Universe Today

February 20, 2010December 24, 2015 by Jean Tate

ESA’s Tough Choice: Dark Matter, Sun Close Flyby, Exoplanets (Pick Two)

Thales Alenia Space and EADS Astrium concepts for Euclid (ESA)

Key questions relevant to fundamental physics and cosmology, namely the nature of the mysterious dark energy and dark matter (Euclid); the frequency of exoplanets around other stars, including Earth-analogs (PLATO); take the closest look at our Sun yet possible, approaching to just 62 solar radii (Solar Orbiter) … but only two! What would be your picks?

These three mission concepts have been chosen by the European Space Agency’s Science Programme Committee (SPC) as candidates for two medium-class missions to be launched no earlier than 2017. They now enter the definition phase, the next step required before the final decision is taken as to which missions are implemented.

These three missions are the finalists from 52 proposals that were either made or carried forward in 2007. They were whittled down to just six mission proposals in 2008 and sent for industrial assessment. Now that the reports from those studies are in, the missions have been pared down again. “It was a very difficult selection process. All the missions contained very strong science cases,” says Lennart Nordh, Swedish National Space Board and chair of the SPC.

And the tough decisions are not yet over. Only two missions out of three of them: Euclid, PLATO and Solar Orbiter, can be selected for the M-class launch slots. All three missions present challenges that will have to be resolved at the definition phase. A specific challenge, of which the SPC was conscious, is the ability of these missions to fit within the available budget. The final decision about which missions to implement will be taken after the definition activities are completed, which is foreseen to be in mid-2011.
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Euclid is an ESA mission to map the geometry of the dark Universe. The mission would investigate the distance-redshift relationship and the evolution of cosmic structures. It would achieve this by measuring shapes and redshifts of galaxies and clusters of galaxies out to redshifts ~2, or equivalently to a look-back time of 10 billion years. It would therefore cover the entire period over which dark energy played a significant role in accelerating the expansion.

By approaching as close as 62 solar radii, Solar Orbiter would view the solar atmosphere with high spatial resolution and combine this with measurements made in-situ. Over the extended mission periods Solar Orbiter would deliver images and data that would cover the polar regions and the side of the Sun not visible from Earth. Solar Orbiter would coordinate its scientific mission with NASA’s Solar Probe Plus within the joint HELEX program (Heliophysics Explorers) to maximize their combined science return.

Thales Alenis Space concept, from assessment phase (ESA)

PLATO (PLAnetary Transit and Oscillations of stars) would discover and characterize a large number of close-by exoplanetary systems, with a precision in the determination of mass and radius of 1%.

In addition, the SPC has decided to consider at its next meeting in June, whether to also select a European contribution to the SPICA mission.

SPICA would be an infrared space telescope led by the Japanese Space Agency JAXA. It would provide ‘missing-link’ infrared coverage in the region of the spectrum between that seen by the ESA-NASA Webb telescope and the ground-based ALMA telescope. SPICA would focus on the conditions for planet formation and distant young galaxies.

“These missions continue the European commitment to world-class space science,” says David Southwood, ESA Director of Science and Robotic Exploration, “They demonstrate that ESA’s Cosmic Vision programme is still clearly focused on addressing the most important space science.”

Source: ESA chooses three scientific missions for further study

February 20, 2010December 24, 2015 by Jean Tate

Ozone on Mars: Two Windows Better Than One

An illustration showing the ESA's Mars Express mission. Credit: ESA/Medialab)

Understanding the present-day Martian climate gives us insights into its past climate, which in turn provides a science-based context for answering questions about the possibility of life on ancient Mars.

Our understanding of Mars’ climate today is neatly packaged as climate models, which in turn provide powerful consistency checks – and sources of inspiration – for the climate models which describe anthropogenic global warming here on Earth.

But how can we work out what the climate on Mars is, today? A new, coordinated observation campaign to measure ozone in the Martian atmosphere gives us, the interested public, our own window into just how painstaking – yet exciting – the scientific grunt work can be.

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The Martian atmosphere has played a key role in shaping the planet’s history and surface. Observations of the key atmospheric components are essential for the development of accurate models of the Martian climate. These in turn are needed to better understand if climate conditions in the past may have supported liquid water, and for optimizing the design of future surface-based assets at Mars.

