Posted on by Jean Tate

Pioneer Anomaly

Artist impression of the Pioneer 10 probe (NASA)

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Named after the Pioneer 10 and 11 space probes, the Pioneer anomaly refers to the fact that they seem to be moving a teensy bit different from how we think they should be moving (or, more technically, the spacecraft seem to be subject to an unmodeled acceleration whose direction is towards the Sun).

The anomaly was first noticed, by John Anderson, in 1980, when analysis of tracking data from the spacecraft showed a small, unexplained acceleration towards the Sun (this was first published in 1995, with the main paper appearing in 1998). Since then it has been studied continuously, by quite a few scientists.

The Pioneer anomaly is one of the (very few!) true mysteries in contemporary physics, and is a great example of how science is done.

The first step – which Anderson and colleagues took – was to work out where the spacecraft were, and how fast they were traveling (and in what direction), at as many times as they could. Then they estimated the effects of gravity, from all known solar system objects (from the Sun to tiny asteroids and comets). Then they estimated the effects of things like radiation pressure, and possible outgassing. Then … They also checked whether other spacecraft seemed to have experienced a similar anomalous acceleration (the net: not possible to get an unambiguous answer, because all others have known – but unmodelable – effects much bigger than the Pioneer anomaly). Several independent investigations have been conducted, using different approaches, etc.

In the last few years, much effort has gone into trying to find all the raw tracking data (this has been tough, many tapes have been misplaced, for example), and into extracting clean signals from this (also tough … the data were never intended to be analyzed this way, meta-data is sorely lacking, and so on).

And yet, the anomaly remains …

… there’s an unmodeled acceleration of approximately 9 x 10-10 m/s2, towards the Sun.

The Planetary Society has been funding research into the Pioneer anomaly, and has a great summary here! And you can be a fly on the wall at a meeting of a team of scientists investigating the Pioneer anomaly, by checking out this Pioneer Explorer Collaboration webpage.

Universe Today has several stories on the Pioneer anomaly, for example The Pioneer Anomaly: A Deviation from Einstein Gravity?, Is the Kuiper Belt Slowing the Pioneer Spacecraft?, and Ten Mysteries of the Solar System.

Astronomy Cast has two episodes covering the Pioneer anomaly, The End of Our Tour Through the Solar System, and the November 18th, 2008 Questions Show.

Source:
The Planetary Society

Posted on by Fraser Cain

Pictures of Alaska

Northern Alaska

Here are some pictures of Alaska, taken from space by a variety of Earth observation satellites. These satellites capture images of Alaska to help scientists understand the natural processes that shape our planet. But, in our case, they also make for really pretty pictures.

This is a picture of Alaska; the Brooks Range in Northern Alaska. This picture was taken by the true-color Moderate Resolution Imaging Spectroradiometer on board NASA’s Terra satellite, which was launched in 1999. The Beaufort Sea is at the top of the image.

Alaska and Northwest Canada

This is an image of the point between Alaska and Northwest Canada. You can see the sea ice off the coast of Northern Alaska. This image was taken in Spring, as the northern tundra is just starting to be visible under the melting snow.

Eastern Alaska

This is a photograph of Eastern Alaska. You can see the Aleutian Islands and Kodiak Island, as well as the Yukon River. The cloud bank is hiding a plankton bloom in Bristol Bay.

This is a satellite photo of the Coast of Alaska. Perhaps the most famous feature is Prince William Sound, the site of the Exxon oil tanker spill. The lighter colors in the ocean comes from sediment coming off the ground and being carried into the ocean by currents.

Aurora Over Alaska

Of course, one of the most famous features of Alaska are the spectacular Northern Lights. This image was captured by Joshua Strang at an air base in Alaska. We see the Northern Lights when particles from the Sun’s solar wind are channeled by the Earth’s magnetic field, creating ionized particles in the upper atmosphere.

We’ve written many articles about Alaska for Universe Today. Here’s an article about the recent eruption of Alaska’s Redoubt volcano, and more information about ice loss in Alaska.

If you’d like more Alaska photos, check out Visible Earth Homepage. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Posted on by Steve Nerlich

Astronomy Without A Telescope – More Than Meets The Eye

Whatever hectic pressures may be at play in your life, you can always look forward to one quiet moment each week to contemplate the night sky in peace. I refer, of course, to when you have to take out the garbage – or as the Americans would have it – the trash.

