The Universe

The Universe

The universe is a big, big place. But how big? And how do we know?

Throughout history, humans have used a variety of techniques and methods to help them answer the questions 'How far?' and 'How big?' Generations of explorers have looked deeper and deeper into the vast expanse of the universe. And the journey continues today, as new methods are used, and new discoveries are made. (To learn more about distance, visit How Big is Our Universe.)

In the third century B.C., Aristarchus of Samos asked the question 'How far away is the Moon?' He was able to measure the distance by looking at the shadow of the Earth on the Moon during a lunar eclipse.

It was Edmund Halley, famous for predicting the return of the comet that bears his name, who three centuries ago found a way to measure the distance to the Sun and to the planet Venus. He knew that the planet Venus would very rarely, every 121 years, pass directly between the Earth and the Sun. The apparent position of the planet, relative to the disk of the Sun behind it, is shifted depending on where you are on Earth. And how different that shift is depends on the distance from both Venus and the Sun to the Earth. This rare event, the transit of Venus, occurred again quite recently, June 8, 2004.

It was knowing this fundamental distance from the Earth to the Sun that helped us find the true scale of the entire Solar system for the first time.

Image to right: Our sun, the nearest star, is 93 million miles away. That's why the sun, which is a million times the size of the Earth, looks so small. It would take the Space Shuttle seven months to fly there. Credit: SOHO - ESA & NASA

When we leave the solar system, we find our star and its planets are just one small part of the Milky Way galaxy. The Milky Way is a huge city of stars, so big that even at the speed of light, it would take 100,000 years to travel across it. All the stars in the night sky, including our Sun, are just some of the residents of this galaxy, along with millions of other stars too faint to be seen.

The further away a star is, the fainter it looks. Astronomers use this as a clue to figure out the distance to stars that are very far away. But how do you know if the star really is far away, or just not very bright to begin with? This problem was solved in 1908 when Henrietta Leavitt discovered a way to tell the 'wattage' of certain stars that changed their pulse rate linked to their wattage. This allowed their distances to be measured all the way across the Milky Way.

Image above: How Big is the Milky Way? Imagine that our entire Solar System were the size of a quarter. The Sun is now a microscopic speck of dust, as are its nine planets, whose orbits are represented by the flat disc of the coin. How far away is the nearest star to our sun? In our model, Proxima Centauri (and any planets that might be around it) would be another quarter, two soccer fields away. This is the typical separation of stars in our part of the galaxy. Credit: Hubble Heritage Team (AURA/STSCI/NASA); US Mint

Beyond our own galaxy lies a vast expanse of galaxies. The deeper we see into space, the more galaxies we discover. There are billions of galaxies, the most distant of which are so far away that the light arriving from them on Earth today set out from the galaxies billions of years ago. So we see them not as they are today, but as they looked long before there was any life on Earth.

Finding the distance to these very distant galaxies is challenging, but astronomers can do so by watching for incredibly bright exploding stars called supernovae. Some types of exploding stars have a known brightness - wattage - so we can figure out how far they are by measuring how bright they appear to us, and therefore how far away it is to their home galaxy.

Image to right: The picture on the right was taken three weeks after the one on the left. In that time, a star at the edge of one of these distant galaxies has exploded -- "gone supernova." Can you spot the supernova in the picture at right? Even though the explosion is as bright as a billion suns, it is so far away that it is just a speck of light. Credit: NASA and J. Blakeslee (JHU)

The image below is both the oldest and youngest picture ever taken. It is the oldest because it has taken the light nearly 14 billion years to reach us. And it is the youngest because it is a snapshot of our newborn universe, long before the first stars and galaxies formed. The bright patterns show clumps of simple matter that will eventually form stars and galaxies. This is as far as we can see into the universe. It is time, not space, which limits our view. Beyond a certain distance, light hasn't had time to reach us yet.

Image above: What is the furthest we can see? In 2003, NASA's WMAP satellite took images of the most distant part of the universe observable from Earth. The image shows the furthest we can see using any form of light. The patterns show clumps of matter that eventually formed into galaxies of stars. Credit: NASA/WMAP Science Team

So how big is the universe? No one knows if the universe is infinitely large, or even if ours is the only universe that exists. And other parts of the universe, very far away, might be quite different from the universe closer to home. Future NASA missions will continue to search for clues to the ultimate size and scale of our cosmic home.

Go on the full exploration of the size of our universe at: How big is our universe? Beautiful images and straight-forward methods and ideas take you from our solar system, into the realm of the stars, the galaxies and finally into the vast panorama of the observable universe. You can also download and print a pdf version of these explorations.

from : NASA informations

Mars Gives us rover's-eye view

A new Mars movie clip gives us a rover's-eye view of a bluish Martian sunset, while another clip shows the silhouette of the moon Phobos passing in front of the sun.
America's Mars Exploration Rover Opportunity, carefully guided by researchers with an artistic sense, has recorded images used in the simulated movies.
These holiday treats from the rover's panoramic camera, or Pancam, offer travel fans a view akin to standing on Mars and watching the sky.
"These visualizations of an alien sunset show what it must have looked like for Opportunity, in a way we rarely get to see, with motion," said rover science team member Mark Lemmon of Texas A&M University, College Station. Dust particles make the Martian sky appear reddish and create a bluish glow around the sun.
Lemmon worked with Pancam Lead Scientist Jim Bell, of Cornell University, Ithaca, N.Y., to plot the shots and make the moving-picture simulation from images taken several seconds apart in both sequences.
The sunset movie, combining exposures taken Nov. 4 and Nov. 5, 2010, through different camera filters, accelerates about 17 minutes of sunset into a 30-second simulation. One of the filters is specifically used to look at the sun. Two other filters used for these shots provide color information. The rover team has taken Pancam images of sunsets on several previous occasions, gaining scientifically valuable information about the variability of dust in the lower atmosphere. The new clip is the longest sunset movie from Mars ever produced, taking advantage of adequate solar energy currently available to Opportunity.
The two Martian moons are too small to fully cover the face of the sun, as seen from the surface of Mars, so these events -- called transits or partial eclipses -- look quite different from a solar eclipse seen on Earth. Bell and Lemmon chose a transit by Phobos shortly before the Mars sunset on Nov. 9, 2010, for a set of Pancam exposures taken four seconds apart and combined into the new, 30-second, eclipse movie. Scientifically, images years apart that show Phobos' exact position relative to the sun at an exact moment in time aid studies of slight changes in the moon's orbit. This, in turn, adds information about the interior of Mars.
The world has gained from these movies and from more than a quarter million other images from Opportunity and its twin, Spirit, since they landed on Mars in January 2004. Those gains go beyond the facts provided for science.
Bell said, "For nearly seven years now, we've been using the cameras on Spirit and Opportunity to help us experience Mars as if we were there, viewing these spectacular vistas for ourselves. Whether it's seeing glorious sunsets and eclipses like these, or the many different and lovely sandy and rocky landscapes that we've driven through over the years, we are all truly exploring Mars through the lenses of our hardy robotic emissaries.
"It reminds me of a favorite quote from French author Marcel Proust: 'The real voyage of discovery consists not in seeking new landscapes, but in having new eyes,'" he added.
NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover Project for NASA's Science Mission Directorate, Washington. For more information about the mission, see http://marsrovers.jpl.nasa.gov .


From: NASA informations