Find your Galactic Address Lecture 1.1 The Scale of the Cosmos

Astronomy deals with objects on a vast range of size scales and time scales. Most of these size and time scales are way beyond our every-day experience. Humans, the Earth, and even the solar system are tiny and unimportant on cosmic scales.

FIND YOUR GALACTIC ADDRESS http://www.classzone.com/books/earth_science/terc/content/visualizations/es2808/es2808page01.cfm?chapter_no=visualization

Now… we’ll check your answers… Lecture 1.1 Journey through the vast range of scales in the Universe. From each image to the next we are zooming out by a factor of 100.

Marco Polo journeyed east and Columbus west. You will travel outward away from your home on Earth; out past the moon, sun, and other planets; past the stars you see in the evening sky; and past billions more that can be seen only with the aid of the largest telescopes.

You live on a small planet circling a small sun drifting through the universe. Astronomy can take you beyond these boundaries and help you not only see where you are in the universe but understand what you are. To understand you must consider the word: SCALE You have a right to know these things. Perhaps, you have a duty to know them.

Scale of Universe Our sense of the Universe has changed over the years:

Each successive picture in the powerpoint 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—the region you can see in the image—by a factor of 100.

A Campus Scene something familiar 16 x 16 m

Your field changes by a factor of 100 A City View Your field changes by a factor of 100 1 mile x 1 mile 1.609 km x 1.609 km 16 m x 16 m

The Landscape of Pennsylvania The photo in the figure is 1 mile in diameter. A mile equals 1.609 kilometers. So, you can see in the photo that a kilometer is a bit over two-thirds of a mile— 1 mile x 1 mile 1.609 km x 1.609 km 100 miles × 100 miles 160 km x 160 km

Diameter of the Earth: 12,756 km The Allegheny Mountains of southern Pennsylvania cross the image in the upper left. The Susquehanna River flows southeast into Chesapeake Bay. What look like white bumps are a few puffs of clouds This is an infrared photograph in which healthy green leaves and crops show up as red. Human eyes are sensitive to only a narrow range of colors. 100 miles × 100 miles 160 km x 160 km Diameter of the Earth: 12,756 km

Earth–Moon distance: 384,000 km Earth and Moon At the next step in your journey, you will see your entire planet—which is 12,756 km in diameter. Earth rotates on its axis once a day, exposing half of its surface to daylight at any particular moment. The photo shows most of the daylight side of the planet. The blurriness at the extreme right is the sunset line. The rotation of the planet causes the cycle of day and night Rotation of the earth is eastwards Earth–Moon distance: 384,000 km

Sun–Earth distance: 150,000,000 km Earth Orbiting around the Sun Earth is the small blue dot in the center. The moon—whose diameter is only one-fourth that of Earth—is an even smaller dot along its orbit 380,000 km from Earth. Sun–Earth distance: 150,000,000 km

Earth Orbiting around the Sun In order to avoid large numbers beyond our imagination, we introduce new units: 1 astronomical unit (AU) = Sun–Earth distance = 150 000 000 km 150 million km

– This is nothing more than a simple way to write numbers without writing lots of zeros. – In scientific notation, you would write 380,000 as ______________. – The universe is too big to discuss without using scientific notation.

The Solar System 1 AU Approximately 100 AU Like Earth, Venus and Mercury are planets—small, non-luminous bodies that shine by reflected light. 1 AU Approximately 100 AU

(Almost) Empty Space Around our Solar System Approximately 10,000 AU

Our Solar System to Scale

The Solar Neighborhood There are not any stars visible except for the sun. The sun is a fairly typical star, and it seems to be located in a fairly average neighborhood in the universe. Although there are many billions of stars like the sun, none is close enough to be visible in the diagram— which shows an area only 11,000 AU in diameter. Approximately 17 light years

Approximately 17 light years In the figure, the sizes of the dots represent not the sizes of the stars but their brightness. Bright stars make larger spots on a photo than faint stars. The size of a star image in a photo informs you not how the star is but only how bright it looks. These stars are so distant that it is not reasonable to give their distances in astronomical units. 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 Approximately 17 light years  In other words, light from Alpha Centauri takes 4.2 years to reach Earth.

The Extended Solar Neighborhood Approximately 1,700 light years or 1 million Approximately 17 light years

The Milky Way Galaxy Most stars are concentrated in spiral arms A galaxy is a great cloud of stars, gas, and dust bound together by the combined gravity of all the matter. Galaxies range from 1,500 to over 300,000 ly in diameter and can contain over 100 billion stars. Most stars are concentrated in spiral arms Diameter of the Milky Way: ~75,000 ly

Distance to the nearest large galaxies: several million light years The Local Group of Galaxies a common grouping of galaxies Distance to the nearest large galaxies: several million light years

Superclusters: a group of clusters The superclusters are linked to form long filaments and walls outlining voids that seem early empty of galaxies. These appear to be the largest structures in the universe. Clusters of galaxies are grouped into superclusters. Superclusters form filaments and walls around voids.

3 Conclusions: The solar system is the sun and its planets. The galaxy contains billions of stars and whatever planets orbit around them. The universe includes everything—all the galaxies, stars, and planets, including our galaxy and our solar system.

A Flight Through the Universe Explanation: What would it be like to fly through the universe? Possibly the best simulated video of this yet has been composed from recently-released galaxy data from the Sloan Digital Sky Survey. Every spot in the above video is a galaxy containing billions of stars. Many galaxies are part of huge clusters, long filaments, or small groups, while expansive voids nearly absent of galaxies also exist. The movie starts by flying right through a large nearby cluster of galaxies and later circles the SDSS-captured universe at about 2 billion light years (a redshift of about 0.15) from Earth. Analyses of galaxy positions and movements continues to bolster the case that our universe contains not only the bright matter seen, like galaxies, but also a significant amount of unseen dark matter and dark energy. http://www.youtube.com/watch?feature=player_embedded&v=08LBltePDZw http://apod.nasa.gov/apod/ap120813.html

Use your notes- answer on an index card A quick review

1. How is a planet different than a star? Planets are larger than stars. Planets reflect light while stars produce their own light. Stars move faster in the sky than planets. Planets are brighter than stars. 2

2. The average distance from Earth to the sun is 1 AU. True False 1

3. A light-year is the distance light travels in one year. True False 1

4. A typical galaxy like our Milky Way galaxy contains primarily planets. gas only. stars (some with planets), gas and dust. a single star and planets. thousands of superclusters. 3

5. Which sequence is correct when ordered by increasing size? Earth, Solar System, Milky Way Galaxy, clusters of galaxies Solar System, Earth, galaxy clusters, Milky Way Galaxy Earth, Milky Way Galaxy, Solar System, galaxy clusters Galaxy clusters, Solar System, Milky Way Galaxy, Earth 1

6. The sun is a star in the Milky Way Galaxy. True False 1

7. A supercluster refers to a large group of stars within the Milky Way. True False 2

Answers 2 1 3