The universe
Look up into the sky at night and what do you see? An endless blanket of stars, some bright, some dim, some blinking alone, some part of a constellation. For centuries, people have pondered questions about the origin and structure of the universe. Discovering the actual age of the universe has been called the Holy Grail of cosmology. The truth is, no one really knows for sure. Before Hubble, scientists guessed the universe dated back to anywhere from 10 to 20 billion years. Scientists, however, believe they are closer to the answer, thanks to Hubble. In 1999, scientists came up with their best estimate yet for dating the universe - 12 billion years.
Our own galaxy measures about 120,000 light-years or 708,000 trillion miles across. Earth's circumference is about 25,000 miles. If we wanted to travel one light-year, we would have to circle the Earth about 240 million times!
Many scientists believe the universe is fairly uniform, that stars and clusters of stars form galaxies, which are the same everywhere and in every direction. A popular notion among the astronomical community is: The older the universe, the bigger it becomes.
This claim is fostered by the Big Bang Theory, which says that at one point the universe did not exist. All of the sudden, there was something like a hot fireball that "exploded" and expanded rapidly, creating all matter now found in space.
Edwin Hubble, for whom Hubble was named, observed evidence of an expanding universe in the 1920s. He first identified galaxies outside our Milky Way Galaxy and determined that most are speeding away from Earth. Hubble's Law says the more distant a galaxy is, the faster that galaxy is receding from Earth. To put it in simpler terms, think of this law as an expanding balloon.
Say we paint some dots on a deflated balloon. Each dot represents a galaxy in the universe. As the balloon is blown up, we would notice the distance between the dots (or galaxies) becoming greater as the balloon expands. The more distant the dot is from any particular point on the balloon, the faster it will appear to move away from that point. This is true for every dot, regardless of where it is on the balloon. Similarly, from the vantage point of any galaxy, all other galaxies appear to move away. This is the same for any expanding object, such as a loaf of bread rising in the oven, the surface of a balloon or the expanding universe.
Missions and discoveries
When it comes down to numbers, Hubble has plenty. In its first decade of operation (1990-2000), Hubble studied more than 14,000 objects and made more than 271,000 individual observations. In fact, so much data has been collected that scientists have generated more than 2,600 research papers on the topic.
One can only imagine how much this data has contributed to the world of astronomy. For example, Hubble has helped us better understand the planets in our own solar system. Amid a long laundry list of discoveries, it detected a thin atmosphere of oxygen around Europa, one of Jupiter's larger moons, imaged the surface of Pluto and observed a rare storm on Saturn that was larger than Earth.
Observing the intricacies of planetary nebulae also tell us about our own neighborhood, the Milky Way. A planetary nebula is a giant cloud of gas in space surrounding a dying star. Data retrieved about these nebulae give scientists clues about what the future of our sun will be. A nebula represents the last stages of life for stars like the sun, so it's likely that our sun will go through a similar episode in about five or six billion years from now. Studying dying stars and nebulae help scientists look into the future of our own solar system and understand how it might evolve and change.
With so many discoveries, it is an impossible task to pick and choose which ones to highlight. From nebulae to star clusters and black holes to planetary atmospheres, each discovery is unique and precious to our understanding of the universe. However, we have compiled a comprehensive list of Hubble links. For the latest Hubble news and discoveries, visit our related-links section.