Ozone is an important tracer of photochemical processes in the atmosphere of Mars. Its abundance, which can be derived from the molecule’s characteristic absorption spectroscopy features in spectra of the atmosphere, is intricately linked to that of other constituents and it is an important indicator of atmospheric chemistry. To test predictions by current models of photochemical processes and general atmospheric circulation patterns, observations of spatial and temporal ozone variations are required.

The Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars (SPICAM) instrument on Mars Express has been measuring ozone abundances in the Martian atmosphere since 2003, gradually building up a global picture as the spacecraft orbits the planet.

These measurements can be complemented by ground-based observations taken at different times and probing different sites on Mars, thereby extending the spatial and temporal coverage of the SPICAM measurements. To quantitatively link the ground-based observations with those by Mars Express, coordinated campaigns are set up to obtain simultaneous measurements.

Infrared heterodyne spectroscopy, such as that provided by the Heterodyne Instrument for Planetary Wind and Composition (HIPWAC), provides the only direct access to ozone on Mars with ground-based telescopes; the very high spectral resolving power (greater than 1 million) allows Martian ozone spectral features to be resolved when they are Doppler shifted away from ozone lines of terrestrial origin.

A coordinated campaign to measure ozone in the atmosphere of Mars, using SPICAM and HIPWAC, has been ongoing since 2006. The most recent element of this campaign was a series of ground-based observations using HIPWAC on the NASA Infrared Telescope Facility (IRTF) on Mauna Kea in Hawai’i. These were obtained between 8 and 11 December 2009 by a team of astronomers led by Kelly Fast from the Planetary Systems Laboratory, at NASA’s Goddard Space Flight Center (GSFC), in the USA.

About the image: HIPWAC spectrum of Mars’ atmosphere over a location on Martian latitude 40°N; acquired on 11 December 2009 during an observation campaign with the IRTF 3 m telescope in Hawai’i. This unprocessed spectrum displays features of ozone and carbon dioxide from Mars, as well as ozone in the Earth’s atmosphere through which the observation was made. Processing techniques will model and remove the terrestrial contribution from the spectrum and determine the amount of ozone at this northern position on Mars.

The observations had been coordinated in advance with the Mars Express science operations team, to ensure overlap with ozone measurements made in this same period with SPICAM.

The main goal of the December 2009 campaign was to confirm that observations made with SPICAM (which measures the broad ozone absorption spectra feature centered at around 250 nm) and HIPWAC (which detects and measures ozone absorption features at 9.7 μm) retrieve the same total ozone abundances, despite being performed at two different parts of the electromagnetic spectrum and having different sensitivities to the ozone profile. A similar campaign in 2008, had largely validated the consistency of the ozone measurement results obtained with SPICAM and the HIPWAC instrument.

The weather conditions and the seeing were very good at the IRTF site during the December 2009 campaign, which allowed for good quality spectra to be obtained with the HIPWAC instrument.

Kelly and her colleagues gathered ozone measurements for a number of locations on Mars, both in the planet’s northern and southern hemisphere. During this four-day campaign the SPICAM observations were limited to the northern hemisphere. Several HIPWAC measurements were simultaneous with observations by SPICAM allowing a direct comparison. Other HIPWAC measurements were made close in time to SPICAM orbital passes that occurred outside of the ground-based telescope observations and will also be used for comparison.

The team also performed measurements of the ozone abundance over the Syrtis Major region, which will help to constrain photochemical models in this region.
Analysis of the data from this recent campaign is ongoing, with another follow-up campaign of coordinated HIPWAC and SPICAM observations already scheduled for March this year.

Putting the compatibility of the data from these two instruments on a firm base will support combining the ground-based infrared measurements with the SPICAM ultraviolet measurements in testing the photochemical models of the Martian atmosphere. The extended coverage obtained by combining these datasets helps to more accurately test predictions by atmospheric models.

It will also quantitatively link the SPICAM observations to longer-term measurements made with the HIPWAC instrument and its predecessor IRHS (the Infrared Heterodyne Spectrometer) that go back to 1988. This will support the study of the long-term behavior of ozone and associated chemistry in the atmosphere of Mars on a timescale longer than the current missions to Mars.

Sources: ESA, a paper published in the 15 September 2009 issue of Icarus

February 20, 2010December 24, 2015 by Jean Tate

Does Zonal Swishing Play a Part in Earth’s Magnetic Field Reversals?

