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The observable universe is thus a sphere with a diameter of about 28.5 gigaparsecs [32] (93 billion light-years or 8.8 × 10 26 m). [33] Assuming that space is roughly flat (in the sense of being a Euclidean space), this size corresponds to a comoving volume of about 1.22 × 10 4 Gpc 3 (4.22 × 10 5 Gly 3 or 3.57 × 10 80 m 3). [34]
A conjunction is when two astronomical objects or spacecraft appear to be close to each other in the sky. Learn about different types of conjunctions, such as appulse, syzygy, eclipse, transit, and occultation, and how they depend on the observer's position and the planets' orbits.
The idea is that since all the stars share a common space velocity, they will appear to move towards a point of common convergence ("vanishing point") on the sky. This is essentially a perspective effect. Using the moving-cluster method, the distance to a given star cluster (in parsecs) can be determined using the following equation:
Binary stars which are both visual and spectroscopic binaries also can have their distance estimated by similar means, and do not suffer from the above geometric uncertainty. The common characteristic to these methods is that a measurement of angular motion is combined with a measurement of the absolute velocity (usually obtained via the ...
Learn how astronomers use spectroscopy to measure the spectrum of electromagnetic radiation from stars and other celestial objects. Find out how spectroscopy can reveal the chemical composition, temperature, density, mass, distance and luminosity of stars, and how different methods are used for visible light, radio waves and X-rays.
In Greek antiquity the ideas of celestial spheres and rings first appeared in the cosmology of Anaximander in the early 6th century BC. [7] In his cosmology both the Sun and Moon are circular open vents in tubular rings of fire enclosed in tubes of condensed air; these rings constitute the rims of rotating chariot-like wheels pivoting on the Earth at their centre.
Observational astronomy is the practice and study of observing celestial objects with various instruments and methods. It is a division of astronomy that records data about the observable universe, in contrast with theoretical astronomy.
The Hubble Deep Field is an image of a small region in the constellation Ursa Major, constructed from 342 exposures by the Hubble Space Telescope. It reveals about 3,000 galaxies, some of which are among the youngest and most distant known, and has become a landmark image in the study of the early universe.