Common Astronomy Terms and Definitions


Common Astronomy Terms and Definitions
1.)Absorption Spectrums – Also called a “dark-line” Spectrum, this occurs when certain energies of light (colors) are absorbed by atoms.
2.)Achromatic Lens – A color corrected lens formed by cementing together two different glass lenses

3.)Aperture – The effective diameter of the objective telescope lens
4.)Aphelion – The farthest point in the orbit of a planet about the sun
5.)Azimuth Telescope Mount – This telescope mount moves the telescope in elevation and azimuth
6.)Celestial Equator – The projection of the Earth’s equator on the celestial sphere
7.)Celestial Sphere – All the fixed stars in the sky
8.)Charge-Coupled Device or CCD – A modern light detector capable of detecting faint light sources and when connected to a computer, this system can capture images and store them in the computer memory
9.)Chromatic Aberration – This occurs in a simple lens where different colors of light are focused at different places
10.)Constructive Interference – This occurs when the crest of one wave meets the crest of a second wave in time and space so that a larger wave is generated from the sum of the two original waves
11.)Continuous Spectra – When the light from a heated source passes through a prism or diffraction grating, the light is spread out into a beautiful band of all colors from red through blue
12.)Convex Lens – A simple glass lens that is thick in the center and thin at the edges
13.)Counter Weights – Sliding adjustable weights attached to the main body of the telescope to aid in the balance of the telescope as it is driven across the sky following a celestial object
14.)Cryogenics – The science of low temperatures
15.)Days in the Week – The days of the week were named after the five planets: Mercury, Venus, Mars, Jupiter and Saturn plus the Sun and the Moon
16.)Declination – A measure in degrees north and south of the celestial equator on the celestial sphere
17.)Deferent – The name for the perfect circular path, centered on the Earth, on which the Sun, Moon and other planets orbited the Earth in the Geocentric solar system
18.)Destructive Interference – Where the crest of one wave meets the trough of a second wave
19.)Diffraction – The bending of waves around corners or obstacles
20.)Dispersion – The breaking-up of white light into the spectrum of colors
21.)Doppler Effect – The change of wavelength due to the relative motion between the source of the wave and the observer of the wave
22.)Ecliptic – The apparent path of the Sun on the Celestial Sphere
23.)Electromagnetic Spectrum – Know the six major regions of this spectrum. In the order of increasing energy, they are named: Radio, Infared, Visible Lighe, Ultraviolet, X-rays and Gamma Rays
24.)Emission Spectrum – Also called the bright line spectrum, it looks like a series of bright colored lines
25.)Epicycle – Small perfect circles centered on the deferent where planets would move in the geocentric model of the solar system
26.)Equatorial Telescope Mount – A useful mount for a telescope having two reference circles, the declination circle and the right-ascension circle
27.)Extended Objects – Objects that have a discernible area or disk when viewed through a telescope and may benefit from magnification
28.)Finder Telescope – It is usually the shortest accessory telescope, having a wide field of view, low magnificaiotn, and cross hairs
29.)Galileo Galilei – Born in 1564, at Pisa, he was one of the first to make detailed observations of the Moon, new stars, the moons of Jupiter, Saturn, the phases of Venus, sunspots and comets
30.)Geocentric Model – the earth centered model of the solar system
31.)Gravity Wave Telescope – A large aluminum cylinder that vibrates or “rings” when a gravity wave excites it
32.)Guide Telescope – Often a “middle-sized” accessory telescope, usually pointed “off-axis” at a nearby star. The nearby star is used as a reference for position checks during timed exposure photography taken through the main telescope. One looks through the guide telescope to check the reference position of the star and if corrections are needed, then slow-motion corrections to the right ascension and declination dricers are applied to the drive mode.
33.)Heliacal Rising – Occurs on the first day each year when the star can be seen just before dawn.
34.)Heliacal Setting – Occurs on the last day of the year when the star can be seen at dusk.
35.)Heliocentric Model – The Sun-centered model of the solar system. Copernicus wrote of this model in his work, DE REVOLUTIONIBUS ORBIUM COELESTIUM.
36.)Isaac Newton - Born on Jan. 4, 1643, at Woolstrhorpe in Lincolnshire we admire him for sharing insight into the Physics of motion and the law of gravity. His interests included astronomy, pure mathematics, optics, chemistry, heat, chronology, and theology.
