Due to Mercury's rotation and highly elliptical orbit, the Sun appears to rise briefly, set, and rise again before it travels westward across the sky. At sunset, the Sun appears to set, rise again briefly, and then set again.
Mercury is only about one-third the size of the Earth. It is smaller than any other planet except Pluto. Mercury is very close to the Sun and has no substantial atmosphere. These factors contribute to the fact that the surface of Mercury has the greatest temperature range of any planet or natural satellite in our solar system. The surface temperature on the side of Mercury closest to the Sun reaches 427 degrees Celsius, a temperature hot enough to melt tin. On the side facing away from the Sun, or the night side, the temperature drops to -183 degrees Celsius. Scientists have detected a magnetic field surrounding Mercury, though it is not as strong as the field around the Earth. Scientists theorize that Mercury's field is due to an iron-bearing core or possibly to the solar winds. Mercury's atmosphere is very thin and is composed of helium and sodium. The surface of Mercury has been shaped by three processes: impact cratering where large objects struck the surface resulting in crater formation, volcanism where lava flooded the surface, and tectonic activity where the planet's crust moved in order to adjust to the planetary cooling and contracting. Mercury does not have any naturally occurring satellites
4 billion years ago, a 100 kilometer-wide asteroid struck Mercury creating an impact crater that is 1300 kilometers wide. The Caloris Basin, as the crater is called, could hold the entire state of Texas!
A
ACCREDITED
An educational institution which has been recognized as maintaining standards that qualify graduates for admission to higher, or more specialized, institutions or professional practice.
ASTEROID
A rocky space object which can be from a few hundred feet to several hundred km wide. Most asteroids in our solar system orbit the Sun in a belt between Mars and Jupiter.
ASTRONOMER
An expert in the study of the Sun, Moon, stars, planets, and other space bodies.
ASTRONOMICAL UNIT
The approximate distance from the Sun to the Earth which is equal to 150,000,000 kilometers.
ASTROPHYSICS
The branch of astronomy that deals with the physics of stellar phenomena.
ATMOSPHERE
The layers of gases which surround a star, like our Sun, or a planet, like our Earth.
AXIS
An imaginary straight line around which an object rotates.
B
BACTERIA
Living things that have only one cell and are so small they can only be seen with a microscope.
BASALT
A dark, fine-grained volcanic rock.
BIG BANG THEORY
A theory which states that the Universe began to expand after a super powerful explosion of concentrated matter and energy.
BLACK HOLE
The leftover core of a super massive star after a supernova. Black holes exert a tremendous gravitational pull.
C
CELSIUS
A scale on a thermometer where the interval between the boiling point and the freezing point of water is divided into 100 degrees. Freezing point is represented by 0 degrees and boiling point is represented by 100 degrees. The same scale is also utilized in Centigrade.
CENTIGRADE
See CELSIUS.
CHARGED PARTICLES
electrons, protons, ions.
COMA
A hazy cloud which surrounds the nucleus of a comet.
COMET
Frozen masses of gas and dust which have a definite orbit through the solar system.
CORONA
The very hot outermost layer of a star's atmosphere. Our Sun's corona can only be seen during a total solar eclipse.
COSMONAUT
An astronaut from the former Soviet Union or the current republic of Russia.
COSMOLOGICAL
Having to do with the study of the history, structure, and changes in the Universe.
D
DECAYING ORBIT
A path around an object which decreases in size with time. For example, when a satellite enters a decaying orbit above Earth, its orbit size decreases to the point that it enters Earth's atmosphere where it burns up.
DENSITY
The mass per unit of volume of a substance.
DOPPLER SHIFT
A shift in an object's spectrum due to a change in the wavelength of light that occurs when an object is moving toward or away from Earth.
