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A contemporary German popular astronomical book also noticed that light-year is an odd name. [25] In 1868 an English journal labelled the light-year as a unit used by the Germans. [26] Eddington called the light-year an inconvenient and irrelevant unit, which had sometimes crept from popular use into technical investigations. [27]
A light-year is the distance light travels in one Julian year, around 9461 billion kilometres, 5879 billion miles, or 0.3066 parsecs. In round figures, a light year is nearly 10 trillion kilometres or nearly 6 trillion miles. Proxima Centauri, the closest star to Earth after the Sun, is around 4.2 light-years away. [89]
Dawn begins with the first sight of lightness in the morning, and continues until the Sun breaks the horizon. The morning twilight is divided in three phases, which are determined by the angular distance of the centre of the Sun (degrees below the horizon) in the morning. These are astronomical, nautical and civil twilight.
The first direct measurement of the distance to a star (61 Cygni at 11.4 light-years) was made in 1838 by Friedrich Bessel using the parallax technique. Parallax measurements demonstrated the vast separation of the stars in the heavens. [citation needed] Observation of double stars gained increasing importance during the 19th century. In 1834 ...
The Milky Way Galaxy has a diameter of 100,000–200,000 light-years and is estimated to contain 100–400 billion stars and at least that number of planets. The Solar System is located on the inner edge of one of the Milky Way's spiral arms, about 27,000 light-years from the Galactic Center, which the Sun orbits with a period of 240 million ...
Multiple other interstellar clouds exist in the region within 300 light-years of the Sun, known as the Local Bubble. [262] The latter feature is an hourglass-shaped cavity or superbubble in the interstellar medium roughly 300 light-years across. The bubble is suffused with high-temperature plasma, suggesting that it may be the product of ...
This is the first time that these galaxies have been imaged in such detail, and the first time scientists were able to confirm that they produced enough radiation to end the light-less tyranny of ...
A 1740 map of Paris. Ortelius World Map, 1570. Historical geography is the branch of geography that studies the ways in which geographic phenomena have changed over time. [1] In its modern form, it is a synthesizing discipline which shares both topical and methodological similarities with history, anthropology, ecology, geology, environmental studies, literary studies, and other fields.