Kirchhoff’s Laws and Stellar Properties

Posted on Feb 12, 2025 in Physics

Kirchhoff’s Laws

Kirchhoff’s Laws describe the behavior of light interacting with matter, resulting in different types of spectra:

Law 1: Continuous Spectrum: A solid, liquid, or dense gas excited to emit light will radiate at all wavelengths, producing a continuous spectrum.
Law 2: Emission Spectrum: A low-density gas excited to emit light will do so at specific wavelengths, producing an emission spectrum.
Law 3: Absorption Spectrum: If light comprising a continuous spectrum passes through a cool, low-density gas, the result is an absorption spectrum.

Filament: A solar eruption, seen from above, silhouetted against the bright photosphere.
Spicule: A small, flamelike projection in the chromosphere of the Sun (gases that last 5 to 15 minutes).
Coronagraph: A telescope designed to capture images of faint objects, such as the corona of the Sun, that are near relatively bright objects.
Magnetic Carpet: The network of small magnetic loops that covers the solar surface.
Solar Wind: Rapidly moving atoms and ions that escape from the solar corona and blow outward through the solar system.
Helioseismology: The study of the interior of the Sun by the analysis of its modes of vibration.

Astronomers can measure magnetic fields on the Sun using the Zeeman Effect.

Differential Rotation: The rotation of a body in which different parts of the body have different periods of rotation.
Dynamo Effect: The process by which a rotating, convecting body of conducting matter can generate a magnetic field.
Convection Zone: A region inside a star where energy is carried outward as rising hot gas and sinking cool gas.
Magnetic Polarity: Orientation and strength of a magnetic field’s north and south poles.
Babcock Model: This is thought to be responsible for the sunspot cycle.

Prominence: Composed of ionized gas trapped in a magnetic arch rising through the photosphere and chromosphere into the lower corona.

The distance between the stakes that astronomers put on the ground is called the baseline.

Stellar Parallax (p): Half the total shift of the star (the shift seen across a baseline of 1 AU).
Parsec (pc): The first unit of distance (distance to a star whose parallax is 1 arc second).

In 1989, the European Space Agency sent the Hipparcos satellite to measure stellar parallaxes above the atmosphere.

Absolute Visual Magnitude (Mv): Apparent visual magnitude that a star would have if it were 10 pc away. The ‘V’ indicates that it is a visual magnitude of the wavelength that we can only see with our eyes.
Luminosity (L): The total amount of energy a star radiates per second at all wavelengths.

Hot stars emit ultraviolet radiation that you can’t see, and cool stars emit infrared radiation.

Spectral Class: A star’s label in the temperature classification system based on the appearance of the star’s spectrum.
Spectral Sequence: The arrangement of spectral classes (O, B, A, F, G, K, M) from hottest to coolest.
Brown Dwarf: A very cool, low-luminosity star whose mass is not sufficient to ignite nuclear fusion.
L Dwarf, T Dwarf: Spectral classes of brown dwarf stars with lower surface temperatures and luminosities than M dwarfs.
Y Dwarf: A substellar object with a temperature below 500 K, having properties between brown dwarfs and Jovian planets.

Hertzsprung-Russell (H-R) Diagram: A plot of the intrinsic brightness versus the surface temperature of stars. It separates the effects of temperature and surface area on stellar luminosity.
Main Sequence: The region of the H-R diagram going from the upper left to the lower right, which includes roughly 90% of all stars generating energy by nuclear fusion.
Giant: A large, cool, highly luminous star in the upper right of the H-R diagram, typically 10 to 100 times the diameter of the Sun.
Supergiant: An exceptionally luminous star whose diameter is 100 to 1000 times that of the Sun.
Red Dwarf: A faint, cool, low-mass, main-sequence star.