AST 104 (jeffery ial) EXAM 2

Visible light is a form of

electromagnetic radiation

Visible light is conventionally divided into:

violet, blue, green, yellow, indigo orange, red (ROYGBIV)

Electromagnetic radiation (EMR) is:

WAVE PHENOMENON, NOT EXCITATIONS OF A
MEDIUM, HIGHER.

AM radio typically broadcasts at about 1 MHz = 106 cycles per second. What is the approximate wavelength of this radiation?

∼ 3 × 104 cm = 300 m

The electromagnetic spectrum is:

the entire wavelength range of electromagnetic radiation: i.e., the electromagnetic radiation range
from zero to infinite wavelength, not counting the limit end points themselves.

What is the form of electromagnetic radiation that is usually most dangerous for life?

gamma-rays.

The wavelength range of visible light is about:

400-700 nm.

Astronomers must observe the gamma-ray, X-ray, and most of the ultraviolet bands from space since the Earth's atmosphere is quite in those bands.

opaque

The eye may have evolved to be sensitive to a form of radiation that was ________ on the Earth's surface thereby making a __________ of the electromagnetic radiation resource.

ABUNDANT, GOOD USE

For better vision in NIGHT conditions, nocturnal animals have evolved large pupils (which are the apertures of the eyes). Light gathering power is proportional to the:

SQUARE OF APERTURE DIAMETER

The quantum or "particle" of light is called a:

photon

If the wavelength of light is changed by a multiplicative factor of 3, the energy of its photons is changed by a multiplicative factor of:

1/3

The Moon has almost no atmosphere. In what wavelength bands could an astronomer observe space from the Moon?

In practically all bands.

An ion is a:

charged atom.

Internal energy or heat energy is:

statistically distributed forms of the other kinds of energy: most notably microscopic kinetic energy, microscopic potential energy, and electromagnetic radiation.

Any body at a non-zero temperature or range of temperatures will radiate:

electromagnetic radiation

A solid, liquid, or dense gas at a uniform temperature will:

radiate a blackbody spectrum

What is the star's approximate photospheric temperature?

6000 K.

The line spectrum of an atom, ion, or molecule is:

an almost unique identifier of the atom, ion, or molecule

The layer of a star (e.g., the Sun) from which most of the emitted electromagnetic radiation comes is called the:

photosphere

The Sun emits a spectrum that is approximately a blackbody spectrum. It isn't exactly a blackbody spectrum because, the photospheric emission forms over a range of temperatures and there is an __________________________________ superimposed on the photospheric emission.

ABSORPTION LINE SPECTRUM

The Hα line (AKA the H-alpha line), usually the strongest VISIBLE line of hydrogen, has a wavelength of 656 nm It is a/an line.

RED

At 254 K the Earth would be colder than the freezing point of water. The reason the Earth isn't
this cold is because of the greenhouse __________ effect.

HEATING

The Doppler effect for light causes the wavelength of a wave phenomenon to change when its ___________________ are moving with respect to each other along the source-receiver line

SOURCE AND RECEIVER

The first source is Doppler shifted to the _______ (i.e., to longer wavelength). The second source is _______ significantly Doppler shifted unless its velocity is not small compared to the vacuum speed of light.

RED, NOT

The star line would be _________ due to the Doppler effect. The part of the star moving toward the observer would broaden the line in the __________________. The part of the star moving away from the observer would broaden the line in the ___________________.

BROADER, SHORT WAVELENGTH (BLUEWARD) DIRECTION, LONG WAVELENGTH (REDWARD) DIRECTION.

The diameter of the Sun is about:

109 Earth diameters.

The solar luminosity is L⊙ is:

3.846 × 1026 W.

The temperature of the solar photosphere is about:

6000 K.

What is the electromagnetic radiation energy per unit time per unit area from the Sun at 1 astronomical unit from the Sun?

constant

The solar constant (i.e., the electromagnetic radiation energy per unit time per unit area from the Sun at 1 astronomical unit from the Sun) is:

1367.6 W/m2

How many 100 watt light bulbs could you run on solar power?

