General Relativity Rules: Einstein Victorious In Unprecedented Gravitational Redshift Test

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 an Exoplanet?

An exoplanet or extrasolar planet is a planet outside our solar system that orbits a star. The first evidence of an exoplanet was noted as early as 1917, but was not recognized as such. However, the first scientific detection of an exoplanet was in 1988. Shortly afterwards, the first confirmed detection was in 1992. As of 1 April 2018, there are 3,758 confirmed planets in 2,808 systems, with 627 systems having more than one planet.

The High Accuracy Radial Velocity Planet Searcher (HARPS, since 2004) has discovered about a hundred exoplanets while the Kepler space telescope (since 2009) has found more than two thousand. Kepler has also detected a few thousand candidate planets, of which about 11% may be false positives.

In several cases, multiple planets have been observed around a star. About 1 in 5 Sun-like stars have an “Earth-sized” planet in the habitable zone. Assuming there are 200 billion stars in the Milky Way, one can hypothesize that there are 11 billion potentially habitable Earth-sized planets in the Milky Way, rising to 40 billion if planets orbiting the numerous red dwarfs are included.

The least massive planet known is Draugr (also known as PSR B1257+12 A or PSR B1257+12 b), which is about twice the mass of the Moon. The most massive planet listed on the NASA Exoplanet Archive is HR 2562 b, about 30 times the mass of Jupiter, although according to some definitions of a planet, it is too massive to be a planet and may be a brown dwarf instead.

There are planets that are so near to their star that they take only a few hours to orbit and there are others so far away that they take thousands of years to orbit.

Some are so far out that it is difficult to tell whether they are gravitationally bound to the star. Almost all of the planets detected so far are within the Milky Way. Nonetheless, evidence suggests that extragalactic planets, exoplanets further away in galaxies beyond the local Milky Way galaxy, may exist. The nearest exoplanet is Proxima Centauri b, located 4.2 light-years (1.3 parsecs) from Earth and orbiting Proxima Centauri, the closest star to the Sun.

Besides exoplanets, there are also rogue planets, which do not orbit any star and which tend to be considered separately, especially if they are gas giants, in which case they are often counted, like WISE 0855−0714, as sub-brown dwarfs. The rogue planets in the Milky Way possibly number in the billions (or more).

Some planets orbit one member of a binary star system, and several circumbinary planets have been discovered which orbit around both members of binary star. A few planets in triple star systems are known and one in the quadruple system Kepler-64.

Methods of detecting exoplanets

1° Radial velocity

A star with a planet will move in its own small orbit in response to the planet’s gravity. This leads to variations in the speed with which the star moves toward or away from Earth, i.e. the variations are in the radial velocity of the star with respect to Earth. The radial velocity can be deduced from the displacement in the parent star’s spectral lines due to the Doppler effect. The radial-velocity method measures these variations in order to confirm the presence of the planet using the binary mass function.

2º Transit photometry

While the radial velocity method provides information about a planet’s mass, the photometric method can determine the planet’s radius. If a planet crosses (transits) in front of its parent star’s disk, then the observed visual brightness of the star drops by a small amount; depending on the relative sizes of the star and the planet. 

3° Direct Imaging

Exoplanets are far away, and they are millions of times dimmer than the stars they orbit. So, unsurprisingly, taking pictures of them the same way you’d take pictures of, say Jupiter or Venus, is exceedingly hard.

New techniques and rapidly-advancing technology are making it happen.

The major problem astronomers face in trying to directly image exoplanets is that the stars they orbit are millions of times brighter than their planets. Any light reflected off of the planet or heat radiation from the planet itself is drowned out by the massive amounts of radiation coming from its host star. It’s like trying to find a flea in a lightbulb, or a firefly flitting around a spotlight.

On a bright day, you might use a pair of sunglasses, or a car’s sun visor, or maybe just your hand to block the glare of the sun so that you can see other things.

This is the same principle behind the instruments designed to directly image exoplanets. They use various techniques to block out the light of stars that might have planets orbiting them. Once the glare of the star is reduced, they can get a better look at objects around the star that might be exoplanets.

4° Gravitational Microlensing

Gravitational microlensing occurs when the gravitational field of a star acts like a lens, magnifying the light of a distant background star. This effect occurs only when the two stars are almost exactly aligned. Lensing events are brief, lasting for weeks or days, as the two stars and Earth are all moving relative to each other. More than a thousand such events have been observed over the past ten years.

If the foreground lensing star has a planet, then that planet’s own gravitational field can make a detectable contribution to the lensing effect. Since that requires a highly improbable alignment, a very large number of distant stars must be continuously monitored in order to detect planetary microlensing contributions at a reasonable rate. This method is most fruitful for planets between Earth and the center of the galaxy, as the galactic center provides a large number of background stars.

