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Derek Haselden - Astronomical Glossary Category: Meteorology and astronomy > Astronomy Date & country: 05/11/2007, UK Words: 796

Harrington
A comet in our solar system with an orbital period of 6.78years. More data in TABLE 14. NOTABLE PERIODIC COMETS

Harrington-Abell
A comet in our solar system with an orbital period of 7.59years. More data in TABLE 14. NOTABLE PERIODIC COMETS

Hebe
One of the `minor planets` of our solar system. Discovered by Hencke on 1 Jul 1847. Diameter in km: 204. More data in TABLE 13. THE MINOR PLANETS

Helene
Satellite of the planet Saturn. See TABLE 8. SATURN - SATELLITE DATA

Heliocentric
Meaning: As seen from the centre of the Sun. A system of co-ordinates.

Hercules
English name: Hercules. Genitive name: Herculis. Visibility: Visible from the UK See TABLE 20: THE CONSTELLATIONS.

Hercules
The constellation Hercules. Genitive name: Herculis. Visibility: Visible from the UK See TABLE 20: THE CONSTELLATIONS.

Herculis
The constellation Hercules. English name: Hercules. Visibility: Visible from the UK See TABLE 20: THE CONSTELLATIONS.

Hermippe
Satellite of the planet Jupiter. See TABLE 7. JUPITER - SATELLITE DATA

Herschel-Rigollet
A comet in our solar system with an orbital period of 155years. More data in TABLE 14. NOTABLE PERIODIC COMETS

Hertzsprung-Russell diagram
A diagram in which stars are plotted according to their spectral type and their absolute magnitude.

Hestia
One of the `minor planets` of our solar system. Discovered by Pogson on 16 Aug 1857. Diameter in km: 164. More data in TABLE 13. THE MINOR PLANETS

Himalia
Satellite of the planet Jupiter. See TABLE 7. JUPITER - SATELLITE DATA

Holmes
A comet in our solar system with an orbital period of 7.06years. More data in TABLE 14. NOTABLE PERIODIC COMETS

Honda-Mrkos-Pajdusakova
A comet in our solar system with an orbital period of 5.30years. More data in TABLE 14. NOTABLE PERIODIC COMETS

Horizon
The great circle on the celestial sphere which is everywhere 90 degrees from the observers zenith, the point directly overhead the observer.

Horologii
The constellation Horologium. English name: The Pendulum Clock. Visibility: Never visible from the UK. See TABLE 20: THE CONSTELLATIONS.

Horologium
English name: The Pendulum Clock. Genitive name: Horologii. Visibility: Never visible from the UK. See TABLE 20: THE CONSTELLATIONS.

Howell
A comet in our solar system with an orbital period of 5.94years. More data in TABLE 14. NOTABLE PERIODIC COMETS

Hubble's constant
The rate of increase of the recession of a galaxy with increased distance from the Earth. This figure varies depending on which observational data one uses but is often around 50 miles per second per Megaparsec.

Hydra
English name: The Water-Snake. Genitive name: Hydrae. Visibility: Visible from the UK See TABLE 20: THE CONSTELLATIONS.

Hydrae
The constellation Hydra. English name: The Water-Snake. Visibility: Visible from the UK See TABLE 20: THE CONSTELLATIONS.

Hydrus
English name: The Small Water-Snake Hydri. Genitive name: Hyi. Visibility: Never visible from the UK. See TABLE 20: THE CONSTELLATIONS.

Hygeia
One of the `minor planets` of our solar system. Discovered by De Gasparis on 12 Apr 1849. Diameter in km: 430. More data in TABLE 13. THE MINOR PLANETS

Hyi
The constellation Hydrus. English name: The Small Water-Snake Hydri. Visibility: Never visible from the UK. See TABLE 20: THE CONSTELLATIONS.

Hyperion
Satellite of the planet Saturn. See TABLE 8. SATURN - SATELLITE DATA

Iapetus
Satellite of the planet Saturn. See TABLE 8. SATURN - SATELLITE DATA

Ijiraq
Satellite of the planet Saturn. See TABLE 8. SATURN - SATELLITE DATA

Indi
The constellation Indus. English name: The Indian. Visibility: Never visible from the UK. See TABLE 20: THE CONSTELLATIONS.

Indus
English name: The Indian. Genitive name: Indi. Visibility: Never visible from the UK. See TABLE 20: THE CONSTELLATIONS.

