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M0
Short for MAssive Compact Halo Objects, which are non-nuclear objects that normally surround galaxies.
A dark spot.
Magellanic Clouds
A force field generated by moving electrical charges. An electrical current running through a loop of wire generates a magnetic field. The strength of the field depends on the current and area of the wire loop. Plasma churning through the atmosphere of the Sun drives powerful magnetic fields that sometimes produce cool magnetic storms called sunspots. A magnetic dynamo underneath Earth's crust generates a magnetic field around Earth.
Magnetic
Pole
A special telescope which analyzes the color and polarization of sunlight in order to measure the magnetic field of the Sun.
The boundary of the magnetosphere, lying inside the bow shock.
The region of space in which a planet's magnetic field dominates that of the solar wind.
The portion of a planetary magnetosphere which is pushed in the direction of the solar wind.
In a telescope, an increase in the apparent size of an object. The process of magnification expands the apparent size of an object by spreading the image, or light, across a large area. A large primary mirror or objective lens of a telescope focuses incoming light toward an eyepiece lens that actually magnifies what the telescope sees.
The ratio of the apparent image size and actual size of an object in a telescope. Telescope magnifying power is the objective lens or primary mirror focal length divided by the eyepiece focal length. This is why the high power eyepieces are tiny, and the wide field eyepieces are huge.
A scale on which the brightness of a star is measured. This scale is logarithmic, meaning each successive magnitude is increasingly brighter/dimmer than the last. To be more precise, each change of five magnitudes is equivalent to a change by a factor of 100. Also, stars with a lower magnitude are the brightest. Stars may have negative magnitudes. For example, a star with a magnitude of -1 is 100 times brighter than one of a magnitude of 4.
A group of stars on the HR diagram that all shine via hydrogen thermonuclear fusion, and are all in a state of hydrodynamic equilibrium. Stars spend the greatest portion of their luminous (nuclear fusion) life on the main sequence.
Major Axis
The rocky layer that lies between the crust and the core inside a planet.
Plural: Maria. Latin for "sea," it is an area of recent basalt rock on the surface of the Moon created by oozing lava. Perhaps a violent impact cracked the surface open. The maria formed while lava bled from the cracks and healed the impact crater. Maria are the most crater-free regions on the Moon's surface.
Amount of matter making up a body.
Mass-Light Ratio
Mass-Luminosity Relation
1: A substance of which a physical object is composed. 2: A substance that constitutes the observable universe and together with energy forms the basis of objective phenomena.
Maunder Minimum
Mean Solar Day
Mega-Ton 1 mega-ton = 4 x 1022 ergs = 4 x 1015 joules.
Mesa, flat-topped elevation.
Merger (of galaxies)
An imaginary line on the sky that runs due north and south and passes through your zenith.
Messier
Catalog
A shooting star; a meteoroid that travels between 11.18 and 72 km/s and vaporizes within Earth's atmosphere because of intense friction between it and the air.
A part of a meteoroid that survives through the Earth's atmosphere.
A small rock in space.
Meteor Shower
Meter
(m)
A gas made of carbon and hydrogen.
Metric
System
One millionth of a meter.
Microquasar
A type of radio wave, which has the shortest of the radio wavelengths.
Microwave Background Radiation The radiation from the glowing of the hot early universe, now so greatly red-shifted that it appears not as light but as microwaves (radio waves with a wavelength of a few centimeters).
A soft, glowing band of light encircling the sky, it is the disk of the spiral galaxy in which the sun lies, seen from the inside.
1/1000 of a bar. Standard sea-level pressure is about 1013 millibars.
One of many tiny black holes with the mass of a mountain but the size of an atom that are believed to have been created in the Big Bang.
If you say, "there is some energy", this means "it has an ability to work (physically) on something else. For example, imagine there is a moving ball, and there is a tofu at the end of its trajectory. If the ball crashes into tofu, tofu will be squashed. The moving ball has some energy because "it can give some kind of an effect on something." But what if this ball wasn't moving? It wouldn't crash into tofu, and even if it stuck to tofu, it will not affect the tofu. The unmoving ball doesn't have any energy. So let's think about dropping a ball from top downwards. Tofu is on the ground. Same as before, if there is some height, the ball can drop and squash the tofu. But a ball that was already placed on tofu, can not squash it (of course if ball isn't too heavy!). Let's change the point of view. Fix the ball at that place and dig the ground underneath tofu. And place tofu on the dug ground, and unfix the ball. This time, the ball drops to the depth of the dug hole and will squash tofu. Therefore if the base point changes, the existing energy differs. In this case, because the place of ground changed, it changed from the state of no energy to the state with energy. Thus amount of energy differs according to standard position. So you can not define a condition where energy is zero. If standard position changes, it will not be a zero. If energy is zero at a fixed condition, meaning in an energy condition that will not decrease more, is said that energy is minimum.