Bin night observing receives less attention than perhaps it should in the astronomical literature. The chance to check the night sky once a week and at about the same hour gives you a chance to experience the difference between solar and sidereal time since the same stars now rise about 28 minutes earlier they did last week. And of course, you can quickly check the ecliptic for planets and for the Moon’s phase if it’s up.

Rarely, there may also be opportunities for educational outreach. A neighbor, aware of my astronomical tendencies, once asked me whatever happened to the Milky Way, which she recalled seeing as a child. I didn’t consider this a dumb question, since I remember seeing it as a kid too – it really is a ghost of its former self.

We had a useful chat about light pollution and then she said it. What’s that red one? Is it Mars? Not being on the ecliptic, it wasn’t – and the proximity of Orion’s Belt was a bit of a give-away. It’s Betelgeuse, I told her and she remembered the name from a Douglas Adams story and then we said good night. Astronomy advocacy in sixty seconds.

Betelgeuse image reconstructed from interferometry measurements in infra red. Credit: Xavier Haubois (Observatoire de Paris) et al. (An APOD for January 6 2010).

But I hate that color thing. I’ve spent years unsuccessfully squinting to make out the allegedly red color of Mars or the yellowish tinge of Saturn – while as soon as I get someone interested in the night sky they start picking out M type supergiants. I’m not color blind and I manage just fine in the daytime. But bin nights have always been a strictly black and white affair.

That is until now. I saw that Mythbusters episode about how early sailors wore an eye patch so that during a cannon battle they always had one dark-adapted eye. Allegedly, this was so they could go into the powder room for more ammunition without having to light a match.

As you probably know it’s all about the rods and the cones in your retina. The cones carry three types of photopsins – that preferentially absorb red, green and blue, while the rods carry the all important rhodopsin – which enables you to see in very dim light, though just in black and white. Apparently, it takes rhodopsin 30 mins to recover from light bleaching, but only nine minutes for the photopsins. Nine minutes is all I need to decant the kitchen scraps, grab the recyclables and wheel the bins out to the kerb. Then patch off, I can enjoy an opsins-optimized, monocular view of the night sky and yep, there’s a little hint of orangey-red. Awesome.

You should try it. In fact I’d be grateful if everyone would try it and spread the word. So the next time someone in my street asks… Who’s that nut taking out his garbage dressed like a pirate? There’ll be someone nearby to explain… It’s OK. He’s an astronomer.

Posted on by Tammy Plotner

Weekend SkyWatcher’s Forecast – January 22-24, 2010

Greetings, fellow SkyWatchers! I don’t know about everyone else, but most observations here have been of the big M0. Clouds, clouds and more clouds! Perhaps we’re really in a nebula? However, for those fortunate few that do have clear skies, let’s take a look at what’s happening on the lunar surface each night. And, since we’ve got to deal with a little “Moonlight Sonata”, we’ll also inspect some bright stars and alternative catalog studies to add to your knowledge and pleasure of the night sky! Whenever you are ready, dust off your optics and I’ll meet see you in the backyard….

January 22, 2010: Start the astronomical day by observing the 1592 birth on this date of Pierre Gassendi, French scientist, mathematician, philosopher… and the first to use a Galilean telescope to observe a Mercury transit by the projection method. Gassendi was a prodigious observer, known for his humor, and was friends with Cassini, Galileo, Hevelius, and Kepler. His writings included work on falling bodies – a rare coincidence, since the only known piece of ‘‘space junk’’ to ever re-enter our atmosphere and strike a human occurred on the 405th anniversary of his birth!

Let’s begin our weekend by taking a look with binoculars at the first quarter Moon and see what we can discover… First repeat our first litany: #1—Mare Crisium, #2—Mare Fecunditatis, and #3—Mare Nectaris. Head north to the huge area of #4, Mare Tranquillitatis, which appears with its irregular borders. Beneath the smooth appearing regolith, the ‘‘Tranquil Sea’’ basin is cracked and overlapped by accompanying basins – lava spilling and flowing into other areas as large as the Kimberley region of Australia, or three times larger than England! Now, #5 Mare Serenitatis, the ‘‘Sea of Serenity.’’ Home to a violent past, its outer edges appear darker than the interior—mute testimony to continued seismic and volcanic activity allowing the basin to fill with lava more than once. Take a telescopic look at the rilles adorning this lunar desert, whose surface is the size of Italy. Then go north for #6, Mare Frigoris, the ‘‘Sea of Cold.’’ Congratulations on another learning exercise and if you’re thinking about how cold you are, think about how cold you’d be if you were observing Earth from Mare Frigoris!