1.3676 × 107

This astrophysical body has three main interior layers: 1) a core (in which thermonuclear reactions occur) that extents out to about 25 % of the body's radius; 2) a radiative transfer zone which extends OUT to about 71 % of the body's radius; 3) a convective zone that extends FROM about 71 % of the body's radius to the body's surface:

the Sun

Out to about 71 % of the Sun's radius, the dominant energy transfer mechanism is:

radiative transfer (i.e., transfer by
electromagnetic radiation)

Why can't we see deeper into the Sun than the photosphere?

Radiation from deeper layers is absorbed before it can escape the Sun

A granule is:

The top of a rising current of HOT gas in the Sun. The risen gas COOLS and then sinks.

The five outermost layers of the Sun (defining layers of the Sun generously) can be labeled:

CONVENTION ZONE, photosphere, chromosphere, corona, and SOLAR WIND.

Two of the five outermost layers of the Sun (defining layers of the Sun generously) are:

photosphere and chromosphere

The corona of the Sun is only visible to the naked eye when:

there is a total solar eclipse

How far has the corona been traced out in astronomical units and does this trace of the corona reach to the orbit of Mercury which has a mean radius of 0.38709893 AU?

0.14 AU and no.

The solar wind is:

the plasma gas that streams from the Sun out into INTERSTELLAR SPACE.

The solar wind near the Earth is typically moving at a radial velocity of about:

400 to 500 km/s.

The Sun loses mass at a rate of about 2 × 109 kg/s. Convert this rate into solar masses per year to the same number of significant figures as given.

3 x 10 ^ NEGATIVE FOURTEEN

Stars are spheres:

of hot gas.

The Sun's surface composition by mass (which approximates the average cosmic composition and is typical of non-ancient stars) is about:

71 % hydrogen, 27 % helium, and 2 % everything else.

The angular motion of stars on the sky as seen against the background of more distant stars due to the Earth's motion around the Sun.

stellar parallax

Van Maanen's star has a stellar parallax of 0.232 arcseconds. About how far away is this star?

4.3 pc

The closest star to Earth (not counting the Sun) is at 1.30 pc

Proxima Centauri

If all the stellar parallaxes (i.e., parallax angles measured during a half revolution of the Sun) were INCREASING with time, this would mean that the stars were all:

moving closer

A dim star is located at about 2 million astronomical units from Earth.

2mil AU = 10 pc

In galaxy collisions, direct star-star collisions in which star matter impacts occur:

very rarely because interstellar distances are very large compared to star sizes

Because gravity is a long-range, inverse-square-law force, significant gravitational interactions between two stars:

are relatively common

The total power of a star (i.e., energy output per unit time) is called:

luminosity

The brightest stars are of order times more luminous than the Sun and the dimmest are of order times the Sun's luminosity

10 POWER OF SIX ; 10 POWER OF NEGATIVE FOUR

The energy per unit time per unit area?

flux

The study of emission is called:

photometry

The flux of light from a star obeys a/an:

inverse-square law

THIS general physical principle when applied to a star and its surrounding vacuum space in a steady state condition

conservation of energy principle

If you knew the luminosity of a star, then it's distance could be determined directly by:

a measurement of its flux using the inverse-square law.

This metaphorical expression is the name for the collection of distance measurement techniques used to establish cosmic distances on all scales.

distance ladder

The first rung of the distance ladder uses the distance measurement technique of:

stellar parallax

temperature of an ordinary star can be determined from:

the shape of its BLACKBODY spectrum or an analysis of its ABSORPTION line spectrum

The surface (i.e., photosphere) temperature of an ordinary star can be determined by:

identifying its spectral type

The main sequence spectral star types are:

OBAFGKM
Remember the mnemonic: "Oh, be a fine girl/guy kiss me."

Each stellar spectral types is divided into these subtypes

0, 1, 2, . . . , 9

The Sun's spectral type is:

G2.

The hydrogen Balmer lines in main sequence stars:

are strongest at surface temperature of order 10, 000 K.

