What Came Before the Big Bang?

Illustration of the Big Bang Theory

Astronomers are pretty sure what happened after the Big Bang, but what came before? What are the leading theories for the causes of the Big Bang?

About 13.8 billion years ago the Universe started with a bang, kicked the doors in, brought fancy cheeses and a bag of ice, spiked the punch bowl and invited the new neighbors over for all-nighter to encompass all all-nighters from that point forward.
But what happened before that?

What was going on before the Big Bang? Usually, we tell the story of the Universe by starting at the Big Bang and then talking about what happened after. Similarly and completely opposite to how astronomers view the Universe… by standing in the present and looking backwards. From here, the furthest we can look back is to the cosmic microwave background, which is about 380,000 years after the big bang.

Before that we couldn’t hope to see a thing, the Universe was just too hot and dense to be transparent. Like pea soup. Soup made of delicious face burning high energy everything.
In traditional stupid earth-bound no-Tardis life unsatisfactory fashion, we can’t actually observe the origin of the Universe from our place in time and space.

Damn you… place in time and space.

Fortunately, the thinky types have come up with some ideas, and they’re all one part crazy, one part mind bendy, and 100% bananas. The first idea is that it all began as a kind of quantum fluctuation that inflated to our present universe.

Artistic view of a radiating black hole.  Credit: NASA
Artistic view of a radiating black hole. Credit: NASA

Something very, very subtle expanding over time resulting in, as an accidental byproduct, our existence. The alternate idea is that our universe began within a black hole of an older universe.
I’m gonna let you think about that one. Just let your brain simmer there.

There was universe “here”, that isn’t our universe, then that universe became a black hole… and from that black hole formed us and EVERYTHING around us. Literally, everything around us. In every direction we look, and even the stuff we just assume to be out there.

Here’s another one. We see particles popping into existence here in our Universe. What if, after an immense amount of time, a whole Universe’s worth of particles all popped into existence at the same time. Seriously… an immense amount of time, with lots and lots of “almost” universes that didn’t make the cut.

 BICEP2 Telescope at twilight at the South Pole, Antartica (Credit: Steffen Richter, Harvard University)
BICEP2 Telescope at twilight at the South Pole, Antartica (Credit: Steffen Richter, Harvard University)

More recently, the BICEP2 team observed what may be evidence of inflation in the early Universe.
Like any claim of this gravity, the result is hotly debated. If the idea of inflation is correct, it is possible that our universe is part of a much larger multiverse. And the most popular form would produce a kind of eternal inflation, where universes are springing up all the time. Ours would just happen to be one of them.

It is also possible that asking what came before the big bang is much like asking what is north of the North Pole. What looks like a beginning in need of a cause may just be due to our own perspective. We like to think of effects always having a cause, but the Universe might be an exception. The Universe might simply be. Because.

You tell us. What was going on before the party started? Let us know in the comments below.

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What’s Causing The Universe To Expand?

We’ve all heard that the Universe is expanding, but why is it expanding? What’s the force pushing everything outwards?

If still you don’t know that we live in an expanding Universe, then I’m clearly not doing my job.

And so once more, with feeling… the Universe is expanding. But that certainly doesn’t answer all the questions that go along with the it.

Like what’s the Universe expanding into? Which we did in another video, which I’ll list at the end of this episode. You might also want to know why is the Universe expanding? What’s making this happen? Did it give up its gym membership? Did it sign up for the gallon of ice cream of the month club? Has it completely embraced the blerch?

Edwin Hubble, the astronomer made famous by being named after a space telescope, provided the definitive evidence that the Universe was expanding. Observing distant galaxies, he observed they were fleeing outwards, in fact he was able to come up with calculations to show just how fast they were moving away from us.

Or to be more precise, he was able to show how fast all the galaxies are moving away from each other. Which was your question! Just like a minute ago! See you’re just as smart as Hubble!

So up until about 15 years ago, the only answer was momentum. The idea was that the Universe received all the energy it needed for its expansion in the first few moments after the Big Bang.

Imagine the beginning of the Universe, BOOM, like an explosion from a gun. And all the rest of the expansion is the Universe coasting outwards. For the longest time, astronomers were trying to figure out what this momentum would mean for the future of the Universe.