Now open your eyes and let’s head for the star on Orion’s western shoulder, Gamma. Named Bellatrix, the 243 light-year distant ‘‘Amazon’’ is not actually part of the Orion association. Gamma is a foreground star and is the hottest of its type visually observable. Historically this star was used as a luminosity standard to compare with other stars to check for variability. But it was later discovered that Bellatrix itself is an eruptive variable, changing in luminosity by a few percent over time. It ranges in magnitude from 1.59 to 1.64. Sure, it’s a minor change – but still a change! There are a couple of types of eruptive variable stars, some with a broad range of increase in luminosity and a fixed time line. These types of eruptive variables include flare stars – very faint stars on the main sequence; novae and dwarf novae – which are caused by the sharing of material between evolved stars in binary systems; and supernovae – the violent and uber brilliant end for several classes of star.


Use binoculars to spot a fainter star about a half degree northeast and say hello to alternative catalog study Dolidze 21 (RA 05 26 50 Dec +06 58 30). This loose association of stars contains a few solar types, and many stars fainter than small optics can resolve – an unusual observation for your notes. Here we have what is considered a “poor” open cluster. Not because it isn’t nice – but because it isn’t populous. It is home to around 20 or so low wattage stars of mixed magnitude with no real asterism to make it special.

January 23, 2010: On the Moon the clockwork movement of the terminator has slowly marched across the surface, revealing more lunar landscape and its 12 maria for exploration. While it ticks along the ecliptic, Luna is passing by other orbiting bodies. Want a challenge? Then we’ll pass on the Moon and aim binoculars towards the constellation of Leo and take on an asteroid! Although Vesta isn’t as exciting, now is a good time to practice observing these rocky Solar System bodies. Spinning completely on its axis about every 5.5 hours and spanning 525 kilometers, this Arizona-sized minor planet is a treat for amateurs because its surface is highly reflective. At times Vesta can reach near unaided-eye visibility, but moonlight steals away fainter objects from easy view. Chances are very good that even in a starry field Vesta will be one of the brightest points visible. See if you can discover Vesta tonight!

Looking for an unusual star to spark your imagination? Then set your sights on the westernmost star of Orion’s ‘‘belt’’ – Mintaka. Like clockwork, astronomical objects can also keep incredibly accurate time. Located around 1,500 light-years away, Delta Orionis is a multiple star system: its companion star is almost equal in brightness and orbiting at a clockwork rate of 5.7325 days from only 8 million kilometers away. In astronomical terms, these two white-hot suns are nearly touching! Mintaka is a prime example of a spectroscopic binary star – a pair so close they are only detectable by changes in the stars’ spectra. Its stationary spectral lines proved the existence of interstellar matter! Take a closer look, and Delta Orionis will reveal a visible 6.7 magnitude companion to its north – a challenge well suited to small optics.

January 24, 2010: Tonight, let’s take time to work toward learning more major lunar features by sailing across 12 seas. The key to learning is to repeat these again and again: #1: Mare Crisium, #2: Mare Fecunditatis, #3: Mare Nectaris, #4: Mare Tranquillitatis, #5: Mare Serenitatis, and #6: Mare Frigoris. Excellent work! Now let’s go have a closer look at #7: Mare Imbrium. Identical in size to Saudi Arabia and about one-fourth the size of the United States, the ‘‘Sea of Rains’’ basin was formed 38 million years ago during a dramatic impact causing a Moon-wide series of faults. The massive strike shattered the lithosphere to a depth of 100 kilometers, embedding the impactor as a mascon. Seismic waves traveled through the interior—re-shaping the far side and creating magnetic anomalies—while the basin floor rebounded and flung ejecta 800 kilometers away. Over 500 million years, at least three areas of distinct lava flow poured into the impact basin (the oldest and largest about 1,200 kilometers long), far out-producing any earthly volcano. The youngest and smallest is about 400 kilometers in length, matching our terrestrial Columbia River Flood Basalt, an area stretching from Idaho to the Pacific Ocean! Now, here are some more to learn: #8: Mare Vaporum, #9: Mare Insularum, #10: Mare Cognitum, #11: Mare Nubium, and #12: Mare Humorum. Remember: repeat, repeat, repeat!