5° Astrometry

This method consists of precisely measuring a star’s position in the sky, and observing how that position changes over time. Originally, this was done visually, with hand-written records. By the end of the 19th century, this method used photographic plates, greatly improving the accuracy of the measurements as well as creating a data archive. If a star has a planet, then the gravitational influence of the planet will cause the star itself to move in a tiny circular or elliptical orbit. 

Effectively, star and planet each orbit around their mutual centre of mass (barycenter), as explained by solutions to the two-body problem. Since the star is much more massive, its orbit will be much smaller. Frequently, the mutual centre of mass will lie within the radius of the larger body. Consequently, it is easier to find planets around low-mass stars, especially brown dwarfs.

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source (+ Methods of detecting exoplanets)

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images: NASA/ESA, ESO

animations: x, x, x, x, x

+ Exoplanets

Some intriguing exoplanets

(Source)

Esmeralda finding the King of Fools.

Earth: Our Oasis in Space

Earth: It’s our oasis in space, the one place we know that harbors life. That makes it a weird place – so far, we haven’t found life anywhere else in the solar system…or beyond. We study our home planet and its delicate balance of water, atmosphere and comfortable temperatures from space, the air, the ocean and the ground.

To celebrate our home, we want to see what you love about our planet. Share a picture, or several, of Earth with #PictureEarth on social media. In return, we’ll share some of our best views of our home, like this one taken from a million miles away by the Earth Polychromatic Imaging Camera (yes, it’s EPIC).

From a DC-8 research plane flying just 1500 feet above Antarctic sea ice, we saw a massive iceberg newly calved off Pine Island Glacier. This is one in a series of large icebergs Pine Island has lost in the last few years – the glacier is one of the fastest melting in Antarctica.

It’s not just planes. We also saw the giant iceberg, known as B-46, from space. Landsat 8 tracked B-46’s progress after it broke off from Pine Island Glacier and began the journey northward, where it began to break apart and melt into the ocean.

Speaking of change, we’ve been launching Earth-observing satellites since 1958. In that time, we’ve seen some major changes. Cutting through soft, sandy soil on its journey to the Bay of Bengal, the Padma River in Bangladesh dances across the landscape in this time-lapse of 30 years’ worth of Landsat images.  

Our space-based view of Earth helps us track other natural activities, too. With both a daytime and nighttime view, the Aqua satellite and the Suomi NPP satellite helped us see where wildfires were burning in California, while also tracking burn scars and smoke plumes..

Astronauts have an out-of-this-world view of Earth, literally. A camera mounted on the International Space Station captured this image of Hurricane Florence after it intensified to Category 4.

It’s not just missions studying Earth that capture views of our home planet. Parker Solar Probe turned back and looked at our home planet while en route to the Sun. Earth is the bright, round object.

Want to learn more about our home planet? Check out our third episode of NASA Science Live where we talked about Earth and what makes it so weird. 

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

Saturn, Dione, Rhea, and Epimetheus & Saturn and Enceladus.

Credit: NASA/JPL-Caltech/SSI/CICLOPS/Kevin M. Gill

10 Things: How to Photograph a Meteor Shower

Taking photographs of a meteor shower can be an exercise in patience as meteors streak across the sky quickly and unannounced, but with these tips – and some good fortune – you might be rewarded with a great photo.

These tips are meant for a DSLR or mirrorless camera, but some point-and-shoot cameras with manual controls could be used as well.

1. The Photo Op: Perseids Meteors

The Perseids are dusty remnants of comet 109P/Swift-Tuttle.

Earth passes through the comet’s invisible, multi-billion mile trail of tiny debris each year around August, creating a meteor shower of so-called “shooting stars” as the particles are vaporized in our atmosphere.

Perseid meteors already are streaking across the sky. This year’s shower peaks on a moonless summer night -from 4 pm on the 12th until 4 am on the 13th Eastern Daylight Time.

Read more on the Perseids ›

2. Get away from city lights and find a place with dark skies.

In this 30 second exposure, a meteor streaks across the sky in Spruce Knob, West Virginia, during the 2016 Perseids meteor shower. Credit: NASA/Bill Ingalls

Too much light and it will be hard for your eyes to see fainter meteors, plus your image will get flooded with the glow of light. Turning down the brightness of the camera’s LCD screen will help keep your eyes adjusted to the dark. The peak of the 2018 Perseid meteor shower occurs just after the new moon, meaning a thin crescent will set long before the best viewing hours, leaving hopeful sky watchers with a moonlight-free sky!

