Astronomy Test 2 Flashcards Ch. 1.3-2.7

Fahrenheit temperature at which water boils

212 degrees

Kelvin temperature at which water freezes

273 degrees

opacity

A quantity that measures a material's ability to block electromagnetic radiation. Opposite of transparency.

molecules

A tightly bound collection of atoms held together by the atoms' electromagnetic fields. Emit and absorb photons at specific wavelengths.

Doppler effect

Any motion-induced change in the observed wavelength (or frequency) of a wave.

electromagnetic radiation

Another term for light; transfers energy and information from one place to another.

ion

Atom that has lost one or more of its electrons.

emission line

Bright line in a specific location of the spectrum of radiating material, corresponding to emission of light at a certain frequency. A heated gas in a glass container produces these in its spectrum.

electric field

Extends outward in all directions from a charged particle, such as a proton or an electron. Determines the electric force exerted by the particle on all other charged particles in the universe; the strength decreases with increasing distance from the charge according to an inverse-square law.

The Doppler shift for light emitted by an object moving transversely to the left would appear different to an observer than the Doppler shift for light emitted by one moving transversely to the right.

FALSE; Although at extremely high speeds (far beyond those considered in this chapter) there is a subtle effect known as the transverse Doppler shift, the formulas and effects we have been discussing here apply only to radial relative motion, not to transverse motion.

Electrons are attracted to one another.

FALSE; Electrons repel one another. They are attracted to particles such as protons that have the opposite charge.

Galileo felt that his discovery of moons orbiting Jupiter proved Copernicus wrong since it showed that not everything orbited the Sun.

FALSE; Galileo believed that his discovery supported Copernicus because it showed that objects could orbit something besides the Earth.

Kepler's third law states that period is independent of the size of a planet's orbit.

FALSE; Kepler's third law actually states that the square of the period is proportional to the cube of the size of a planet's orbit.

Light can be absorbed at any wavelength by a dilute gas.

FALSE; Photons of light can be absorbed or emitted in a dilute gas only at particular wavelengths that are characteristic of each of the atoms or molecules.

The eccentricity (e) gives us the size of an ellipse.

FALSE; To specify the overall size of an ellipse, we need to know the dimension of its semimajor axis, which is also approximately the average distance from the planet to the Sun. The eccentricity only tells us how "squashed" it appears.

A gamma ray typically has a wavelength of about 1 m.

FALSE; Typical gamma-ray dimensions are much smaller than the size of an atom.

If you double the distance between two objects, their mutual gravitational attraction will be halved.

FALSE; gravitational force varies inversely as the square of the distance between centers of the objects.

photon

Individual packet of electromagnetic energy that makes up electromagnetic radiation.

Wein's law

Relation between the wavelength at which a blackbody curve peaks and the temperature of the emitter. The peak wavelength is inversely proportional to the temperature, so the hotter the object, the bluer its radiation.

Stefan's law

Relation that gives the total energy emitted per square centimeter of its surface per second by an object of a given temperature. Shows that the energy emitted increases rapidly with an increase in temperature, proportional to the temperature raised to the fourth power.

All properties of the blackbody curve depend only on the temperature of the blackbody from which it originates.

TRUE; All properties, including the peak of the intensity, the total amount of energy, and the range of emitted radiation from a blackbody, are completely determined by its temperature.

The value for the astronomical unit (AU) is determined by measuring the distance from the Earth to Venus using radar.

TRUE; Since Kepler had worked out the distance to Venus in terms of the astronomical unit, it is possible to determine the value of the astronomical unit when the distance from the Earth to Venus is determined.

A photon of blue light has more energy than a photon of green light.

TRUE; Since blue photons have shorter wavelengths (and therefore higher frequencies) than green photons, they are also more energetic.

Rotation of a star can broaden the width (on an intensity versus frequency plot) of its spectral lines.

TRUE; The observed line broadens to lower frequencies for light coming from the receding side of the star and to higher frequencies for light from the approaching side. They all merge together to form a broadened line so the star just looks like a point to us.

diffraction

The ability of waves to bend around corners. The diffraction of light establishes its wave nature.

blackbody radiation

The characteristic way in which the intensity of radiation emitted by a hot object depends on frequency. The frequency at which the emitted intensity is highest is an indication of the temperature of the radiating object. Also referred to as the Planck curve.

frequency

The number of wave crests passing any given point per unit time.

spectroscopy

The study of the way in which atoms absorb and emit electromagnetic radiation. Allows astronomers to determine the chemical composition of stars.