# Astronomy Assignment

1.7. Explain why different constellations are above the horizon at noon as compared with midnight on the same day.

2.4. We cannot see the Sun in the sky map at midnight. Can we predict which constellation will be behind the Sun at midnight in January? Why?

3.2. Fill in the blanks that correctly complete the sentences:

Right ascension is one coordinate in the (horizontal / equatorial) coordinate system. Right ascension is analogous to terrestrial (latitude / longitude). Right ascension is zero on the celestial (equator / prime meridian) and increases (eastwards / northwards).

The Sun’s (daily / yearly) path on the celestial sphere is called the ecliptic. The celestial equator and ecliptic meets at two points called (equinoxes / solstices). Where the Sun crosses the equator moving south is called the (March / September) equinox. On an equinox, the Sun rises at the (east / west) cardinal point, and sets at the (east / west) cardinal point, and there are (more than 12 hours / exactly 12 hours / less than 12 hours) of daylight.

4.3. Label the following statements as true or false. If false, re-write the statement so that it is true:

[True / false] When photon energy increases, then photon frequency also increases. The relationship between photon energy and photon frequency is said to be inverse.

[True / false] Color is not real, it is just our eyes’ perception of photon energy. That is why different people can disagree upon the color of the same object.

[True / false] Gamma rays and radio waves are both made of photons. That is why they both travel at the same speed, even though they have different energies.

[True / false] Photons do not travel in straight lines.

5.4. Apply the concept of flux to write a description of why, when driving north on I-94 from Chicago to Kenosha, the signal from radio station KPBX-Zion gets stronger, but the signal from KRFA-Schaumburg gets weaker.

7.2. In each of the following sentences, circle the word which completes correctly the statement:

The peak of a blackbody spectrum is defined as the wavelength where the spectral curve is (brightest / faintest / reddest / bluest).

The luminosity of a blackbody spectrum is defined graphically as (the height of the peak / the area under the spectral curve).

According to Planck’s law, a blackbody spectrum has a single (peak / trough).

According to Wien’s law, when you compare two blackbody radiators, then the higher temperature radiator peaks farther to the (red / blue).

According to the law of Stefan & Boltzmann, the area under the curve of a blackbody spectrum is an indicator of (only surface temperature / only surface area / both surface temperature and surface area).

9.4. Complete the staircase analogy: identify all the crucial parts of Bohr’s model, and their corresponding parts on a staircase.

10.1. Extend the staircase analogy from the previous section to include the formation of absorption and emission lines.

11.6. Label the following statements as true or false. If false, re-write the statement so that it is true:

[True / false] The bright star Rigel is blue to the eye, therefore it must be moving towards us.

[True / false] The bright star Sirius is closer to us than Rigel, therefore Sirius must be more blue shifted than Rigel.

[True / false] The north star, Polaris, has a radial velocity of -12 km/sec. A negative velocity means it must be moving towards us.

[True / false] The n=2→3 jump in hydrogen absorbs light at a wavelength 656 nanometers (nm). The corresponding absorption line from Polaris must be observed on Earth at a wavelength smaller than 656 nm.

[True / false] Blue shifted light is moving more quickly than red shifted light.

12.1. Label the following statements as true or false. If false, re-write the statement so that it is true:

[True / false] A star with mass 2 Msun has twice as much mass as our Sun. [True / false] The Russell-Vogt rule tells us that a star’s entire life cycle is determined by its mass only.

[True / false] Stars are, parametrically speaking, one dimensional objects. In other words, stars are shaped like long thin lines.

14.1. What is the cause of stellar evolution?

15.2. Why does stellar nucleosynthesis not produce gold or silver?

16.6. Complete the following table:

Low mass stars High mass stars

Mass range

Evolution driven by

Mass loss event

Elements returned to space by mass loss

Remnant type

17.5. Define isotropic. What part of this exercise enforces isotropy?

19.4. Draw a diagram of a bunch of atoms moving in a confined space; illustrate that the collision rate is higher when the temperature is higher, i.e., when the atoms are moving faster.

20.3. In each case, state which cluster is the youngest:

Cluster A with turnoff point at 2 Msun, or cluster B with turnoff point at 3 Msun.

Cluster C with turnoff point at 1 Lsun, or cluster D with turnoff point at 0.5 Lsun.

Cluster E with turnoff point at 5,000 K, or cluster F with turnoff point at 15,000 K.

22.6. Fill in the table.

Star Annual shift (as) Parallax shift (as) Distance (pc)

Proxima Cen 1.6

Luhman 16 0.5

Wolf 359 2.5

Kruger 60 0.5

Gliese 832 0.2

γ Pav 10