May 15

NOAA’s Joint Polar Satellite System (JPSS) to revolutionize Earth-watching

By Ethan Siegel

If you wSP-Logo-300.enant to collect data with a variety of instruments over an entire planet as quickly as possible, there are two trade-offs you have to consider: how far away you are from the world in question, and what orientation and direction you choose to orbit it. For a single satellite, the best of all worlds comes from a low-Earth polar orbit, which does all of the following:

• orbits the Earth very quickly: once every 101 minutes,
• is close enough at 824 km high to take incredibly high-resolution imagery,
• has five separate instruments each probing various weather and climate phenomena,
• and is capable of obtaining full-planet coverage every 12 hours.

The type of data this new satellite – the Joint Polar Satellite System-1 (JPSS-1) — will take will be essential to extreme weather prediction and in early warning systems, which could have severely mitigated the impact of natural disasters like Hurricane Katrina. Each of the five instruments on board are fundamentally different and complementary to one another. They are:

1. The Cross-track Infrared Sounder (CrIS), which will measure the 3D structure of the atmosphere, water vapor and temperature in over 1,000 infrared spectral channels. This instrument is vital for weather forecasting up to seven days in advance of major weather events.

2. The Advanced Technology Microwave Sounder (ATMS), which assists CrIS by adding 22 microwave channels to improve temperature and moisture readings down to 1 Kelvin accuracy for tropospheric layers.

3. The Visible Infrared Imaging Radiometer Suite (VIIRS) instrument, which takes visible and infrared pictures at a resolution of just 400 meters (1312 feet), enables us to track not just weather patterns but fires, sea temperatures, nighttime light pollution as well as ocean-color observations.

4. The Ozone Mapping and Profiler Suite (OMPS), which measures how the ozone concentration varies with altitude and in time over every location on Earth’s surface. This instrument is a vital tool for understanding how effectively ultraviolet light penetrates the atmosphere.

5. Finally, the Clouds and the Earth’s Radiant System (CERES) will help understand the effect of clouds on Earth’s energy balance, presently one of the largest sources of uncertainty in climate modeling.

The JPSS-1 satellite is a sophisticated weather monitoring tool, and paves the way for its’ sister satellites JPSS-2, 3 and 4. It promises to not only provide early and detailed warnings for disasters like hurricanes, volcanoes and storms, but for longer-term effects like droughts and climate changes. Emergency responders, airline pilots, cargo ships, farmers and coastal residents all rely on NOAA and the National Weather Service for informative short-and-long-term data. The JPSS constellation of satellites will extend and enhance our monitoring capabilities far into the future.


Images credit: an artist’s concept of the JPSS-2 Satellite for NOAA and NASA by Orbital ATK (top); complete temperature map of the world from NOAA’s National Weather Service (bottom).

Apr 15

Hubble Shatters The Cosmic Record For Most Distant Galaxy

By ESP-Logo-300.enthan Siegel
The farther away you look in the distant universe, the harder it is to see what’s out there. This isn’t simply because more distant objects appear fainter, although that’s true. It isn’t because the universe is expanding, and so the light has farther to go before it reaches you, although that’s true, too. The reality is that if you built the largest optical telescope you could imagine — even one that was the size of an entire planet — you still wouldn’t see the new cosmic record-holder that Hubble just discovered: galaxy GN-z11, whose light traveled for 13.4 billion years, or 97% the age of the universe, before finally reaching our eyes.

There were two special coincidences that had to line up for Hubble to find this: one was a remarkable technical achievement, while the other was pure luck. By extending Hubble’s vision away from the ultraviolet and optical and into the infrared, past 800 nanometers all the way out to 1.6 microns, Hubble became sensitive to light that was severely stretched and redshifted by the expansion of the universe. The most energetic light that hot, young, newly forming stars produce is the Lyman-α line, which is produced at an ultraviolet wavelength of just 121.567 nanometers. But at high redshifts, that line passed not just into the visible but all the way through to the infrared, and for the newly discovered galaxy, GN-z11, its whopping redshift of 11.1 pushed that line all the way out to 1471 nanometers, more than double the limit of visible light!

