Meaning astrometry12/21/2023 An object whose velocity is increasing has a positive acceleration.Īn accretion disk is a flat disk of gas and dust in space that surrounds a newborn star, black hole, or other enormous object that is growing by attracting matter to it with its gravitational field.Īn achondritic meteorite is a stony meteorite, coarsely crystallized, with large bits of various minerals visible to the naked eye.Īcid rain is polluted and harmful to the environment. When an object is moving at a constant velocity (or if it is standing still) it has zero acceleration. Astronomers can determine the composition of gases in stars by looking for their characteristic frequencies (this is called spectroscopy).Īcceleration is the rate of change of velocity. Each different element and molecule absorbs light at a unique set of frequencies. An absorption spectrum is created when light from an incandescent source passes through a cooler gas that absorbs photons. Each dark line is formed as a cooler gas absorbs photons emitted by a particular element from a hotter source.Īn absorption spectrum (also called a dark-line spectrum) consists of dark absorption lines superimposed on a bright continuous spectrum. ![]() Absolute zero would occur at -273.16☌, -459.69☏, or 0 K.Ībsorption Lines are dark lines superimposed over a bright continuous absorption spectrum. All actual temperatures are above absolute zero. Negative numbers indicate extreme brightness.Īt absolute zero, a hypothetical temperature, all molecular movement stops. The lower the number, the brighter the object. This scale is defined as the apparent magnitude a star would have if it were seen from a standard distance of 32.6 light-years (10 parsecs). Some spacecraft use ablative heat shields their outer surface is coated with heat-dissipating material (like a phenolic epoxy resin, a reinforced plastic) that burns rapidly, and then falls away during re-entry.Ībsolute magnitude is a measure of the inherent brightness of a celestial object. The discovery of the aberration of light was one of the first proofs that the speed of light was finite it also provided an early estimate of the speed of light (Bradley calculated that the time it took for light to travel from the Sun to the Earth was 8 minutes and 12 seconds).Īblation is a cooling process in which heat is carried away from an object (like a falling meteorite) as the flow of air blows away the hot, melted or vaporized outer layers of the object. The aberration of light was discovered and demonstrated by James Bradley (an English amateur astronomer) in 1725. (An analogous situation is watching rain fall from a moving train - although a raindrop is falling straight to the ground, it will appear to fall at a slant, and the slant increases as the train's speed increases.) The aberration of light is due to the fact that light travels at a finite speed (as do the raindrops). The aberration of light is a phenomenon in which light appears to be slanted (the angle at which the light appears to be coming is different than the angle at which it's actually coming) if the observer is in motion. Our subscribers' grade-level estimate for this page:Ĭlick on an underlined word for more information on that subject. ![]() ![]() Today's featured page: Label Shark Anatomy Printout is a user-supported site.Īs a bonus, site members have access to a banner-ad-free version of the site, with print-friendly pages.
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