E
ELECTROMAGNETIC SPECTRUM
The entire range of the different types of electromagnetic radiation, or waves. It goes from the very long wave, low frequency, radio waves through infrared waves and visible light waves to the very high frequency and short waves of the gamma-rays and X-rays. Those wavelengths in the visible light range have a specific color associated with them when they pass through a prism. The lower frequency, longer wavelengths produce a red while those with higher frequency, shorter wavelengths produce a violet. Those wavelengths which fall somewhere in between these two points produce the orange, yellow, green, and blue also found in a spectrum.
ELECTROMAGNETIC WAVE
A wave of electric and magnetic energy that is generated when an electric charge is accelerated.
ELLIPTICAL
Shaped like an elongated closed curve.
ENERGY
Usable heat or power; in physics, it is the capacity of a physical system to perform work.
F
FAHRENHEIT
A scale on a thermometer where the freezing point of water is represented by 32 degrees and the boiling point is represented by 212 degrees.
FUSION
A nuclear reaction in which an element with small atoms fuses to form an element with larger atoms, releasing large amounts of energy.
G
GALAXY
A cluster of stars, dust, and gas held together by gravity.
GAMMA-RAYS
Penetrating short wave electromagnetic radiation of very high frequency.
GEOSYNCHRONOUS
An orbit in which a satellite's rate of revolution matches the Earth's rate of rotation. This allows the satellite to stay over the same site on the Earth's surface at all times.
GRAVITATIONAL FIELD
The volume over which an object exerts a gravitational pull.
GRAVITATIONAL FORCE
See Gravity
GRAVITATIONAL PULL
See Gravity
GRAVITY
The force of attraction between two objects which is influenced by the mass of the two objects and the distance between the two objects.
GYROSCOPE
A heavy wheel or disk mounted so that its axis can turn freely in one or more directions. A spinning gyroscope tends to resist change in the direction of its axis.
H
HABITAT
The place in which an organism lives and obtains the materials it needs in order to survive.
HELIOCENTRIC
Having the Sun as a center, such as a heliocentric solar system.
I
IMPACT CRATERS
Craters which are the result of a collision between a large body, such as a planet or satellite, and a smaller body such as an asteroid or meteorite.
INFRARED WAVES
Electromagnetic radiation with long wavelengths which is found in the invisible part of the spectrum. Human beings experience infrared waves as heat.
ION
An electrically charged particle. Ions may be negatively or positively charged.
J
K
KELVIN
A scale for measuring temperature where 0 Kelvin is equal to -273.16 degrees Celsius. Zero Kelvin is referred to as absolute zero, the point at which all motion within molecules comes to a stop.
KILOGRAM
1000grams. A kilogram equals 2.2 pounds.
KILOMETER
1000 meters. A kilometer equals 0.6214 miles.
KILOPARSEC
1000 parsecs. A parsec equals 3.26 light years.
L
LIGHT YEAR
The distance light can travel in one year, which is 9,500,000,000,000 kilometers.
M
MAGNETIC FIELD
The area in which an attractive or repelling force exists between two magnets or in association with the element iron. The Earth's magnetic field is thought to be due to the liquid iron-nickel which is in its core. This magnetic field protects Earth from constant bombardment by high-energy charged particles.
MANTLE
The middle layer of a planet located between the crust, or surface, and the core.
MASS
The measure of the amount of matter in an object.
MATTER
Anything which has mass and occupies space.
METEOR
Meteoroids which burn up in the atmosphere of a space body, such as the Earth, prior to impacting on the surface.
METEORITE
Fragments of material that fall from space and impact on other larger space bodies.
METEOROID
Fragments of material which vaporize when they have a close encounter with a space body which has an atmosphere.
METRIC TON
1000 kilograms. A metric ton equals 2,204 pounds.
MICROMETEOROID
Very small pieces of matter which are encountered in space.
MICROWAVE
Electromagnetic radiation which has a long wavelength (between 1 mm and 30 cm). Microwaves can be used to study the Universe, communicate with satellites in orbit around Earth, and cook popcorn.
MYLAR
A tough polyester material used as an insulator.
N
NASA
The National Aeronautics and Space Administration which oversees the space program in the United States.
NEBULA
A low density cloud of gas and dust in which a star is born.