Hubble itself did the follow-up spectroscopic observations to confirm the existence of this galaxy, but it also got lucky: the only reason this light was visible is because the region of space between this galaxy and our eyes is mostly ionized, which isn’t true of most locations in the universe at this early time! A redshift of 11.1 corresponds to just 400 million years after the Big Bang, and the hot radiation from young stars doesn’t ionize the majority of the universe until 550 million years have passed. In most directions, this galaxy would be invisible, as the neutral gas would block this light, the same way the light from the center of our galaxy is blocked by the dust lanes in the galactic plane. To see farther back, to the universe’s first true galaxies, it will take the James Webb Space Telescope. Webb’s infrared eyes are much less sensitive to the light-extinction caused by neutral gas than instruments like Hubble. Webb may reach back to a redshift of 15 or even 20 or more, and discover the true answer to one of the universe’s greatest mysteries: when the first galaxies came into existence!


Images credit:  (top); NASA, ESA, P. Oesch (Yale University), G. Brammer (STScI), P. van Dokkum (Yale University), and G. Illingworth (University of California, Santa Cruz) (bottom), of the galaxy GN-z11, the most distant and highest-redshifted galaxy ever discovered and spectroscopically confirmed thus far.

Apr 10

Gravitational Wave Astronomy Will Be The Next Great Scientific Frontier


By Ethan Siegel

Imagine a world very different from our own: permanently shrouded in clouds, where the sky was never seen. Never had anyone see the Sun, the Moon, the stars or planets, until one night, a single bright object shone through. Imagine that you saw not only a bright point of light against a dark backdrop of sky, but that you could see a banded structure, a ringed system around it and perhaps even a bright satellite: a moon. That’s the magnitude of what LIGO (the Laser Interferometer Gravitational-wave Observatory) saw, when it directly detected gravitational waves for the first time.

An unavoidable prediction of Einstein’s General Relativity, gravitational waves emerge whenever a mass gets accelerated. For most systems — like Earth orbiting the Sun — the waves are so weak that it would take many times the age of the Universe to notice. But when very massive objects orbit at very short distances, the orbits decay noticeably and rapidly, producing potentially observable gravitational waves. Systems such as the binary pulsar PSR B1913+16 [the subtlety here is that binary pulsars may contain a single neutron star, so it’s best to be specific], where two neutron stars orbit one another at very short distances, had previously shown this phenomenon of orbital decay, but gravitational waves had never been directly detected until now.

When a gravitational wave passes through an objects, it simultaneously stretches and compresses space along mutually perpendicular directions: first horizontally, then vertically, in an oscillating fashion. The LIGO detectors work by splitting a laser beam into perpendicular “arms,” letting the beams reflect back and forth in each arm hundreds of times (for an effective path lengths of hundreds of km), and then recombining them at a photodetector. The interference pattern seen there will shift, predictably, if gravitational waves pass through and change the effective path lengths of the arms. Over a span of 20 milliseconds on September 14, 2015, both LIGO detectors (in Louisiana and Washington) saw identical stretching-and-compressing patterns. From that tiny amount of data, scientists were able to conclude that two black holes, of 36 and 29 solar masses apiece, merged together, emitting 5% of their total mass into gravitational wave energy, via Einstein’s E = mc2.

During that event, more energy was emitted in gravitational waves than by all the stars in the observable Universe combined. The entire Earth was compressed by less than the width of a proton during this event, yet thanks to LIGO’s incredible precision, we were able to detect it. At least a handful of these events are expected every year. In the future, different observatories, such as NANOGrav (which uses radiotelescopes to the delay caused by gravitational waves on pulsar radiation) and the space mission LISA will detect gravitational waves from supermassive black holes and many other sources. We’ve just seen our first event using a new type of astronomy, and can now test black holes and gravity like never before.


Image credit: Observation of Gravitational Waves from a Binary Black Hole Merger B. P. Abbott et al., (LIGO Scientific Collaboration and Virgo Collaboration), Physical Review Letters 116, 061102 (2016). This figure shows the data (top panels) at the Washington and Louisiana LIGO stations, the predicted signal from Einstein’s theory (middle panels), and the inferred signals (bottom panels). The signals matched perfectly in both detectors.


Mar 01

What’s Up in the Sky

What’s Up in the Sky – March, 2016

In the Middle Ages (before science) it was generally believed that heavier objects would fall to Earth faster than lighter objects. Some of my students still believed that twenty years ago. Galileo Galilei thought otherwise and just to demonstrate his theory (according to legend) he went to the top of the leaning tower of Pisa and dropped a 10-pound and a 5-pound cannon ball simultaneously. They both hit the ground at the same time.

