Astronomy Ch 12 The Sun

prominences

a cloud of hot gas in the Sun's outer atmosphere. This cloud is often shaped like an arch, supported by the Sun's magnetic field.

sunspot

a dark, cooler region on the Sun's visible surface created by intense magnetic fields.

spicule

a hot, thin column of gas in the Sun's chromosphere.

perfect gas law (ideal)

a law relating the pressure, density, and temperature of a gas. It states that the pressure is proportional to the density times the temperature.

coronal hole

a low density region in the Sun's corona. The solar wind may originate in these regions.

solar flare

a sudden increase in brightness of a small region on the Sun. This flare is caused by a magnetic disturbance.

cosmic rays

extremely energetic particles (protons, electrons, and so forth) traveling at nearly the speed of light. Some rays are emitted by the Sun, but most come from more-distant sources, perhaps exploding supernovas.

granulation

texture seen in the Sun's photosphere. Granulation is created by clumps of hot gas that rise to the Sun's surface.

nuclear fusion

the binding of two light nuclei to form a heavier nucleus, with some nuclear mass converted to energy. For example, the fusion of hydrogen into helium. This process supplies the energy of most stars and is commonly called "burning" by astronomers.

hydrostatic equilibrium

the condition in which pressure and gravitational forces in a star or planet are in balance. Without such balance, bodies will either collapse or expand.

solar cycle

the cyclic change in solar activity, such as sunspots and solar flares, rising and declining about every 11 years.

pressure

the force exerted by a substance such as a gas on an area divided by that area.

strong force (nuclear)

the force that holds protons and neutrons together in the nucleus.

chromosphere

the lower part of the Sun's outer atmosphere that lies directly above the Sun's visible surface. (photosphere)

proton-proton chain

the nuclear fusion process that converts hydrogen into helium in stars like the Sun and thereby generates their energy. This is a dominant energy-generation mechanism in cool, low-mass stars.

corona

the outer, hottest part of the Sun's atmosphere.

solar wind

the outflow of low-density, hot gas from the Sun's upper atmosphere. It is partially this wind that creates the tail of a comet, by blowing gas away from the comet's immediate surroundings.

convection zone

the region immediately below the Sun's visible surface in which its heat is carried by convection.

radiative zone

the region inside a star where its energy is carried outward by radiation. (that is protons)

Zeeman effect

the splitting of a single spectrum line into two or three lines by a magnetic field. A method for detecting magnetic fields in objects from their spectra.

Maunder minimum

the time period, from about AD 1600 to 1740, during which the Sun was relatively inactive. Few sunspots were observed during this period.

photosphere

the visible surface of the Sun. When we look at the Sun in the sky, we are seeing its photosphere.

neutrino

tiny neutral particles with little or no mass and immense penetrating power. These particles are produced in great numbers by the Sun and other stars as they fuse hydrogen into helium, and also by supernova explosions.