Io
Satellite of the planet Jupiter. See TABLE 7. JUPITER - SATELLITE DATA

Iocaste
Satellite of the planet Jupiter. See TABLE 7. JUPITER - SATELLITE DATA

iota Aquarids
Meteor shower. Most active day is Aug.6. 2 radiants, rich in faint meteors.

Irene
One of the `minor planets` of our solar system. Discovered by Hind on 19 May 1851. Diameter in km: 150. More data in TABLE 13. THE MINOR PLANETS

Iris
One of the `minor planets` of our solar system. Discovered by Hind on 13 Aug 1847. Diameter in km: 208. More data in TABLE 13. THE MINOR PLANETS

Isis
One of the `minor planets` of our solar system. Discovered by Pogson on 23 May 1856. Diameter in km: 94. More data in TABLE 13. THE MINOR PLANETS

Isonoe
Satellite of the planet Jupiter. See TABLE 7. JUPITER - SATELLITE DATA

Jackson-Neujmin
A comet in our solar system with an orbital period of 8.24years. More data in TABLE 14. NOTABLE PERIODIC COMETS

Janus
Satellite of the planet Saturn. See TABLE 8. SATURN - SATELLITE DATA

Johnson
A comet in our solar system with an orbital period of 6.94years. More data in TABLE 14. NOTABLE PERIODIC COMETS

Jovian
Pertaining to the planet Jupiter.

Julian day
A system of counting days from noon 1st January 4713 BC. The name has nothing to do with Julius Caesar but was invented by the mathematician Scaliger who named it in honour of his father, Julius Scaliger. So, 30th August 2000 is Julian Day J2 451 786.0. Figures may be added after the decimal point and they will represent the decimal fraction of the day. So, 6pm, 30th August 2000 will be J2 451 786.25.

Juliet
Satellite of the planet Uranus. See TABLE 9. URANUS - SATELLITE DATA

Juno
One of the `minor planets` of our solar system. Discovered by Harding on 1 Sep 1804. Diameter in km: 288x230. More data in TABLE 13. THE MINOR PLANETS

Jupiter
SOLAR SYSTEM - PLANETARY ORBITAL DATA
Average dist.from Sun (AU) - 5.203
Min. distance from Sun (AU) - 4.952
Max. distance from Sun (AU) - 5.455
Eccentricity of orbit - 0.048
Inclination to ecliptic(°) - 1.31
SOLAR SYSTEM - PLANETARY PERIODS AND MOTIONS
Sidereal period (days or years) - 11.863 y
Mean orbital velocity(km/sec.) - 13.07
Sidereal period of axial rotation - 9.842 h
Inclination of equator to ecliptic(°) - 3.13
SOLAR SYSTEM - PLANETARY PHYSICAL DATA
Equatorial dia.(km) - 142 984
Polar dia.(km) - 133 708
Mass (Earth=1) - 317.83
Volume (Earth=1) - 1321.0
Oblateness (Earth=1) - 0.065
Surface gravity (Water=1) - 2.364
Density - 1.33

Kale
Satellite of the planet Jupiter. See TABLE 7. JUPITER - SATELLITE DATA

Kalyke
Satellite of the planet Jupiter. See TABLE 7. JUPITER - SATELLITE DATA

Kelvin (degrees)
A measurement of temperature, symbol 'K'. Kelvin is measured in degrees from absolute zero. So, 0 degrees Kelvin equals minus -273.16 degrees Centigrade.

Kepler's laws of planetary motion
Set of laws laid down between 1609 and 1618 by Johannes Kepler. These laws are: (1). The planets move in elliptical orbits with the Sun at one focus of the orbit. (2). The line joining the centre of the Sun and the centre of the planet sweeps out an equal area in equal times. (3). In the case of a planet, the square of the sidereal period is proportional to the cube of the mean distance from the Sun.

Kiloparsec
One thousand parsecs, equal to 3260 light years.

Kirkwood gaps
Regions in the asteroid belt where very few asteroid are found. The gaps are caused by Jupiter's gravitational influence which shifts asteroids out of orbit if their orbital period is a precise fraction of Jupiter's orbit.