Zonal swishing in the Earth's outer core (Credit: Akira Kageyama, Kobe University)

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Why does the Earth’s magnetic field ‘flip’ every million years or so? Whatever the reason, or reasons, the way the liquid iron of the Earth’s outer core flows – its currents, its structure, its long-term cycles – is important, either as cause, effect, or a bit of both.

The main component of the Earth’s field – which defines the magnetic poles – is a dipole generated by the convection of molten nickel-iron in the outer core (the inner core is solid, so its role is secondary; remember that the Earth’s core is well above the Curie temperature, so the iron is not ferromagnetic).

But what about the fine structure? Does the outer core have the equivalent of the Earth’s atmosphere’s jet streams, for example? Recent research by a team of geophysicists in Japan sheds some light on these questions, and so hints at what causes magnetic pole flips.

About the image: This image shows how an imaginary particle suspended in the liquid iron outer core of the Earth tends to flow in zones even when conditions in the geodynamo are varied. The colors represent the vorticity or “amount of rotation” that this particle experiences, where red signifies positive (east-west) flow and blue signifies negative (west-east) flow. Left to right shows how the flow responds to increasing Rayleigh numbers, which is associated with flow driven by buoyancy. Top to bottom shows how flow responds to increasing angular velocities of the whole geodynamo system.

The jet stream winds that circle the globe and those in the atmospheres of the gas giants (Jupiter, Saturn, etc) are examples of zonal flows. “A common feature of these zonal flows is that they are spontaneously generated in turbulent systems. Because the Earth’s outer core is believed to be in a turbulent state, it is possible that there is zonal flow in the liquid iron of the outer core,” Akira Kageyama at Kobe University and colleagues say, in their recent Nature paper. The team found a secondary flow pattern when they modeled the geodynamo – which generates the Earth’s magnetic field – to build a more detailed picture of convection in the Earth’s outer core, a secondary flow pattern consisting of inner sheet-like radial plumes, surrounded by westward cylindrical zonal flow.

This work was carried out using the Earth Simulator supercomputer, based in Japan, which offered sufficient spatial resolution to determine these secondary effects. Kageyama and his team also confirmed, using a numerical model, that this dual-convection structure can co-exist with the dominant convection that generates the north and south poles; this is a critical consistency check on their models, “We numerically confirm that the dual-convection structure with such a zonal flow is stable under a strong, self-generated dipole magnetic field,” they write.

This kind of zonal flow in the outer core has not been seen in geodynamo models before, due largely to lack of sufficient resolution in earlier models. What role these zonal flows play in the reversal of the Earth’s magnetic field is one area of research that Kageyama and his team’s results that will now be able to be pursued.

Sources: Physics World, based on a paper in the 11 February, 2010 issue of Nature. Earth Simulator homepage

February 19, 2010December 24, 2015 by Jerry Coffey

Atom Model

[/caption]The most widely accepted atom model is that of Niels Bohr. Bohr’s model was first introduced in 1913. This model of the atom depicts a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus much like the planets travel around the Sun, but the electrostatic forces product attraction instead of gravity. The model’s key success was in explaining the Rydberg formula for the spectral emission lines of atomic hydrogen. It is, basically, a modification of the Rutherford model used for quantum physics purposes.

The Bohr model was an improvement on older atomic models, but it too has been rendered obsolete by ongoing scientific research. Although considered to be obsolete, it is still taught as an introduction to quantum mechanics and in early secondary school science classes. Once students are advanced enough in their comprehension, they are introduced to the more accurate valence shell atom. At some time in the future this model of the atom may be proven to be too rigid in its scope.

The Bohr model built on the Rutherford theory. Rutherford proposed that electrons orbited the nucleus much like a planet around the Sun. The drawback to the theory was that based on his theory, electrons would be emitting(losing) their charge and spiral into the nucleus, making all atoms unstable. Bohr proposed several changes to that model: electrons can only travel in special orbits at a certain set of distances from the nucleus with specific energies, electrons do not continuously lose energy as they travel. They can only gain and lose energy by jumping from one allowed orbit to another, absorbing or emitting electromagnetic radiation with a frequency determined by the energy difference of the levels according to the Planck relation, and that the frequency of the radiation emitted at an orbit is the reciprocal of the classical orbit period. This model is restricted in a few ways, but does allow for classical mechanics to explain many things while having an allowance for quantum rules.

The Bohr model begins to run into problems with heavier atoms. Other shortcomings of the model are:gives an incorrect value for the ground state orbital angular momentum, fails to explain much of the spectra of larger atoms, and the model also violates the uncertainty principle because it considers electrons to have known orbits and definite a radius. These two things can not be directly known at the same time.

