What causes mirages?
http://www.midas-migraine.net/About_Migraine/newback02.asp Many people mistakenly believe that migraine is a psychological disease. This is not true. Migraine is an organic neurological disease and headache is one of its symptoms. A number of theories have been put forward to explain the biological mechanisms involved in a migraine attack. One of the most popular theories is that a migraine is caused when a physiological trigger, or triggers, cause vasodilation (expansion of the blood vessels) in the cranial blood vessels, which activates trigeminal nerve endings in the brain. This activation of the ‘trigeminovascular system’ is thought to cause the release of chemical substances called neurotransmitters, of which the neurotransmitter serotonin (also known chemically as 5-hydroxytryptamine or 5-HT) is an important factor in the development of migraine. During a migraine attack, inflammation of the t
When light passes through a lens, it is bent: once as it enters the lens on one side, and again when is leaves the lens on the other side. This is refraction. It also happens when light passes from water to air (your legs appear shorter in a bathtub or pool). In these examples, the light passes suddenly from one medium (material) to another. The bending is associated with light slowing down or speeding up, which is related to a measureable optical property of each medium called the index of refraction. Light can also be bent by gradual change in density within the same material or medium, such as air. For example, air at high altitudes is much thinner; as sunlight enters the atmosphere at an angle, it slows down and its path is bent by the gradual increase in density. One subtle effect of this is that on the date of an equinox, the time from sunrise to sunset is a actually a few minutes over 12 hours; that’s because at sunset, we actually see a sun that has (geometerically) already set
Mirages are often shown in movies and cartoons as people seeing false images, like halucinations, but a mirage is strictly related to seeing refracted images. I’m not sure where you live, but in Florida (and other hot states) you can see this phenomenon on highways during the summer. Heat rising off of the asphalt causes light to be reflected in a rippling pattern close to the ground surface, which makes objects look like they are dancing when you look through the heat waves. Also, if you are looking at the heat waves from a higher point, like a crest in the road, the rippling makes the ground look like water, which is where the seeing water in the desert mirage comes from. mi·rage /mɪˈrɑʒ/ Pronunciation Key –