Kiviuq
Satellite of the planet Saturn. See TABLE 8. SATURN - SATELLITE DATA

Klemola
A comet in our solar system with an orbital period of 10.9years. More data in TABLE 14. NOTABLE PERIODIC COMETS

Kohoutek
A comet in our solar system with an orbital period of 6.67years. More data in TABLE 14. NOTABLE PERIODIC COMETS

Kojima
A comet in our solar system with an orbital period of 7.89years. More data in TABLE 14. NOTABLE PERIODIC COMETS

Kwerns-Kwee
A comet in our solar system with an orbital period of 8.99years. More data in TABLE 14. NOTABLE PERIODIC COMETS

Lacerta
English name: The Lizard. Genitive name: Lacertae. Visibility: Visible from the UK See TABLE 20: THE CONSTELLATIONS.

Lacertae
The constellation Lacerta. English name: The Lizard. Visibility: Visible from the UK See TABLE 20: THE CONSTELLATIONS.

Lagrangian points
Five places where small bodies can exist in stable orbits in the plane of two larger bodies. Three of these points lie in a line joining the two large bodies; one point between the two larger bodies (L1); the other two points either side of them (L2 & L3). The remaining points lie 60° ahead of and behind one of the larger bodies in its orbit around the other (L4 & L5).

Larissa
Satellite of the planet Neptune. See TABLE 10. NEPTUNE - SATELLITE DATA

Latitude, celestial
The angular distance of a celestial object from the nearest point on the ecliptic.

Leda
Satellite of the planet Jupiter. See TABLE 7. JUPITER - SATELLITE DATA

Leda
One of the `minor planets` of our solar system. Discovered by Chacornac on 12 Jan 1856. Diameter in km: 13.00. More data in TABLE 13. THE MINOR PLANETS

Leo
English name: The Lion. Genitive name: Leonis. Visibility: Visible from the UK See TABLE 20: THE CONSTELLATIONS.

Leo Minor
English name: The Smaller Lion. Genitive name: Leonis Minoris. Visibility: Visible from the UK See TABLE 20: THE CONSTELLATIONS.

Leonids
Meteor shower. Most active day is Nov.17. Fast, often bright meteors with trains.

Leonis
The constellation Leo. English name: The Lion. Visibility: Visible from the UK See TABLE 20: THE CONSTELLATIONS.

Leonis Minoris
The constellation Leo Minor. English name: The Smaller Lion. Visibility: Visible from the UK See TABLE 20: THE CONSTELLATIONS.

Leporis
The constellation Lepus. English name: The Hare. Visibility: Visible from the UK See TABLE 20: THE CONSTELLATIONS.

Lepus
English name: The Hare. Genitive name: Leporis. Visibility: Visible from the UK See TABLE 20: THE CONSTELLATIONS.

Leucothea
One of the `minor planets` of our solar system. Discovered by Luther on 19 Apr 1855. Diameter in km: ±67. More data in TABLE 13. THE MINOR PLANETS

Libra
English name: The Scales. Genitive name: Librae. Visibility: Visible from the UK See TABLE 20: THE CONSTELLATIONS.

Librae
The constellation Libra. English name: The Scales. Visibility: Visible from the UK See TABLE 20: THE CONSTELLATIONS.

Libration
The apparent tilting of the Moon as seen from Earth. The result is that over a period of time it is possible to see 59% of the surface of the Moon from Earth, though of course, only 50% at any one time.

Light year (l.y.)
The unit of distance in which light travels in one year - 9 464 566 100 km (5 878 612 500 miles).

Light, speed of
299 792.5 km (186 291 miles) per second in a vacuum, the fastest speed in the Universe.

Limb
The apparent edge of a body such as the Moon as seen from Earth.

Local group
A term used to describe the local cluster of galaxies of which the Milky Way galaxy is part. The largest member of the Local Group is the Andromeda Galaxy, Messier 31.

Longmore
A comet in our solar system with an orbital period of 6.98years. More data in TABLE 14. NOTABLE PERIODIC COMETS

Lunation
One complete cycle of phases by the Moon, 29.53 days. A lunation is also known as a Synodic month.

Lupi
The constellation Lupus. English name: The Wolf. Visibility: Parts visible from the UK. See TABLE 20: THE CONSTELLATIONS.

Lupus
English name: The Wolf. Genitive name: Lupi. Visibility: Parts visible from the UK. See TABLE 20: THE CONSTELLATIONS.

Lutetia
One of the `minor planets` of our solar system. Discovered by Goldschmidt on 15 Nov 1852. Diameter in km: 108. More data in TABLE 13. THE MINOR PLANETS

Lyncis
The constellation Lynx. English name: The Lynx. Visibility: Visible from the UK See TABLE 20: THE CONSTELLATIONS.