Here is a good ink about the Bohr atom model. Here on Universe Today we have a couple of great articles on the topic: one is about the Bohr model and the other is about Dr. Bohr himself. Astronomy Cast offers a good episode about how molecules behave in space.

February 19, 2010December 24, 2015 by Fraser Cain

Space Shuttle Photos

Want some space shuttle photos? Here are some photos that you can use for your computer wallpaper. Just click on an image to enlarge it, and then right-click and choose “Set as Desktop Background”.

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Here’s an image of the space shuttle Endeavour docked to the International Space Station. You can see how the atmosphere at the Earth’s horizon fades slowly into the blackness of space.

This is a closeup picture of the space shuttle Atlantis taken by astronauts on board the International Space Station. Many images are taken during each mission to study the shuttle and evaluate if there was any damage during the launch that could risk the lives of the crew during re-entry.

Here’s a picture of the space shuttle Atlantis landing at night in Cape Canaveral, ending mission STS-115. During this mission, astronauts attached the P3/P4 integrated truss to the International Space Station.

Here’s an image of the space shuttle Enterprise being mated to its external fuel tank and solid rocket boosters. This was for a test of the space shuttle to see how vibrations experienced during launch would affect the shuttle.

Here’s a photograph of the space shuttle Endeavour blasting off to begin mission STS-118. During this mission, Endeavour delivered the starboard truss segment S5 to the International Space Station.

We’ve written many articles about the space shuttle for Universe Today. Here’s an article about the last night launch of the shuttle, and here’s an article with some cool images from a recent shuttle mission.

If you’d like more information on the shuttle, here’s a link to NASA’s Official space shuttle page, and here’s the homepage for NASA’s Human Spaceflight.

We’ve recorded an episode of Astronomy Cast all about the space shuttle. Listen here, Episode 127: The US Space Shuttle.

February 19, 2010December 24, 2015 by Nancy Atkinson

What’s the Internet Really Like in Space?

The space chicken seen in the STS-130 execute packages.

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With the internet now part of daily life on the International Space Station, inquiring minds want to know! Can astronauts visit any websites they want, and what kinds of download speeds do they have in space? And what about that chicken, seen above, that has been gracing the STS-130 execute packages? And what’s the view from the new cupola really like? Astronauts answered those questions and more, at the joint crew news conference last night, where I had the chance to talk the crew members of Endeavour and the ISS.

“Thanks for asking about the internet!” replied ISS astronaut T.J. Creamer with a laugh. “This is a project that many people have worked on to make this possible for us, and some have pulled their hair out to make it successful, so many thanks to those folks. We have access to any website we are allowed to go to as government employees – that’s my best answer! And in terms of download speeds – you know, back in the old days, it kind of compares to 9.6 and the 14.4 kilobyte modems, so it’s not really fast enough to do large file exchange or videos, but it certainly lets us to do browsing and the fun reading we want to do, or get caught up on current events on that day. It’s a nice outreach for us, and of course you’ve heard about the Twittering which is a nice feature that we can partake in also.”

Later, Soichi Noguchi said he could keep up with results of the Olympics just like those of on the ground. Noguchi has been taking advantage of Twitter by sending several Twitpics from space.

The personal web access on the ISS takes advantage of existing communication links to and from the station provides astronauts with email, texting, Twittering and other direct private communications, which NASA says will “enhance their quality of life during long-duration missions by helping to ease the isolation associated with life in a closed environment.”

As for the chicken on the STS-130 execute packages, the STS-130 crew was perplexed. “That is possibly an inside joke that we are not on the inside of,” answered Commander George Zamka. “We don’t see the front pages, so it’s probably on the front pages of the execute package that we don’t get.”

You can see the STS-130 execute packages (and chickens) at this link.

Asked about the views from the new cupola, the astronauts waxed poetic. “It’s so hard to put into words the view that we see out those beautiful seven windows,” Kay Hire said. “It’s like comparing a black-and-white analog picture to a super high-def color picture. It’s just phenomenal what we can see out there. The most stunning thing I’ve seen so far is just some beautiful thunderstorms from above. It’s really interesting to watch the way the lightning jumps from cloud to cloud far below us.”

