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109 Gm (0.7 au) – distance between Venus and the Sun; 149.6 Gm (93.0 million mi; 1.0 au) – average distance between the Earth and the Sun – the original definition of the astronomical unit; 199 Gm (1.3 au) – diameter of Rho Persei, an asymptotic giant branch star, fusing carbon into neon in a shell surrounding an inert core. [179]
Solar sails rely on the fact that light reflected from a surface exerts pressure on the surface. The radiation pressure is small and decreases by the square of the distance from the Sun, but unlike rockets, solar sails require no fuel. Although the thrust is small, it continues as long as the Sun shines and the sail is deployed. [24]
One astronomical unit (about 150 million kilometres; 93 million miles) is defined as the mean distance between the centers of the Sun and the Earth. The instantaneous distance varies by about ± 2.5 million kilometres (1.6 million miles) as Earth moves from perihelion around 3 January to aphelion around 4 July. [36]
Minimum orbit intersection distance (MOID) is a measure used in astronomy to assess potential close approaches and collision risks between astronomical objects. [1] [2] It is defined as the distance between the closest points of the osculating orbits of two bodies. Of greatest interest is the risk of a collision with Earth.
Trained marine mammal observers alerted the crew to any sign of whales or other animals; the sound generated with this kind of technology can be disruptive and harm marine creatures.
The ionosphere is a region of the upper atmosphere, from about 80 km (50 miles) to 1000 km (600 miles) in altitude, where neutral air is ionized by solar photons, solar particles, and cosmic rays. When high-frequency signals enter the ionosphere at a low angle they are bent back towards the Earth by the ionized layer. [ 1 ]
The effect of progressively shifting Sun angle on the appearance of a vista as seen from Canyonlands National Park. In each image air quality is the same. 1, 2 – represents a moment after sunrise; 3, 4 – a vista around noon, when the angular distance to the Sun is the biggest, hence visibility is the best (Malm, 2016).
The celebrated Challenger Expedition was a grand tour of the world covering 68,000 nautical miles (125,936 km), organised by the Royal Society in London in collaboration with the University of Edinburgh. Charles Thomson was the leader of a large scientific team. Captains: George Nares (1873 and 1874) and Frank Tourle Thomson (1875 and 1876)