Astr 1202 Test 2

Front 1

____________ - the apparent shift in location

Back 1

parallax

Front 2

The closer something is, the ____________ the parallax.

Back 2

larger

Front 3

If an object's distance is 1 pc, it will have a parallax shift of ____________ over the course of Earth's orbit.

Back 3

1 arcsec

Front 4

If a star appears to move back and forth within a year (1 earth orbit), then the apparent motion is ____________.

Back 4

likely parallax

Front 5

If a star has a set motion from year to year, then this motion is due to ____________.

Back 5

actual motion of the star (it has a velocity relative to the sun)

Front 6

Every star has a parallax less than ____________.

Back 6

1 arcsec

Front 7

From Earth, we can't measure much farther than ____________.

This is because, it is difficult to measure parallax less than ____________.

Back 7

100 pc

0.01 arcsec

Front 8

From space, parallaxes of ____________ can be measured.

From space we can see ____________ of pc.

Back 8

0.001 arcsec

several hundred

Front 9

The size of our galaxy is approximately ____________.

Back 9

50,000 pc across

Front 10

__________: the apparent intensity of a star's light (units: W/m^2)

__________: the total energy emitted by a star (units: W)

Back 10

brightness

luminosity

Front 11

What is the formula for Luminosity?

L =

Back 11

L = (b) *4(pi)(d)^2

Front 12

Light __________ as it travels farther from an object.

If you double the distance, you are left with __________ of light.

Back 12

spreads out

1/4

Front 13

To compare the Luminosity, we use an equation like

L1/L2 =

Back 13

L1/L2 = (d1^2/d2^2) (b1/b2)

Front 14

__________: a scale that measures the brightness of a star.

__________: a scale that measures the luminosity of a star.

Back 14

Apparent Magnitude

Absolute Magnitude

Front 15

For magnitude, the larger the number, the __________ the object

A negative number is __________ than a positive number.

Back 15

dimmer

brighter

Front 16

A star that is one magnitude higher than another is __________ times dimmer.

So a star that is 5 magnitudes higher is _________ times dimmer.

(__________)^5 = __________

Back 16

2.512

100

2.512^5 = 100

Front 17

How much brighter is a 2nd magnitude star compared to a 5th magnitude star?

Back 17

The 2nd magnitude star is 15.93

or ~16 times brighter

Front 18

Absolute magnitudes serve to compare stars' luminosity by calculating what their magnitude would be if every star was located __________ away from us.

Back 18

10 pc

Front 19

If the Sun was located at 10 pc, its absolute magnitude would be ______.

Back 19

14.8

Front 20

_________ - A quicker way to estimate a star's temperature is to measure its brightness in different "colors".

Back 20

UBV Photometry

Front 21

What does UBV stand for in UBV Photometry?

Back 21

U = Ultraviolet

B = Blue

V = Visible

Front 22

In UBV Photometry, the larger the ratios (bV/bB & bB/bU), the ____________ the star.

___________ stars have more red light.

Back 22

cooler

cooler

Front 23

Pro's of UBV Photometry:

Can apply these color filters to _____________.

Can estimate the _______________ of very faint stars.

Back 23

many stars at once

temperature

Front 24

Cons of UBV Photometry:

______________ than measuring whole spectrum to find (lambda max).

______________ can redden the appearance of a star's light (lessen the blue light.)

Back 24

Less precise

Interstellar dust

Front 25

Doppler Effect in the Universe:

Almost everything in the universe is moving ____________.

If an object is moving away from us it will have the wavelength of its light lengthened, so it appears _____________.

Back 25

away from us

"reddened"

Front 26

The effect of the reddening from the Doppler shift is _________________.

Back 26

very small and doesn't contribute to any apparent color change

Front 27

All star are made up about the same:

~____% Hydrogen

~____% Helium

~____% other

Back 27

75% Hydrogen

25% Helium

1% other

Front 28

The hotter the star, the less apparent the _______________.

Back 28

absorption lines

Front 29

What is the mnemonic for the spectral class from hottest to coolest?

Back 29

Oh Be A Fine Girl, Kiss Me

Front 30

Stellar spectra can be used to measure ___________ as well as _____________.

Back 30

temperature

chemical composition

Front 31

Absorption lines are also broadened by _________________. This is caused by a larger ____________ exerted on the gas.

The larger the ______________, the more compact the star. The more compact, the lower the ____________.

Back 31

higher gas pressure

gravitational force

gravitational force

luminosity

Front 32

Broader absorption lines correlates to lower ______________.

Back 32

luminosity

Front 33

On the H-R diagram, the higher the Roman numeral, the lower the ______________.

Back 33

luminosity

Front 34

Using the H-R diagram, we can know the luminosity of stars which can tell of the ____________ and ___________ of even the most distant stars.

Back 34

radius

distance

Front 35

Because of the H-R diagram, if we know the distance and brightness, we can evaluate a star's _____________.

Back 35

luminosity

Front 36

Using information about a star's luminosity and spectrum to determine its distance is called ______________.

Back 36

spectroscopic parallax.

