Bioluminescence Vs Fluorescence

Bioluminescence is light produced by a chemical reaction within an organism. The protein which produces the light is generically called luciferin and the enzyme that catalyzes the reaction is called luciferase. The luciferase catalyzes the oxidation of luciferin resulting in light and an inactive oxyluciferin. In most cases, fresh luciferin must be brought into the system, either through the diet or by internal synthesis.

Sometimes the luciferin and luciferase as well as a co-factor such as oxygen, are bound together to form a single unit called a photoprotein. This molecule can be triggered to produce light when a particular type of ion (frequently Calcium)is added to the system .

Bioluminescence is not the same as "fluorescence" or "phosphorescence". In bioluminescence or chemiluminescence the excitation energy is supplied by a chemical reaction rather than from a source of light.

Fluorescence

In fluorescence, energy from a source of light is absorbed and reemitted as another photon. Fluorescence does not occur in complete darkness.

1. An electron (yellow) "orbits" the nucleus (blue), minding its own business.
2. A source of light of an appropriate wavelength (indicating its energy) strikes.
3. It drives the electron into a higher-energy orbital.
4. The electron is only stable there for a short time.
5. Shortly it returns to the lower energy level.
6. This way it emits the energy as a longer wavelength photon.
7. The electron continues on its way.

Due to energy loss while in the excited state, the photon emitted will always be of longer wavelength (more red, lower energy) than the exciting photon. This is how laundry detergents can get things "whiter than white": by absorbing non-visible UV light and fluorescing in the visible spectrum.

Phosphorescence

Phosphorescence is similar to fluorescence except that the excited product is more stable, so that the time until the energy is released is much longer, resulting in a glow after the light has been removed. This is the basis behind glow-in-the-dark stickers.

Chemiluminescence

Chemiluminescence is a general term for production of light when the excitation energy has come from a chemical reaction (as opposed to the absorption of photons, in fluorescence).

Bioluminescence is a subset of chemiluminescence, where the light-producing chemical reaction occurs inside an organism.

Types of Luciferens

There are few basic luciferins (light emitters).

Bacterial Luciferin 

Dinoflagellate luciferin

Vargulin or Cypridina-type luciferin

Coelenterazine

Firefly luciferin

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The Solstices and The Equinoxes

(click on the images to enlarge) 

     Solstice refers to either of the the two days during the year when the Earth is so located in its orbit that the inclination (about 23½°) of the polar axis is toward the Sun. This occurs on June 20 or 21 (summer solstice), when the North Pole is tilted toward the Sun; and on December 21 or 22 (winter solstice) when the South Pole is tilted toward the Sun. The adjectives summer and winter, used above, refer to the Northern Hemisphere; seasons are reversed in the Southern Hemisphere. The name is solstice is derived from the Latin sol (sun) and sistere (to stand still) because at the solstices, the Sun stands still in declination i.e. the apparent movement of the Sun's path north or south comes to a stop before reversing direction.

     The two equinoxes occur roughly midway between the solstices: the autumnal equinox (September 22 or 23) and spring/vernal equinox (March 20 or 21). The term equinox is derived from the Latin for equal nights, indicating that the day and night are of equal duration.
     The two solstices and the two equinoxes mark the beginning of four seasons.

* The dates drift with the difference between the actual solar years and 365 days, and are corrected by leap years
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Insolation

Insolation is the incident solar energy emitted by the Sun, which reaches a unit horizontal area of the Earth's surface. The term is a contraction of INcoming SOLar radiATION.

Direct insolation is the solar irradiance measured at a given location on Earth with a surface element perpendicular to the Sun's rays, excluding diffuse insolation (the solar radiation that is scattered or reflected by atmospheric components in the sky). Direct insolation is equal to the solar constant minus the light reflected, scattered, or absorbed by clouds and atmospheric particles.

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Albedo

Albedo is the fraction of solar energy (shortwave radiation) reflected from the Earth back into space. It is a measure of the reflectivity of the earth's surface.

Ice, especially with snow on top of it, has a high albedo: most sunlight hitting the surface bounces back towards space. (The word is derived from Latin albedo "whiteness", in turn from albus "white") Water is much more absorbent and less reflective. So, if there is a lot of water, more solar radiation is absorbed by the ocean than when ice dominates.

Albedo is not important at high latitudes in winter: there is hardly any incoming sunlight to worry about. It becomes important in spring and summer when the radiation entering through leads can greatly increase the melt rate of the sea ice.
 

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Solar Constant

     The solar constant is the amount of incoming solar electromagnetic radiation per unit area that would be incident upon the top of the Earth's atmosphere at a distance of one astronomical unit, or AU(1.496 × 108 km or 9.3 × 107 mi, roughly the mean distance from the Sun to the Earth). The value of solar constant is about 1.96 cal · cm⁻² · min⁻¹ (1367 W^-1 m⁻²).

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