Scholars Online Astronomy - Chapter 7: Basic Planetology
Reading: Astronomy, Chapter 7: Our Solar System
Study Notes: notes on your assigned reading from the text
We move now from methods of observing and basic physics of orbital motion to examining the physical bodies in the solar system: the planets, their moons and rings, stray bits called asteroids, occasional visitors called comets. The sun we treat as a special case of a star. In chapter 7, we have an overview and look at the current theories proposed for the formation of the solar system.
- Section 7.1 "Terrestrial" and "Jovian" planets differ in size, mass, density, and structure. Most of what we know about the physical characteristics of these planets (other than mass, which can be determined from orbital mechanics) is the result of unmanned missions beginning with Pioneer, Viking, and Voyager, in the 1970s, to Magellan, Messenger, Galileo and Cassini in the past decade. We'll come back to these characteristics when we look at the theory of the formation of the solar system a bit later in the chapter.
- Section 7.2 Planetary moons share some characteristics with the planets; in other ways, they are unique, giving some indications of how their formation may differ from the formation of planets.
- Section 7.3 Spectroscopy (the study of the spectra of light emitted or reflected by a substance) gives us clues about the surface composition of the planets and their atmospheres. Spectral patterns identify the type of elements or molecules present, and the strength of different lines indicates temperature. Lack of spectra we expect to see (for example, lines missing from sunlight reflected from the surface) can indicate the composition of the absorbing atmosphere.
- Section 7.4 One theory is that the solar system formed as a result of gravitational collapse. We expect to find the heavy elements at the center and the lighter ones to the outside, and to some extent this is true. But other factors such as light and heat from the sun also influence the distribution of the elements.
- Section 7.5 Beside planets (formally identified as bodies orbiting the sun that are heavy enough to form spheroids under their own gravitational collapse and massive enough to have swept clean the volume of space along their own orbits), we find smaller bodies: comets, asteroids, Kuiper objects.
- Section 7.6 Crater formation and patterns can indicate the past history of a planet.
- Section 7.7 Planets have magnetic fields that reflect their core composition and structure, so all satellite exploration of these planets carry instruments to detect the shape and intensity of the magnetosphere.
- Section 7.8 Several physical models have been proposed for the formation of the solar system; now we need a way to test each model to see which best accounts for the observed phenomena.
Key Formulae to Know
- Average Density:
- Kinetic energy and temperature
- Average speed of gas atom or molecule
- Escape velocity
Read the following weblecture before chat: The Solar System
Use your planetarium program to view magnified images of the terrestrial planets (Mercury, Venus, Earth, Mars), and the asteroid Ceres from different positions in space. Alternatively, The Nine Planets website has an interactive solar system model. It takes awhile to load so be patient.
- Which planets have clouds?
- Which planet or asteroid shows the heaviest cratering?
- Which of these planets show evidence of liquid water?
Now use your planetarium program to look at the Jovian planets (Jupiter, Saturn, Uranus, and Neptune).
- Which planet has the greatest color contrast in its cloud tops?
- Which has the least color contrast?
- What can you say about the thickness of the rings of each planet compared to the diameter of the planet?
UNL Tools Exercises
- Under Miscellaneous, rank planet densities.
- Under Solar System Objects, concentrate on planetary densities (5-7), orbit characteristics and planetary types (8-10, 15), classification of planets (14)
- NAAP Labs:
- Review Kepler's Laws and Newton's laws, then use the Planetary Orbits simulator to explore the modern theory of orbits (ellipses).
Optional Websites: Bill Arnett is a software engineer by profession. Early on in the adventure of the web, he started putting together The Nine Planets site, where collected lots of information about the planets. This is a good starting place for almost everything named in the solar system: the planets, their moons, major comets and asteroids, and exploration. I usually don't recommend sponsored sites (this one is sponsored by Google Ads) because I can't count on the information or presentation being appropriate in all cases for students, but I've never seen anything offensive here (annoying yes -- ads are inherently so); still, visit this at your own risk.
Chat Preparation Activities
- Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
- Go over the list of Key Words and Key Ideas at the end of the chapter. If you don't remember the definition of the key word, review its use (the page number on which it is explained is given).
- Read through the Review Questions and be prepared to discuss them in class. If any of them confuses you, ask about it!
- Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.
- Required: Complete the Mastery exercise with a passing score of 85% or better.
- Go to the Moodle and take the quiz for this chat session to see how much you already know about astronomy!
Read through the lab for this week; bring questions to chat on any aspect of the lab, whether you intend not perform it or not. If you decide to perform the lab, be sure to submit your report by the posted due date.
- Lab instructions: Observe Venus and Mercury -- see Moodle assignment notes.
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