10 Things: How To Photograph A Meteor Shower

Ask Ethan: Why Do Gravitational Waves Travel Exactly At The Speed Of Light?

We know that the speed of electromagnetic radiation can be derived from Maxwell’s equation[s] in a vacuum. What equations (similar to Maxwell’s - perhaps?) offer a mathematical proof that Gravity Waves must travel [at the] speed of light?

If you were to somehow make the Sun disappear, you would still see its emitted light for 8 minutes and 20 seconds: the amount of time it takes light to travel from the Sun to the Earth across 150,000,000 km of space. But what about gravitation? Would the Earth continue to orbit where the Sun was for that same 8 minutes and 20 seconds, or would it fly off in a straight line immediately?

There are two ways to look at this puzzle: theoretically and experimentally/observationally. From a theoretical point of view, this represents one of the most profound differences from Newton’s gravitation to Einstein’s, and demonstrates what a revolutionary leap General Relativity was. Observationally, we only had indirect measurements until 2017, where we determined the speed of gravity and the speed of light were equal to 15 significant digits!

Gravitational waves do travel at the speed of light, which equals the speed of gravity to a better precision than ever. Here’s how we know.

What is Gravitational Lensing?

A gravitational lens is a distribution of matter (such as a cluster of galaxies) between a distant light source and an observer, that is capable of bending the light from the source as the light travels towards the observer. This effect is known as gravitational lensing, and the amount of bending is one of the predictions of Albert Einstein’s general theory of relativity.

This illustration shows how gravitational lensing works. The gravity of a large galaxy cluster is so strong, it bends, brightens and distorts the light of distant galaxies behind it. The scale has been greatly exaggerated; in reality, the distant galaxy is much further away and much smaller. Credit: NASA, ESA, L. Calcada

There are three classes of gravitational lensing:

1° Strong lensing: where there are easily visible distortions such as the formation of Einstein rings, arcs, and multiple images.

Einstein ring. credit: NASA/ESA&Hubble

2° Weak lensing: where the distortions of background sources are much smaller and can only be detected by analyzing large numbers of sources in a statistical way to find coherent distortions of only a few percent. The lensing shows up statistically as a preferred stretching of the background objects perpendicular to the direction to the centre of the lens. By measuring the shapes and orientations of large numbers of distant galaxies, their orientations can be averaged to measure the shear of the lensing field in any region. This, in turn, can be used to reconstruct the mass distribution in the area: in particular, the background distribution of dark matter can be reconstructed. Since galaxies are intrinsically elliptical and the weak gravitational lensing signal is small, a very large number of galaxies must be used in these surveys.

The effects of foreground galaxy cluster mass on background galaxy shapes. The upper left panel shows (projected onto the plane of the sky) the shapes of cluster members (in yellow) and background galaxies (in white), ignoring the effects of weak lensing. The lower right panel shows this same scenario, but includes the effects of lensing. The middle panel shows a 3-d representation of the positions of cluster and source galaxies, relative to the observer. Note that the background galaxies appear stretched tangentially around the cluster.

3° Microlensing: where no distortion in shape can be seen but the amount of light received from a background object changes in time. The lensing object may be stars in the Milky Way in one typical case, with the background source being stars in a remote galaxy, or, in another case, an even more distant quasar. The effect is small, such that (in the case of strong lensing) even a galaxy with a mass more than 100 billion times that of the Sun will produce multiple images separated by only a few arcseconds. Galaxy clusters can produce separations of several arcminutes. In both cases the galaxies and sources are quite distant, many hundreds of megaparsecs away from our Galaxy.

Gravitational lenses act equally on all kinds of electromagnetic radiation, not just visible light. Weak lensing effects are being studied for the cosmic microwave background as well as galaxy surveys. Strong lenses have been observed in radio and x-ray regimes as well. If a strong lens produces multiple images, there will be a relative time delay between two paths: that is, in one image the lensed object will be observed before the other image.

