# Distances and Models

Learning Goal: I’m working on a astronomy discussion question and need an explanation and answer to help me learn.

### INTRODUCTION

In our daily lives we use relationships between angular size of a known object and its distance all the time without really being aware of it. For example an average sized car looks larger when it is closer to our eyes. If the car is half as big as its normal size, it must therefore be twice as far away. This means that it subtends an angle half as large as another car which is in close proximity. The eye can measure only the angular separations or angular sizes of objects; it takes the mind to convert to real physical measurements. In science we want to make this process more systematic and quantitative, and use a simple and practical technique for measuring angles to measuring distances of various objects. In astronomy the distances are huge compared to the distances we are used to. Astronomers need to use different tools to find the distances of far away objects. This leads to what we call the cosmic distance ladder which we will explore in detail in the various lab exercises in this course.We will start with exploring the lower rungs of the distance ladder.

A journey through the universe – So how large is the universe?

In the previous lab course we built a scale model of the solar system. Because we spend most of our time as humans interacting with the world on a scale that is human-sized, things we can touch and see and investigate with our senses, it is easy to miss that we are part of a vast universe with objects both unimaginably large and incredibly small compared to the world of our senses. This short introductory exercise is designed to help you shrink down domains of the astronomical world to a size that will give you a sense of relative proportions and distances. We will explore the realms of earth and moon, sun, solar system, and galaxies by shrinking them in turn down to two inch circles.

In order to shrink each of the realms in a way that is consistent we need to use ratios. Ratios are ways of comparing two elements, in this case usually size of an object and distances between objects.

### PRE-LAB ACTIVITY

The web address below will lead you to a flash scale of the universe. This flash scale shows you how the sizes of the objects we know relate to each other. By moving the slider you can finally determine that we are not the center of the universe.

http://htwins.net/scale/

Answer all questions in the answer sheet and create a PDF file. Upload the PDF file in the drop box for Lab 1.

The second file contains a paper meter stick. Print the file and glue the 4 pieces of the meter stick together. Use it to perform the measurements in part II.

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