Please solve the following questions. This is not an assignment, it will not be graded, and you do not need to submit your solutions to anyone. The questions are simply intended to help you practice for the exam.

These questions will not appear in the exam itself. Students who don't genuinely attempt to solve the questions on their own, and only memorize the solutions, will have a very hard time in the actual exam!

These questions are not multiple-choice, to encourage you to think of the answers on your own, but the questions in the actual exam will be multiple-choice.

If you need any clarifications for these questions, you can ask for them on the course Teams channel.

Question 1 Show/hide solution

What are the two most abundant gases in the Sun?

Solution: Hydrogen and helium.

Question 2 Show/hide solution

What is plasma?

Solution: It's a gas where the atoms break down into individual components: nuclei (positive charge) and electrons (negative charge).

Question 3 Show/hide solution

What are the layers of the Sun, from innermost to outermost?

Solution: Core, radiative zone, convective zone, photosphere, chromosphere, transition region, and corona.

Question 4 Show/hide solution

Which of the Sun's layers can we see, and when?

Solution: The photosphere is the part we usually see. None of the layers below the photosphere are visible. The chromosphere and corona are only visible to the naked eye during a total solar eclipse, or using a coronagraph.

Question 5 Show/hide solution

What is the solar cycle?

Solution: The solar cycle is the periodic change in the frequency of sunspots. The number of sunspot increases from minimum to maximum and then back to minimum. Each solar cycle starts and ends on consecutive minima.

Question 6 Show/hide solution

How long will it take a CME traveling at 500 km/s to reach the Earth and pose a risk to the orbiting space station? Will we have enough notice in advance?

Solution: The distance to the Sun is 150 million km, so the time it will take the CME to reach the Earth is 150,000,000 / 500 = 300,000 seconds. Given that there are 86,400 seconds in a day, this is approximately 300,000 / 86,400 = 3.5 days.

Question 7 Show/hide solution

What is the hottest part of the Sun?

Solution: The core, at ~15.7 million K.

Question 8 Show/hide solution

What are the main similarities and differences between the radiative and convective zones?

Solution: Both transport energy from the core outwards. However, the radiative zone transports this energy via radiation (photons are moving), while the convective zone transports it via convection (the plasma is moving).

Question 9 Show/hide solution

What are granules?

Solution: Bright areas on the surface of the Sun, each the size of a country, that rise from the solar interior like in boiling soup.

Question 10 Show/hide solution

What's unusual about the fact that the chromosphere is hotter than the photosphere?

Solution: The chromosphere is farther away from the core, where all the heat is generated, so naively speaking, it should be colder. The fact that is it actually hotter is surprising.

Question 11 Show/hide solution

Which part of the Sun exhibits the most steep increase in temperature?

Solution: The transition region.

Question 12 Show/hide solution

What is the penumbra, in the context of sunspots?

Solution: The outer part of the sunspot, which is brighter than the umbra (the dark middle part).

Question 13 Show/hide solution

Which solar cycle were we in during 2010?

Solution: Cycle 24.

Question 14 Show/hide solution

Water has a density of 1000 kg/m³. Is the Sun more or less dense than water? Does this differ between different locations?

Solution: The average density of the Sun is 1400 kg/m³, so on average it is more dense than water. However, notice that this is only an average. The photosphere is actually less dense than Earth's atmosphere, so it's definitely less dense than water.

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