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Astronomical Terms & Definitions | World General Astronomical Terms & Definitions | World General Knowledge Albedo: In astronomy, the term albedo refers to the brightness of an object in space. Derived from Latin, albedo means “whiteness” (albus= “white”). Albedo is measured on a scale from 0 to 1, where 0 refers to an object that is completely dark, i.e., it does not reflect any light. 1 on the scale refers to a perfectly reflective object. The Moon has an Albedo of 0.12, while Earth’s average albedo is 0.3. Altitude (elevation): Altitude or elevation is the vertical angle an object makes with the horizon. Annular Solar Eclipse: An annular solar eclipse happens when the Moon covers the Sun’s center, leaving the Sun’s visible outer edges to form a “ring of fire” or annulus around the Moon. Antumbra: The antumbra is the lighter part of a shadow that forms at a certain distance from the object casting the shadow. It is involved in annular solar eclipses and planet transits. Asterism A pattern of stars recognizable to observers from Earth. Asterisms may or may not be part of a constellation. The Big Dipper is one of the most well-known asterisms. Its stars belong to the constellation Ursa Major. Asteroid These are found between the orbits of Mars and Jupiter. These are celestial bodies with sizes ranging from a few meters to hundreds of the kilometres of diameter, revolving around the sun. They have originated by the disintegration of the planets. Astronomical Season Astronomers and scientists use the dates of equinoxes and solstices to mark the beginning and end of seasons in a year. In the Northern Hemisphere, the four astronomical seasons are: Downloaded from www.csstimes.pk | 1 Astronomical Terms & Definitions | World General Knowledge Spring: March equinox to June solstice. Summer: June solstice to September equinox. Fall (autumn): September equinox to December solstice. Winter: December solstice to March equinox. Astronomical Twilight Astronomical twilight is the darkest of the three twilight phases. It is the earliest stage of dawn in the morning and the last stage of dusk in the evening. Astronomical Unit The average distance between Earth and the Sun, 1.5 x 108 km Atmospheric Phenomena Atmospheric phenomena occur when light, usually from a natural source, but sometimes from artificial sources, is reflected or refracted as it passes through the atmosphere, for example by air molecules, ice crystals, or different types of particles. Aurora The glowing light from solar particles interact with Earth’s magnetic field is called aurora Aurora Borealis and Aurora Australis An aurora is a natural phenomenon that creates bright and colorful light displays in the sky. In the Arctic Circle, they are known as aurora borealis or northern lights; in the Antarctic Circle, they are called aurora australis or southern lights. Axial Tilt – Obliquity Earth’s axis is tilted by about 23.4 degrees to the perpendicular to the orbital plane. Earth rotates the Sun at a slant. This means that different amounts of sunlight reach the Northern and Southern Hemispheres throughout the year. This is the reason we have seasons on Earth. Axis An axis in astronomy refers to the (imaginary) line that an object, usually a planet, rotates Downloaded from www.csstimes.pk | 2 Astronomical Terms & Definitions | World General Knowledge around. Earth’s rotational axis is an imaginary straight line that runs through the North and South Poles Azimuth An object’s cardinal direction, such as north, east, south, or west Black Hole A Neutron Star remains contracting and, thus, mass in a large quantity, concentrates on one point. Such body with high density is called Black Hole. It does not allow anything to escape, including the light due to which it can be seen. It is John Wheeler who propounded the concept of Black Hole Black Moon It can be the third New Moon in an astronomical season with four New Moons or the second New Moon in the same calendar month. Two Definitions of Blue Moon Seasonal Blue Moon = The third Full Moon in an astronomical season with four Full Moons (versus the usual three). Monthly Blue Moon = The second Full Moon in a month with two Full Moons. If the moon actually looks blue, it’s caused by a rare type of dust in the atmosphere. Celestial Equator The celestial equator is the projection of Earth’s equator onto the celestial sphere. From our perspective, it is the part of the sky directly above the equator. Celestial Horizon The imaginary horizontal line separating the two hemispheres of the celestial sphere is called the celestial horizon. Celestial Pole The celestial poles are imaginary lines that trace Earth’s rotation axis in space. From our perspective, they are the points in the sky directly above