Solar Spectrum

laws of thermal radiation

1. hotter objects emit more light per unit surface area at all frequencies of light 2. Wien's Law says hotter objects emit photons with higher typical energies

When an atom absorbs a photon containing energy, any of the following can happen except which?

An electron moves from an upper energy level to a lower one

Each diagram below shows a pair of spectra with a set of spectral lines. The top spectrum always shows the lines as they appear in a spectrum created in a laboratory on Earth ("Lab") and the bottom spectrum shows the same set of lines from a distant star. The left (blue/violet) end of each spectrum corresponds to shorter wavelengths and the right (red) end to longer wavelengths. Rank the five stars based on the Doppler shifts of their spectra, from largest blueshift, through no shift, to largest redshift.

As your answer correctly indicates, lines that are shifted to the left (toward the blue/violet) compared to the laboratory spectrum represent blue shifts, and lines shifted to the right (toward the red) represent redshifts.

The diagrams below each show the motion of a distant star relative to Earth (not to scale). The red arrows indicate the speed and direction of the star's motion: Longer arrows mean faster speed. Rank the stars based on the Doppler shift that we would detect on Earth, from largest blueshift, through no shift, to largest redshift.

As your correct answer indicates, the star moving fastest toward Earth will have the greatest blueshift, the star moving across our line of sight will have no shift at all, and the star moving fastest away from us will have the greatest redshift.

Suppose we want to know what the Sun is made of. What should we do?

Compare the wavelengths of lines in the Sun's spectrum to the wavelengths of lines produced by chemical elements in the laboratory-Each chemical element (or ion or molecule) produces a unique set of spectral lines; the wavelengths of these lines can be measured in the laboratory. If the Sun's spectrum contains the set of lines for some particular element, we conclude that the Sun contains that element. We determine the Sun's overall chemical composition by examining all the lines in its spectrum.

According to our theory of solar system formation, what three major changes occurred in the solar nebula as it shrank in size?

It got hotter, its rate of rotation increased, and it flattened into a disk.

How can an electron in an atom lose energy to go from a higher energy level to a lower energy level?

It releases a photon equal in energy to its own energy drop

An important line of hydrogen occurs at a rest wavelength (as measured in a laboratory) of 656 (a nanometer () is a billionth of a meter). Each diagram below has this line labeled with its wavelength in the spectrum of a distant star. Rank the motion of the stars along our line of sight (radial motion) based on their speed and direction, from moving fastest toward Earth, through zero (not moving toward or away from Earth), to moving fastest away from Earth.

Notice that your correct answer ranks the stars in wavelength order. The first two stars are moving toward us, because their lines have wavelength shorter than the rest wavelength of 656 nm. The last two stars are moving away from us, because their lines have wavelength longer than the rest wavelength of 656 nm.

Which of the following procedures would allow you to make a spectrum of the Sun similar to the one shown, though with less detail?

Pass a narrow beam of sunlight through a prism-The prism bends different wavelengths of light by different amounts, causing the white light from the Sun to spread out into a rainbow of colors. Absorption features appear as dark lines against the brighter background of the spectrum.

Which of the following best describes why the Sun's spectrum contains black lines over an underlying rainbow?

The Sun's hot interior produces a continuous rainbow of color, but cooler gas at the surface absorbs light at particular wavelengths.-The Sun's spectrum is an absorption line spectrum, which is produced when continuous light from a hot source (the Sun's interior) passes through a cooler cloud of gas (the gas that makes up the Sun's visible surface).

Suppose you see two stars: a blue star and a red star. Which of the following can you conclude about the two stars? Assume that no Doppler shifts are involved. (Hint: Think about the laws of thermal radiation.)

The blue star has a hotter surface temperature than the red star

You observe a distant galaxy. You find that a spectral line normally found in the visible part of the spectrum is shifted toward the infrared. What do you conclude?

The galaxy is moving away from you.

If one object has a large redshift and another object has a small redshift, what can we conclude about these two objects?

The one with the large redshift is moving away from us faster than the one with the small redshift

Any spectrum can be displayed either in photographic form as shown to the left or as a graph. Which of the following graphs could represent a portion of the Sun's visible light spectrum?