The approximate colors of the hydrogen Balmer lines Hα, Hβ, Hγ, and Hδ are, respectively:

red, blue-green, blue-violet, and violet

It is a plot of stellar luminosity (or absolute magnitude) versus star temperature (or spectral type)

Hertzsprung-Russell (HR) diagram

The main sequence on a Hertzsprung-Russell (HR) diagram is a curve (actually a narrow band) of ________ luminosity with increasing __________.

increasing; surface temperature

Main sequence stars, giants, supergiants, and white dwarfs all give rise to easily identifiable groups on a:

Hertzsprung-Russell (HR) diagram

On a Hertzsprung-Russell diagram contours of constant radii run:

linearly DOWNWARD to the right.

Stars:

usually cannot be resolved, but with special techniques close, large ones can be.

The luminosity classes of stars are:

0, Ia, Ib, II, III, IV, V, VI, VII.

They are the most luminous stars (i.e., luminosities of order 106 L⊙) and put in luminosity class 0. They are called:

hypergiants

These objects appear on Hertzsprung-Russell diagrams and they are assigned a luminosity class VII.

white dwarfs

They are the kind of stars to which the mass-luminosity relation applies.

main-sequence

On a log-log plot the mass-luminosity relation approximates a:

straight line that increases with mass.

Two stars gravitationally bound to each other and orbiting their mutual center of mass constitute a:

binary star system

The evolution of stars in close binary systems have additional complexity beyond single star systems because the binary stars:

can interact

These are loosely-bound, irregularly-shaped groups of stars consisting of order 100 to 1000 stars and having size scales of order 4 to 20 pc

open clusters

A physical group of stars in the constellation Taurus, sometimes called the Seven Sisters or, in Japan, Subaru, of which at least 6 stars are usually visible to the naked eye under reasonable seeing conditions

Pleiades

These are structures of a few to a few hundred stars and span of order 10 to 100 pc. They are generally gravitationally unbound though gravitationally interacting

associations

They can have from 20,000 to several million stars and their central
concentrations have diameters of order to 5 to 25 pc

globular clusters

The ages of the stars in globular clusters put a lower limit on the age of the observable universe. The calculated ages of these stars are about:

12.5 Gyr

Two groups of populations are called

Population I and Population II

The life history of our own star, the Sun, is known to us by:

direct observations of its current stage plus observations of other stars in all their stages and modeling.

The interstellar medium (ISM) consists of:

gas and dust

In modern astronomy, a nebula (plural nebulae) is a:

cloud of a gas in space

The dense, cold component of the interstellar medium from which stars are believed to form is made of:

molecular clouds

The composition of molecular clouds in the interstellar medium is dominated by:

molecular hydrogen gas and helium gas

Molecular clouds are probably about 1 per cent dust by mass. This dust is:

VERY IMPORTANT and HIGHLY OPAQUE

Interstellar dust probably varies widely in composition, size scale, and structure. But there some ideas about typical dust that are generally accepted:

it has NONVOLATILE material and forms in STELLAR WINDS AND SUPERNOVA EJECTA

It happens whenever a star changes its luminosity and/or its surface temperature

movement

Star formation in a dusty molecular cloud probably requires some triggering event to initiate the collapse to dense cores that will become stars. Two possible trigger mechanisms are:

SUPERNOVAE which compress molecular clouds and CLOUD-CLOUD COLLISIONS which also compress the colliding molecular clouds

In a FREE-FALL contraction of part of molecular cloud:

Pressure forces are negligible in slowing the fall because it is a free-fall contraction

The collapsing dense regions that develop into stars and initially have temperatures of order 10 K are called

dense cores

A protostar is sometimes conveniently defined to be a:

dense core of gas contracting to become a star that is hot enough to radiate in the infrared, but not yet sufficiently hot for nuclear burning

The contraction of a protostar is halted eventually by:

the heat generated by the turning on of nuclear burning which INCREASES the gas pressure inside the protostar

The gas region ionized by an OB associations is called a/an:

H II region