Saturday, February 03, 2007

The Moon & TIME

La Luna - copyright - 2005 Jerry Lodriguss

The Moon makes a complete orbit about the Earth with respect to the fixed stars (its sidereal period) approximately once every 27.3 days. However, since the Earth is moving in its orbit about the Sun at the same time, it takes slightly longer for the Moon to show its same phase to Earth, which is about 29.5 days (its synodic period). Unlike most satellites of other planets, the Moon orbits near the ecliptic and not the Earth's equatorial plane.

Most of the tidal effects seen on the Earth are caused by the Moon's gravitational pull, with the Sun making only a small contribution. Tidal effects result in an increase of the mean Earth-Moon distance of about 4 meters per century, or 4 centimetres per year. As a result of the conservation of angular momentum, the increasing semimajor axis of the Moon is accompanied by a gradual slowing of the Earth's rotation by about 0.002 seconds per day per century

How Does Your Brain Tell Time? Study Challenges Theory Of Inner Clock

For decades, scientists have believed that the brain possesses an internal clock that allows it to keep track of time.

The changing colours reflect how a brain cell network evolves over time in response to stimuli. (Credit: Buonomano Lab)

Now a UCLA study in the Feb. 1 edition of Neuron proposes a new model in which a series of physical changes to the brain's cells helps the organ to monitor the passage of time.

The most popular theory assumes that a clock-like mechanism -- which generates and counts regular fixed movements -- underlies timing in the brain. In contrast, Buonomano suggests a physical model that operates without using a clock. He offers an analogy to explain how it works.

"If you toss a pebble into a lake," he explained, "the ripples of water produced by the pebble's impact act like a signature of the pebble's entry time. The farther the ripples travel the more time has passed.

"We propose that a similar process takes place in the brain that allows it to track time," he added. "Every time the brain processes a sensory event, such as a sound or flash of light, it triggers a cascade of reactions between brain cells and their connections. Each reaction leaves a signature that enables the brain-cell network to encode time."

The UCLA team used a computer model to test this theory. By simulating a network of interconnected brain cells in which each connection changed over time in response to stimuli, they were able to show that the network could tell time.

Their simulations indicated that a specific event is encoded within the context of events that precede it. In other words, if one could measure the response of many neurons in the brain to a tone or a flash of light, the response would not only reveal the nature of the event, but the other events that preceded it and when they occurred.

Note: This story has been adapted from a news release
issued by
University of California - Los Angeles.

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