Greek letter in the context of Alpha

In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, troughs, or zero crossings. Wavelength is a characteristic of both traveling waves and standing waves, as well as other spatial wave patterns. The inverse of the wavelength is called the spatial frequency. Wavelength is commonly designated by the Greek letter lambda (λ). For a modulated wave, wavelength may refer to the carrier wavelength of the signal. The term wavelength may also apply to the repeating envelope of modulated waves or waves formed by interference of several sinusoids.

Assuming a sinusoidal wave moving at a fixed wave speed, wavelength is inversely proportional to the frequency of the wave: waves with higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths.

The 2005 Atlantic hurricane season was a record-breaking, devastating and deadly Atlantic hurricane season. It is the second-costliest hurricane season, just behind the 2017 season. It featured 28 tropical and subtropical storms, which was the most recorded in a hurricane season until the 2020 season. The United States National Hurricane Center named 27 storms, exhausting the annual pre-designated list, requiring the use of six Greek letter names, and adding an additional unnamed subtropical storm during a post-season re-analysis. A record 15 storms attained hurricane status, with maximum sustained winds of at least 74 miles per hour (119 km/h). Of those, a record seven became major hurricanes, rated Category 3 or higher on the Saffir–Simpson scale. Four storms of this season became Category 5 hurricanes, the most of any season on record.

The four Category 5 hurricanes during the season were: Emily, Katrina, Rita, and Wilma. In July, Emily reached peak intensity in the Caribbean Sea, becoming the first Category 5 hurricane of the season, later weakening and striking Mexico twice. It was the first Category 5 hurricane recorded in the month of July and was the earliest-forming Category 5 hurricane on record, until Hurricane Beryl surpassed the record in July 2024. In August, Katrina reached peak winds in the Gulf of Mexico but weakened by the time it struck the U.S. states of Louisiana and Mississippi. The most devastating effects of the season were felt on the Gulf Coast of the United States, where Katrina's storm surge crippled New Orleans, Louisiana, for weeks and devastated the Mississippi coastline. Katrina became the costliest U.S. hurricane, leaving $125 billion in damage and 1,392 deaths. Rita followed in September, reaching peak intensity in the Gulf of Mexico before weakening and hitting near the border of Texas and Louisiana. The season's strongest hurricane, Wilma, became the most intense Atlantic hurricane on record, as measured by barometric pressure. Lasting for ten days in October, Wilma moved over Cozumel, the Yucatán Peninsula, and Florida, causing over $22 billion in damage and 52 deaths.

Micro (Greek letter μ, mu, non-italic) is a unit prefix in the metric system denoting a factor of one millionth (10). It comes from the Greek word μικρός (mikrós), meaning "small".

It is the only SI prefix which uses a character not from the Latin alphabet. In Unicode, the symbol is represented by U+03BC μ GREEK SMALL LETTER MU or the legacy symbol U+00B5 µ MICRO SIGN. The prefix "mc" is also commonly used; for example, "mcg" denotes a microgram (whereas mg denotes a milligram).

The kappa opacity mechanism is the driving mechanism behind the changes in luminosity of many types of pulsating variable stars. The term Eddington valve has been used for this mechanism, but this is increasingly obsolete.

Here, the Greek letter kappa (κ) is used to indicate the radiative opacity at any particular depth of the stellar atmosphere. In a normal star, an increase in compression of the atmosphere causes an increase in temperature and density; this produces a decrease in the opacity of the atmosphere, allowing energy to escape more rapidly. The result is an equilibrium condition where temperature and pressure are maintained in a balance. However, in cases where the opacity increases with temperature, the atmosphere becomes unstable against pulsations. If a layer of a stellar atmosphere moves inward, it becomes denser and more opaque, causing heat flow to be checked. In return, this heat increase causes a build-up of pressure that pushes the layer back out again. The result is a cyclic process as the layer repeatedly moves inward and then is forced back out again.