A: Sunlight is scattered by oxygen and nitrogen molecules in the earth's atmosphere. Since blue light has a shorter wavelength than red light, it is scattered more easily. In fact, violet has the shortest wavelength of visible light but our eyes are more sensitive to blue which is why we see a blue sky rather than a violet sky. As for the clouds, the ice and water present scatters all color wavelengths by the same amount. Thus, we see white as a result.
A: The lift force is caused because there is more pressure below the wing than above it. Air moving over a longer path has less pressure than the same volume of air moving over a shorter path. When the air is bent around the top of the wing, it pulls on the air above it accelerating that air downward. It is the acceleration of the air above the wing in the downward direction that gives lift. Newton's third law applies here: for every reaction there is an equal and opposite reaction. The wing causes a force to be exerted on the air which bends it downwards (action) and as a result, an equal and opposite force is exerted on the wing (reaction) which causes the lift. To generate lift a wing must divert lots of air down.
A: Most stars, like our sun, are main sequence stars and will only burn hydrogen into helium during their lifetime. They produce nuclear energy by doing this in order to provide enough radiation pressure to avoid collapse from the gravitational force that is exerted on them and every object in space. For stars of 5 solar masses or greater, they are able to burn up to an iron core, with lighter elements burning in their outer layers. But after iron, trying to fuse together heavier elements will only absorb energy. As a result, the star eventually collapses and explodes into what is called a supernovae. During collapse, the nuclei in the outer parts of the star are pushed close enough together to form heavier elements. It's only during a supernovae explosion, that enough energy can be released to form the other elements up to uranium.
A: While driving, cell phones are known to reduce alertness and could put you at risk in traffic. In terms of whether or not the emitted radiation is harmful to your body, well it may be nothing to worry about but do keep in mind that there are studies being conducted because some do believe there is a link between cell phones and brain cancer. On a reassuring note, cellular phones in use give off low levels of radio frequency (RF) energy, a non-ionizing radiation which is too low to break chemical bonds. Thus, this radiation does not have enough energy to damage genetic material and potentially lead to cancer or birth defects. However, if someone tried to sell you a cell phone and told you that there may be a risk of getting brain cancer from it, would you still want one ?
A: Seasons occur because the Earth orbits the sun at a 23.4 degree angle. That is, the Earth's axis of rotation is tilted 23.4 degrees from the axis that is perpendicular to the Earth's orbital plane. During June, the northern hemisphere is tilted more towards the sun and experiences summer. In December, the northern hemisphere is tilted away from the sun and experiences winter. The seasons are of course reversed for the southern hemisphere.
A: The solar calendar has 365 days and is based on the amount of time it takes for the Earth to complete one orbit around the Sun. Beacause it's based on the orbital period of the Earth, the seasons occur around the same time each year. The lunar calendar has 354 days in the year and it's based on the phases of the moon and tides. For this reason, the phases of the moon occurs around the same time each month.
A: Green flashes are real phenomena seen near sunrise and sunset, when some part of the Sun suddenly changes color. Just before sunrise or sunset some faint green (or aquamarine) light may be seen just above the solar disk. This usually only lasts one or two seconds. The classic theory for a green flash is that scattering of sunlight by atmospheric gases causes a green image lying slightly above the red image of the Sun at the horizon.
A: All compact discs and other optical disc players read from the inside of the CD out. A CD has a track of tiny pits in a silvery reflective layer on a plastic disc. A CD is read by a laser which enters the CD on the play side, travels through the CD's clear plastic layer, picks up information from the data layer on the silvery surface between the pits, then bounces off the reflective coating on the back side of the data layer. The reflected laser beam then travels back through the clear plastic layer, out of the CD, and into the CD player's "detector". As the CD rotates, the information is translated into a sequence of signals. These signals are interpreted by the detector as strings of zeros and ones. The decoded numbers are translated back into voltages, and the resulting electric signals are sent to a speaker as sound.
A: When a tectonic plate moves over the layer in the Earth known as the Asthenosphere, it may move over a fixed spot deeper in the Earth where magma (molten lava) forms. When this happens, a new volcano can punch through this plate and create an island. The Hawaiian Islands are believed to be formed from one such 'hot spot'. These hot spots represent regions where magma continuously breaks through the lithosphere, i.e. they represent stationary magma sources in the asthenosphere. As the plate moves away, the volcano stops erupting and a new one is formed in its place. With time, the volcanoes keep drifting westward and getting older relative to the one active volcano that is over the hot spot.
Islands can also be formed another way. Polyps, tiny animals in the sea related to jellyfish, protect their soft bodies by building limestone walls around them. As these colonies grow, they form reefs. Eventually, these reefs can cover hundreds of square miles. The polyps don't build their reefs above the surface of the water, but if the sea level drops or the land below the reef rises, the reef may emerge from the water. Then water-borne sand and wind-borne dust will accumulate on the reef and form an island.