Universe: Solar System, Stars, and Galaxies 8th Edition – Ebook PDF Version
All rights reserved. Galaxies are sprawling systems of dust, gas, dark matter , and anywhere from a million to a trillion stars that are held together by gravity. Nearly all large galaxies are thought to also contain supermassive black holes at their centers. The deeper we look into the cosmos, the more galaxies we see. One study estimated that the observable universe contains two trillion—or two million million—galaxies.
All rights reserved. A correct, albeit less soothing, rendition might be: Emit, emit, gigantic ball of gas. Stars are huge celestial bodies made mostly of hydrogen and helium that produce light and heat from the churning nuclear forges inside their cores. Aside from our sun, the dots of light we see in the sky are all light-years from Earth. They are the building blocks of galaxies, of which there are billions in the universe.
Everything has a shadow! Shadows illustrate how three-dimensional objects can be viewed in two dimensions. Students explore the Earth and Sun's postions in relation to the constellations of the ecliptic with a small model. They explore the motions of the Earth and inner planets in a larger classroom-size model. A very interactive and fun activity. Does the Moon always look the same?
These galaxies are seen when the Universe was much younger than it is now so the infant galaxies are unlikely to have undergone many previous episodes of star formation, which might otherwise have confused the results. Zhang and his team developed a new technique -- analogous to radiocarbon dating also known as carbon dating -- to measure the abundances of different types of carbon monoxide in four very distant, dust-shrouded starburst galaxies . They observed the ratio of two types of carbon monoxide containing different isotopes . The mass of a star is the most important factor determining how it will evolve. Massive stars shine brilliantly and have short lives and less massive ones, such as the Sun, shine more modestly for billions of years. Knowing the proportions of stars of different masses that are formed in galaxies therefore underpins astronomers' understanding of the formation and evolution of galaxies throughout the history of the Universe.