Dark Energy
The Hubble Space Telescope image of the inner regions of the lensing cluster Abell 1689 that is 2.2 billion light?years away. Light from distant background galaxies is bent by the concentrated dark matter in the cluster (shown in the blue overlay) to produce the plethora of arcs and arclets that were in turn used to constrain dark energy. Image courtesy of NASA?ESA, Jullo (JPL), Natarajan (Yale), Kneib (LAM)

Would the mutual gravity of all the objects in the Universe cause it to slow to a halt at some point in the distant future, or maybe even collapse in on itself, leading to a Big Crunch? Or just clump up in piles and stay on the couch all summer because it’s maybe a little lazy and isn’t ready to start going back to the gym yet?

In 1999, astronomers discovered something completely unexpected… dark energy. As they were doing their observations to figure out exactly how the Universe would coast to a stop, they discovered that it’s actually speeding up. It’s as if that bullet is actually a rocket and it’s accelerating.

Now it appears that the Universe will not only expand forever, but the speed of its expansion will continue to accelerate faster and faster. So what’s causing this expansion? Currently, we believe it’s mostly momentum left over from the Big Bang, and the force of dark energy will be accelerating this expansion. Forever.

How do you feel about a rapidly accelerating expanding Universe? Tell us in the comments below.

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When Did the First Stars Form?

Shortly after the Big Bang, the Universe had cooled to the point that the first stars could form out of the primordial hydrogen. How long did it take, and what did these first stars like?

Hydrogen soup. Doesn’t that sound delicious? Perhaps not for humans, but certainly for the first stars!

Early in the Universe, in a spectacular show of stellar soupification, clouds of hydrogen atoms gathered together. They combined with one another. The collected mass got bigger and bigger, and after a time, ignition. The first stars were alive!

Well, alive in the sense that they were burning – not that they had feelings or knew what was going on, or had opinions, or were beginning to write would what would eventually become the first Onion article or anything.

But where did all that gas come from, and can we spot the evidence of those long-ago stars today? As you know, the Big Bang got our Universe off to a speedy start of expansion. It then took 400,000 years for us to see any light at all. Protons and electrons and other small particles were floating around, but it was far too hot for them to interact.

Once the power of the Big Bang finally faded, those protons and electrons paired up and created hydrogen. This is called, rather uninventively, “recombination”. I’d rather just call it hydrogen soup. We’ve got energy. But what is the secret ingredient that sparked these stars? It was just that soup clumping together over time.

A map of the faint microwave radiation left over after the big bang shows superclusters (red circles) and supervoids (blue circles). Credit: B. Granett, M. Neyrinck, I. Szapudi
A map of the faint microwave radiation left over after the big bang shows superclusters (red circles) and supervoids (blue circles). Credit: B. Granett, M. Neyrinck, I. Szapudi

We can’t say to the minute when the first stars formed, but we have a pretty good idea. The Wilkinson Microwave Anisotropy Probe, aka WMAP examined what happened when these clouds of hydrogen molecules got together, creating tiny temperature differences of only a millionth of a degree.

Over time, gravity began to yank matter from spots of lower density into the higher-density regions, making the clumps even bigger. Fantastically bigger. So big that about 200 million years after the clumps were formed, it was possible for these hydrogen molecules to ram into each other at very high speeds.

This process is called nuclear fusion. On Earth, it’s a way to produce energy. Same goes for a star. With enough nuclear reactions happening, the cloud of gas compresses and creates a glow. And these stars weren’t tiny – they were monsters! NASA says the first stars were 30 to 300 times as massive as the sun, shining millions of times brighter.

The supernova that produced the Crab Nebula was detected by naked-eye observers around the world in 1054 A.D. This composite image uses data from NASA’s Great Observatories, Chandra, Hubble, and Spitzer, to show that a superdense neutron star is energizing the expanding Nebula by spewing out magnetic fields and a blizzard of extremely high-energy particles. The Chandra X-ray image is shown in light blue, the Hubble Space Telescope optical images are in green and dark blue, and the Spitzer Space Telescope’s infrared image is in red. The size of the X-ray image is smaller than the others because ultrahigh-energy X-ray emitting electrons radiate away their energy more quickly than the lower-energy electrons emitting optical and infrared light. The neutron star is the bright white dot in the center of the image.
The supernova that produced the Crab Nebula was detected by naked-eye observers around the world in 1054 A.D. This composite image uses data from NASA’s Great Observatories, Chandra, Hubble, and Spitzer.

But this flashy behavior came at a price, because in only a few million years, the stars grew unstable and exploded into supernovae. These stars weren’t only exploding. They were also altering the soup around them. They were big emitters of ultraviolet light. It’s a very energetic wavelength, best known for causing skin cancer.