A view from the new Cupola, with all the window shutters open. Credit: NASA

“Getting to look out the shuttle windows and the station windows has been awesome,” added pilot Terry Virts. “But when we looked out the cupola, it’s impossible to put into words, but it took my breath away. We’ve only had a few opportunities to go down there because we have been busy inside doing work, but I think the favorite view that I’ve had has been watching a sunrise.

“At night, you can see cities if you’re over land and then when you pass into the sunlight you get the blue limb (of Earth) and then it turns into pink and different colors like that and then when the sun pops up, it’s like an instantaneous floodlight in your eyes, it kind of overwhelms you. But the view is amazing. You can sit there and perceive the entire Earth limb and you can really see the Earth has that round shape. It’s just amazing.”

ISS Commander Jeff Williams agreed. “To be able to see the entire Earth in one glance and see the entire limb of the Earth all the way around and see the spherical shape of the Earth is going to be new to us. Obviously, we’ve seen a lot of those segments of that view before, but only one segment at a time through a narrower field of view,” he said. “We have taken a lot of photography up here, we will continue to do so. The cupola will offer us a very unique and new opportunity for photography in a new way, particularly with wide angle lenses, which we’re already playing with a little bit to try to be able to share that experience with folks on Earth.”

Spacewalker Bob Behnken said the view from the cupola was as good as or maybe better than the view from a being out on an EVA.

“The reason being you actually have time to look around through all the windows,” he said. “Usually during a spacewalk, there’s a fair amount of work to get done. There wasn’t a lot of time for the sightseeing you might like to do out of a window like cupola.

“The other thing the cupola affords you is the opportunity to share some of those views with other people. We’re really limited on the photography we can do during a spacewalk, but taking one of the HD cameras or some still photos inside the cupola is really going to allow us to share those beautiful sunrises and sunsets and Earth views in general with everyone on the ground.”

You can watch the entire ISS/STS-130 news conference below.

February 19, 2010December 24, 2015 by Tammy Plotner

Weekend SkyWatcher’s Forecast: February 19-21, 2010

Weekend SkyWatcher’s Forecast: February 19-21, 2010

Greetings, fellow SkyWatchers! It’s a lunatic weekend as we head towards the Moon’s surface to study its features. Need more of a challenge? Then we’ll take a look at an area of sky where a Sakurai’s Object may have appeared. Just into stargazing? Then watch the Pleiades and the Moon dance together as our weekend ends! Whenever you’re ready, I’ll see you in the backyard…

February 19, 2010 – On this date we celebrate the 1473 birth of Nicolaus Copernicus, creator of the modern Solar System model.

‘‘Finally we shall place the Sun himself at the center of the Universe. All this is suggested by the systematic procession of events and the harmony of the whole Universe, if only we face the facts, as they say, ‘with both eyes open.’’’

Take a look at Copernican theory just as the master did:

‘‘For a traveler going from any place toward the north, that pole of the daily rotation gradually climbs higher, while the opposite pole drops down an equal amount… I shall now recall to mind that the motion of the heavenly bodies is circular, since the motion appropriate to a sphere is rotation in a circle.’’

Tonight we’ll explore a heavenly body – the Moon – as we take out binoculars or a telescope to explore “The Sea of Nectar”…

At around 1000 meters deep, Mare Nectaris covers an area of the Moon equal to that of the Great Sandhills in Saskatchewan, Canada. Like all maria, it is part of a gigantic basin which is filled with lava, and there is evidence of grabens along the western edge of the basin. While Nectaris’ basaltic flows appear darker than those in most maria, it is one of the older formations on the Moon, and as the terminator progresses you’ll be able to see where ejecta belonging to Tycho crosses its surface. For a real challenge, look for an ancient and ruined crater which lies on the southern shore of Mare Nectaris. To binoculars, Fracastorius will look like a shallow, light colored ring, but a telescope will reveal its northern wall is missing – perhaps melted away by the lava flow which formed the mare. This is all that remains of a once grand crater which was more than 117 kilometers in diameter. The tallest of its eroded walls still stand at an impressive 1758 meters, placing them as high as the base elevation of Mt. Hood, yet in places nothing more than a few ridges and low hills still stand to mark the crater’s remains. Power up and look for interior craterlets. Be sure to mark your lunar observing challenge notes with your observations! As Copernicus would have said:

‘‘Although all the good arts serve to draw man’s mind away from vices and lead it toward better things, this function can be more fully performed by this art, which also provides extraordinary intellectual pleasure.’’

