Professional astronomy is split into
observational and
theoretical branches. Observational astronomy is focused on acquiring data from observations of astronomical objects. This data is then analyzed using basic principles of physics. Theoretical astronomy is oriented toward the development of computer or analytical models to describe astronomical objects and phenomena. These two fields complement each other. Theoretical astronomy seeks to explain observational results and observations are used to confirm theoretical results.
Astronomy is one of the few sciences in which amateurs play an
active role. This is especially true for the discovery and observation of
transient events.
Amateur astronomers have helped with many important discoveries, such as finding new comets. (Full article...)
Image 2Artist conception of the
Big Bang cosmological model, the most widely accepted out of all in physical cosmology (neither time nor size to scale) (from Physical cosmology)
Image 6An example of a gravitational lens found in the DESI Legacy Surveys data. There are four sets of lensed images in DESI-090.9854-35.9683, corresponding to four distinct background galaxies—from the outermost giant red arc to the innermost bright blue arc, arranged in four concentric circles. All of them are gravitationally warped—or lensed—by the orange galaxy at the very center. Dark matter is expected to produce gravitational lensing also. (from Physical cosmology)
Image 9Segment of the
astronomical ceiling of Senenmut's Tomb (circa 1479–1458 BC), depicting constellations, protective deities, and twenty-four segmented wheels for the hours of the day and the months of the year (from History of astronomy)
Image 12An image of the
Cat's Paw Nebula created combining the work of professional and amateur astronomers. The image is the combination of the 2.2-metre MPG/ESO telescope of the La Silla Observatory in Chile and a 0.4-meter amateur telescope. (from Amateur astronomy)
Image 13Portrait of the Flemish astronomer
Ferdinand Verbiest who became head of the Mathematical Board and director of the Observatory of the Chinese emperor in 1669 (from Astronomer)
Image 14An amateur astrophotography setup with an automated guide system connected to a laptop (from Observational astronomy)
Image 15Overview of types of observational astronomy by observed wavelengths and their observability. (from Observational astronomy)
Image 17The inflationary theory as an augmentation to the Big Bang theory was first proposed by Alan Guth of MIT. Inflation solves the 'horizon problem' by making the early universe much more compact than was assumed in the standard model. Given such smaller size, causal contact (i.e., thermal communication) would have been possible among all regions of the early universe. The image was an adaptation from various generic charts depicting the growth of the size of the observable universe, for both the standard model and inflationary model respectively, of the Big Bang theory. (from Physical cosmology)
Image 19Amateur astronomer recording observations of the sun. (from Amateur astronomy)
Image 20Places like
Paranal Observatory offer crystal clear skies for observing astronomical objects with or without instruments. (from Amateur astronomy)
Image 21The main platform at
La Silla hosts a huge range of telescopes with which astronomers can explore the Universe. (from Observational astronomy)
Image 26ALMA is the world's most powerful telescope for studying the Universe at submillimeter and millimeter wavelengths. (from Observational astronomy)
Image 35Comparison of
CMB (Cosmic microwave background) results from satellites
COBE,
WMAP and Planck documenting a progress in 1989–2013 (from History of astronomy)
This is a
Featured article, which represents some of the best content on English Wikipedia.
Enceladus imaged by the Cassini orbiter, October 2015
Enceladus is the sixth-largest
moon of Saturn and the 18th-largest in the
Solar System. It is about 500
kilometers (310
miles) in diameter, about a tenth of that of
Saturn's largest moon,
Titan. It is mostly covered by fresh, clean ice, making it one of the most reflective bodies of the Solar System. Consequently, its surface temperature at noon reaches only −198
°C (75.1
K; −324.4
°F), far colder than a light-absorbing body would be. Despite its small size, Enceladus has a wide variety of surface features, ranging from old, heavily
cratered regions to young,
tectonically deformed
terrain.
Enceladus was discovered on August 28, 1789, by
William Herschel, but little was known about it until the two
Voyager spacecrafts, Voyager 1 and Voyager 2, flew by Saturn in 1980 and 1981. In 2005, the spacecraft Cassini started multiple close flybys of Enceladus, revealing its surface and environment in greater detail. In particular, Cassini discovered water-rich
plumes venting from the south
polar region.
Cryovolcanoes near the south pole shoot
geyser-like jets of
water vapor,
molecular hydrogen, other volatiles, and solid material, including
sodium chloride crystals and ice particles, into space, totaling about 200
kilograms (440
pounds) per second. More than 100 geysers have been identified. Some of the water vapor falls back as "snow"; the rest escapes and supplies most of the material making up Saturn's
E ring. According to
NASA scientists, the plumes are similar in composition to
comets. In 2014, NASA reported that Cassini had found evidence for a large south polar
subsurface ocean of liquid water with a thickness of around 10 km (6 mi). The existence of Enceladus' subsurface ocean has since been mathematically modelled and replicated. (Full article...)
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