3. Use a tripod.

In this ten-second exposure, a meteor streaks across the sky above Washington, DC during the 2015 Perseids meteor shower, Credit: NASA/Joel Kowsky

Meteor photography requires long exposures, and even the steadiest of hands can’t hold a camera still enough for a clear shot. Heavier tripods help reduce shaking caused by wind and footsteps, but even a lightweight tripod will do. You can always place sandbags against the feet of the tripod to add weight and stability. If you don’t have a tripod, you might be able to prop your camera on or up against something around you, but be sure to secure your camera.

4. Use a wide-angle lens.

In this 30 second exposure taken with a circular fish-eye lens, a meteor streaks across the sky during the 2016 Perseids meteor shower as a photographer wipes moisture from the camera lens Friday, August 12, 2016 in Spruce Knob, West Virginia. Credit: NASA/Bill Ingalls

A wide-angle lens will capture more of the sky and give you a greater chance of capturing a meteor in your shot, while a zoom lens captures a smaller area of the sky. The odds of a meteor streaking past that small patch are lower.

5. Use a shutter release cable or the camera’s built-in timer.

Long exposures are not just for meteors. In this shot taken at Joshua Tree National Park, a hiker’s headlamp leaves a trail of light along a twilight path. Credit: National Park Service / Hannah Schwalbe

A tripod does a great job of reducing most of the shaking your camera experiences, but even the act of pressing the shutter button can blur your extended exposure. Using the self-timer gives you several seconds for any shaking from pressing the shutter button to stop before the shutter is released. A shutter release cable (without a self-timer) eliminates the need to touch the camera at all. And if your camera has wifi capabilities, you might be able to activate the shutter from a mobile device.

6. Manually focus your lens.

In this 30 second exposure, a meteor streaks across the sky during the annual Perseids meteor shower Friday, August 12, 2016 in Spruce Knob, West Virginia. Credit: NASA/Bill Ingalls

At night, autofocus will struggle to find something on which to focus. Setting your focus to infinity will get you close, but chances are you’ll have to take some test images and do some fine tuning. With your camera on a tripod, take a test image lasting a few seconds, then use the camera’s screen to review the image. Zoom in to a star to see how sharp your focus is. If the stars look like fuzzy blobs, make tiny adjustments to the focus and take another test image.

Repeat until you are happy with the result.

If your camera has a zoomable electronic viewfinder or live view option, you might be able to zoom to a star and focus without having to take a test image.

7. Aim your camera.

The Perseids appear to radiate from the constellation Perseus, visible in the northern sky soon after sunset this time of year.

Even though we don’t know when or where a single meteor will appear, we do know the general area from which they’ll originate.

Meteor showers get their name based on the point in the sky from which they appear to radiate. In the case of the Perseids, during their peak, they appear to come from the direction of the constellation Perseus in the northern sky.

8. Calculate your exposure time.

In this 20-second exposure, a meteor lights up the sky over the top of a mountain ridge near Park City, Utah. Even though this image was captured during the annual Perseid meteor shower, this “shooting star” is probably not one of the Perseid meteors, which originate from material left behind by Comet Swift-Tuttle. Instead, it’s likely one of the many bits of rock and dust that randomly fall into the atmosphere on any given night. Credit: NASA/Bill Dunford

As Earth rotates, the stars in the sky appear to move, and if your shutter is open long enough, you might capture some of that movement. If you want to avoid apparent star movement, you can follow the 500 Rule. Take 500 and divide it by the length in millimeters of your lens. The resulting number is the length of time in seconds that you can keep your shutter open before seeing star trails. For example, if you’re using a 20 mm lens, 25 seconds (500 divided by 20) is the longest you can set your exposure time before star trails start to show up in your images.

9. Experiment!

In this 30 second exposure photo, hikers find their way to the top of Spruce Knob in West Virginia to view the annual Perseids meteor shower, Friday, August 12, 2016. Credit: NASA/Bill Ingalls

Once you know the maximum exposure time, you can set your shutter priority to that length and let the camera calculate other settings for your first image. Depending on how the image turns out, you can manually adjust aperture (set it to a lower number if the image is too dark) and ISO (set it to a higher number if the image is too dark) to improve your next images. Changing only one setting at a time will give you a better understanding of how those changes affect your image.

10. Enjoy the show.

The crew of the International Space Station captured this Perseid meteor falling to Earth over China in 2011. Credit: NASA

With your camera settings adjusted, capturing that perfect photo is just a matter of time and luck. The highest rate of meteors visible per hour is in the hours after midnight and before dawn. Set up your camera next to a lounge chair or a blanket to witness the wonder of a meteor shower for yourself – and, with any luck, you’ll take home some envy-inducing shots, too!

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Loving Vincent (2017) dir. Dorota Kobiela, Hugh Welchman

Chandra Spots Extremely Long Cosmic Jet in Early Universe

http://www.sci-news.com/astronomy/chandra-extremely-long-cosmic-jet-early-universe-09436.html

All cats are beautiful 🐱❤️