SPEAKING OF ASTRONOMY

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SPEAKING OF ASTRONOMY

• Words and terms used.
• In scientific and technical discussions it is
  important that everyone use the words and terms
  that are generally defined and accepted by others.

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UNIVERSE

• The universe is everything, all matter and energy
  that is in existence.

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ASTRONOMY

• Astronomy is the scientific study of space,
  including the planets, stars, galaxies, comets,
  and nebulae.

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CELESTIAL SPHERE The celestial sphere is an
imaginary sphere whose center is the Earth. This
sphere is used by astronomers to map celestial
objects.
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CONSTELLATION

• Any one of the 88 areas into which the sky - or
  the celestial sphere - is divided.

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ASTERISM

• A pattern of stars seen in Earth's sky which is
  not an official constellation.

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DECLINATION

• Declination is a celestial coordinate that is
  used to measure the degrees of latitude above or
  below the celestial equator on the celestial
  sphere.

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RIGHT ASCENSION

• Right ascension is a celestial coordinate that is
  used to measure the degrees of longitude on the
  on the celestial sphere. Zero degrees of right
  ascension is the position of the Sun during the
  vernal (spring) equinox (March 21).

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ZENITH

• An observer's zenith is the point directly
  overhead.

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ALTITUDE

• Altitude is a measurement in mapping astronomical
  objects on the celestial sphere (the sky as
  visible from Earth). Altitude is the angle of the
  object from the observer's horizon. If an object
  is on the horizon, its altitude is 0 degrees. If
  it is at the observer's zenith, its altitude is
  90 degrees. To find an object in the sky, two
  coordinates are needed, its azimuth and its
  altitude.

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AZIMUTH

• Azimuth is a measurement in mapping astronomical
  objects on the celestial sphere (the sky as
  visible from Earth). Azimuth is the angle of the
  object from the observer's north point (projected
  onto the horizon). If an object is due north, its
  azimuth is 0 degrees. If it is due east, its
  azimuth is 90 degrees, etc. To find an object in
  the sky, two coordinates are needed, its altitude
  and its azimuth.

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ORBIT

• An orbit is a closed path that an object takes as
  it revolves around another body. Orbits are
  generally elliptical, but may be perturbed by the
  presence of yet other bodies and may even form
  unusual figures.

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APHELION

• For an object (a planet or comet) orbiting the
  Sun, the aphelion is the point in its orbit which
  is farthest from the sun.

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PERIHELION

• The perihelion is a planet or comet's closest
  approach to the Sun. The Earth is at perihelion
  (the Earth is closest to the Sun) in January.

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APOGEE

• For an object orbiting the Earth, the apogee is
  the point in its orbit which is farthest from the
  Earth.

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PERIGEE

• For an object orbiting the Earth, the perigee is
  the point in each orbit which is closest to the
  Earth. The perigee varies a small amount from
  orbit to orbit. The closest perigee is called the
  proxigee.

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ECLIPTIC

• The ecliptic is the plane defined by the Earth's
  orbit around the Sun conversely, in the course
  of a year, the sun traces a path in the sky along
  the ecliptic. Most of the planets in our solar
  system appear close to the ecliptic plane from
  Earth. The Earth's axis is tilted at a 23.5 from
  the ecliptic (which causes the seasons).

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UMBRA PENUMBRA

• The penumbra is the area of partial shadow
• The umbra is the area of total shadow

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CONJUNCTION

• The apparent close approach of a planet to the
  Sun (or another planet), from the point of view
  of an observer on the Earth.

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CONJUNCTION

• A planet is in conjunction when the Sun is
  exactly between that planet and the Earth or, for
  Mercury and Venus (the two inferior planets),
  when that planet, the Sun, and the Earth are
  lined up. Mercury and Venus have two positions of
  conjunction when either planet is directly
  between the earth and the Sun, it is in inferior
  conjunction when either planet is on the far
  side of the Sun from the earth, it is in superior
  conjunction. During conjunction, a planet cannot
  be seen from Earth (unless it is in transit) it
  is either behind the Sun or is lost in the glare
  of the Sun.

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OCCULTATION

• When a smaller astronomical body passes behind a
  larger astronomical body (wholly obscuring its
  view). One example of occultation is when a
  planet passes behind the Sun (from our
  perspective) and it is hidden from our view.

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TRANSIT

• When a smaller body passes in front of a larger
  one (for example, when an object passes between
  the Sun and the Earth). During this time, the
  object seems to be crossing the disk of the Sun.
  The only planets that ever pass between the Earth
  and the Sun are Mercury and Venus (since they are
  closer to the Sun than the Earth). Therefore, the
  only planets that can produce a transit are
  Mercury and Venus.

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ECLIPSE

• An eclipse happens when the moon blocks the Sun
  or the Earth's shadow falls on the moon.

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GALAXY

• A galaxy is a huge group of stars and other
  celestial bodies bound together by gravitational
  forces. There are spiral, elliptical, and
  irregularly shaped galaxies. Our Sun and solar
  system are a small part of the Milky Way Galaxy.

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SOLAR SYSTEM

• A solar system is a group of planets, moons,
  asteroids, and comets that orbit around a sun. In
  our solar system, nine planets, over 61 moons,
  and many other objects orbit around our Sun.