February 20, 2010 – On this date in 1962, John Glenn was rocketing around Earth on his first orbit as our friends ‘‘down under’’ made history. Residents of Perth, Australia, simultaneously switched on lights as Glenn flew over—the first city spotted from space! When you’re ready, let’s change our perception of the size of the things we see on the lunar surface by exploring the edges of Mare Serenitatus – a feature that’s about the same size as the state of New Mexico.

On its southwest border stands the Haemus Mountains, which will continue on beyond the terminator. Look in their midst for the sharp punctuation of Class I Menelaus. This small crater has a brilliant west inner wall and deeply shadowed floor. Like Taruntius, Menelaus is another fine crater to watch for expansive ray systems as the terminator progresses. While the Montes Haemus look pretty impressive, they are nothing more than foothills compared to the Apennines which have yet to emerge into the sunlight. Look at Serenitatus’ northwest edge to view some real mountains! These are the Montes Caucasus, rising up to 5182 meters above the plains. Look closely at the maps and you will find this is also home to the Apollo 11, Apollo 16 and Apollo 17 landers, as well as Luna 21. It is an area that you can deeply appreciate for its historical significance. Like its earthly counterpart, the Caucasus Mountain Range has peaks that reach upwards of six kilometers – summits as high as Mount Elbrus! Nearby and slightly smaller than its terrestrial namesake, the lunar Apennine mountain range extends some 600 kilometers with peaks rising as high as five kilometers. Be sure to look for the summit of Mons Hadley, one of the tallest peaks you will see at the northern end of this chain. It rises above the surface to a height of 4.6 kilometers, making that single mountain about the size of asteroid Toutatis.

Today in 1996 also marks the discovery of Sakurai’s Object, a star in collapse.While studying Sagittarius and photographing what appeared to be a typical nova, Yukio Sakurai became only the third twentieth-century astronomer to witness a star in final helium flash. When this occurs, the star is switching its nuclear fuel from hydrogen to helium and then burning the helium to carbon in the final stage, burping forth an envelope from its interior.

If you’re up to a challenge, then wait until the Moon is set and let’s examine an open cluster where stars have gone through this same evolutionary step. Begin by identifying Delta Geminorum and hop a fist-width east for open cluster NGC 2420 (RA 07 38 23 Dec +21 34 24). This magnitude 8.5 group is visible under dark-sky conditions to binoculars as a weak, round, hazy patch and requires a mid-sized telescope to begin resolution of its long, looping chains of stars. Some members are similar to Sakurai’s Object, while others have evolved to helium depletion. Studying clusters like NGC 2420 is important: they are areas where stars are all about the same age, yet their different masses mean they evolve at different rates. Average telescopes will only see the primary stars, while large aperture notices the distinct glow of hundreds of stars on the verge of resolution. If you get the impression of a weak globular cluster, you’d be correct. With a thousand members packed into a 30-light-year sphere, a lot has happened during its 1.7-billion-year lifetime. It may have started in our own galaxy’s cluster-forming region and been thrown clear by an encounter with a large mass. Or, it might have once been part of a smaller galaxy absorbed by our own. But one thing is clear: its unusual Sun-like elements so far from where they belong make NGC 2420 a prime playground for study. Some of its members could even be blue stragglers—unions of two stars into one!

February 21, 2010 – This day in 1972, Luna 20 made a safe touchdown in the Apollonius highlands, where it captured 30 grams of surface material to return to Earth. Now it’s time to look take a closer look at Sinus Medii – the “Bay in the Middle” of the visible lunar surface.

Central on the terminator, and the adopted “center” of the lunar disc, this the point from which latitude and longitude are measured. This smooth plain may look small, but it covers about as much area as the states of Massachusetts and Connecticut combined. During full daylight temperatures in Sinus Medii can reach up to 212 degrees! On a curious note, in 1930 Sinus Medii was chosen by Edison Petitt and Seth Nicholson for a surface temperature measurement at full Moon. Experiments of this type were started by Lord Rosse as early as 1868, but on this occasion Petit and Nicholson found the surface to be slightly warmer than boiling water. Around a hundred years after Rosse’s attempt, Surveyor 6 successfully landed in Sinus Medii on November 9, 1967, and became the very first probe to “lift off” from the lunar surface.

Now, just kick back and relax as you take a closer look at what’s around the Moon to discover the Pleiades! For a great deal of western Africa, this is an occultation event – so be sure to check IOTA for times and information in your area!

