What is a star?
A star is a luminous ball of plasma held together by its own gravitational field. The elements that make up most stars are mainly hydrogen and helium in the plasma phase of matter. The nearest star to Earth is the Sun. Stars are the most common astronomical objects.
How do stars make light?
Stars use a nuclear reaction to make their own light. Stars fuse hydrogen atoms to form helium. In this process, huge amounts of energy are released. Some of this energy is released in the form of visible light. Other electromagnetic waves, such as radio, microwaves, X-rays, and gamma rays are also released during the fusion process.
How are stars classified?
Stars are classified in several different ways, such as by their mass, their radius, their luminosity, or their age. Most of the time using the first three classification systems, stars are compared to Earth’s Sun. For instance, the star Betelgeuse has a mass about 15 times greater than the Sun, a luminosity about 50,000 times brighter than our Sun, and over a 1,200 times greater solar radius than the Sun.
What is a solar radius?
The solar radius of a star is the average distance from the star’s center to its outermost edge.
What is luminosity?
Luminosity is the brightness of a star and can be measured in terms of intrinsic brightness and apparent brightness.
What is the difference between the apparent brightness and intrinsic brightness of a star?
The intrinsic brightness of a star is a measure of the total electromagnetic output of the star. This value does not significantly vary with the distance away from the star. The apparent brightness of a star is based on how bright a star appears in Earth’s sky and is directly impacted by the distance the star is away from Earth. The farther away from Earth, the dimmer the star.
What does Fc represent?
The abbreviation “Fc” stands for “foot-candle” and is a measure of the intensity of light. One Fc is the illumination of a one-foot radius sphere with a point source of one candela or lumen. A typical classroom has a light intensity of about 80 Fc.
How are stars classified by their temperature?
The brightness of a star is dependent on the temperature of the star. While hot stars are expected to be brighter than cooler stars, the color of the light emitted by the star is a good measure of the star’s temperature. The hottest stars appear blue, while the coolest stars are red. The frequency range of the visible part of the electromagnetic spectrum coincides with the temperature range of stars. The image below shows the average surface temperatures (measured in Kelvin) of stars and their common colors.
What is the Hertzsprung-Russell (H-R) diagram?
The H-R diagram is a tool used by astronomers to classify stars based on their history, age, function, and rate of mass loss. Using this system, stars are broadly classified into four main classes: giants, supergiants, main sequence, and white dwarfs. Stars are further classified on the diagram into various types using a letter system that indicates the evolution of the star. These types range from O, B, A, F, G, K, to M with type O being the youngest stars and M the oldest. A version of the H-R diagram appears below.
Why are some stars in the night sky brighter than other stars? Get started now investigating the causes of the apparent brightness of stars in the sky.)
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