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SUN

• The Sun is a star at the center of our solar
  system. Our Sun is a medium-sized yellow star
  that is 93,026,724 miles (149,680,000 km) from
  Earth. Its diameter is 865,121 miles (1,391,980
  km). At its core, nuclear reactions produce
  enormous amounts of energy, through the process
  of converting hydrogen atoms into helium atoms
  (nuclear fusion). Its absolute magnitude is
  4.83. The solar mass is 1.99 x 1030 kg.

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ELLIPSE

• An ellipse looks like a flattened circle. It
  consists of all the points in a plane that
  satisfy the following ab(twice the length of
  the semi-major axis), where a is the distance
  from one focus to the point on the ellipse, and b
  is the distance from the other focus to the same
  point on the ellipse.

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ELLIPTICAL ORBIT

• An elliptical orbit is an orbit that traces out
  an ellipse as the orbiter rotates around another
  body (which is located at one focus of the
  ellipse).

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EARTH SUN RELATIONSHIP
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METEOROID

• Tiny stones or pieces of metal that travel
  through space.

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METEOR

• A meteor is a meteoroid that has entered the
  Earth's atmosphere, usually making a fiery trail
  as it falls. It is sometimes called a shooting
  star. Most burn up before hitting the Earth.

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METEORITE

• A meteor that has fallen to Earth. Meteorites are
  either stone, iron, or stony-iron.

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ASTEROID

• An asteroid is a large rocky object or very small
  planet (planetoid). Most asteroids orbit the Sun
  in the asteroid belt between Mars and Jupiter. A
  few asteroids approach the Sun more closely. An
  asteroid impact with the Earth may have caused
  the extinction of the dinosaurs. The largest
  asteroid and first one ever discovered (by
  Giuseppe Piazzi on January 1, 1801) is Ceres,
  whose mass is equal to over one-third of the 2.3
  x 1021 kg estimated total mass of all the 3,000
  catalogued asteroids.

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TELESCOPE

• A telescope is a device that makes faraway
  objects appear closer and larger, allowing us to
  see distant objects in space. The first
  refracting telescope was invented by Hans
  Lippershey in 1608. Early telescopes used glass
  lenses and/or mirrors to detect visible light.
  Later telescopes gathered electromagnetic
  radiation from the entire spectrum, from radio
  waves to gamma rays.

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REFRACTING TELESCOPE

• A refracting telescope uses two lenses which
  magnify what is viewed the large primary lens
  does most of the magnification.

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REFLECTING TELESCOPE

• A reflecting (or Newtonian) telescope uses two
  mirrors which magnify what is viewed. The first
  reflecting telescope was first described by James
  Gregory in 1663.

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CASSEGRAIN TELESCOPE

• A Cassegrain telescope is a wide-angle reflecting
  telescope with a concave mirror that receives
  light and focuses an image. A second mirror
  reflects the light through a gap in the primary
  mirror, allowing the eyepiece or camera to be
  mounted at the back end of the tube.

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SCHMIDT-CASSEGRAIN

• A correcting plate (a lens) was added in 1930 by
  the Estonian astronomer and lens-maker Bernard
  Schmidt (1879-1935), creating the
  Schmidt-Cassegrain telescope which minimized the
  spherical aberration of the Cassegrain telescope.

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EYEPIECE

• SOMETHING ELSE TO MAKE US SPEND MONEY.

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GIBBOUS MOON

• A gibbous moon is between a full moon and a half
  moon, or between a half moon and a full moon.

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REVOLUTION

• Revolution is the movement of one object around
  another. For example, the revolution of the Earth
  around the Sun takes one year.

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ROTATE

• When an object rotates, it turns around a central
  point or axis. One planetary day is defined as
  the time it takes the a planet to rotate around
  its axis.

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SIDEREAL TIME

• Sidereal time is time measured relative to the
  stars (the period between successive conjunctions
  with any star) instead of relative to the motion
  of the Sun). One sidereal day, equal to 23 hours
  and 56 minutes, is the period during which the
  earth completes one rotation on its axis (this is
  the same as the time it takes to come into
  alignment with a particular star).

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SIDEREAL YEAR

• A sidereal year is measured relative to the stars
  (the period between successive conjunctions with
  any star). One sidereal year, equal to 365 days,
  6 hours, 9 minutes, and 9.5 seconds, is the
  period during which the earth completes one
  revolution around the Sun

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HOW MANY DAY IN A YEAR?

• THE EARTH ROTATES ON ITS AXIS 366 TIMES IN ONE
  REVOLUTION AROUND THE SUN.

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SPEED OF LIGHT

• The speed of light is the speed at which
  electromagnetic waves can move in a vacuum
  299,792,458 meters/sec (186,000 miles/second).
  According to Einstein's Theory of Relativity,
  nothing can go faster than the speed of light.

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LIGHT YEAR

• A light-year is the distance that light can
  travel in one year in a vacuum, which is about
  5,880,000,000,000 miles or 63,240 AU or 9.46053 x
  1012 kilometers.

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MESSIER OBJECTS

• During the late 18th century (1759-1781), the
  French astronomer Charles Messier made a list of
  103 fuzzy objects in space in order not to
  mistake star clusters, galaxies, and nebulae for
  comets (for which he was searching).

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NGC

• The NGC (New General Catalog) is a list of over
  13,000 deep-sky celestial objects. It was
  developed in 1888. For example, the Great Nebula
  in Orion is NCG 1976 (and M42). NGC4414 is a
  spiral galaxy 60 million light-years away.

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TERMINATOR

• The terminator is the day-night line on a planet
  (or other body).
• Its also the end of this presentation