So, this UV light struck the hydrogen surrounding the stars. This split the atoms apart into electrons and protons again, leaving quite the mess in space. But it’s through this process that we can learn more about these earliest stars.The stars are long gone, but like a criminal fleeing the scene, they left a pile of evidence behind for their existence. Splitting these atoms was their evidence. This re-ionization is one key piece of understanding how these stars came to be.

So it was an action-packed time for the universe, with the Big Bang, then the emergence of soup and then the first stars. It’s quite an exciting start for our galactic history.

What do you think the first stars looked like?

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How Big is the Universe?

The Universe is big, but how big is it? That all depends on whether the Universe is finite or infinite. Even the word “big” is tough to get clear. Are we talking about the size of the Universe we can see, or the Universe’s actual size right now?

The Universe is big, but how big is it? And what the heck kind of question is that? Are elephants big? Trucks? Dinosaurs? Cheese? Is cheese big? How big is cheese? How big is big?

The word “big” is tough to get clear. Are we talking about the size of the Universe we can see, or the Universe’s actual size right now? This becomes even more complicated when we are trying to work under assumptions of either the Universe is finite or the Universe is infinite.

One difficulty with talking about the size, is that the Universe is expanding. Light takes time to travel from distant galaxies, and while that light travels, the Universe continues to expand. So our problem with talking about how big it is, is that there is no single meaning to distance when it comes to the universe. For this reason, astronomers usually don’t worry about the distance to galaxies at all, and instead focus on redshift, which is measured by z. The bigger the z, the more redshift, and the more distant the galaxy.

As an example, consider one of the most distant galaxies we’ve observed, which has a redshift of 7.5. Using this, we can determine distance by calculating how long the light has traveled to reach us. With a redshift of 7.5, that comes out to be about 13 billion years. You might think that means it’s 13 billion light years away, but 13 billion years ago the universe was smaller, so it was actually closer at the time the light left that galaxy. Using this, if you calculate that distance, it was only a short 3.4 billion light years away.

Now the galaxy is much farther than that. After the light left the galaxy, the galaxy continued to move away from us. It is now about 29 billion light years away. Which is definitely more than 13, and quite a bit more than its original 3.4.

Usually it is this big distance that people mean when they ask for the size of the universe. This is known as the co-moving distance. Of course, we can only see so far. So, how far can we see? The most distant light we are able to observe is from the cosmic microwave background, which has a redshift of about z = 1,000.

This means the co-moving distance of the cosmic background is about 46 billion light years. Sticking us at the center of a massive sphere, the currently observable universe has a diameter of about 92 billion light years. Even with this observed distance, we know that it extends much further than that. If what we could see was all there is, we would see galaxies tend to gravitate towards us, which we don’t observe.

Multiverse Theory
Artist concept of the multiverse. Credit: Florida State University

In fact we don’t see any kind of galaxy clumping to a particular point at all. So as far as we know the universe could extend forever. It could be even stranger than that. Despite some media controversy, if the BICEP2 detection of early inflation is correct, it is likely the Universe undergoes a type of inflation with the intimidating moniker of “eternal inflation”. If it is the case, our observable universe is merely one bubble within an endless sea of other bubble universes. This is otherwise referred to as… the multiverse.

So, in the immortal words of Douglas Adams, “Space,” it says, “is big. Really big. You just won’t believe how vastly, hugely, mindbogglingly big it is. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space”

What do you think? Does the Universe go on for ever? Tell us in the comments below. And if you like what you see, come check out our Patreon page and find out how you can get these videos early while helping us bring you more great content!

Is Andromeda Drifting Towards Us?

In a Universe that’s expanding apart, isn’t it strange that Andromeda is actually drifting towards us? Dr. Thad Szabo from Cerritos College explains why this is happening.

“I’m Thad Szabo, and I teach astronomy and physics at Cerritos College.”

Is Andromeda drifting towards us?

“The reason that we see Andromeda moving toward us is because it’s nearby enough, and the Milky Way is massive enough and Andromeda is massive enough that they’re gravity is strong enough that there is not enough space between them that the space was able to expand and push them apart against the force of gravity. So if you take the Milky Way, all of its stars and all of its gas and dust, all of its dark matter, you’re looking at something that’s a trillion times the mass of the sun. You have the same for Andromeda, and they’re less than a mega parsec apart – to Andromeda, its about 2.2 billion light years. And so with that distance and that much mass, that’s close enough that gravity is drawing them together. Most galaxies, because they’re so distant, you do see them moving away due to the expansion of the universe.”

