Stars

Magnitude

The magnitude of a star is its apparent brightness as seen on Earth. The smaller the number on the scale, the brighter the apparent magnitude of the star is. The brightest star in Virgo, Scarpa has a magnitude of 1. The limited magnitude of the naked eye is around 6.5. It is a logarithmic scale. Each step on the scale means an increase of apparent brightness by 100 times.

Luminosity

Luminosity is the absolute magnitude of a star. It is the amount of light energy the star emits from its surface. It is independent from the position of the observer. It is also defined as the apparent magnitude of a star as viewed from 10 parsecs away. Its scale is logarithmic, and it is possible to convert from apparent to absolute.

Stellar mass

Mass is the most important stellar property as it is directly related to the gravity of the star. The more mass a star has, the greater its gravity. The determination of stellar mass is related to binary star systems.

As the stars in the binary system orbit each other, shifts in the spectral lines are observed. It is necessary to know their masses to figure out which spectral line belongs to which star.

Metallicity

Metallicity refers to the amount of elements that are heavier than hydrogen and helium present in the object. It doesn't specifically refer to only metals in the periodic table. Younger stars are more metal-rich than older stars as the early universe is theorised to not have as many metals. Thus, the age of a star can be figured out by figuring out its colour and metallicity.

Surface temperature

The stellar temperature can be determined from the spectrum of the colour of the light the star emits. Red and orange stars are cooler than blue and violet stars. 

The Stefan-Boltzmann Law states that the energy radiated per unit time of a black body across all wavelengths per unit time is directly proportional to the fourth power of the black body's thermodynamic temperature T.

Stellar classification

The Morgan-Keenan classification system is used to classify stars based on their spectral characteristics. It ranges from O-type stars to M-type stars. O-type stars are the hottest stars while M-type stars are the coolest stars. Luminocity is added to the classification system using Roman numerals.

The Hertz Sprung-Russel diagram is another stellar classification system.

Main sequence

Main sequence stars are a specific type of stars that fall on the specific part of the Hertz Sprung-Russel diagram. Stars on this band are called main-sequence stars. They fall along with the band but can vary depending on the age or composition on the band. It generates thermal energy in its core through the fusion of hydrogen into helium. The gravitational force of a star determines the rate in which it uses its hydrogen fuel.

Reflection

I feel that the rate of the lesson is ok, although it was sometimes hard to type out the information quick enough before the slides are switched.