An interstellar cloud made up of molecules such as hydrogen and carbon monoxide.
The smallest particle of an element or compound capable of retaining chemical identity with the substance in mass.
Momentum
Mountain (plural: montes).
A planet's natural satellite. Earth's satellite is called the Moon; those of other planets have unique names, such as Io, Jupiter's moon.
Three or more stars held in orbit around each other by gravity.
Unassisted human eyesight. The term naked eye is used for any object that should be visible to an average observer in good conditions.
One billionth of a meter.
NASA
Near-Earth Object (NEO)
A diffuse mass of interstellar dust and gas.
A "stellar womb" composed of hydrogen, helium, interstellar gas and dust that is illuminated with the light and energy of new born stars. Example: Orion Nebula (M42), located in Orion's sword.
Mainly composed of cool interstellar dust that reflects and scatters light from nearby stars. These nebulae are mainly bluish in color, a clue to the size of the dust grains. In order to scatter the blue light, the dust grain size must be on the order of microns, close to the wavelength of blue light.
Usually look like a donut, sometimes with a small hot rapidly evolving star visible in the center. The nebulosity occurs when the central star blows off its outer atmosphere. M 57, the Ring Nebula in Lyra is an example.
Results from a supernova explosion ripping apart the stellar atmosphere. Radiation and the shock wave illuminate interstellar gas. As the shock wave plunges through the gas like a snowplow, the accumulating gas glows all across the electromagnetic spectrum. An example is the Crab Nebula, M1, between the horns of Taurus the Bull.
A subatomic entity
with virtually zero mass and charge that rarely interacts with
matter. While a
single photon emitted from a stellar core journeys for millions of
years to the
photosphere, a neutrino zips straight out of the
star. A neutrino telescope
could probe the interior of a star and confirm/deny present theoretical models
for nuclear thermonuclear fusion reactions. An uncharged (neutral) elementary
particle, stable when
bound in an atomic nucleus and having a mean lifetime of about 12 minutes as a
free particle (note: the neutron is found in all known elementary nuclei except
for the hydrogen nuclei). In stellar evolution, one step beyond white dwarf. Neutron stars are named after their composition: neutrons. Stars with core masses between than 1.4 and 2 solar masses collapse, combining the electrons and protons into neutrons. Neutron star density averages 10^14 grams/cubic centimeter. A full bathtub of neutron star (instead of water) weighs about two Mt. Everest's'. A solar mass neutron star is between 10 and 15 km wide, with a liquid neutron core and an atmosphere of iron. Some neutron stars, called pulsars, spin rapidly at about one revolution a second and sustain a powerful magnetic field. Stars born with 8 to 20 solar masses blow most of their mass away into interstellar space (supernova), then evolve into neutron stars. Heavier stars collapses into a black hole.
A popular place for the eyepiece on a reflecting telescope. A diagonally aligned mirror reflects the telescope's focal point outside the telescope tube for convenient viewing. This type of telescope is called a Newtonian reflector.
Newton's
Law of Universal Gravitation
Newton's Laws of Motion
Newton's
Second Law of Motion
Newton's
Third Law of Motion
A gas that makes up 79% of Earth's atmosphere.
The idea that the universe is finite but has no boundary (in imaginary time).
A point at which the path of a planet or comet intersects the ecliptic. A node passed as the body goes north is called an ascending node, that passed in going south, the descending node.
Noise
The star Polaris, in the constellation Ursa Minor, around which the northern sky appears to rotate.
Plural: Novae. A white dwarf star in a binary system that brightens suddenly by several magnitudes as gas pulled away from its companion star explodes in a thermonuclear reaction.
Nuclear
Bulge
A nuclear process whereby several small nuclei are combined to make a larger one whose mass is slightly smaller than the sum of the small ones. The difference in mass is converted to energy by Einstein's famous equivalence E=mc2. This is the source of the Sun's energy and, ultimately, of (almost) all energy on Earth.
Spontaneous disintegration of atomic nuclei by the emission
of subatomic particles called alpha particles and
beta particles, or of
electromagnetic rays called X rays and gamma
rays. Nucleosynthesis
Plural: Nuclei. The positively charged central region of an atom, composed
of protons and neutrons and containing almost all of the mass of the atom. A term describing more than one nucleus. Here is the ascending order of names of numbers: hundred, thousand, million, billion, trillion, quadrillion, quintillion, sextillion, septillion, octillion, nonillion, decillion, undecillion, duodecillion, tredecillion, quat(t)uordecillion, quindecillion, sexdecillion, septendecillion, octodecillion, novemdecillion, vigintillion.
A periodic libratory motion of the Earth's axis, like the nodding of a top, by which its inclination to the plane of the ecliptic varies with a range of only a few seconds of arc, so that the celestial poles describe wavy tracks, not circular, around the poles of the ecliptic. |