CH 04

1. The number of electrons identifies whether an atom carries a charge as an iron or is neutral.

2. The number of protons identifies the type of element

Compared with a spectrum from a ground-based observation, the spectrum of a star observed from above Earth's atmosphere would show

The visible spectrum of sunlight reflected from Saturn's cold moon Titan would be expected to be

Figure 4.3 in the textbook ("Elemental Emission") shows the emission spectrum of neon gas. If the temperature of the gas was increased, we would observe

Compared with a star having many blue absorption lines, a star with many red and blue absorption lines must be

What are the basic components of a simple spectroscope?

Check all that apply.

What the additional components in spectrographs used by astronomers for modern observations?

Check all that apply.

An atom that has been ionized

How many different photons (i.e., photons of different frequencies) can be emitted as a hydrogen atom in the third excited state falls back, directly or indirectly, to the ground state?        

Compared with an electron transition from the first excited state to the ground state, a transition from the third excited state to the second excited state emits a photon of

Compared with a complex atom like neon, a simple atom such as hydrogen has

Astronomers analyze starlight to determine a star's

Compared with cooler stars, the hottest stars have absorption lines that are

Compared with slowly rotating stars, the fastest spinning stars have absorption lines that are

It is possible that an abundant element in a star does not produce strong lines, if the electrons of most of the atoms of that element are not in a condition to absorb light of the corresponding wavelength.

For example, the Hα absorption line of hydrogen results from electrons jumping from the second to the third atomic orbital. If a star's outer atmosphere is rather cool, relatively few atoms have electrons that have absorbed enough energy to jump to the second excited state or higher; most are in the ground state. Hence, the second to third level transition occurs rarely, and the wavelength of light corresponding to the Hα absorption line is rarely absorbed. A weak spectral line results.

If the star is very hot, then the electrons of most the hydrogen atoms may have too much energy, and may have left the atoms entirely. Such stars are mostly hydrogen, but the ionized hydrogen has no electrons to absorb light. Only a small part of hydrogen is capable of absorbing, and so the lines of hydrogen are weak.

List three properties of a star that can be determined from observations of its spectrum.

The three properties of a star that can be determined from observations of its spectrum are composition, temperature, and motion. When it comes to the first step, composition, it is when every element leaves a special pattern in the star's light, such as hydrogen, helium, and iron, for example. This is important because it reveals what's inside a star, helping us understand its origin and how it evolves. The second property of a star would be its temperature, which helps us determine how much a star would glow. The hotter the stars, the glow would seem more blue and the cooler the stars, the redder it would seem. Not only does the temperature help us determine the glow of a star, but also the life span of the star and how long it will shine. The last property of a star would be motion, which helps us determine if the star is moving towards or away from us. With motion, it helps us better understand how the stars and galaxies are around in space.