As an exoplanet passes in front of a more distant star, its gravity causes the trajectory of the starlight to bend, and in some cases results in a brief brightening of the background star as seen by a telescope. The artistic concept illustrates this effect. This phenomenon of gravitational microlensing enables scientists to search for exoplanets that are too distant and dark to detect any other way.Credits: NASA Ames/JPL-Caltech/T. Pyle

Explanation in terms of space–time curvature

Simulated gravitational lensing by black hole by: Earther

In general relativity, light follows the curvature of spacetime, hence when light passes around a massive object, it is bent. This means that the light from an object on the other side will be bent towards an observer’s eye, just like an ordinary lens. In General Relativity the speed of light depends on the gravitational potential (aka the metric) and this bending can be viewed as a consequence of the light traveling along a gradient in light speed. Light rays are the boundary between the future, the spacelike, and the past regions. The gravitational attraction can be viewed as the motion of undisturbed objects in a background curved geometry or alternatively as the response of objects to a force in a flat geometry.

A galaxy perfectly aligned with a supernova (supernova PS1-10afx) acts as a cosmic magnifying glass, making it appear 100 billion times more dazzling than our Sun. Image credit: Anupreeta More/Kavli IPMU.

To learn more, click here. 

The galaxy is perfect

Working too hard, feeling overwhelmed by family responsibilities, or dealing with an ongoing challenge? 

Maybe it’s time to turn your attention back to yourself and to your own self-care. Although we often brush it aside, self-care is not optional if you want to be happy and healthy.

Sixty Years of Exploration, Innovation, and Discovery!

Exactly sixty years ago today, we opened our doors for the first time. And since then, we have opened up a universe of discovery and innovation. 

There are so many achievements to celebrate from the past six decades, there’s no way we can go through all of them. If you want to dive deeper into our history of exploration, check out NASA: 60 Years and Counting. 

In the meantime, take a moonwalk down memory lane with us while we remember a few of our most important accomplishments from the past sixty years!

In 1958, President Eisenhower signed the National Aeronautics and Space Act, which effectively created our agency. We officially opened for business on October 1. 

To learn more about the start of our space program, watch our video: How It All Began. 

Alongside the U.S. Air Force, we implemented the X-15 hypersonic aircraft during the 1950s and 1960s to improve aircraft and spacecraft. 

The X-15 is capable of speeds exceeding Mach 6 (4,500 mph) at altitudes of 67 miles, reaching the very edge of space. 

Dubbed the “finest and most productive research aircraft ever seen,” the X-15 was officially retired on October 24, 1968. The information collected by the X-15 contributed to the development of the Mercury, Gemini, Apollo, and Space Shuttle programs. 

To learn more about how we have revolutionized aeronautics, watch our Leading Edge of Flight video. 

On July 20, 1969, Neil Armstrong and Buzz Aldrin became the first humans to walk on the moon. The crew of Apollo 11 had the distinction of completing the first return of soil and rock samples from beyond Earth. 

Astronaut Gene Cernan, during Apollo 17, was the last person to have walked on the surface of the moon. (For now!)

The Lunar Roving Vehicle was a battery-powered rover that the astronauts used during the last three Apollo missions. 

To learn more about other types of technology that we have either invented or improved, watch our video: Trailblazing Technology.

Our long-term Earth-observing satellite program began on July 23, 1972 with the launch of Landsat 1, the first in a long series (Landsat 9 is expected to launch in 2020!) We work directly with the U.S. Geological Survey to use Landsat to monitor and manage resources such as food, water, and forests. 

Landsat data is one of many tools that help us observe in immense detail how our planet is changing. From algae blooms to melting glaciers to hurricane flooding, Landsat is there to help us understand our own planet better. 

Off the Earth, for the Earth.

To learn more about how we contribute to the Earth sciences, watch our video: Home, Sweet Home. 

Space Transportation System-1, or STS-1, was the first orbital spaceflight of our Space Shuttle program. 

The first orbiter, Columbia, launched on April 12, 1981. Over the next thirty years, Challenger, Discovery, Atlantis, and Endeavour would be added to the space shuttle fleet. 

Together, they flew 135 missions and carried 355 people into space using the first reusable spacecraft.

On January 16, 1978, we selected a class of 35 new astronauts–including the first women and African-American astronauts. 

And on June 18, 1983, Sally Ride became the first American woman to enter space on board Challenger for STS-7. 

To learn more about our astronauts, then and now, watch our Humans in Space video.

Everybody loves Hubble! The Hubble Space Telescope was launched into orbit on April 24, 1990, and has been blowing our minds ever since. 

Hubble has not only captured stunning views of our distant stars and galaxies, but has also been there for once-in-a-lifetime cosmic events. For example, on January 6, 2010, Hubble captured what appeared to be a head-on collision between two asteroids–something no one has ever seen before.