Until next week? Dreams really do come true when you keep on reaching for the stars!

This week’s awesome lunar shots were done by Peter Lloyd and Greg Konkel. NGC 2420 – Credit: Palomar Observatory, courtesy of Cal Tech.

February 19, 2010December 24, 2015 by Jean Tate

Einstein’s General Relativity Tested Again, Much More Stringently

Einstein and Relativity — Albert Einstein

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This time it was the gravitational redshift part of General Relativity; and the stringency? An astonishing better-than-one-part-in-100-million!

How did Steven Chu (US Secretary of Energy, though this work was done while he was at the University of California Berkeley), Holger Müler (Berkeley), and Achim Peters (Humboldt University in Berlin) beat the previous best gravitational redshift test (in 1976, using two atomic clocks – one on the surface of the Earth and the other sent up to an altitude of 10,000 km in a rocket) by a staggering 10,000 times?

By exploited wave-particle duality and superposition within an atom interferometer!

Cesium atom interferometer test of gravitational redshift (Courtesy Nature)

About this figure: Schematic of how the atom interferometer operates. The trajectories of the two atoms are plotted as functions of time. The atoms are accelerating due to gravity and the oscillatory lines depict the phase accumulation of the matter waves. Arrows indicate the times of the three laser pulses. (Courtesy: Nature).

Gravitational redshift is an inevitable consequence of the equivalence principle that underlies general relativity. The equivalence principle states that the local effects of gravity are the same as those of being in an accelerated frame of reference. So the downward force felt by someone in a lift could be equally due to an upward acceleration of the lift or to gravity. Pulses of light sent upwards from a clock on the lift floor will be redshifted when the lift is accelerating upwards, meaning that this clock will appear to tick more slowly when its flashes are compared at the ceiling of the lift to another clock. Because there is no way to tell gravity and acceleration apart, the same will hold true in a gravitational field; in other words the greater the gravitational pull experienced by a clock, or the closer it is to a massive body, the more slowly it will tick.

Confirmation of this effect supports the idea that gravity is geometry – a manifestation of spacetime curvature – because the flow of time is no longer constant throughout the universe but varies according to the distribution of massive bodies. Exploring the idea of spacetime curvature is important when distinguishing between different theories of quantum gravity because there are some versions of string theory in which matter can respond to something other than the geometry of spacetime.

Gravitational redshift, however, as a manifestation of local position invariance (the idea that the outcome of any non-gravitational experiment is independent of where and when in the universe it is carried out) is the least well confirmed of the three types of experiment that support the equivalence principle. The other two – the universality of freefall and local Lorentz invariance – have been verified with precisions of 10^-13 or better, whereas gravitational redshift had previously been confirmed only to a precision of 7×10^-5.

In 1997 Peters used laser trapping techniques developed by Chu to capture cesium atoms and cool them to a few millionths of a degree K (in order to reduce their velocity as much as possible), and then used a vertical laser beam to impart an upward kick to the atoms in order to measure gravitational freefall.

Now, Chu and Müller have re-interpreted the results of that experiment to give a measurement of the gravitational redshift.

In the experiment each of the atoms was exposed to three laser pulses. The first pulse placed the atom into a superposition of two equally probable states – either leaving it alone to decelerate and then fall back down to Earth under gravity’s pull, or giving it an extra kick so that it reached a greater height before descending. A second pulse was then applied at just the right moment so as to push the atom in the second state back faster toward Earth, causing the two superposition states to meet on the way down. At this point the third pulse measured the interference between these two states brought about by the atom’s existence as a wave, the idea being that any difference in gravitational redshift as experienced by the two states existing at difference heights above the Earth’s surface would be manifest as a change in the relative phase of the two states.

The virtue of this approach is the extremely high frequency of a cesium atom’s de Broglie wave – some 3×10²⁵Hz. Although during the 0.3 s of freefall the matter waves on the higher trajectory experienced an elapsed time of just 2×10^-20s more than the waves on the lower trajectory did, the enormous frequency of their oscillation, combined with the ability to measure amplitude differences of just one part in 1000, meant that the researchers were able to confirm gravitational redshift to a precision of 7×10^-9.

As Müller puts it, “If the time of freefall was extended to the age of the universe – 14 billion years – the time difference between the upper and lower routes would be a mere one thousandth of a second, and the accuracy of the measurement would be 60 ps, the time it takes for light to travel about a centimetre.”

