Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
31 Cards in this Set
- Front
- Back
|
Light Year
|
The distance that light travels in one year.
|
|
|
Heliacal Rising
|
The first time in a year that an astronomical body rises sufficiently far ahead of the sun that it can be seen in the morning sky.
|
|
|
Ecliptic
|
The path followed by the sun across the celestial sphere in the course of a year.
|
|
|
Retrograde Motion
|
The apparent motion of the planets when they appear to move backwards (westward) with respect to the stars from the direction that they move ordinarily.
|
|
|
Epicycle
|
In the Ptolemaic theory, a small circle, riding on a larger circle called the deferent, on which a planet moves. The epicycle is used to account for retrograde motion.
|
|
|
Deferent
|
In the Ptolemaic system of the universe, the larger circle, centered at the Earth, on which the centers of the epicycles revolve.
|
|
|
Conjunction
|
Where two celestial objects reach the same celestial longitude; approximately corresponds to their closest apparent approach in the sky. When only one body is named, it is understood that the second body is the sun.
|
|
|
Opposition
|
An object's having a celestial longitude 180 degrees from that of the sun.
|
|
|
Ephemeris
|
A listing of astronomical positions and other data that change with time. From the same root as ephemeral.
|
|
|
Heliocentric
|
Sun-centered; using the sun rather than the Earth as the point to which we refer. A heliocentric measurement, for example, omits the effect of the Doppler shift caused by the earth's orbital motion.
|
|
|
Geocentric
|
Earth-centered.
|
|
|
Gnomon
|
The vertical stick or triangle used to cast the sun's shadow in a sundial.
|
|
|
Major Axis
|
The longest diameter of an ellipse; the line from one side of an ellipse to the other that passes through the foci. Also, the length of that line.
|
|
|
Semimajor Axis
|
Half the major axis, that is, for an ellipse, half the longest diameter.
|
|
|
Minor Axis
|
The shortest diameter of an ellipse; the line from one side of an ellipse to the other that passes midway between the foci and is perpendicular to the major axis. Also, the length of that line.
|
|
|
Eccentricity
|
A measure of the flatness of an ellipse, defined as half the distance between the foci divided by the semi-major axis.
|
|
|
Astronomical Unit
|
The average distance from the Earth to the sun.
|
|
|
Earthshine
|
Sunlight illuminating the moon after having been reflected by the Earth.
|
|
|
Inertia
|
A property of mass used by Isaac Newton in his first law of motion to keep a body at rest if it was at rest or at motion with the same direction and speed unless acted on by a force.
|
|
|
Wavelength
|
The distance over which a wave goes through a complete oscillation.
|
|
|
Resolution
|
The ability of an optical system to distinguish detail.
|
|
|
Focal Length
|
The distance from a lens or mirror to the point to which rays from an object at infinity are focused.
|
|
|
Field of View
|
The angular expanse viewable.
|
|
|
Refracting Telescope
|
A type of telescope in which the primary image is formed by a lens or lenses.
|
|
|
Reflecting Telescope
|
A type of telescope that uses a mirror or mirrors to form the primary image.
|
|
|
Seeing
|
The steadiness of the Earth's atmosphere as it affects the resolution that can be obtained in astronomical observations.
|
|
|
Transparency
|
Clarity of the sky.
|
|
|
Magnification
|
An apparent increase in angular size.
|
|
|
Electromagnetic Spectrum
|
Energy in the form of electromagnetic waves, in order of wavelength.
|
|
|
Resolution
|
The ability of an optical system to distinguish detail.
|
|
|
Photon
|
A packet of energy that can be thought of as a particle traveling at the speed of light.
|