The smooth part of the curve represents the graph of the background rainbow of color; the dips in the curve represent the black lines where light is missing from the rainbow.

From laboratory measurements, we know that a particular spectral line formed by hydrogen appears at a wavelength of 486.1 nanometers (nm). The spectrum of a particular star shows the same hydrogen line appearing at a wavelength of 485.9 nm. What can we conclude?

The star is moving toward us

We can learn a lot about the properties of a star by studying its spectrum. All of the following statements are true except one. Which one?

The total amount of light in the spectrum tells us the star's radius.

Which of the following is always true about images captured with X-ray telescopes?

They are always shown with colors that are NOT the true colors of the objects that were photographed

What is the angular resolution of the human eye?

about 1 arcminute, or 1/60 of a degree

When white light passes through a cool cloud of gas, we see

an absorption line spectrum

What type of visible light spectrum does the Sun produce?

an absorption line spectrum-The Sun can simplistically be pictured as a hot interior light source surrounded by a thin, cooler layer of gas (the Sun's photosphere). The interior produces a continuous spectrum, while the overlying gas acts like a cloud to produce absorption lines.

If you heat a gas so that collisions are continually bumping electrons to higher energy levels, when the electrons fall back to lower energy levels the gas produces

an emission line spectrum

The absorption line spectrum shows what we see when we look at a hot light source (such as a star or light bulb) directly behind a cooler cloud of gas. Suppose instead that we are looking at the gas cloud but the light source is off to the side instead of directly behind it. In that case, the spectrum would __________.

be an emission spectrum-Because the cloud absorbs light from the hot source, conservation of energy demands that it must re-emit light with the same total amount of energy. However, this re-emitted light is sent in all directions, not just along the direction from which it originally came. Therefore, if we view the cloud from a location from which we can see only the light that the cloud itself emits, we will see an emission line spectrum.

The set of spectral lines that we see in a star's spectrum depends on the star's:

chemical composition

When an electron in an atom goes from a higher energy state to a lower energy state, the atom

emits a photon of a specific frequency

The spectra of most galaxies show redshifts. This means that their spectral lines

have wavelengths that are longer than normal

In the illustration of the solar spectrum, the upper left portion of the spectrum shows the __________ visible light.

lowest frequency-Red light is the longest wavelength visible light, and longer wavelength means lower frequency (because wavelength x frequency = speed of light

Click "show" for the emission line spectrum, then click "choose gases" and study the emission line spectrum for neon. The neon "OPEN" sign appears reddish-orange because __________.

neon atoms emit many more yellow and red photons than blue and violet photons-The many more lines in the yellow and red parts of the spectrum are what make "pure" neon lights look red or orange. (When you see "neon lights" glowing with other colors (besides reddish-orange), it is generally because they contain additional elements (besides neon) making them glow.)

A spectral line that appears at a wavelength of 321 in the laboratory appears at a wavelength of 328 in the spectrum of a distant object. We say that the object's spectrum is:

redshifted going further away from us

Without telescopes or other aid, we can look up and see the Moon in the night sky because it

reflects visible light

Study the graph of the intensity of light versus wavelength for continuous spectra, observing how it changes with the temperature of the light bulb. Recall that one of the laws of thermal radiation states that a higher-temperature object emits photons with higher average energy (Wien's law). This law is illustrated by the fact that for a higher temperature object, the graph peaks at __________.

shorter wavelength- Wien's law states that the thermal radiation from a hotter object peaks at a shorter wavelength.

What does angular resolution measure?

the angular size of the smallest features that the telescope can see

Notice that the Sun's spectrum appears brightest (or most intense) in the yellow-green region. This fact tells us __________.

the approximate temperature of the Sun's surface-One of the two laws of thermal radiation (Wien's law) states that the peak wavelength of a spectrum is directly related to an object's temperature. A peak at yellow-green wavelengths corresponds to a temperature of about 5800 K.

If we observe one edge of a planet to be redshifted and the opposite edge to be blueshifted, what can we conclude about the planet?

the planet is rotating