Now turn your eyes towards Orion and its Alpha star – Betelgeuse. Early in the evening, Orion the ‘‘Hunter’’ is beginning its journey across the night sky. Alpha stands out as an orangish star in the northeastern corner. It is a giant among stars! Betelgeuse has a long literary history and was one of the most massive stars known. In the mid-1800s, John Herschel observed that Betelgeuse varied in brightness, its light intensity changing by as much as a magnitude in under 6 years. The red giant is continually contracting and expanding to a formidable size – one that would fill the orbit of Jupiter around our own small star. But, it’s not alone…. Alpha also has four companion suns! Estimated to be 6 million years old, the light you see tonight from Betelgeuse left the
star around the time Nostradamus was making his predictions. Should it go supernova tomorrow, it would be almost another half century before this spectacular sight would be seen in our night sky!

Until next week? Ask for the Moon… But keep on reaching for the stars!

This week’s awesome images are an historical photo of Gassendi, lunar images we done by Greg Konkel. Stellar and cluster images are from Palomar Observatory, courtesy of Caltech and the Betelgeuse diagram is courtesy of NASA. We thank you so much!

Posted on by Jean Tate

Nucleosynthesis

‘Nucleo-‘ means ‘to do with nuclei’; ‘synthesis’ means ‘to make’, so nucleosynthesis is the creation of (new) atomic nuclei.

In astronomy – and astrophysics and cosmology – there are two main kinds of nucleosynthesis, Big Bang nucleosynthesis (BBN), and stellar nucleosynthesis.

In the amazingly successful set of theories which are popularly called the Big Bang theory, the early universe was very dense, and very hot. As it expanded, it cooled, and the quark-gluon plasma ‘froze’ into neutrons and protons (and other hadrons, but their role in BBN was marginal), which interacted furiously … lots and lots of nuclear reactions. The universe continued to cool, and soon became too cold for any further nuclear reactions … the unstable isotopes left then decayed, as did the neutrons not already in some nucleus or other. Most matter was then hydrogen (actually just protons; the electrons were not captured to form atoms until much later), and helium-4 (alpha particles) … with a sprinkling of deuterium, a dash of helium-3, and a trace of lithium-7.

That’s BBN.

The atoms in your body – apart from the hydrogen – were all made in stars … by stellar nucleosynthesis.

Stars on the main sequence get the energy they shine by from nuclear reactions in their cores; off the main sequence, the energy comes from nuclear reactions in a shell (or more than one shell) around the core. There are several different nuclear reaction cycles, or processes (e.g. triple alpha, s process, proton-proton chain, CNO cycle), but the end result is the fusion of hydrogen (and helium) to produce carbon, nitrogen, oxygen, … and the iron group (iron, cobalt, nickel). In the red giant phase of a star’s life, much of this matter ends up in the interstellar medium … and one day in your body.

There are other ways new nuclei can be created, in the universe (other than BBN and stellar nucleosynthesis); for example, when a high energy particle (a cosmic ray) collides with a nucleus in the interstellar medium (or the Earth’s atmosphere), it breaks it into two or more pieces (this process is called cosmic ray spallation). This produces most of the lithium (apart from the BBN 7Li), beryllium, and boron.

And one more: in a supernova, especially a core collapse supernova, huge quantities of new nuclei are synthesized, very quickly, in the nuclear reactions triggered by the flood of neutrons. This ‘r process’, as it is called (actually there’s more than one) produces most of the elements heavier than the iron group (copper to uranium), directly or by radioactive decay of unstable isotopes produced directly.

Like to learn more? Here are a few links that might interest you: Nucleosynthesis (NASA’s Cosmicopia), Big Bang Nucleosynthesis (Martin White, University of California, Berkeley), and Stellar Nucleosynthesis (Ohio University).

Plenty of Universe Today stories on this topic too; for example Stars at Milky Way Core ‘Exhale’ Carbon, Oxygen, Astronomers Simulate the First Stars Formed After the Big Bang, and Neutron Stars Have Crusts of Super-Steel.

Check out this Astronomy Cast episode, tailor-made for this Guide to Space article: Nucleosynthesis: Elements from Stars.

Sources:
NASA
Wikipedia
UC-Berkeley

Posted on by Ken Kremer

Endeavour aiming for on time launch with coolant hose fix ahead of schedule

STS 130 Crew of Endeavour at Pad 39 A press briefing. Credit: NASA

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The crew of Endeavour said on Wednesday (Jan 20) that construction of new coolant hoses required to connect the new Tranquility module, or Node 3, to the space station is running ahead of schedule and they are optimistic for an on time launch of the STS 130 mission currently set for Feb 7.

