Here and Now
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Transcript of Here and Now
Here and Now
Chapter 1
As you study astronomy, you will learn about yourself. You are a planet walker, and this chapter will give you a preview of what that means. The planet you live on whirls around a star drifting through a universe filled with other stars and galaxies. You owe it to yourself to know where you are in the universe because that is the first step to knowing what you are.
In this chapter, you will meet three essential questions about astronomy:
• Where are you in the universe?
• How does human history fit into the time scale of the universe
• Why should you study astronomy?
Guidepost
As you study astronomy, you will see how science gives you a way to know how nature works. In this chapter, you can begin thinking about science in a general way. Later chapters will give you more specific insights into how scientists work and think and know about nature.
This chapter is a jumping-off place for your exploration of deep space and deep time. The next chapter continues your journey by looking at the night sky as seen from Earth.
Guidepost (continued)
Where are You?
To find our place among the stars, we will zoom out from a familiar scene, to the
largest scales in the universe.
From each frame to the next, we zoom out by about a factor 100.
A Campus Scene
16 x 16 m
A City View
1 mile x 1 mile
The Landscape of Pennsylvania
100 miles x 100 miles
The Earth
Diameter of the Earth: 12,756 km
Earth and Moon
Distance Earth – Moon: 384,000 km
Earth Orbiting Around the Sun
Distance Sun – Earth = 150,000,000 km
Earth Orbiting Around the Sun (2)
In order to avoid large numbers beyond our imagination, we introduce new units:
1 Astronomical Unit (AU) = Distance Sun – Earth =
150 million km
The Solar System
Diameter of Pluto’s orbit: Approx. 100 AU
(Almost) Empty Space Around Our Solar System
Approx. 10,000 AU
The Solar Neighborhood
Approx. 17 light years
The Solar Neighborhood (2)
Approx. 17 light years
New distance scale:
1 light year (ly) =
Distance traveled by light in 1 year
= 63,000 AU = 1013 km
= 10,000,000,000,000 km
(= 1 + 13 zeros)
= 10 trillion km
Nearest star to the Sun:
Proxima Centauri, at a distance of 4.2 light years
The Extended Solar Neighborhood
Approx. 1,700 light years
The Milky Way Galaxy
Diameter of the Milky Way: ~ 75,000 ly
The Local Group: Our Cluster of Galaxies
Distance to the nearest large galaxies: several million light years
The Universe on Very Large Scales
Clusters of galaxies are grouped into superclusters.
Superclusters form filaments and walls around voids.