Scholars Online Astronomy - Chapter 1 Introduction to Astronomy

Homework

Reading Preparation
- Study Guide/Reading Notes
Key Formulae to Know
Web Lecture
Study Activity
Chat Preparation Activities
Chapter Quiz
Lab Work

Reading Preparation

Reading: Astronomy, Chapter 1: Astronomy and the Universe

Study Notes: notes on your assigned reading from the text

Section 1: Scientific methods guide astronomical observations as investigators move from hypothesis to experiment to theory, but in astronomy, experiment must often be replaced with model development. Using the principles of physics, astronomers simulate the behavior of celestial objects.
Section 2-4: By studying planets, stars, and galaxies, astronomers attempt to determine the life cycles of solar systems, star systems, and the universe itself.
Section 5: Astronomers use angular measurements to locate stars relative to specific points in the sky. A full circle has 360 degrees; each degree can be divided into 60 minutes of arc, and each minute of arc can be divided into 60 seconds of arc. Do not confuse minutes and seconds of arc (parts of a degree) with minutes and seconds of Right Ascension (parts of an hour of RA). 1 hour RA = 15 degrees of arc. 1/60 hr RA = 1 min RA = 1/60 of 15 degrees = 15 minutes of arc. What this means in practical terms is that in 1 minute of time, the sky turns 15 minutes of arc. You can test this by looking at the moon -- approximately 0.5 degrees or 30 minutes of arc wide. It should take the full moon 2 minutes to rise completely above the horizon.
Section 6: Scientific notation (using powers-of-ten) allows astronomers to write large numbers unambiguously. 3.154*10² means a number accurate to four digits: 315.4.
Section 7: As with most sciences, astronomy has its own units. For distance, these are km, astronomical units (AU), light years (ly), and parsecs (pc).
Section 8: Required standard pep talk about how great astronomy is. This section is in the tradition of everyone since Plato, who wrote in the Timaeus that the study of the stars lifts men's minds above the mundane.
Box 1: Small angle formula (see below)
Box 2: Powers of ten rules:(see below)
Box 3: Converting units: if $x {unit}_{A} = y {unit}_{B}$ then $\frac{x {unit}_{A}}{y {unit}_{B}} = 1$
We can multiply by "1" without changing the value, so we can convert units from one form to another. This first chapter of our text presents an overview of the course, listing the objects we will study and some of the common ways of describing them. As a result, it appears somewhat easier than the following chapters, but don't let appearances fool you. If you have any problems with the concepts presented here, be sure that you ask questions in class and then practice using them until you feel comfortable with them.

Key Formulae to Know

Powers of 10 Rules:
- Multiplication: add exponents $\begin{array}{l} 10^{a} * 10^{b} = 10^{a + b} \\ 10^{4} * 10^{5} = 10^{4 + 5} = 10^{9} \end{array}$
- Division: subtract exponents $\begin{array}{l} \frac{10^{a}}{10^{b}} = 10^{a - b} \\ \frac{10^{4}}{10^{5}} = 10^{4 - 5} = 10^{- 1} = \frac{1}{10} \end{array}$
- Enponentiation: multiply exponents $\begin{array}{l} {{(10}^{a})}^{b} = 10^{a * b} \\ {{(10}^{4})}^{5} = 10^{4 * 5} = 10^{20} \end{array}$
Unit conversions:
1 AU = 1.496 * 10⁸km (about 150 million km) = 92.96 * 10⁶ miles (about 93 million miles).
1 LY = 9.46 * 10¹²km (about 10 trillion km or 10¹³) km) = 63,240 AU
1 pc = 3.09 * 10¹³km (about 3 trillion km) = 3.26 ly [or to reverse that, 3 PC is about 10 LY]
Small Angle Formula: $D = \frac{α d}{206265}$
D = linear distance (length of object perpendicular to line of sight)
d = distance to object along line of sight
α = angular size of object in arc seconds (1/60 of 1 minute of arc)
Note: 206265 arcseconds = 57.296 ° = 1 radian

Web Lecture

Read the following weblecture before chat: Introduction to Astronomical Concepts and Methods

Study Activity

Planetarium program exercise

Use Stellarium to complete the exercise below. (These tasks should be possible on any computer-based planetarium program). You will need to review the user guide for your program to identify exactly how to do each one.

Check the date and time on the display screen. By default, this should be the same as your system time, but you can control it (see below).
Use your location setting method to enter your latitude and longitude or find a city near you to use as your home location.
Use your date and time tools to advance the clock forward and backwards, or to run the display at a rate faster than normal time. When you have finished experimenting, set the time to 9pm for today's date.
Find and set your field of view size. In most cases, you can set this to 180°, 270°, or 360° around your horizon, and control the range above or below your horizon (-90° to +90°).
Find and set your horizon to display so that you can see the horizon line and the star field above and below it. Some programs default to a "solid" horizon, so you may need to set this. Turn on direction markings (N, E, S, W) so that you know which direction you are looking.
Turn on the planetary displays.
For Tuesday night, Sept 14, 2021, at 9pm, here is something close to what you should be seeing:
- Sky Safari at 9pm, for Seattle, WA, with horizon set to transparent and line:
Your sky may be different, depending on your location, but after before sunset, you should be able to see Jupiter and Saturn near the southeastern horizon, and the Moon setting to the southwest. Venus will be visible around 7:30 once the sky is dark enough, but it will be close to the western horizon and will have set by 8:15 pm.
Find the tool to enter a specific object's name. Type in "Vega" (the brightest star in Lyra) and have your display center on Vega. See if you can still find the planets in relation to this star and the constellation Lyra.
Using your program, determine what constellations will be rising (due east), on your meridian above the horizon (due south), and setting (due west) for some night within the next two weeks where you might be able do some observing.

UNL Tools Exercises

Interactives: Work through the exercises under Angular Diameter.
Class Actions: Work through the questions under Introductory Concepts.
Labs: No exercises for this unit.

Optional websites:

While astrology is NOT the subject of this course, astrological symbols are often used as a "shorthand" on astronomy charts, so it is work becoming familiar with them.

Constellation symbols for those in the zodiac:
See the Wikipedia article on the Zodiac, and scroll down to the table that matches the symbols with the constellation name. Although astronomers are not usually also astrologers, they use these signs as a shorthand on maps and when taking notes.

Check out the planetary symbols used by both astronomers and astrologers: these can be a useful shorthand when marking observing maps and charts.
Planetary Symbols

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.

Chapter Quiz

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!

Lab Work

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: Basic Observing: Techniques

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Astronomy

Chapter 1: Homework