Astronomy and related astronomical terms

The orbits and positions of the planets or "wanderers" could not be accurately accounted for before the invention of the telescope although star positions were known.

Understanding came with the revolutionary work of Galileo, Brahe, and Kepler which, together with Newton's contributions, finally swept away the Greek concept of an earth-centered universe and established the present model of the solar system.

The Greeks had simplified celestial mechanics according to the simple doctrine that "matter behaves according to nature."

1. The distance between two successive crests of a wave.
2. The distance between successive peaks, or troughs, of a wave.

1. A dense, small low-luminosity star of mass less than the Chandrasekhar limit (1.4 solar masses) left as the remnant of a supernova explosion.
2. A type of star that has collapsed after exhausting its nuclear fuel.

Leftover heat causes it to shine faintly.

A star may remain a giant or supergiant for several million years before all nuclear reactions cease.

Gravitational collapse then occurs with no outward pressure to stop it, and the final result may be a white dwarf.

Such a star is small, about the same size as the earth, but has about one million times the density of water and the temperature at the surface is a hundred thousand degrees, yet the luminosity is quite low; about one-thousandth of the sun.

A German-born British astronomer, technical expert and composer who became famous for discovering Uranus.

He also discovered infrared radiation and made many other discoveries in astronomy. In his later career, Herschel discovered two moons of Saturn, Mimas and Enceladus; as well as two moons of Uranus, Titania, and Oberon.

The moons were named by his son John Herschel in 1847 and 1852, respectively, well after the death of his father, William Herschel.

1. The shortening of a sunspot lying close to the edge of the sun's visible disk.
2. An effect in which the penumbra of a sunspot appears narrower in the direction toward the sun's center than in the direction toward the sun's limb.

In 1769, a Scottish astronomer named Alexander Wilson noticed that the shape of sunspots noticeably flattened as they approached the Sun's limb due to the solar rotation.

A member of a class of stars undergoing rapid mass loss, and having peculiar spectra.

Most Wolf-Rayet stars have companions in binary systems.

In astronomy, any of a class of cosmic objects that emit radiation at X-ray wavelength.

Because the earth’s atmosphere absorbs X-rays very efficiently, X-ray telescopes and detectors must be carried high above it by spacecraft to observe objects that produce such electromagnetic radiation.

Advances in instrumentation and improved observational techniques have led to the discovery of an increasing number of X-ray sources.

By the late 20th century, thousands of these objects had been detected throughout the universe.

1. The point in the sky directly above an individual: John looked up into the sky after dark and saw the moon at its zenith.
2. High point, peak, best moment: Being elected mayor was the zenith of Bill's political career.
3. Most successful, peak, greatest success: The United States was at its zenith before Donald Trump became President.
4. Etymology: from Arabic samt, "path over the head". The Arabic samt became the English zenith because a medieval scribe copied the word samt incorrectly, making it "senit", which became our zenith.

Another explanation: about 1387, from Old French cenith then French zénith; which came from Medieval Latin (Latin as written and spoken c.700-c.1500) cenit, senit, a bungled scribal transliteration of Arabic samt, "road, path"; an abbreviation of samt ar-ras, literally, "the way over the head".

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1. The angle between the direction of interest (of the sun, for example) and the zenith (directly overhead).
2. The angle between the direction to the zenith (point of the celestial sphere vertically overhead) and the direction of a light ray.

A point on the celestial sphere directly above an observer on the earth.

The point 180° opposite the zenith, directly underfoot, is the nadir and the astronomical zenith is defined by gravity; that is, by sighting up a plumb line.

If the line were not deflected by such local irregularities in the earth’s mass as mountains, it would point to the geographic zenith.

Because the earth rotates and is not a perfect sphere, the geocentric zenith is slightly different from the geographic zenith except at the Equator and the poles.

Geocentric zenith is the intersection with the celestial sphere of a straight line drawn through the observer’s position from the geometric center of the earth.

The point on the Hertzsprung-Russell diagram occupied by a star that has a core temperature high enough for nuclear reactions.

In ancient Mesopotamia, a monumental pyramidal structure composed of brick or stone stories, or steps, of decreasing size built on top of each other which was built in the center of most major Babylonian cities.

Many ziggurats were dedicated to celestial gods; for example, the one at Ur, was dedicated to Su'en, the moon god.

As with many other ancient civilizations, Babylonian astronomy was a composition of religion, mythology, and astrology.

The priests were apparently the best-educated sector of the population; therefore, they were largely responsible for the development of Babylonian science, including astronomy.

The Babylonian empire lasted from about 2700 B.C. to 500 B.C., during which time the priests apparently did much to demystify astronomy and to put it on a scientific basis.

The dominant belief that the zones of the sky contain twelve zodiacal constellations through which the paths of the sun, moon, and planets appear to move.

"The Sun does not move", wrote Leonardo da Vinci in 1495

Well, everything in the Cosmos moves, including the sun, the earth and the Star Signs of the Zodiac. The Signs of the Zodiac were first mapped by the ancient Babylonians about 3,000 years ago when, indeed, there were 12 Star Signs.

Movement on the Cosmic time-scale is very slow compared with the time-scale of a human life. The Star Signs are slipping by a small amount each year, so that there are now 13 Signs in the Zodiac.

The Sign of Ophiuchus (30 November-17 December) moved into the Zodiac over 1,000 years ago. Most astrologers continued to use the traditional 12 Signs of the Zodiac because they were unaware of star movements. That practice has continued to the present day.

To illustrate just how slowly the Cosmic clock advances: the Age of Pisces replaced the Age of Aries about 1,400 years ago, and the much-heralded Age of Aquarius will not be here for another 600 years!

The New Signs of the Zodiac

1. The New Pisces: First Sign of the Zodiac: 12 March to 18 April.
2. The New Aries: Second Sign of the Zodiac: 19 April to 13 May.
3. The New Taurus: Third Sign of the Zodiac: 14 May to 20 June.
4. The New Gemini: Fourth Sign of the Zodiac: 21 June to 19 July.
5. The New Cancer: Fifth Sign of the Zodiac: 20 July to 19 August.
6. The New Leo: Sixth Sign of the Zodiac: 20 August to 15 September.
7. The New Virgo: Seventh Sign of the Zodiac: 16 September to 30 October.
8. The New Libra: Eighth Sign of the Zodiac: 31 October to 22 November.
9. The New Scorpio: Ninth Sign of the Zodiac: 23 to 29 November.
10. The New Ophiuchus: Tenth Sign of the Zodiac: 30 November to 17 December.
11. The New Sagittarius: Eleventh Sign of the Zodiac: 18 December to 18 January.
12. The New Capricorn: Twelfth Sign of the Zodiac: 19 January to 15 February.
13. The New Aquarius: Thirteenth Sign of the Zodiac: 16 February to 11 March.