The Size, Scale and Structure of the Universe Image courtesy of The Cosmic Perspective by Bennett, Donahue, Schneider, & Voit; Addison Wesley, 2002

Remember your universal address?? Azusa Pacific University, CA, USA, North America, Earth, Solar System, Milky Way Galaxy, The Local Group, The Local (Virgo) Supercluster, The Universe! Even beyond Earth itself, the rest of our solar system bears the marks of design. Saturn and Jupiter, gas giants in the outer region of the solar system, are close enough to protect us from incoming earth-bound comets and asteroids, but not so close as to disturb our perfect, but fragile, orbit around the sun. (end)

Earth Planet where we all live Comprised primarily of rock Spherical in shape 12,700 km in diameter It would take 17 days to circumnavigate the globe driving a car at 100 km/hr At the speed of light, it would take 0.13 seconds to go all the way around Earth.

Our Moon, 1.3 light-seconds from Earth Our Moon has not only helped ancient people keep time, but it is also largely responsible for our Ocean Tides. If it were bigger or much closer, it would cause tidal waves, submerging continents on a regular basis. If it were smaller or much further away, there would be no tides, and shoreline waters would quickly stagnate. The moon is also just the right size to stabilize earth’s rotation axis at a 23.5 degree tilt, as well as to slow the earth’s rotation rate to 24 hours per day. If the earth had more (or less) than one moon, our tides, daily rotation rate, and tilt would ALL be impacted. (end)

Mars, 4 light-seconds away In the other direction we have Mars, significantly smaller than Earth and a little farther from the sun, with very little atmosphere and its only water is frozen, so there is no life-giving water cycle. So in between Mars and Venus, here on Earth …we are just the perfect distance from the sun for life! (end) Mars, 4 light-seconds away

Sol, the Sun 8.3 light-minutes from Earth Star that Earth orbits Composed primarily of hydrogen and helium gas Uses nuclear fusion in its core to generate heat and light to allow itself to resist the crushing weight of its own mass Spherical in shape 1.39 Million km in diameter And our star, the Sun, is the perfect size, brightness, and age for life. (end)

Earth & Sun The Sun’s diameter is 109 times greater than that of Earth Over 1 million Earths would fit inside the Sun’s volume Earth orbits the Sun at an average distance of 150 million kilometers. This distance is called an Astronomical Unit (AU) It would take 11,780 Earths lined up side to side to bridge the 1 AU between Earth and Sun.

Pluto, 4 light-hours from Earth… Even beyond Earth itself, the rest of our solar system bears the marks of design. Saturn and Jupiter, gas giants in the outer region of the solar system, are close enough to protect us from incoming earth-bound comets and asteroids, but not so close as to disturb our perfect, but fragile, orbit around the sun. (end)

The Solar System 8 planets, thousands and thousands of planetoids and asteroids, billions of comets and meteoroids Mostly distributed in a disk about the Sun Sun blows a constant wind of charged gas into interplanetary space, called the Solar Wind Boundary between Solar Wind and interstellar space at 100 AU from the Sun (200 AU diameter)

Kuiper Belt: ~10 light hours; Oort Cloud: ~1 light-month from Earth Comets: Kuiper Belt: ~10 light hours; Oort Cloud: ~1 light-month from Earth Even beyond Earth itself, the rest of our solar system bears the marks of design. Saturn and Jupiter, gas giants in the outer region of the solar system, are close enough to protect us from incoming earth-bound comets and asteroids, but not so close as to disturb our perfect, but fragile, orbit around the sun. (end)

The Solar Neighborhood The region of the Galaxy within about 32.6 light-years of the Sun (65 light-years diameter) is considered its neighborhood. Here stars move generally with the Sun in its orbit around the center of the Galaxy This region is inside a large bubble of hot interstellar gas called the Local Bubble. Here the gas temperature is about 1 million degrees Kelvin and the density is 1000 times less than average interstellar space. To Center of Galaxy The image is 390 light-years across. Direction of Galactic Rotation

Alpha Centauri: 4.3 light-years from Earth (end) Even beyond Earth itself, the rest of our solar system bears the marks of design. Saturn and Jupiter, gas giants in the outer region of the solar system, are close enough to protect us from incoming earth-bound comets and asteroids, but not so close as to disturb our perfect, but fragile, orbit around the sun. (end)

The Milky Way Galaxy You Are Here The Milky Way Galaxy is a giant disk of stars 160,000 light-years across and 1,000 light-years thick (central bulge is about 10,000 LY thick). You Are Here The Sun is located at the edge of a spiral arm, ~28,000 light-years from the center It takes 250 Million years for the Sun to complete one orbit There are ~100-200 Billion stars in the Milky Way The Spiral arms are only 5% more dense than average, and are the locations of new star formation

The Local Group Contains 3 large spiral galaxies--Milky Way, Andromeda (M31), and Triangulum (M33)—plus a few dozen dwarf galaxies with elliptical or irregular shapes. Gravitationally bound together—orbiting about a common center of mass Ellipsoidal in shape About 6.5 million light-years in diameter

The Local (Virgo) Supercluster A cluster of many groups and clusters of galaxies Largest cluster is the Virgo cluster containing over a thousand galaxies. Clusters and groups of galaxies are gravitationally bound together, however the clusters and groups spread away from each other as the Universe expands. The Local Supercluster gets bigger with time It has a flattened shape The Local Group is on the edge of the majority of galaxies The Local Supercluster is about 130 Million light-years across The Local (Virgo) Supercluster

The Universe 1.3 Billion light-years Surveys of galaxies reveal a web-like or honeycomb structure to the Universe Great walls and filaments of matter surrounding voids containing no galaxies Probably 100 Billion galaxies in the Universe The plane of the Milky Way Galaxy obscures our view of what lies beyond. This creates the wedge-shaped gaps in all-sky galaxy surveys such as those shown here.

The observable Universe is ~92 billion light-years in diameter… The Universe The observable Universe is ~92 billion light-years in diameter… The whole thing is estimated to be > 156 billion light-years in diameter Computer Simulation

Measuring astronomical distances To measure cosmological distances a ladder of methods is used to reach further out into the Universe. Each “rung” in the ladder of distance measuring methods depends on the calibration of the methods “below.”