1. Foundations of Astronomy | 13e Seeds
Chapter 1
Here and Now
© Cengage Learning 2016

2. Guidepost
In this chapter, you will consider three important questions about astronomy
Where are you in the universe?
How does human history fit into the history of the Universe?
Why study astronomy?

3. 1-1 Where are you?
To find your place among the stars, we can take a cosmic zoom — a ride out through the Universe — to preview the kinds of objects you are about to study
From each frame to the next, we will zoom out by about a factor of 100

4. A Campus Scene (16 m)
Figure 1-1: An area about 50 feet (16 m) across on a college campus. Includes small objects (trees, people, sidewalks) with sizes we can understand. Note: Each successive picture in this “zoom” will show you a region of the Universe that is 100 times wider than the preceding picture. That is, each step will widen your field of view, which is the region you can see in the image, by a factor of 100 .

5. A City View (1.6 km)
Figure 1-2: An area 1 mile (1.6 km) across in the next image. Small objects (people, trees, sidewalks) are too small to discern, but now you can view an entire college campus plus surrounding streets and houses. The dimensions of houses and streets are familiar to us.

6. The Landscape of Pennsylvania (160 km)
Figure 1-3: Infrared image (field of view is 160 km) in which healthy green leaves and crops are shown as red. Cities and towns appear as patches of gray.
Wilmington, Delaware is visible at the lower right. At this scale, you can see some of the natural features of Earth’s surface. The Allegheny Mountains of southern Pennsylvania cross the image in the upper left, and the Susquehanna River flows southeast into Chesapeake Bay. What look like white bumps are a few puffs of cloud.

7. The Earth (Diameter: 12,756 km)
Figure 1-4: In this photograph, we can see our entire planet, which is nearly 13,000 km in diameter.

8. Earth → Moon (3.8 × 105 km)
Figure 1-5: Earth-Moon system, view is 1,600 ,000 km wide. Earth is the small blue dot in the center, and the Moon, the diameter of which is only one-fourth of Earth’s, is an even smaller dot along its orbit 380,000 km away.
(The relative sizes of Earth and Moon are shown in the inset at the bottom right of Figure 1-5 .)

9. Earth → Sun (1.5 × 108 km or one AU)
Figure 1-6: This image (1.6 x 10^8 km) shows the Sun and two other planets that are part of our Solar System.

10. The Solar System (Mars → Sun: 1.5 AU)
Figure 1-7: This image shows the entire planetary region of our Solar System. The Sun, Mercury, Venus, and Earth lie so closely together that you cannot see them separately at this scale, and they are lost in the red square at the center of this diagram that shows the size of the previous figure. You can see only the brighter, more widely separated objects (Mars, Jupiter, Saturn, Uranus, and Neptune.)

11. The Solar Neighborhood (~11,000 AU)
Figure 1-8: In this image, the Sun is only a point of light, and all the planets and their orbits are now crowded into the small red square at the center. The planets are too small and too faint to be visible so near the brilliance of the Sun.

12. The Solar Neighborhood (17 Light Years)
Figure 1-9: This image (FOV 1.1 million AU) shows our Sun at the center, and at this scale you can see a few of the nearest stars.

13. Common Misconceptions, Part 1
Misconception: A light-year is a unit of time
Truth: A light-year is a distance, not a time
1 light year (ly) = distance traveled by light in 1 year = 1.1 million AU
Misconception: Stars look like disks when seen through a telescope
Truth: Stars are so far away that astronomers only see them as points of light

14. The Solar Neighborhood (1,700 ly)
Figure 1-10: Expanding your field of view by another factor of 100, and the Sun and its neighboring stars vanish into the background of thousands of other stars. The field of view is now 1700 ly in diameter. The Sun is a relatively faint star that would not be easily located in a photo at this scale.

15. The Milky Way Galaxy (~80,000 ly D)
Figure 1-11: Expanding your field of view by a factor of 100 , you see artist’s conception of our galaxy, with a visible disk of stars about 80,000 ly in diameter.
A galaxy is a great cloud of stars, gas, and dust held together by the combined gravity of all of its matter.
Galaxies range from 1000 ly to more than 300,000 ly in diameter, and the biggest ones contain more than a trillion (10^12) stars.

16. The Milky Way Galaxy How can we visualize the Milky Way?
Artists use descriptions based on scientific evidence to create images
Better than guesses
Show events that our senses cannot detect
Search the Internet for images of other galaxies
In the night sky, our galaxy looks like a band of stars known as the Milky Way. These images are much better than guesses; they are scientifically based illustrations guided by the best information astronomers can gather.
How else do we know what our galaxy looks like? Indeed, galaxy NGC 1073 is known as the Milky Way twin (a barred spiral galaxy located 55 million light-years away in the constellation of Cetus).

17. The Local Group: Our Cluster of Galaxies
Distance to the nearest large galaxies: several million light years
Expanding the field of view by another factor of 100, we can see a few of these other galaxies. Our galaxy appears as a tiny luminous speck surrounded by other specks in a region 17 million light-years in diameter, with each speck representing a galaxy
Notice that our galaxy is part of a cluster of a few dozen galaxies. Galaxies are commonly grouped together in such clusters.

18. Common Misconceptions, Part 2
Misconception: People often say Galaxy when they mean Solar System, and they sometimes confuse both terms with Universe
Truth: The Milky Way Galaxy contains our Solar System plus billions of other stars and whatever planets orbit around them, or billions of planetary systems

19. The Universe On Very Large Scales
Clusters → superclusters → filaments/walls
Figure 1-13: If you expand the field of view one more time, we see that clusters of galaxies are connected in a vast network.
Clusters are grouped into superclusters — clusters of clusters — and the superclusters are linked to form long filaments and walls outlining
nearly empty voids. These filaments and walls appear to be the largest structures in the Universe.

20. 1-2 When Is Now? The Universe is ~14 billion years old
Began with the Big Bang
Our solar system formed 9 billion years later (4.6 billion years ago)
~3.4 billion years ago: Earliest forms of microscopic life
~0.4 billion years ago: Emergence of life on land
~65 million years ago: Dinosaurs go extinct
~10,000 years ago: Civilization began
Humanity is very new to the Universe
Imagine stretching that ribbon from goal line to goal line down the center of a U.S. football field, a distance of 100 yards (about 91 meters ), as shown on the inside front cover of this book. Imagine that one end of the ribbon represents today, and the other end represents the beginning of the Universe—the moment that astronomers call the big bang.
Ribbon = 14 billion years
First half-inch of ribbon = hot, glowing gas
½” to 3 yards = no light
~4.5 yards = galaxy formation begins
50 yard line = Universe is full of galaxies
33 yard line = formation of the Solar System
26 yard line = earliest evidence for microscopic life on Earth
3 yard line = emergence of life on land
2 yard line = appearance of dinosaurs
½ yard line = dinosaurs go extinct
inches from goal = civilization begins (½ the thickness of a paper)

21. 1-3 Why Study Astronomy?
Two fundamental questions are addressed throughout this text
What are we?
How do we know?
In what ways will this knowledge helps you enjoy a richer life and be a better citizen?
One answer: To understand the world around you and to make wise decisions for yourself, for your family, and for your nation, you need to understand how science works.

22. How Do We Know? The scientific method
Form hypotheses that explain how nature works and test with experiments/observations:
If contradicted, the hypothesis is revised or discarded
If confirmed, the hypothesis is tested further
How is a statement in a political campaign speech different from a statement in a scientific discussion?