Müller hopes to further improve the precision of the redshift measurements by increasing the distance between the two superposition states of the cesium atoms. The distance achieved in the current research was a mere 0.1 mm, but, he says, by increasing this to 1 m it should be possible to detect gravitational waves, predicted by general relativity but not yet directly observed.

Sources: Physics World; the paper is in the 18 February, 2010 issue of Nature

February 19, 2010March 2, 2016 by Nancy Atkinson

Double Spaceship Sighting Alert!

Space shuttle Endeavour will undock from the ISS on late Friday (7:54 p.m. EST) or early Saturday (00:54 GMT) depending where you live, providing an opportunity to see the two spaceships flying in tandem. This is an incredible sight, and as the shuttle program comes to a close, one that will happen only about four more times. Early morning sightings are favored for those in the northern hemisphere. The two spacecraft will be seen as separate but closely-spaced points of light. The ISS is bigger, so will appear as the brighter object trailing the smaller Endeavour as they move across the sky. Double flybys will continue until the shuttle lands, currently scheduled for late Sunday or early Monday, with the two getting farther apart each day. Of course, your viewing ability will depend on cloud cover. Above, you can watch the ceremony as the shuttle crew returned to Endeavour and closed the hatches from the ISS.

To find out if you’ll be able to see spaceships in your area, there are a few different sites to check out:
Continue reading “Double Spaceship Sighting Alert!”

February 18, 2010December 24, 2015 by Jean Tate

What is a Supernova?

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What is a supernova? Well, “nova” means “new star”, and “super” means “really big”, like supermarket, so a supernova is a really bright new star. That’s where the word comes from, but today it has a rather more precise meaning, namely a once-off variable star which has a peak brightness similar to, or greater than, that of a typical galaxy.

Supernovae aren’t new stars in the sense that they were not stars before they became supernovae; the progenitor – what the star was before it went supernova – of a supernova is just a star (or a pair of stars), albeit an unusual one.

From what we see – the rise of the intensity of light (and electromagnetic radiation in general) to a peak, its decline; the lines which show up in the spectra (and the ones which don’t), etc – we can classify supernovae into several different types. There are two main types, called Type I and Type II. The difference between them is that Type I supernovae have no lines of hydrogen in their spectra, while Type II ones do.

Centuries of work by astronomers and physicists have given us just two kinds of progenitors: white dwarfs and massive (>8 sols) stars; and just two key physical mechanisms: nuclear detonation and core collapse.

Core collapse supernovae happen when a massive star tries to fuse iron in its core … bad move, because fusing iron requires energy (rather than liberates it), and the core suddenly collapses due to its gravity. A lot of interesting physics happens when such a core collapses, but it either results in a neutron star or a black hole, and a vast amount of energy is produced (most of it in the form of neutrinos!). These supernovae can be of any type, except a sub-type of Type I (called Ia). They also produce the long gamma-ray bursts (GRB).

Detonation is when a white dwarf star undergoes almost simultaneous fusion of carbon or oxygen throughout its entire body (it can do this because a white dwarf has the same temperature throughout, unlike an ordinary star, because its electrons are degenerate). There are at least two ways such a detonation can be triggered: steady accumulation of hydrogen transferred from a close binary companion, or a collision or merger with a neutron star or another white dwarf. These supernovae are all Type Ia.

One other kind of supernova: when two neutron stars merge, or a ~solar mass black hole and a neutron star merge – as a result of loss of orbital energy due to gravitational wave radiation – an intense burst of gamma-rays results, along with a fireball and an afterglow (as the fireball cools). We see such an event as a short GRB, but if we were unlikely enough to be close to such a stellar death, we’d certainly see it as a spectacular supernova!

Would you like to read more about what a supernova is? Check out these webpages: Hubblesite’s News Releases on Supernova, Supernova Cosmology Project (Lawrence Berkeley Lab), and Supernovae, Supernova Remnants (etc) (Talk Origins).

Everyone has a fascination for things which go bang!, and so you won’t be at all surprised to learn that Universe Today has many articles on supernovae, what a supernova is, etc. Here is selection for your enjoyment and education: Merging White Dwarfs Set Off Supernovae, GRB Central Engines Observed in Nearby Supernovae?, and Another Antimatter Supernova Discovered.

Astronomy Cast too has several episodes on what a supernova is; for example We’re All Made of Supernovae, and Gamma-Ray Bursts.

Reference:
NASA