Lynx
English name: The Lynx. Genitive name: Lyncis. Visibility: Visible from the UK See TABLE 20: THE CONSTELLATIONS.

Lyra
English name: The Lyre. Genitive name: Lyrae. Visibility: Visible from the UK See TABLE 20: THE CONSTELLATIONS.

Lyrae
The constellation Lyra. English name: The Lyre. Visibility: Visible from the UK See TABLE 20: THE CONSTELLATIONS.

Lyrids
Meteor shower. Most active day is Apr.22. Swift, bright meteors.

Lysithea
Satellite of the planet Jupiter. See TABLE 7. JUPITER - SATELLITE DATA

Macholtz 2
A comet in our solar system with an orbital period of 5.23years. More data in TABLE 14. NOTABLE PERIODIC COMETS

Magnetosphere
The region of the magnetic field of a planet or other solar system body. Only Mercury, Earth, Jupiter, Saturn, Uranus and Neptune are known to have a magnetosphere.

Magnitude (Brightness)
The brightness of a celestial object. The lower the magnitude, the less bright the object and vice-versa. For mainly historical reasons magnitude has the peculiar attribute of having brighter objects at negative values and vice-versa. Each whole number of magnitude is equal to a factor of 2.5:1. So, an object of magnitude +1 is 2.5 times brighter than an object of magnitude +2 but is 2.5 times fainter than an object of magnitude 0. Five whole units of magnitude are equal to a factor of approximately 100 times. So, a magnitude +6 object is 100 times fainter than an object of magnitude +1. (See also Absolute magnitude and Apparent magnitude.)

Main Sequence
A band within the Hertzsprung-Russell diagram that contains the majority of normal stars except for giant stars and white dwarfs.

Maksutov telescope
A type of telescope that uses mirrors and lenses. Maksutov's are in fact Cassegrain telescopes: In the case of a Maksutov the light enters the front of the telescope via a curved corrector plate or lens (curved towards the interior of the telescope) which directs the light onto the concave primary mirror (which has a hole at its centre) which lies at the rear of the telescope. The primary mirror then reflects the light back toward the corrector plate which has a small convex secondary mirror coated onto the centre of the corrector plate. This secondary mirror then directs the light through the hole in the centre of the primary mirror and on into the eyepiece which is attached to the rear of the telescope. Like all Cassegrain telescopes the Maksutov has the advantage to being able to have a longer focal ratio than a Newtonian reflector of equal optical size but at the expence of a more complicated optical train.

Mars
SOLAR SYSTEM - PLANETARY ORBITAL DATA
Average dist.from Sun (AU) - 1.524
Min. distance from Sun (AU) - 1.381
Max. distance from Sun (AU) - 1.666
Eccentricity of orbit - 0.093
Inclination to ecliptic(°) - 1.85
SOLAR SYSTEM - PLANETARY PERIODS AND MOTIONS
Sidereal period (days or years) - 686.980 d
Mean orbital velocity(km/sec.) - 24.13
Sidereal period of axial rotation - 24.624 h
Inclination of equator to ecliptic(°) - 25.19
SOLAR SYSTEM - PLANETARY PHYSICAL DATA
Equatorial dia.(km) - 6 794
Polar dia.(km) - 6 750
Mass (Earth=1) - 0.11
Volume (Earth=1) - 0.15
Oblateness (Earth=1) - 0.0065
Surface gravity (Water=1) - 0.377
Density - 3.94

Mass
A measure of a body's inertia (resistance to acceleration), the amount of matter that a body contains. Strictly speaking, mass is not the same as weight or gravity, although on Earth they are often regarded as the same thing. Mass is measured in Kilogrammes. Apart from speeds approaching that of light, the mass of a body remains constant whereas weight or gravity is dependant on the masses of two or more bodies and the distance between them.

Massalia
One of the `minor planets` of our solar system. Discovered by De Gasparis on 19 Sep 1852. Diameter in km: 134. More data in TABLE 13. THE MINOR PLANETS

Mean
The average of a series of values.

Mean Sun
An imaginary Sun travelling at a speed equal to the average rate that the real Sun travels along the ecliptic.

Megaclite
Satellite of the planet Jupiter. See TABLE 7. JUPITER - SATELLITE DATA