History of Star in Timeline

Stars are giant balls of plasma held together by their own gravity. The Sun is the closest star to Earth. Many other stars are visible at night but appear as tiny points of light due to their vast distance from us. Astronomers have grouped the most recognizable stars into constellations and asterisms, giving individual names to many of the brightest stars. They've also created catalogs listing and classifying all known stars. Our observable universe likely contains a staggering number of stars, but we can only see a tiny fraction with the naked eye, and all of those visible stars are within our own Milky Way galaxy.

1913: Development of the Hertzsprung-Russell Diagram

The Hertzsprung-Russell diagram, a crucial tool for understanding stellar evolution, was developed in 1913.

1921: First Measurement of Stellar Diameter

In 1921, Albert A. Michelson conducted the first measurement of a star's diameter utilizing an interferometer at the Mount Wilson Observatory.

1925: Proposal of Stellar Composition

Cecilia Payne-Gaposchkin, in her 1925 PhD thesis, put forward the idea that stars are mainly composed of hydrogen and helium.

2005: Discovery of Star with Lowest Iron Content

In 2005, the dwarf star HE1327-2326 was identified as having the lowest iron content ever measured, with only 1/200,000th that of the Sun.

2012: Definition of the Astronomical Unit

The IAU defined the astronomical unit (AU), roughly the average distance between Earth and the Sun, as a precise length in meters in 2012: 149,597,870,700 m.

2014: Estimate of Newtonian Constant of Gravitation

The most recent estimate for the Newtonian constant of gravitation, G, was made in 2014.

June 2015: Evidence for Population III Stars

Astronomers reported evidence of Population III stars, the first stars formed after the Big Bang, in the Cosmos Redshift 7 galaxy in June 2015.

2015: Definition of Nominal Solar Values

In 2015, the International Astronomical Union (IAU) established a set of standard solar values, defined as SI constants to be used for expressing stellar parameters.

2015: IAU Nominal Constants for Stellar Parameters

While the precise values of luminosity, radius, mass parameter, and mass might be revised in the future due to observational uncertainties, the IAU's 2015 nominal constants remain fixed SI values, serving as valuable references for quoting stellar parameters.