Front 37

According to the H-R diagram, the more luminous the star, the ________________ its mass.

Back 37

greater

Front 38

The _____________ is made up of low density gas (hydrogen) and dust.

Back 38

interstellar medium

Front 39

Interstellar medium can produce _________________, as well as scatter and reflect light.

Back 39

emission and absorption lines

Front 40

Light is ____________ as it passes through interstellar medium. (Not via red-shifting of doppler effect).

Back 40

reddened

Front 41

Clouds of interstellar medium are called ___________________.

Back 41

nebula (pl. nebulae)

Front 42

Emission Nebulae

These are clouds of __________ gas.

Since nearly all interstellar gas is H, it glows ________ from H _____________.

Back 42

excited

red

emission lines

Front 43

In emission nebulae

Hydrogen is getting energy to glow from absorbing __________ from other stars.

(The red light is not due to temperature.)

Typically have between ________________ solar masses spread over a volume light-years across.

Back 43

UV light

100 to about 10,000

Front 44

Dark Nebulae

Both dark and reflection nebulae are composed of _______________.

Dark nebulae have high densities of dust such that _____________ cannot escape.

Back 44

grains of dust

visible light

Front 45

Reflection Nebulae

These nebulae are the result of ___________ being scattered by the dust in our direction.

[Only long wavelength (red) light can pass through this dust]

Back 45

blue light

Front 46

Short explanation of each type of nebulae:

Emission nebula:

Dark nebula:

Reflection nebula:

Back 46

emission nebula: excited glowing gas

dark nebula: dust scatters background light

reflection nebula: dust scattering blue light towards us

Front 47

_______________ - the intensity of the light is lessened by passing through the interstellar medium.

_______________ - blue light is scattered by the interstellar medium leaving behind "reddened" light.

Back 47

extinction

reddening

Front 48

Inside a dark nebula, a longer wavelength light, such as ____________, may pass through the nebula. Thus it is a good way for viewing the nebula and _____________.

Back 48

infrared light

young stars

Front 49

Since the interstellar medium exists between stars, this medium is concentrated where stars are concentrated, in _____________.

Back 49

galaxies

Front 50

Interstellar dust and gas in galaxies are concentrated in the _____________ of the galaxy.

Therefore, new stars are made in the ______________ of galaxies.

Back 50

plane (disk)

planes

Front 51

Hydrostatic equilibrium is a balance between the internal ______________ outwards and the external ____________ inwards.

Back 51

thermal pressure

gravitational pressure

Front 52

In the life of a star:

__________ starts the process to start fusion.

Star reaches _______________.

Near the end of its life the ____________ begins to grow greater and the star bloats.

In the end, _________ finally wins when the star collapses.

Back 52

gravity

hydrostatic equilibrium

internal pressure

gravity

Front 53

Before a star is classified as a "star" it is called a ____________.

A ____________ becomes a star when fusion starts.

Back 53

protostar

protostar

Front 54

Protostars are formed within ____________.

Back 54

dark nebulae

Front 55

_____________ are dark nebulae which are dense and low in temperature.

This environment is ___________ for the creation of protostars.

Back 55

Bok globules

favorable

Front 56

Bok Globules

High density: ~ _____________ particles per cm^3

Low temp: ~_______ K

Back 56

100 to 10,000

10

Front 57

Bok Globules have a similar composition to stars:

~_____% H

~_____% He

~_____% metal

Back 57

~75% H

~25% He

~ <1% metal

Front 58

As a protostar contracts under gravity, it heats and becomes _________.

Back 58

denser

Front 59

Pressure varies as it is ___________ X _________.

Gravitational collapse increases both temperature and density until pressure balances ______________.

This continues until fusion pressure halts _________.

Back 59

temperature

density

gravity

collapse

Front 60

Giant Molecular Clouds

Gasses in _______________ can allow atoms to combine into molecules.

The spiral arms of our galaxy are laced with ________________.

Back 60

very cold nebulae

giant molecular clouds

Front 61

Giant Molecular Clouds

~ _________________ solar masses in size

~__________________ light years in diameter

~__________________ H2 Molecules per cm^3 in density

Back 61

~10^5 to 10^6 solar masses

~50 to 300 light-years

~200 H2 molecules per cm^3

Front 62

Orion cloaked in a Giant Molecular Cloud (GMC)

GMCs emit light in ________________.

These clouds create multiple areas of ______________.

Back 62

microwave light

new star creation

Front 63

GMCs in Galaxies

GMC's are concentrated in the _______________ of the Milky Way

This creates a "traffic jam" that helps to _______________________.

Back 63

spiral arms

spawn more star formation

Front 64

Death Throes of Stars Start the Birth of New Stars

A star is born when gravitational contractions begin to pull _______________.

Normally something is needed to ________________ of an otherwise stable nebula.

Back 64

a nebula together

trigger a collapse

Front 65

The ___________________ of another star can be the trigger for such a collapse.

This explosion also _________________ to the mix.

___________________ can only be made during a supernova. Since we have these elements, we believe that a supernova seeded the _______________________.

Back 65

supernova explosion

adds material

Heavier elements

formation of our solar system