ScienceIQ.com

What Is a Spinal Cord Injury?

Although the hard bones of the spinal column protect the soft tissues of the spinal cord, vertebrae can still be broken or dislocated in a variety of ways and cause traumatic injury to the spinal cord. Injuries can occur at any level of the spinal cord. The segment of the cord that is injured, and the severity of the injury, will determine which ...

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WhatIsaSpinalCordInjury
Medicine

What is Headache?

When a person has a headache, several areas of the head can hurt, including a network of nerves that extends over the scalp and certain nerves in the face, mouth, and throat. The muscles of the head ... Continue reading

WhatisHeadache
Astronomy

Galaxy Cluster RDCS 1252.9-2927

A color composite image of the galaxy cluster RDCS 1252.9-2927 shows the X-ray (purple) light from 70-million-degree Celsius gas in the cluster, and the optical (red, yellow and green) light from the ... Continue reading

GalaxyClusterRDCS125292927
Physics

Torque

A force may be thought of as a push or pull in a specific direction. When a force is applied to an object, the object accelerates in the direction of the force according to Newton's laws of motion. ... Continue reading

Torque
Engineering

Drip, Drip Water Clocks

Water clocks were among the earliest timekeepers that didn't depend on the observation of celestial bodies. One of the oldest was found in the tomb of the Egyptian pharaoh Amenhotep I, buried around ... Continue reading

DripDripWaterClocks

An Old Science Experiment On The Moon

AnOldScienceExperimentOnTheMoonThe most famous thing Neil Armstrong left on the moon 35 years ago is a footprint, a boot-shaped depression in the gray moondust. Millions of people have seen pictures of it, and one day, years from now, lunar tourists will flock to the Sea of Tranquility to see it in person. Peering over the rails ... 'hey, mom, is that the first one?' Will anyone notice, 100 feet away, something else Armstrong left behind? Ringed by footprints, sitting in the moondust, lies a 2-foot wide panel studded with 100 mirrors pointing at Earth: the 'lunar laser ranging retroreflector array.' Apollo 11 astronauts Buzz Aldrin and Neil Armstrong put it there on July 21, 1969, about an hour before the end of their final moonwalk. Thirty-five years later, it's the only Apollo science experiment still running.

University of Maryland physics professor Carroll Alley was the project's principal investigator during the Apollo years, and he follows its progress today. 'Using these mirrors,' explains Alley, 'we can 'ping' the moon with laser pulses and measure the Earth-moon distance very precisely. This is a wonderful way to learn about the moon's orbit and to test theories of gravity.' Here's how it works: A laser pulse shoots out of a telescope on Earth, crosses the Earth-moon divide, and hits the array. Because the mirrors are 'corner-cube reflectors,' they send the pulse straight back where it came from. 'It's like hitting a ball into the corner of a squash court,' explains Alley. Back on Earth, telescopes intercept the returning pulse--'usually just a single photon,' he marvels. The round-trip travel time pinpoints the moon's distance with staggering precision: better than a few centimeters out of 385,000 km, typically.

Targeting the mirrors and catching their faint reflections is a challenge, but astronomers have been doing it for 35 years. A key observing site is the McDonald Observatory in Texas where a 0.7 meter telescope regularly pings reflectors in the Sea of Tranquility (Apollo 11), at Fra Mauro (Apollo 14) and Hadley Rille (Apollo 15), and, sometimes, in the Sea of Serenity. In this way, for decades, researchers have carefully traced the moon's orbit, and they've learned some remarkable things, among them: (1) The moon is spiraling away from Earth at a rate of 3.8 cm per year. Why? Earth's ocean tides are responsible. (2) The moon probably has a liquid core. (3) The universal force of gravity is very stable. Newton's gravitational constant G has changed less than 1 part in 100-billion since the laser experiments began.