The farther the galaxies are, the faster they’re traveling away. They also measured the expansion by observing the Doppler shift in light from galaxies, almost all of which are traveling away from us and from each other. Scientists arrived at that number by measuring the ages of the oldest stars and the rate at which the universe expands. The universe, on the other hand, appears to be about 13.8 billion years old. By studying the radioactive decay of isotopes on Earth and in asteroids, scientists have learned that our planet and the solar system formed around 4.6 billion years ago. While the distant future is difficult to accurately predict, the distant past is slightly less so. After all, humans have only just begun deciphering the cosmos. It might even expand large enough to swallow Earth itself. Several billion years from now, the Sun will expand, swallowing Mercury and Venus, and filling Earth’s sky. Nor will it last forever in its current state. For nearly two-thirds of the time since the universe began, Earth did not even exist. It may feel permanent, but the entire planet is a fleeting thing in the lifespan of the universe. Our planet, Earth, is an oasis not only in space, but in time. ![]() Image created by Reto Stöckli, Nazmi El Saleous, and Marit Jentoft-Nilsen, NASA GSFC The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument aboard NASA’s Terra satellite collected the land surface data over 16 days, while NOAA’s Geostationary Operational Environmental Satellite (GOES) produced a snapshot of the Earth’s clouds and the Moon. The image is a combination of data from two satellites. This true-color image shows North and South America as they would appear from space 22,000 miles (35,000 km) above the Earth. For humans and the other things living on our planet, practically the entire cosmos is a hostile and merciless environment. Earth is a tiny, fragile exception in the cosmos. It just so happens that things live here and the environment near the surface of this particular planet is hospitable for life as we know it. But Earth is a planet, and it’s in space and part of the universe just like the other planets. Humans say “out in space” as if it’s there and we’re here, as if Earth is separate from the rest of the universe. In fact, you’re technically in space right now. About 8,000 miles (12,800 kilometers) below your feet - on the opposite side of Earth - lurks the unforgiving vacuum and radiation of outer space. Day or night, whether you’re indoors or outdoors, asleep, eating lunch or dozing off in class, outer space is just a few dozen miles above your head. Wherever you are right now, outer space is only 62 miles (100 kilometers) away. Though the universe may seem a strange place, it is not a distant one. On the nebula's younger left side, many stars are just beginning to clear away the gas and dust. The dust and gas in the region are swept around even more when those stars die and explode as supernovas. The cavernous red region on the right side of W51 is older, evident in the way it has already been carved out by winds from generations of massive stars (those at least 10 times the mass of our Sun). "Star factories" like this one can operate for millions of years. Refine the design by identifying changes that need to be made and improving the model or prototype.The star-forming nebula W51 is one of the largest "star factories" in the Milky Way galaxy.Select an approach by identifying the design that appears to solve the problem best.Explore possibilities and the pros and cons of each.Generate ideas and develop the most promising ones.Brainstorm possible solutions to the problem or challenge.Identify design requirements and limitations on the design due to available resources and the environment.The engineering design process is a series of steps that engineers use to guide them as they solve problems. All those different systems must be designed before the whole spacecraft can work. For example, a spacecraft has electrical, mechanical, and propulsion systems. Many types of engineering must be performed to design and build a complicated system such as a spacecraft. ![]() The field of engineering is divided into branches such as civil, electrical, mechanical, and chemical engineering. Engineers often specialize in a specific branch of engineering. ![]() They have scientific training that they use to make practical things. Engineers want to know how and why things work. An engineer is a person who designs and builds complex products, machines, systems, or structures. Anything that is built must first be engineered, or planned out.
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