His little demonstration probably did more to get him in trouble than to convince anyone their common sense was wrong. And, thanks to Edmund Halley’s prediction that a comet would return on a certain date (it did) it would take another hundred years or so before science was generally accepted.

Fast forward to now. One of modern science’s best known prediction makers was Albert Einstein. His list of hits is impressive: the bending of light by gravity, time dilation, anomalies in the orbit of Mercury, black holes. All of them have been verified many times. One prediction, however, was so extremely difficult to test that it took over a hundred years to verify. But it has been.

On February 11, scientists working with the Laser Interferometer Gravitational-wave Observatory (LIGO) announced that gravitational waves had been detected by the instrument on September 14, 2015. The time lag is how long it took them to verify the observation.

This is a monumental confirmation of general relativity, right up there with the 1919 test of the deflection of starlight by the eclipsed Sun, which made Einstein famous (he was right that time, also). Not only has this major prediction been verified, but also a new and unprecedented window into the cosmos has been opened.

Gravitational waves can be described as “ripples in the fabric of spacetime” and arrive at Earth after traveling for billions of years from the distant universe. Their existence was first demonstrated in the 1970s and 80s when scientists observing a pulsar and neutron star orbiting each other noticed that the orbit of the pulsar was slowly shrinking. They also showed that this was due to the release of energy in the form of gravitational waves and that measurements of gravitational waves would now be possible.

And that’s exactly what happened. The LIGO detectors are rather amazing pieces of technology. Each consists of two 4 km long, 4-ft diameter tubes kept at an almost perfect vacuum at right angles to each other. Two beams of laser light travel the lengths of the tubes to measure the distance between two precisely placed mirrors at the ends of the arms. According to Einstein, a gravitational wave passing the detector will cause the distance between the mirrors to change infinitesimally. The instrument is so sensitive that it can measure changes as small as one ten-thousandth the diameter of a proton!

Two such instruments are used, one in Washington and one in Louisiana, to determine the direction from which the waves originated and to rule out other possible sources. Interestingly, each had just undergone a major upgrade that increased its sensitivity and they were on their first observational run. Not bad for a first try.

Scientists are anxious to have more such devices at locations around the globe to give them an even better understanding of what’s up in the sky.

Feb 15

What’s Up in the Sky

What’s Up in the Sky – February, 2016

Planets and Stars in February

By now you have undoubtedly heard about the five planets visible in the morning sky so I will offer a few tips for successful viewing.

Go out about an hour before sunrise and look toward the southeast. There you will see the planet Venus, by far the brightest object in the sky, other than the Moon of course. Over in the southwest look for the second brightest non-lunar object, Jupiter. In between Venus and Jupiter are Mars and Saturn. Now, these guys have been visible for most of the winter, but what makes this alignment special is that they are now being joined by Mercury, just to the east (left) of Venus.

The show will continue through mid-February but you can use the Moon for the first week of the month to locate the dim planets in case you are unsure which is which. On February first, it will be close to Mars, on the third it will be just above Saturn, and on the sixth it will be near the eastern horizon very close to Mercury and Venus. In fact, that will probably your best chance to spot Mercury as it is normally faint and lost in the glare of the rising Sun. The best time will probably be 7:20 – 7:30 a.m. each morning.

You may have also heard about the “discovery” of a new planet, “Planet 9”. According to New Horizons project scientist and Holland resident, Harold Reitsema, “this is an interesting possibility but far from a “Discovery”. We don’t know much at all about (Kuiper Belt Objects or) their typical orbits. So this is really speculation. Educated speculation, but speculation none the less.” Clearly further study is needed.

If you are not a morning person, there is still plenty to see in the sky in the evening. In fact, February is one of the best month for stargazing, in spite of the cold weather. Facing south you will surely spot our old friend, Orion, the Hunter, with his distinctive group of four bright stars bisected by three stars that make up his belt and three fainter stars forming his sword.

You can use Orion as a guide to find lots of other cool stuff. Follow the line of belt stars down toward the horizon to find Sirius (as if you need guide stars . . . it’s the brightest star in the sky), and up toward the right to find the star Aldebaran and the V-shaped group of stars that form the head of the constellation Taurus, the Bull.

Finally, follow the line formed by the top two stars in Orion’s shoulders eastward to Procyon then continue straight up to Castor and Pollux. Complete your circle tour with Capella, a yellow/gold star almost directly overhead in the constellation Auriga. For added interest, bring along a pair of binoculars and just scan the area for nebulae and star clusters. Let the stars be your guide to what’s up in the sky.

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