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.

The sleeper legal strategy that could topple abortion bans

 The sleeper legal strategy that could topple abortion bans

Todays Thought

 A THOUGHT FOR TODAY:

Since when do we have to agree with people to defend them from injustice? 

-Lillian Hellman, playwright (20 Jun 1905-1984)

The Hidden Chemicals Destroying American Farms

Visualized: The 4 Billion Year Path of Human Evolution

 Visualized: The 4 Billion Year Path of Human Evolution