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animal astronauts

The first animals intentionally sent into space were fruit flies, launched aboard a V2 rocket by US scientists in 1947. The purpose of the launch was to test the effects of radiation at high altitude. Other animals sent into space include bacteria, cats, chimpanzees, dogs, mice, rabbits, rats, turtles, wine flies, worms, various species of monkey, and even frogs eggs.

aphelion

Aphelion is the point in the orbit of a planet, asteroid, or comet at which it is farthest from the Sun.

apogee

The point in the Moon's orbit farthest from the Earth.

armillary sphere

An armillary sphere is a miniature representation of the Sun, Earth, Moon, planets, important stars, and even signs of the Zodiac, in the form of a terrestrial globe. Its interlocking rings illustrate the paths of these celestial bodies as they revolve around each other.

asterism

The Big Dipper is one of the most well-known and identifiable clusters of stars in the sky. However, it is only a part of the constellation Ursa Major (the ‘Great Bear’). In astronomical terms, the Big Dipper is an asterism, that is, a group of stars forming a recognizable pattern in the sky, but not officially classed as a constellation. An asterism can be part of a constellation, or composed of stars sharing a common vicinity but members of different constellations.

Armillary sphere

Armillary sphere

Ceres

Ceres

Aphelion

Aphelion

asteroids & ceres

With a diameter of 950 km (590 miles), Ceres is the largest asteroid in the inner Solar System. It was discovered on January 1st, 1801, by Italian astronomer, Guiseppe Piazzi, who named the celestial body after the Roman goddess of growing plants, harvesting, and motherly love. Piazzi believed that Ceres was a planet. However, in 1802, British astronomer, William Herschel, coined the term ‘asteroid’, meaning small, star-like object. Writing on this subject Herschel said, “They resemble small stars so much as hardly to be distinguished from them, even by very good telescopes.” Today the term is applied to any of the numerous small, rocky, and often irregularly-shaped objects that circle the Sun, primarily in the Asteroid Belt, the region of space between the orbits of Mars and Jupiter. They range in size from Ceres, measured in the hundreds of kilometres, down to the smallest, measured in the tens of metres. Asteroids form an intermediate category between planets and meteoroids. They are sometimes referred to as minor planets or planetoids. Since Ceres was the first asteroid to be discovered, it is formally designated 1 Ceres. In recent times, however, Ceres has been re-classified as a dwarf planet, and as such, is the only body of this kind in the inner Solar System. NASA’s Dawn spacecraft, launched in September 2007, will be the first probe to visit Ceres and is scheduled to arrive there 2015.

astronomical unit

A derived constant used to indicate distances in the Solar System. The mean distance covered by light travelling (in a little over 8 minutes) from the Sun to the Earth, that is roughly 149,598,000 km (or 93,000,000 miles). Abbreviation = AU.

brightest star

The brightest star in the sky is Sirius, with a visual magnitude of -1.46; almost twice as luminous as Canopus, the next brightest star. From Earth, Sirius is the brightest star because of its intrinsic luminosity and its proximity to us. Located 2.6 parsecs away in the constellation Canis Major, Sirius is considered a close neighbour in astronomical terms, and it is moving towards our Solar System. Sirius is actually a binary star system, the primary being Sirius A, a white main sequence star. The secondary, Sirius B, is a faint white dwarf. The distance between the two stars varies from 8 to 31 AU. Sirius A is twice as massive as our Sun, and 25 times more luminous. The name Sirius is derived from the Ancient Greek word seirios meaning ‘glowing’ or ‘scorcher’. Through its location in the constellation Canis Major, Sirius is also known as the Dog Star.

ecliptic

The plane of the ecliptic is the plane of the Earth's orbit; it is perpendicular to the Earth's axis of rotation. (The Earth's axis is tilted by 23.5 degrees in relation to the ecliptic plane.) It can be thought of as a great circle formed where the plane intersects the celestial sphere. It is the projection of the Earth's equator on to the sky; the path along which the sun appears to move during the year as viewed from the Earth. The ecliptic plane is used as the primary reference plane when describing the position of bodies in the Solar System.

equinox

An equinox occurs twice a year, in spring (around 20 March) and in autumn (around 22 September). It occurs when the tilt of the Earth's axis is inclined neither away from nor towards the Sun, the center of the Sun being in the same plane as the Earth's equator. The term equinox can also be used in a broader sense, meaning the date when such a passage happens. Equinox is derived from the Latin aequus (equal) and nox (night), because around the equinox, night and day have approximately equal length. The equinoxes are the only times when the subsolar point is on the Equator. This point (the place on the Earth's surface where the center of the Sun can be observed exactly overhead) crosses the Equator moving northward at the March equinox and crosses the Equator moving southward at the September equinox. The equinox is a precise moment in time which is common to all observers on Earth.

escape velocity

To leave Earth, an object must break free of the planet's gravity by achieving an escape speed of 11.2 km/s (that is 40,320 km/h, or approx. 25,000 mph). The first spacecraft to reach the escape velocity of Earth was the Soviet Union's Luna 1, launched on January 2, 1959.

However, to escape the Sun’s gravity and exit the Solar System, an object launched from Earth has to reach a speed of 42.1 km/s (151,560 km/h, or approx. 94,175 mph). The first spacecraft to reach the escape velocity of the Sun was Pioneer 10 (launched 1972). However, the first spacecraft ever to exit the Solar System was Voyager 1 (launched 1977), in 2013.

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