37.)John Kepler – Born in 1571, at Weil in Wurtemberg, he studied Tycho’s data in a attempt to understand the truemotions of the planets. He developed three laws of motion that we admire today; 1) Planets move in elliptical orbits with the sun at one focus, 2) An imaginary line connecting the planets to the sun will “sweep out” equal times, or in another way to express it, a planet moves faster in its orbit when closest to the sun and slower when farther away, #0 the square of the orbital of a planet is directly proportional to the cube of the average distance from the sun: The third law points out that the planets are larger orbits move more slowly around the sun, a fact implying that the sun-planet force decreases with distance.
39.)Light – Gathering Ability – The amount of light energy a telescope can collect. The larger the aperture of the telescope the more light is collected and the brighter the image. Since the area of a circle is proportional to the square of the lens or mirror diameter, doubling the telescope diameter allows the telescope to gather four times the light energy.
40.)Light Velocity - The velocity of an electromagnetic wave in a vacuum is 300,000,000 meters per second or 186,000 miles per second.
41.)Local Meridian – A line drawn on the celestial sphere, starting at the north celestial pole, passing through the observers zenith point, and continuing down to the southern horizon. When the sun is located on your local meridian, it is noon.
42.)Lunar Cycle – The length of time taken by the Moon to go through its phases. For example; full phase to the next phase. This takes 29 ½ days.
43.)Magnification – The number of times larger an object appears to be when viewed through a telescope as compared to the unaided eye. We can calculate this number by dividing the focal length of the large objective lens (or mirror) by the focal of the eyepiece. The more we magnify an object, the smaller the field of views becomes and the dimmer the field of view becomes.
44.)Mayan Astronomy – Examples of astronomical connections are; angled stonework, color-coded walls, building alignments, stone glyphs, window alignments, number and accurate calendar, etc.
45.)Medicine Wheel – Located in the Bighorn Mountains in Wyoming and used by the Blackfoot, it is a seasonal calendar and sun watching station. A large stone cairn marks the central hub of a wheel formed by the alignment of stones as spoke and rim. The alignment of the solstices and prominent helical risings and settings of stars is accomplished by additional stone cairs located around the rim of the wheel.
46.)Month – The year is divided into the 12 lunar months because of the 12 lunar cycles that occur in approximately one year.
47.)Newton’s Law of Gravity – The gravitational force of attraction between two masses is directly proportional to the product of the masses and inversely proportional to the square of the distance between their center of masses. The key ideas here are that the gravitational force is attractive, increases with mass and decreases with distance squared.
48.)Newton’s Laws of Motion – 1) An object at rest, or object moving in a straight line at constant speed, will continue to do so unless acted upon by a external force. 2) The net force acting on an object is equal to the object’s mass times its acceleration. 3) For every action there is an equal and opposite reaction between two objects.
49.)Nicholas Copernicus – Born on Feb. 19, 1473 in Prussia, he wrote Commentariolus and De Revolutionibus, expressing his ideas on the Sun- centered of Heliocentric solar system. He thought the motions of the planets in the sky could be explained better by moving the Earth and leaving the Sun stationary.
50.)North Celestial Pole – The intersection of the Earth’s spin axis with the celestial sphere in the northern celestial hemisphere.
51.)Parabola (Paraboloid) – This term describes the curved shape of a telescopic mirror (optical or radio) that focuses all of the light incident on it to one focal point, thus avoiding spherical aberration.
52.)Perihelion – The closest point, between the sun and the planet, in the planets elliptical orbit revolving around the sun.
53.)Photoelectric Effect – Where light of a critical energy (color of wavelength) can force free electrons out of a metal. Increasing the intensity of the light increases the number of free electrons but not their individual energy.
54.)Photons – A wave-packet model of light that can address the wave- particle duality of light.
55.)Point Sources – Astronomical objects that show no disk at high telescope magnification. Examples are most stars, quasars and other objects below the resolution limit of the telescope.
56.)Polaris – The north star today. It is the star closest to the north celestial pole at the current position on the precession circle.
57.)Polarization – This is where the electric waves (for electromagnetic waves) are aligned in one direction after passing through a suitable material.
58.)Precession – The “wobble” of the Earth’s spin axis of rotation in a 26,000 year cycle.