O
OORT CLOUD
A huge cloud which is thought to surround our solar system and reach over halfway to the nearest star. Comets originate in the Oort Cloud.
ORBIT
A specific path followed by a planet, satellite, etc.
P
PARSEC
One parsec equals 3.26 light-years.
PAYLOAD BAY
The main body of the Space Shuttle where the payload, or cargo, is stored.
PHOTOSYNTHESIS
The process by which plants use carbon dioxide, nutrients, and sunlight to produce food.
PHYSICIST
A person who studies physics.
PHYSICS
The science of matter and energy, and of interactions between the two. A person who studies physics is called a physicist.
PLAINS
Vast, flat areas with low elevation.
PROBES
Unmanned spacecraft which are launched into space in order to collect data about the solar system and beyond. Space probes are not necessarily designed to return to Earth.
Q
QUANTUM MECHANICS
A theory in physics which is based on 2 ideas: (1) light can be emitted or absorbed only in discrete quantities called quanta, whose energy is proportional to their wavelength; and (2) you can never be exactly sure of the position and velocity of a particle, the more accurately you know the one, the less accurately you can know the other.
QUASAR
A distant energy source which gives off vast amounts of radiation, including radio waves and X-rays.
R
RADIO WAVES
A type of electromagnetic radiation which has the lowest frequency, the longest wavelength, and is produced by charged particles moving back and forth. Radio waves are not blocked by clouds in the Earth's atmosphere.
RETROGRADE
Having a direction which is opposite that of similar bodies.
REVOLUTION
The circling of a smaller object around a larger object.
ROTATION
The spinning of an object on its axis.
S
SATELLITE
An object that revolves around a larger primary body. Satellites may be naturally occurring, such as the Moon, or they may be man-made, such as the Hubble Space Telescope and the Compton Gamma-Ray Observatory.
SILICON
A non-metallic chemical element.
SOLAR ECLIPSE
A shadow which falls on an area of Earth when the Moon moves between the Sun and Earth.
SOLAR FLARES
A magnetic storm on the Sun's surface which shows up as a sudden increase in brightness.
SOLAR PROMINENCES
Gases trapped at the edge of the Sun which appear to shoot outward from the Sun's surface.
SOLAR SYSTEM
The Sun and all of the planets, comets, etc. which revolve around it.
SOLAR WIND
A continuous stream of charged particles which are released from the Sun and hurled outward into space at speeds up to 800 kilometers per second. Solar winds are very prominent after solar flare activity.
SOLAR WINGS
A panel of solar cells which converts sunlight into electrical energy.
SPECTROGRAPH
The image of the electromagnetic spectrum produced by a spectroscope.
SPECTROSCOPE
An instrument which separates visible light into its various wavelengths. Each wavelength corresponds to a specific color in the spectrum.
SPECTRUM
A band of colors which forms when visible light passes through a prism. The band ranges in color from violet (shorter wavelength) to red (longer wavelength).
SUNSPOT
A magnetic storm on the the Sun's surface which appears as a dark area. A sunspot is approximately 1500 degrees Celsius cooler than it's surrounding material. The number of sunspots we see on the Sun at any given time appears to cycle every 11 years.
T
TECTONIC ACTIVITY
A shifting of an object's surface due to changes in the material underlying the surface.
TELESCOPE
Any of various devices, sometimes made with an arrangement of lenses, mirrors, or both, used to detect and observe distant objects by their emission, transmission, reflection, or other interaction with invisible radiation.
THERMOMETER
An instrument for measuring temperature.
U
ULTRAVIOLET RAYS
Invisible electromagnetic radiation which is comprised of very short wavelengths. Human beings get a sunburn from the ultraviolet rays emitted by the Sun.
UNIVERSE
The vast expanse of space which contains all of the matter and energy in existence.
V
VOLCANISM
Volcanic activity.
W
X
X-RAYS
Penetrating electromagnetic radiation which has an extremely short wavelength.
Y
Z