“But actually M81, which is about 12 million light years away, is also moving towards the Milky Way. It’s the most distant galaxy that doesn’t show red shift. So there’s enough gravity in this local group – I guess the local group is typically the Milky Way galaxy, the Andromeda galaxy, the Triangulum galaxy, and however many tens of dwarf galaxies that we’ve either discovered or haven’t discovered yet. But there’s also a bubble of about ten to twenty major size galaxies extending out to about fifteen million light years or so, and that’s kind of right on the border between where the expansion of the universe would drive things apart and where the gravity is strong enough to hold things together.”

How Old is the Universe?

The Universe is vast bubble of space and time, expanding in volume. Run the clock backward and you get to a point where everything was compacted into a microscopic singularity of incomprehensible density. In a fraction of a second, it began expanding in volume, and it’s still continuing to do so today.

So how old is the Universe? How long has it been expanding for? How do we know? For a good long while, Astronomers assumed the Earth, and therefore the Universe was timeless. That it had always been here, and always would be.

In the 18th century, geologists started to gather evidence that maybe the Earth hadn’t been around forever. Perhaps it was only millions or billions of years old. Maybe the Sun too, or even… the Universe. Maybe there was a time when there was nothing? Then, suddenly, pop… Universe.

It’s the science of thermodynamics that gave us our first insight. Over vast lengths of time, everything moves towards entropy, or maximum disorder. Just like a hot coffee cools down, all temperatures want to average out. And if the Universe was infinite in age, everything should be the same temperature. There should be no stars, planets, or us.

The brilliant Belgian priest and astronomer, George Lemaitre, proposed that the Universe must be either expanding or contracting. At some point, he theorized, the Universe would have been an infinitesimal point – he called it the primeval atom. And it was Edwin Hubble, in 1929 who observed that distant galaxies are moving away from us in all directions, confirming Lemaitre’s theories. Our Universe is clearly expanding.

Which means that if you run the clock backwards, and it was smaller in the distant past. And if you go back far enough, there’s a moment in time when the Universe began. Which means it has an age. The next challenge… figuring out the Universe’s birthdate.

Time line of the Universe (Credit: NASA/WMAP Science Team)
Time line of the Universe (Credit: NASA/WMAP Science Team)

In 1958, the astronomer Allan Sandage used the expansion rate of the Universe, otherwise known as the Hubble Constant, to calculate how long it had probably been expanding. He came up with a figure of approximately 20 billion years. A more accurate estimation for the age of the Universe came with the discovery of the Cosmic Microwave Background Radiation; the afterglow of the Big Bang that we see in every direction we look.

Approximately 380,000 years after the Big Bang, our Universe had cooled to the point that protons and electrons could come together to form hydrogen atoms. At this point, it was a balmy 3000 Kelvin. Using this and by observing the background radiation, and how far the wavelengths of light have been stretched out by the expansion, astronomers were able to calculate how long it has been expanding for.

Initial estimates put the age of the Universe between 13 and 14 billion years old. But recent missions, like NASA’s WMAP mission and the European Planck Observatory have fine tuned that estimate with incredible accuracy. We now know the Universe is 13.8242 billion years, plus or minus a few million years.

We don’t know where it came from, or what caused it to come into being, but we know exactly how our Universe is. That’s a good start.

What Is The Big Rip?

Dr. Thad Szabo is a professor of physics and astronomy at Cerritos College. He’s also a regular contributor to many of our projects, like the Virtual Star Party and the Weekly Space Hangout. Thad has an encyclopedic knowledge of all things space, so we got him to explain a few fascinating concepts.

In this video, Thad explains the strange mystery of dark energy, and the even stranger idea of the Big Rip.

What is the ‘Big Rip?’

If we look at the expansion of the universe, at first it was thought that, as things are expanding while objects have mass, the mass is going to be attracted to other mass, and that should slow the expansion. Then, in the late 1990’s, you have the supernova surveys that are looking deeper into space than we’ve ever looked before, and measuring distances accurately to greater distances than we’ve ever seen before. Something really surprising came out, and that was what we’ll now use “dark energy” now to explain, and that is that the acceleration is not actually slowing down – it’s not even stopped. It’s actually getting faster, and if you look at the most distant objects, they’re actually moving away from us and the acceleration is increasing the acceleration of expansion. This is actually a huge result.

One of the ideas of trying to explain it is to use the “cosmological constant,” which is something that Einstein actually introduced to his field equations to try to keep the universe the same size. He didn’t like the idea of a universe changing, so he just kind of cooked up this term and threw it into the equations to say, alright, well if it isn’t supposed to expand or contract, if I make this little mathematical adjustment, it stays the same size.

