the image) indicates the average height of a person: 1764 [[millimetre|mm]]. This corresponds to the horizontally written binary 14 multiplied by the [[wavelength]] of the message (126 mm). The element on the right depicts the size of human population in 1974, around 4.3 billion. In this case, the number is oriented horizontally rather than vertically, with the least-significant-digit marker to the upper left in the image.
=== Planets ===
[[Image:Arecibo message part 6.png|Part 6 — The Sun and the planets|left]]
Earth
Sun Mercury Venus Mars Jupiter Saturn Uranus Neptune Pluto
{{clr}}
The [[solar system]], showing the [[Sun]] and the planets in the order of their position from the [[Sun]]: [[Mercury (planet)|Mercury]], [[Venus (planet)|Venus]], [[Earth]], [[Mars (planet)|Mars]], [[Jupiter (planet)|Jupiter]], [[Saturn (planet)|Saturn]], [[Uranus (planet)|Uranus]], [[Neptune (planet)|Neptune]], and [[Pluto]]. (Pluto is now classified as a [[dwarf planet]], but was still considered a planet at the time the message was written.)
The Earth is the third planet from the [[Sun]] - its graphic is shifted up to identify it as the planet from which the signal was sent. The human figure is shown "standing on" the Earth graphic.
In addition to showing position, the graphic provides a general, not-to-scale size reference of each planet and the Sun.
=== Telescope ===
[[Image:Arecibo message part 7.png|Part 7 — The Arecibo radio telescope|left]]
bottom two rows:
100101
<--- 111110X --->
100101 111110 (binary) = 2,430 (decimal)
{{clr}}
The last part represents the [[Arecibo radio telescope]] with its [[diameter]] (2430 multiplied by the wavelength gives 306.18 [[Metre|m]]). In this case, the number is oriented horizontally, with the least-significant-digit marker to the lower right in the image.
==See also==
* [[Communication with Extraterrestrial Intelligence]]
* [[Active SETI]]
* [[Arecibo reply]]
* [http://www.cplire.ru/html/ra&sr/index.html Interstellar Radio Messages]
== References ==
{{reflist}}
==External links==
*[http://www.seti.org/seti/seti-background/arecibo.php SETI homepage on the message]
*[http://www.cplire.ru/html/ra&sr/irm/index.html Interstellar Radio Messages]
*[http://alienresearch.wikia.com/wiki/Arecibo_Observatory_message Arecibo Observatory message] on Alien Research
*[http://www.lasnix.com/index.php?section=glossary&p=Laser Cornell news: Arecibo message anniversary]
*[http://www.zwire.com/site/news.cfm?newsid=15663534&BRD=1395&PAG=461&dept_id=216620&rfi=6 Ithaca Times article on 31st anniversary of Arecibo Message broadcast.]
*[http://www.physics.utah.edu/~cassiday/p1080/lec06.html The Arecibo Message explained]
[[Category:Interstellar messages]]
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