SUNSET: 
How Many Planets Are In Our Solar System?
There are eight planets in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
Extreme Volcanoes on Jupiter's Moon Io
Even on Io, a world known for spouting off, the titanic volcanic eruption seen on August 29, 2013, was among the most powerful ever recorded — unleashing an estimated 20 terawatts of energy.
Is space flat or curved?
Locally, spacetime is curved by the presence of massive objects. The total mass and energy density of the universe also has an effect on the overall curvature of space.
What came before the Big Bang?
There was no “before the Big Bang"—the Big Bang created both time and space as we know it.
What is dark matter?
Dark matter is a mysterious type of matter that doesn't interact with any form of electromagnetic radiation, i.e., light. Although we’ve never detected dark matter directly, a large amount of evidence points to its existence.
How fast is the universe expanding?
Just how quickly is the universe expanding? Cosmologists attempt to answer this question in terms of the Hubble Constant, but the exact value of this constant is still a topic of debate.
Is the universe infinite?
Is the universe infinite, or just really, really big? How can we know? To answer these questions, we examine the possible shapes of the universe.
NASA Gears Up for Mars 2020 Rover
Six years from now, there will be a new NASA robot heading to the Red Planet: the Mars 2020 rover. On July 31st mission planners unveiled the rover’s seven scientific instruments, which will pave the way for human exploration of Mars.
Fermi Finds "Transformer" Pulsar
NASA's Fermi Space Telescope recently spotted a pulsar in a rare transitional phase as it devours the matter of its companion star.
X-Ray Glow Evidence of Local Hot Bubble
Scientists have confirmed that the soft X-ray glow permeating the sky has two sources: one inside the solar system, one outside.
How Far is the Closest Star?
Barring the Sun, the closest star to Earth is a triple system called Alpha Centauri, which is over four light years away.
How is Time Changed Inside a Black Hole?
Because black holes severely warp the fabric of spacetime, they have a curious effect on the passage of time as seen by an outside observer.
How do black holes form?
Different types of black holes form through different processes.
Are Black Holes Real? If so, Who Discovered Them?
The concept of a black hole was first contrived in by John Michell 1783. For a long time, many notable scientists, including Albert Einstein, believed black holes were merely theoretical. However, in the last century, astronomers have gathered a good deal of observational evidence for the existence of black holes.
What's the Origin of the Universe? What happened during the Big Bang?
The Big Bang marked the beginning of the universe's expansion from a singularity — a single point that was infinitely small, infinitely hot, and infinitely dense. Cosmologists have designated several distinct eras for the universe's evolution from the first moments after the Big Bang to a billion years later.
What is dark energy?
Cosmologists have invoked the concept of dark energy to explain the accelerated expansion of the universe, but the nature of dark energy remains one of the most pressing questions facing modern cosmology.
Is there a center of the universe?
The universe began as a singularity that started expanding in the Big Bang. But the Big Bang was no regular explosion. Rather, space itself expanded, so there is no center of the entire universe. The observable universe, on the other hand, is a different story.
How Many Galaxies Are There in the Universe?
Astronomers determine the number of galaxies in the universe by counting up the number visible in a tiny portion of the sky, and then accounting for all the regions of the observable universe. A 2013 study estimates that there are 225 billion galaxies in the observable universe.
The End of the Universe: What is our ultimate fate?
During the latter half of the 20th century, cosmologists narrowed the universe’s fate to three possibilities, and they all depend on its density.
Rosetta's Comet has a Split Personality
The Rosetta spacecraft is closing in on Comet 67P/C-G, providing astronomers with an ever more detailed view of its structure. Judging by the latest photos, it actually has two components and is shaped like… a rubber ducky?