In this image, Hubble captures the Carina Nebula illuminating a three-light-year tall pillar of gas and dust. 

To learn more about how we have contributed to our understanding of the solar system and beyond, watch our video: What’s Out There?

Cooperation to build the International Space Station began in 1993 between the United States, Russia, Japan, and Canada. 

The dream was fully realized on November 2, 2000, when Expedition 1 crew members boarded the station, signifying humanity’s permanent presence in space!

Although the orbiting lab was only a couple of modules then, it has grown tremendously since then! 

To learn more about what’s happening on the orbiting outpost today, visit the Space Station page.

We have satellites in the sky, humans in orbit, and rovers on Mars. Very soon, we will be returning humankind to the Moon, and using it as a platform to travel to Mars and beyond.

And most importantly, we bring the universe to you. 

What are your favorite NASA moments? We were only able to share a few of ours here, but if you want to learn about more important NASA milestones, check out 60 Moments in NASA History or our video, 60 Years in 60 Seconds. 

Make sure to follow us on Tumblr for your regular dose of space: http://nasa.tumblr.com.

WE NEED TO ACT NOW

The role plastic products play in the daily lives of people all over the world is interminable. We could throw statistics at you all day long (e.g. Upwards of 300 MILLION tons of plastic are consumed each year), but the impact of these numbers border on inconceivable.

For those living on the coasts, a mere walk on the beach can give anyone insight into how staggering our addiction to plastic has become as bottles, cans, bags, lids and straws (just to name a few) are ever-present. In other areas that insight is more poignant as the remains of animal carcasses can frequently be observed; the plastic debris that many of them ingested or became entangled in still visible long after their death. Sadly, an overwhelming amount of plastic pollution isn’t even visible to the human eye, with much of the pollution occurring out at sea or on a microscopic level.

The short-lived use of millions of tons of plastic is, quite simply, unsustainable and dangerous. We have only begun to see the far-reaching consequences of plastic pollution and how it affects all living things. According to a study from Plymouth University, plastic pollution affects at least 700 marine species, while some estimates suggest that at least 100 million marine mammals are killed each year from plastic pollution. Here are some of the marine species most deeply impacted by plastic pollution.

Sea Turtles

Seals and Sea Lions

Seabirds

Fish

Whales and Dolphins

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More than ever, the fate of the ocean is in our hands. To be good stewards and leave a thriving ocean for future generations, we need to make changes big and small wherever we are. 

Every purchase supports Ocean Conservation. We give a portion of our profits to Organizations that bravely fight for Marine Conservation.

Better Sleep tips.

Astronomers have just assembled one of the most comprehensive portraits yet of the universe’s evolutionary history, based on a broad spectrum of observations by the Hubble Space Telescope and other space and ground-based telescopes. In particular, Hubble’s ultraviolet vision opens a new window on the evolving universe, tracking the birth of stars over the last 11 billion years back to the cosmos’ busiest star-forming period, about 3 billion years after the big bang. This photo encompasses a sea of approximately 15,000 galaxies — 12,000 of which are star-forming — widely distributed in time and space. This mosaic is 14 times the area of the Hubble Ultra Violet Ultra Deep Field released in 2014.

Credits: NASA, ESA, P. Oesch (University of Geneva), and M. Montes (University of New South Wales)

All cats are beautiful 🐱❤️

This Is How To Bring Dark Skies Back In An Increasingly Developed World

“A dark night sky is something we not only all deserve, it’s something that we could very easily have for a relatively small investment. The benefits, in addition to long-term cost savings, education, and the environmental positives, can be taken in all at once by everyone who both lives in, or simply passes through, your town.

And for those of you still asking, “what benefit is that?” As soon as you encounter your first dark sky community, you’ll see for yourself that there’s no explanation required. To take it all in, just look up.”

When was the last time you saw the Milky Way? If you’re like 99% of the United States or Europe, it wasn’t from your own backyard. While you might assume that’s because we need to have well-lit areas where most of us live, that’s only partially correct. It’s because we choose to have brightly-lit areas to meet our safety and commercial nighttime needs, but there’s a fundamental difference between well-lit and brightly-lit. More than 20 independent communities have taken all the steps necessary to restore darkness to their areas, following the recommendations and getting certified by the IDA: the International Dark Sky Association.

Forget about asking, “why aren’t there more?” Instead, try being the change you want to see, and work to bring dark skies, as well as health and environmental benefits, back to your own community!