Astronomy and related astronomical terms

A bright zodiacal constellation in the southern hemisphere between Libra and Sagittarius: Scorpius is represented as a scorpion.

The Sun passes briefly through Scorpius in the last week of November. The heart of the scorpion is marked by the bright red super giant star Antares.

Scorpius contains rich Milky Way star fields, plus the strongest X-ray source in the sky, Scorpius X-1. The whole area is rich in clusters and nebulae.

Half the length of the major axis of an ellipse: A Semi-major axis is a standard element used to describe an elliptical orbit.

In other words, a semi-major axis is,half of the larger diameter of an ellipse.

Half of the smaller diameter is the semi-minor axis.

A navigational instrument for determining latitude: A sextant can measure the angle between a heavenly body and the horizon.

The sextant was invented in 1730 by John Hadley (1682-1744) and can be used only in clear weather.

John Hadley was an English mathematician, inventor of the octant (reflecting quadrant) and precursor to the sextant around 1730.

A type of spiral galaxy first discovered by U.S. astronomer, Karl Seyfert (1911-1960), in the 1940s: The central region of a Seyfert galaxy is distinguished by powerful radiation, much of it is focused into narrow frequencies.

A Seyfert galaxy is a galaxy with an unusually bright central nucleus, often emitting strongly in the infrared region of the electromagnetic spectrum, as a result of hot dust within it.

About two per cent of all galaxies are Seyfert galaxies.

A Seyfert galaxy can be desccribed as a spiral galaxy with a small, compact, bright nucleus that exhibits variable light intensity and radio-wave emission.

A popular name for a meteor: A shooting star, or falling star, occurs when a meteoroid burns up while entering the Earth's atmosphere.

The time required for a celestial body in the solar system to complete one revolution with respect to the fixed stars (as observed from a fixed point outside the system). A planet's sidereal period can be calculated from its synodic period or the length of time during which a body in the solar system makes one orbit of the sun relative to the Earth.

The sidereal period of the Moon or an artificial satellite of the Earth is the time it takes to return to the same position against the background of stars.

1. Time that is measured by the stars rather than by the sun: Sidereal time is based on the sidereal day, which is the unit of measurement.

The sidereal time is a unit of time used in astronomy, equal to the period of time in which the Earth makes one rotation relative to the stars.
2. The time taken between successive meridian passages of the same star (23 hours, 56 minutes, 4.091 seconds): The sidereal day is about four minutes shorter than the twenty-four hours of the "solar day".

The class of iron meteorites, which includes those with about 90 percent iron and 10 percent nickel: The name siderite was given to iron meteorites that are made up almost completely of nickel-iron.

Story-iron meteorites: Siderolites are those meteorites with about 50 percent silicates and 50 percent iron and nickel.

A large group of minerals containing silicon and oxygen: Silicates are very common rocks, usually combined with one or more metals.

1. In astrophysics, the point in space-time at which the known laws of physics break down: Singularity is predicted to exist at the center of a black hole, where infinite gravitational forces compress the infalling mass of a collapsing star to infinite density.

It is also, according to the Big Bang model of the origin of the universe, to be the point from which the expansion of the universe began.

2. A point in space at which an infinitely strong gravitational field exists: A singularity relates to the concept predicted by general relativity to exist at the center of a black hole.

A measure of the year based on Earth's revolution around the Sun, which takes 365.2422 days: The solar calendar is used in most countries of the world today.

The interval between two successive noons: Since the Sun is moving across the sky background at a rate of about one degree per day in an easterly direction, the solar day is slightly longer than the sidereal day. Also, the Sun's rate of motion varies, and it is greatest at perihelion.

The mean solar day is equal to 24 hours, 3 minutes, 36.555 seconds.

Heat and light which is generated from the Sun: The Solar Energy Technologies Program focuses on developing cost-effective solar energy technologies that have the greatest potential to benefit the nation and the world.

Solar technologies diversify the energy supply, reduce the country's dependence on imported fuels, improve air quality, and offset greenhouse gas emissions. A growing solar industry also stimulates the economy by creating jobs in solar manufacturing and installation.

The collective name for the Sun and all the bodies that orbit around it, including the major planets, their satellites, periodic comets and the asteroids: The boundary of the Solar System could be taken as the outermost point reached by Pluto or about fifty astronomical units from the Sun.