Astronomy and related astronomical terms

The NASA launch site on Merritt Island, near Cape Canaveral, Florida, used for "Apollo" and space-shuttle launches: The first flight to land on the Moon (1969) and "Skylab", the first orbiting laboratory (1973), were launched from the Kennedy Space Center.

Three basic laws of planetary motion:

1. The orbit of a planet is an ellipse, with the Sun at one focus.
2. The line joining the position of a planet in its orbit to the Sun (the radius vector) sweeps out equal areas in equal times.
3. The squares of the orbital periods of the planets are proportional to the cube of their mean distances from the Sun.

One of a series of vacancies in the distribution of the orbits of the minor planets, marked by the absence of minor planets whose orbits have periods that are simple fractions of the orbital period of Jupiter. The Kirkwood gaps are an example of gravitational resonance.

The reason for this activity is that in such positions any minor planet would be repeatedly perturbed by Jupiter's gravitational field until it was forced out of the "forbidden" orbit.

1. A ring of small astronomical objects orbiting through the outer solar system, beyond the farthest planets, Neptune and Pluto: It is believed that the Kuiper belt is a source of comets.

2. A disk-shaped swarm of 200 million comets and comet fragments located from just beyond the orbit of Neptune and extending past Pluto: The Kuiper belt was named after Gerard Peter Kuiper (1905-1973), a Dutch-born U.S. astronomer who made extensive studies of the solar system. His discoveries included the atmosphere of the planet Mars and that of Titan, the largest moon of the planet Saturn.

His spectroscopic studies of Uranus and Neptune led to the discovery of features subsequently named "Kuiper bands", which indicate the presence of methane.

He was an adviser to many NASA exploratory missions, and pioneered the use of telescopes on high-flying aircraft.

One of a set of five positions at which a small object can maintain a stable orbit under the influence of two more massive objects: A Lagrangian position is a point in space at which a small body, under the gravitational influence of two large ones, will remain approximately at rest relative to them.

The existence of such points was deduced by the French mathematician and astronomer Joseph-Louis Lagrange in 1772.

In 1906, the first examples were discovered. These were minor planets moving in Jupiter’s orbit, under the influence of Jupiter and the Sun.

The angular length north or south from a planet's equator, estimated along the meridian of that specific point: Latitude is the angular distance of a point from the Earth's equator, measured upon the Earth's surface.

The zodiacal constellation in the northern hemisphere, represented as a lion: The Sun passes through Leo from mid-August to mid-September. Its brightest star is the first-magnitude "Regulus" at the base of a pattern of stars called the Sickle.

A "magnitude" represents the brightness of an astronomical object as a numerical measure of the apparent brightness, on a scale in which a lower number represents a greater brightness.

A chart of graph of the change in brightness of a celestial object: A light curve is expressed in apparent magnitudes, against time of variable stars.

The distance traveled by a beam of light in a vacuum in one year, approximately 9.46 trillion (million million) kilometers or 5.99 trillion miles: A light-year has an average speed of 186,291 miles or 299,792 kilometers, per second; which equals approximately 5.88 trillion miles or 9.4607 trillion kilometers, or 63,246 astronomical units.

The light-year is also divided into light-minutes and light-seconds; for example, the Moon is 1.3 light-seconds from the Earth and the Sun is 8.3 light-minutes away from the Earth.

Although a light-year is a measurement of distance and not time, it does imply time, such as the light from a star that is ten light-years from the Earth takes ten years to reach the Earth. So, an observer on Earth is seeing the star as it appeared ten years ago.

The edge of a planet or other celestial body as seen from far away; When Susan looked through her telescope, she could detect the limb of a planet, or the circumferential border which looked like a disk of a planet,

Electromagnetic radiation emitted or absorbed at discrete frequencies or wavelengths: A spectrum of line emission occurs when a hot gas gives off certain wavelengths of illumination which then produces lines on a dark background.

The upper region of the body of a planet consisting of the crust and top layers of the mantle: The lithosphere is often broken up into tectonic plates.

A cluster of about thirty galaxies that includes our own, the Milky Way: Like other groups of galaxies, the Local Group is held together by the gravitational attraction among its members, and does not become larger with the expanding universe.

Its two largest galaxies are the Milky Way and the Andromeda galaxy. Most of the others are small and faint.

The angular distance measured along the earth's equator between the meridian passing through the point and the Greenwich Meridian or zero meridian: In her astronomy class, Alice learned that a longitude was any imaginary line at right angles to the equator of the planet Earth and which went through the North and South Poles.

A measurement of the total amount of energy given off from a star: Luminosity is the total amount of energy radiated by a luminous object per unit time, for example one second. Common units are watts.

Luminosity can also be described as the speed at which a star's energy is emitted in all directions.