the North Pole and the South Pole. Because of this, objects that lie on the celestial pole do not seem to move at all, while all Downloaded from www.csstimes.pk | 3 Astronomical Terms & Definitions | World General Knowledge other objects, mostly stars, seem to move in a circle around the pole. Celestial Sphere The celestial sphere is an imaginary sphere that extends infinitely into space with Earth at its center. It is the backdrop the horizontal coordinate system uses to map the sky and describe the positions of its objects. Circumpolar Stars Circumpolar stars never set or go below the horizon for observers from specific latitudes. They are visible to observers from these latitudes throughout the year because of their proximity to the celestial pole. Circumpolar objects lie within the circumpolar circle, and stars circumpolar to latitudes in the Northern Hemisphere are not visible in the Southern Hemisphere, and vice versa. Civil Twilight Civil twilight is the brightest of the three twilight phases. The Sun is just below the horizon, so there is generally enough natural light to carry out most outdoor activities. Comet One of the small, icy bodies that orbit the sun that make tails of gas and dust when they get close to the sun. There are the bodies composed of dust, ice and gases, which come from the colder and darker areas, away from the sun. They go around the sun in large and irregular orbits. While moving in their orbits, when they come very close to the sun, they start glowing with a bright gaseous tail always pointing away from the sun. Many a times, comets are visible to the naked eye and present a very spectacular sight. Comet Halley, discovered by Edmund Halley, returns after every 76 years Constellation In the present day, a constellation is a two-dimensional area in space as defined by the International Astronomical Union (IAU). Today, there are 88 officially recognized constellations. This is different from the historical understanding of a constellation dominantly used in astrology which is defined as a group of stars easily identifiable by a pattern to observers on Earth. Downloaded from www.csstimes.pk | 4 Astronomical Terms & Definitions | World General Knowledge Crust The land and oceans at the Earth’s surface lie on an outer layer of cool, hard rock called the crust. Core At the very centre of the Earth is a super-hot ball of iron called the core Dawn Dawn is the transition from night to day as the sky gets brighter. Scientists distinguish between three definitions of dawn civil, nautical, and astronomical dawn. Each one is a specific moment in time, based on the solar elevation angle. Dusk Dusk generally refers to the transition from day to night. Scientists distinguish between three definitions of dusk civil, nautical, and astronomical dusk. Each one is a specific moment in time, based on the solar elevation angle. Diamond Ring Just before the moon completely covers the sun, mountains on the moon allow a bit of light to peek through creating this beautiful diamond ring effect at right Eight planets Solar System consists of eight “planets” Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Ecliptic The path the Sun seems to follow in the sky Downloaded from www.csstimes.pk | 5 Astronomical Terms & Definitions | World General Knowledge Earthshine Earthshine is a dull glow which sometimes lights up the unlit part of the Moon. It usually occurs a few days before and after a New Moon when sunlight reflects off Earth’s surface and illuminates the portion of the Moon’s surface which is not lit up by direct sunlight. Eclipses A solar eclipse happens when the New Moon moves between Earth and the Sun. A lunar eclipse occurs when Earth casts a shadow onto the Full Moon. Ecliptic — Ecliptic Plane – Orbital Plane The ecliptic plane, also called orbital plane, is the imaginary line that traces the Sun’s apparent path in the sky. In other words, it is the projection of our planet’s orbit into the celestial sphere. Any constellations on this line are known as zodiacal or zodiac constellations. Earth’s Axial Tilt or Obliquity When an object the size of Mars crashed into the newly formed planet Earth around 4.5 billion years ago, it knocked our planet over and left it tilted at an angle. Elevation (altitude) Elevation or altitude is the vertical angle an object makes with the horizon. Equinox There are two equinoxes every year – in March and September – when the Sun is directly above the equator and the length of night and day are nearly equal. False Dawn False dawn or zodiacal light is a rare optical phenomenon that occurs around sunset and sunrise, usually during early spring and late fall. Full Moon The Full Moon is the Moon phase when the entire face of the Moon is lit up.
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