UV astronomy
There are also other celestial sources of UV radiation.
Very large young stars shine most of their light in ultraviolet wavelengths. But the Earth's atmosphere blocks much of the UV radiation, and observations are conducted using high-altitude balloons and special orbiting telescopes equipped to observe the UV region of the EM spectrum.
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Substances like minerals, plants, fungi, microbes, and organic and inorganic chemicals, can absorb UV radiation, causing electrons to jump to a higher energy level. When the electrons return to a lower energy level, they emit a portion of the absorbed energy as visible light.
- Fluorescence is used for signs, safety vests, and other applications in which high visibility is important.
- In fluorescent tubes, an electric current is passed through mercury vapour, producing ultraviolet radiation along with a blue light.
UV light comes from the sun and is transmitted in waves or particles at different wavelengths an frequencies.
It makes black-light posters glow, and is responsible for summer tans. But too much exposure to UV radiation damage living tissue.
Some skin conditions can be treated using UV light.
PUVA (psoralen ultraviolet light treatment) is used to treat lymphoma, eczema, psoriasis, and vitiligo. Patients take a drug or apply a lotion to make their skin sensitive to light. Then a UV light is shone on the skin, slowing down the growth of the skin cells.
Most natural UV light comes from the sun. Only 10 % of sunlight is UV, and only one-third of it gets through the atmosphere.
Of the solar UV energy that reaches the equator, 95% is UVA, and 5% is UVB. No measurable UVC from the sun gets to the Earth's surface, because ozone, molecular oxygen, and water vapour in the upper atmosphere absorb the shortest UV wavelengths.
EM is the broad range of wavelengths. It is divided into seven regions and ordered in decreasing wavelength and increasing energy and frequency, namely radio waves, microwaves, infrared (IR), visible light, ultraviolet (UV), X-rays and gamma-rays.
Ultraviolet light falls is the range of the EM spectrum between visible light and X-rays.
UV radiation has enough energy to break chemical bonds. UV photons can cause ionization, meaning chemical bonds will break that otherwise would not.
It can be useful, for instance, in disinfecting a surface, but it can also damage materials and living tissues, particularly the skin and eyes that are affected by UVB and UVC radiation.
A suntan is a reaction to exposure to UVB rays. When the body senses sun damage, it sends melanin, a pigment in the body, to absorb UV light and protect the body from more damage, resulting in a darkened skin.
Continued exposure to UV radiation can damage the body's DNA. When the body senses this destruction, it floods the area with blood and inflammation to help with the healing process. Sometimes the cells with DNA mutated by the sun's rays turn into problem cells, known as skin cancer.
- UVA, or near UV (315-400 nanometers)
- UVB, or middle UV (280-315 nanometers)
- UVC, or far UV (180-280 nanometers)
Radiations with wavelengths from 10nm to 180nm are sometimes referred to as vacuum or extreme UV.
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- Spring is when seeds and roots start to grow. It is often wetter and warmer but not as hot when summer comes.
- Summer is the time when the temperature has the ability to reach its hottest and when forest fires are more frequent.
- Autumn is when the temperature cools down again, plants become dormant, and it is when animals prepare for hibernation in the winter.
- Winter is when some areas experience snowing while others experience cold rain.
Ocean water is full of mineral salts which enter through the rivers, passing through rock and soil. Water has a property of evaporation whereas salt does not, so a lot of salt is left behind.
Oceans are saline throughout the world, but the Mediterranean Sea is saltier. Many oceans are less salty due to the regular mixing of fresh river water.
The idea that food is safe to eat off the floor if you pick it up quickly is not accurate.
A study showed that in some cases, bacteria takes less than a second to transfer to food. The longer food was allowed to stay on a surface, the more bacteria was transferred to the food. The higher the moisture, the higher the risk of transfer.