The Hertzsprung-Russell diagram (HRD), abbreviated H-R diagram or HRD, is a scatter graph of stars showing the relationship between the stars’ absolute magnitudes or luminosities versus their spectral classifications or effective temperatures.

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The Milky Way is the galaxy that contains our Solar System. The Milky Way is a barred spiral galaxy that has a diameter usually considered to be about 100,000-120,000 light-years.

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The kelvin is a unit of measure for temperature based upon an absolute scale. It is one of the seven base units in the International System of Units (SI) and is assigned the unit symbol K.

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The speed of light (SoL) in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. Its precise value is 299.792.458 metres per second.

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A light-year (LY), is a unit of length used informally to express astronomical distances. It is approximately 9 trillion kilometres (9.460.730.472.580 kilometres or 63.241 Astronomical Units). A light-year is the distance that light travels in vacuum in one Julian year (365.25 days).

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