Hubble comes along about ten years later, and is observing galaxies and measuring their red shifts and their distances, and says wait a minute – no the universe is expanding. And actually we should really credit that to Georges Lemaître, who was able to interpret Hubble’s data to come up with the idea of what we now call the Big Bang.

So, the expansion’s happening – wait, it’s getting faster. And now the attempt is to try to understand how dark energy works. Right now, most of the evidence points to this idea that the expansion will continue in the space between galaxies. That the forces of gravity, and especially magnetism and the strong nuclear force that holds protons and neutrons together in the center of an atom, would be strong enough that dark energy is never going to be able to pull those objects apart.

However, there’s a possibility that it doesn’t work like that. There’s actually a little bit of experimental evidence right now that, although it’s not well-established, that there’s a little bit of a bias with certain experiments that dark energy may get stronger over time. And, if it does so, the distances won’t matter – that any object will be pulled apart. So first, you will see all galaxies recede from each other, as space starts to grow bigger and bigger, faster and faster. Then the galaxies will start to be pulled apart. Then star systems, then planets from their stars, then stars themselves, and then other objects that would typically be held together by the much stronger forces, the electromagnetic force objects held by that will be pulled apart, and then eventually, nuclei in atoms.

So if dark energy behaves so that it gets stronger and stronger over time, it will eventually overcome everything, and you’ll have a universe with nothing left. That’s the ‘Big Rip’ – if dark energy gets stronger and stronger over time, it will eventually overcome any forces of attraction, and then everything is torn apart.

You can find more information from Dr. Thad Szabo at his YouTube channel.

What is the Universe Expanding Into?

Come on, admit it, you’ve had this question. “Since astronomers know that the Universe is expanding, what’s it expanding into? What’s outside of the Universe?” Ask any astronomer and you’ll get an unsatisfying answer. We give you the same unsatisfying answer, but really explain it, so your unsatisfaction doesn’t haunt you any more.

The short answer is that this is a nonsense question, the Universe isn’t expanding into anything, it’s just expanding.

The definition of the Universe is that it contains everything. If something was outside the Universe, it would also be part of the Universe too. Outside of that? Still Universe. Out side of THAT? Also more Universe. It’s Universe all the way down. But I know you’re going to find that answer unsatisfying, so now I’m going to break your brain.

Either the Universe is infinite, going on forever, or its finite, with a limited volume. In either case, the Universe has no edge. When we imagine the Universe expanding after the Big Bang, we imagine an explosion, with a spray of matter coming from a single point. But this analogy isn’t accurate.

A better analogy is the surface of an expanding balloon. Not the 3 dimensional balloon, just its 2 dimensional surface. If you were an ant crawling around the surface of a huge balloon, and the balloon was your whole universe, you would see the balloon as essentially flat under your feet.

Imagine the balloon is inflating. In every direction you look, other ants are moving away from you. The further they are, the faster away they’re moving. Even though it feels like a flat surface, walk in any direction long enough and you’d return to your starting point.

You might imagine a growing circle and wonder what it’s expanding into. But that’s a nonsense question. There’s no direction you could crawl that would get you outside the surface. Your 2-dimensional ant brain can’t comprehend an expanding 3-dimensional object. There may be a center to the balloon, but there’s no center to the surface. Just a shape that extends in all directions and wraps in upon itself. And yet, your journey to make one lap around the balloon takes longer and longer as the balloon gets more inflated.

To better understand how this relates to our Universe, we need to scale things up by one dimension, from a 2-d surface embedded in a 3-d world, to a 3-d volume embedded within a 4-d universe. Astronomers think that if you travel in any direction far enough, you’ll return to your starting position. If you could stare far enough into space, you would be looking at the back of your own head.

The Universe 1.6 billion years after the Big Bang. Image credit: Paul Bode and Yue Shen
The Universe 1.6 billion years after the Big Bang. Image credit: Paul Bode and Yue Shen

And so, as the Universe expands, it would take you longer and longer to lap the Universe and return to your starting position. But there’s no direction you could travel in that would take you outside or “off” of the Universe. Even if you could move faster than the speed of light, you’d just return to your starting position more quickly. We see other galaxies moving away from us in all directions just as our ant would see other ants moving away on the surface of the balloon.

