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A-type star In the Harvard spectral classification system, a class of main-sequence star having spectra dominated by Balmer absorption lines of hydrogen. Stars of spectral class A are typically blue-white or white in color, measure between 1.4 and 2.1 times the mass of the Sun, and have surface temperatures of 7,600–10,000 kelvin.
Neptune's and Venus's have even lower eccentricities of 0.008 6 and 0.006 8 respectively, the latter being the least orbital eccentricity of any planet in the Solar System. Over hundreds of thousands of years, the eccentricity of the Earth's orbit varies from nearly 0.003 4 to almost 0.058 as a result of gravitational attractions among the planets.
PDS – is a distributed data system that NASA uses to archive data collected by Solar System missions. PEP – (instrumentation) PhotoElectric Photometry, an observing technique using photometers; PEPE – (instrumentation) Plasma Experiment for Planetary Exploration, an instrument on Deep Space 1; PGC – Principal Galaxies Catalogue
List of Solar System objects most distant from the Sun; List of Solar System objects by size; Lists of geological features of the Solar System; List of natural satellites (moons) Lists of small Solar System bodies; Lists of comets; List of meteor showers; Minor planets. List of minor planets. List of exceptional asteroids; List of minor planet ...
A planetary mnemonic refers to a phrase created to remember the planets and dwarf planets of the Solar System, with the order of words corresponding to increasing sidereal periods of the bodies. One simple visual mnemonic is to hold out both hands side-by-side with thumbs in the same direction (typically left-hand facing palm down, and right ...
Thus, the Sun occupies 0.00001% (1 part in 10 7) of the volume of a sphere with a radius the size of Earth's orbit, whereas Earth's volume is roughly 1 millionth (10 −6) that of the Sun. Jupiter, the largest planet, is 5.2 AU from the Sun and has a radius of 71,000 km (0.00047 AU; 44,000 mi), whereas the most distant planet, Neptune, is 30 AU ...
Astrophysics is a science that employs the methods and principles of physics and chemistry in the study of astronomical objects and phenomena. [1] [2] As one of the founders of the discipline, James Keeler, said, astrophysics "seeks to ascertain the nature of the heavenly bodies, rather than their positions or motions in space—what they are, rather than where they are", [3] which is studied ...
Proper names of planetary systems often follow common themes – for example, the planets of the star Copernicus are named after European astronomers. Proper names for planets outside of the Solar System – known as exoplanets – are chosen by the International Astronomical Union (IAU) through public naming contests known as NameExoWorlds.