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Arecibo message

 Arecibo message

Description

The content of the Arecibo message was designed by Frank Drake, then at Cornell University and creator of the Drake equation, who wrote the message with help from Carl Sagan and others.^[1] The message was meant more as a demonstration of human technological achievement than a serious attempt to enter into a conversation with possible extraterrestrials.^[1] As globular cluster M13, at which the message was aimed, is more than 25,000 light-years from Earth, the message, traveling at the speed of light, will take at least 25,000 years to arrive there. By that time, the core of M13 will no longer be in precisely the same location because of the orbit of the star cluster around the galactic center.^[1] Even so, the proper motion of M13 is small, so the message will still arrive near the center of the cluster.^[5]

The message consists of seven parts that encode the following (from the top down in the image):^[4]

• The numbers one to ten (white)
• The atomic numbers of the elements hydrogen, carbon, nitrogen, oxygen, and phosphorus, which make up deoxyribonucleic acid (DNA) (purple)
• The formulas for the chemical compounds that make up the nucleotides of DNA (green)
• The estimated number of DNA nucleotides in the human genome, and a graphic of the double helix structure of DNA (white and blue, respectively)
• The dimension (physical height) of an average man (blue/white), a graphic figure of a human being (red), and the human population of Earth (white)
• A graphic of the Solar System, indicating which of the planets the message is coming from (yellow)
• A graphic of the Arecibo radio telescope and the dimension (the physical diameter) of the transmitting antenna dish (purple, white, and blue)

The entire message consisted of 1,679 binary digits, approximately 210 bytes, transmitted at a frequency of 2,380 MHz and modulated by shifting the frequency by 10 Hz, with a power of 450 kW. The "ones" and "zeros" were transmitted by frequency shifting at the rate of 10 bits per second. The total broadcast was less than three minutes.^[1][6]

The number 1,679 was chosen because it is a semiprime (the product of two prime numbers), to be arranged rectangularly as 73 rows by 23 columns.^[7] The alternative arrangement, 23 rows by 73 columns, produces an unintelligible set of characters.

Water hole (radio)

 Water hole (radio)

The waterhole, or water hole, is an especially quiet band of the electromagnetic spectrum between 1420 and 1662 megahertz, corresponding to wavelengths of 21 and 18 centimeters, respectively. It is a popular observing frequency used by radio telescopes in radio astronomy.^[1]

Plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation

The strongest hydroxyl radical spectral line radiates at 18 centimeters, and atomic hydrogen at 21 centimeters (the hydrogen line). These two molecules, which combine to form water, are widespread in interstellar gas, which means this gas tends to absorb radio noise at these frequencies. Therefore, the spectrum between these frequencies forms a relatively "quiet" channel in the interstellar radio noise background.

Bernard M. Oliver, who coined the term in 1971, theorized that the waterhole would be an obvious band for communication with extraterrestrial intelligence,^[2] hence the name, which is a pun: in English, a watering hole is a vernacular reference to a common place to meet and talk. Several programs involved in the search for extraterrestrial intelligence, including SETI@home, search in the waterhole radio frequencies.

Visualized: The 4 Billion Year Path of Human Evolution

 Visualized: The 4 Billion Year Path of Human Evolution

The 4 Billion Year Path of Human Evolution

The story of human evolution is a fascinating one, stretching back in an unbroken chain over millions of years.

From the tiniest protocells to modern humans, our species has undergone a remarkable journey of adaptation, innovation, and survival.

In this article, we take a look at the key developmental stages in the evolution of life on Earth that led to the emergence of Homo sapiens—us!

The Æsop for Children

 

The Æsop for Children

About the Æsop for Children

Aesop for Children contains the text of selected fables, color pictures, video, and interactive animations, and will be enjoyed by readers of any age.

“Aesop's Fables”—also called “the Aesopica”—are a collection of stories designed to teach moral lessons credited to Aesop, a Greek slave and story-teller thought to have lived between 620 and 560 BCE.

Aesop's fables are some of the most well known in the world and have been translated in multiple languages and become popular in dozens of cultures through the course of five centuries. They have been told and retold in a variety of media, from oral tradition to written storybooks to stage, film and animated cartoon versions—even in architecture.

The fables remain a popular choice for moral education of children today. Younger scholars will be able to trace the origin of aphorisms such as “sour grapes” and “a bird in the hand.”

This interactive book is presented by the Library of Congress, adapted from the book “The Aesop for Children: with Pictures by Milo Winter,” published by Rand, McNally & Co in 1919. This work is considered to be in the public domain in the United States.

Milo Winter’s pictures have been transformed for this interactive book, and now readers can interact with the charming illustrations to see and hear them move: a choosy heron eyes the fish swimming at his feet, a fox swishes his tail, a mouse chews a rope and frees a lion.