A great analogy comes from my Astronomy Cast co-host, Dr. Pamela Gay. Instead of an explosion, imagine the expanding Universe is like a loaf of raisin bread rising in the oven. From the perspective of any raisin, all the other raisins are moving away in all directions. But unlike a loaf of raisin bread, you could travel in any one direction within the bread and eventually return to your starting raisin.

Remember that our entire comprehension is based on 3-dimensions. If we were 4-dimensional creatures, this would make much more sense. For a much deeper explanation, I highly recommend you watch my good friend, Zogg the Alien explain how the Universe has no edge. After watching his videos, you should totally understand the possible topologies of our Universe.

I hope this helps you understand why there’s no answer to “what is the Universe expanding into?” With no edge, it’s not expanding into anything, it’s just expanding.

You can also listen to our podcast episode explaining this here –
What is the Universe Expanding Into – Show notes and transcript

Or subscribe to: astronomycast.com/podcast.xml

Why “The Big Bang” Is a Terrible Name

Have a discussion about the origins of the Universe and, ere long, someone will inevitably use the term “the Big Bang” to describe the initial moment of expansion of everything that was to everything that is. But in reality “Big Bang” isn’t a very good term since “big” implies size (and when it occurred space didn’t technically exist yet) and there was no “bang.” In fact the name wasn’t ever even meant to be an official moniker, but once it was used (somewhat derisively) by British astronomer Sir Fred Hoyle in a radio broadcast in 1949, it stuck.

Unfortunately it’s just so darn catchy.

This excellent video from minutephysics goes a bit more into depth as to why the name is inaccurate — even though we’ll likely continue using it for quite some time. (Thanks to Sir Hoyle.)

And you have to admit, a television show called “The Everywhere Stretch Theory” would never have caught on. Bazinga!

30 Years of City Growth Seen From Space

Since the launch of its first satellite in 1972, the eight NASA/USGS Landsat satellites have made the longest continuous observations of Earth’s surface, providing invaluable data for research in agriculture, geology, forestry, regional planning, education, mapping, global change research, as well as important emergency response and disaster relief information. In addition, having such a long span of data allows us to easily see the expansion of human development in many areas — unprecedented before-and-after views of city growth seen from space.

These images, taken over the course of the Landsat program, illustrate the visible impact of over three decades of human development:

Chandler, Arizona imaged in 1985 (top) and 2011 (bottom.)  As its economy shifted from agriculture to manufacturing and electronics, Chandler's population multiplied 8 times to over 236,000.
Chandler, Arizona imaged in 1985 (top) and 2011 (bottom.) As its economy shifted from agriculture to manufacturing and electronics, Chandler’s population multiplied 8 times to over 236,000.
The explosion of Istanbul's population from 2 to 3 million people is evident in these Landsat images, comparing 1975 to 2011. Vegetation appears red in the imaging wavelengths used here.
The explosion of Istanbul’s population from 2 to 13 million people is evident in these Landsat images, comparing 1975 to 2011. Vegetation appears red in the imaging wavelengths used here.
A few years ago one of the fastest-growing cities in the US, Las Vegas is seen here in images taken in 1984 (top) and 2011 (bottom.) The sprawling development -- as well as the decrease in water level of Lake Mead -- is evident.
A few years ago one of the fastest-growing cities in the US, Las Vegas is seen here in images taken in 1984 (top) and 2011 (bottom.) The sprawling development — as well as the decrease in water level of Lake Mead — is evident.
Some of the most dramatic -- and rapid --  changes have occurred in Dubai, whose artificial offshore islands suddenly appear between images taken in 2000 (top) and 2010 (bottom.) Once barely visible against the desert landscape, Dubai is now an international center of business, tourism, and oil production.
Some of the most dramatic — and rapid — changes have occurred in Dubai, whose palm- and continent-shaped artificial islands suddenly appear between images taken in 2000 (top) and 2010 (bottom.) Once barely visible against the desert landscape, Dubai is now an international center of business, tourism, and oil production.

See more of these images on NASA Goddard Space Flight Center’s Flickr album here.

The Landsat Program is a series of Earth-observing satellite missions jointly managed by NASA and the U.S. Geological Survey. In 1972, the launch of ERTS-1 (Earth Resources Technology Satellite, later renamed Landsat 1) started the era of a series of satellites that have since continuously acquired space-based land remote sensing data.

The latest satellite in the Landsat series, the Landsat Data Continuity Mission (LDCM) — now named Landsat 8 — was launched on February 11, 2013. Landsat 8 data is now available free to the public online here.

Read more on the USGS Landsat mission page here.

Image credits: USGS/NASA