59.)Prograde Motion – The “forward” or eastward motion of the planets against the stars of the celestial sphere as observed from Earth.
60.)Ptolemy – He lived around 150AD when he wrote the Almagest, which in turn was largely based on the work of Hipparchus. He describes the Geocentric (earth centered) solar system in this work.
61.)Radial Velocity – The relative velocity along the line of sight between the source of the light and the observer. This is the velocity referred to in the Doppler effect.
62.)Radio Telescope – The main parts of this telescope are; a) reflecting dish antenna, b) low noise receiver, c) amplifier, d) noise standard, and e) recorder. This telescope is used to study the microwave emissions from low energy processes in space. Examples are: molecular masers, star birth, and hydrogen mapping.
63.)Radio Inrerferometer – When two or more radio telescopes are connected together electronically, improving the resolution of the radio source.
64.)Reflection – Light “”bounces” off a mirror at the same angle that it entered it, independent of the color of the light.
65.)Refracting Telescope – Basically, a telescope that uses a glass lens as the primary objective element.
66.)Refraction – The bending, in the direction of propagation of the light wave, as it passes from one transparent optical material into another transparent material. The speed of light slows when it is traveling in glass.
67.)Resolution – The ability to discern fine detail in an image. The larger the diameter of the lens or mirror, the better the resolution will be
68.)Retrograde Motion – The “backwards” or westward motion of the planets with respect to the celestial sphere as seen from the Earth.
69.)Revolution – The orbital motion of a planet around the sun. For the Earth, this takes 365.26 days.
70.)Right Ascension – This is a measurement of time along the celestial equator and is one of the coordinate lines used to find a position on the celestial sphere. Once around the equator would take 24 hours. The reference beginning point for right ascension is where the celestial equator crosses the ecliptic in spring.
71.)Rotation – The daily spin on the Earth (or any other planet) on its axis.
72.)Scattering – The absorption and re-emission, diffraction, refraction, and reflection of light as light passes through a planetary atmosphere. Short (blue) waves are scattered more that the longer (red) waves producing a blue sky and red sunsets on Earth.
73.)Schmidt Camera – A sky survey telescopic camera having low magnification, a wide field of view and excellent resolution.
74.)Seeing – A term describing the quality of the night sky for optically observing the stars. Good seeing would generally mean that the sky is clear, steady and dark.
75.)Slow Motion Controls – Mechanical, electrical or electronic correction of the declination and right ascension drives on the telescope. Correction is needed because of misalignment, friction, imbalance and voltage variations in the telescope system.
76.)Spectroscope – An instrument that disperses the light from a source into a spectrum of color. This can be studied to discover the chemical composition of the light source.
77.)Spherical Aberration – A geometrical defect in the shape of a mirror or glass lens that causes the light to come to a “smeared” or fuzzy focal point.
78.)Supernova of 1054 – Today the remnant of this spectacular stellar explosion is called the Crab Nebulae. The “Ancient Ones” recorded this event in Chaco Canyon, and we investigated this in class with the aid of astronomy software on the computer.
79.)Telescope Design – Be able to identify the Prime Focus, Newtonian, Schmidt and Cassegranian telescope design for the first exam.
80.)Tycho (Tyge) Brahe – Tycho was born in 1546 at Knedstrup in the Danish province of Scania. The King of Denmark gave him the island of Hveen where he built Uraniborg and Stjerneborg. The made careful observations of the sky with elaborate sighting instruments including a large quadrant and recorded his observations faithfully.
81.)Wave Amplitude – The vertical height of a wave, from the bottom of the wave through to the top of the wave crest. For light, this is related to the brightness or intensity of the light.
82.)Wavelength – The distance between adjacent wave crests. The shorter the wavelength, the bluer the light and the longer the wavelength, the redder the light. The shorter electromagnetic waves also carry more energy per wave than the longer wavelength light waves.
83.)Year – The length of the year can be found by observing the Heliacal risings and setting of stars and by observing the rising and setting points of the sun on the horizon. As the days grow longer, the sun rises further north each morning.
84.)Zenith – The point on the celestial sphere directly above the observers head and opposite the center of the Earth.
85.)Zodiac – The region of the celestial sphere within eighteen degree’s of the ecliptic. This area was special because the wandering stars only traveled in this part of the sky.

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