Shortly after I attended the rollout to pad 39 A, the launch was thrown into doubt when a set of the 14 ft long external ammonia jumper hoses, which convey coolent critical for temperature control, ruptured during high pressure testing in early January. Tranquility cannot be fully activated until the ammonia lines are installed and functioning properly. Since then, tiger teams of engineers and technicians working at the hose subcontractor and at NASA’s Marshall Spaceflight Center in Huntsville, Ala have worked vigorously to qualify four new replacement hoses. They are also working to modify the original ammonia hoses which will be brought along as a back-up “Plan B” in case problems develop with the new replacement hoses.

Endeavour was rolled out to Pad 39 A during a frigid morning on Jan 6, 2010. Credit: Ken Kremer

During a launch pad press conference with reporters, lead Endeavour spacewalker Robert Behnken said, “We’ve been following these ammonia lines and the story associated with them for 13 months. I think folks paying close attention right now haven’t really heard the entire story. So we’ve been watching them closely for a long time now.”

“Last weekend our crew was at Marshall to see the first line as it was coming together and actually put it on a test rig to make sure it was going to do the job that it was intended. We’re expecting this Saturday to fly up and see all four lines in a pretty good configuration, pretty flight representative. Those lines, after that, will come down here to KSC for processing and installation into the orbiter.”

“Right now, the schedule appears for that set of lines to be a couple of days ahead,” Behnken added. “Our original plan was to do our fit check and our opportunity with them next weekend. But they’re ahead now and we’ll be able to do that this Saturday, which is great news.”

“The program is also pursuing a second set of lines that would allow us to launch at a slightly delayed launch date and still maintain a full capability for Node 3 [Tranquility]. So the program is pursuing two courses. Plan 1 is actually ahead of schedule which allows us to do a fit check a week early. That’s really good news as we move forward to flight”, he concluded.

Tranquility is the primary cargo being lofted in the payload bay of shuttle Endeavour and will be delivered to the International Space Station by the six person crew. During three spacewalks, astronaut teams will attach and activate Tranquility and the Cupola observation module which is joined to Tranquility at one end. The modules were loaded into Endeavour’s payload bay on Wednesday (Jan. 20). See my recent photos of Tranquility and Cupola from inside the Space Station Processing Facility at KSC in earlier reports here and here.

Today (Jan 21), the STS 130 astronauts took part in a mock countdown known as the TCDT, or Terminal Countdown Demonstration Test. While dressed in their orange spacesuits they climbed inside Endeavour at pad 39 A to rehearse all the actual launch procedures right up to the T minus 4 minute point , but not including the point of liftoff. They also practiced emergency evacuation safety procedures in case of a launch pad abort requiring them to rapidly depart the orbiter in a life or death situation and enter the slidewire escape baskets. The crew flies back to Houston on Friday for final pre flight training exercises.

The six person crew comprises of commander George “Zambo” Zamka, pilot Terry Virts, and mission specialists Kathryn Hire, Stephen Robinson, Nicholas Patrick and Robert Behnken.

Senior shuttle managers will meet at KSC on Jan. 27 for an executive-level Flight Readiness Review. They will conduct an in-depth assessment to determine whether the shuttle, crew, payloads and the problematical ammonia lines are fit for launch. Thereafter the team will set an official launch date, which for now is still targeted for Feb 7.

Meanwhile it’s likewise been a busy time up in space for the 5 man crew of Expedition 22 currently in residence aboard the ISS as they conduct essential preparatory work over the next few days which must be completed before Endeavour launches and also to free up the docking port for Tranquility.

Russian cosmonaut Oleg Kotov conducts an EVA on Jan 14 to prepare the Poisk module for future dockings at the ISS. Credit: NASA

Soyuz TMA-16 spacecraft moves from the aft port of the International Space Station's Zvezda service module to the Poisk module. Credit: NASA TV
ISS commander Jeffrey Williams and cosmonaut Max Suraev boarded their Soyuz TMA-16 spacecraft today in order to relocate it to a different docking port. First they undocked from the aft port of the Russian built Zvezda service command module and then maneuvered the capsule over to redock at the Poisk module, which is russia’s newest pressurized module and which is connected to Zvezdas zenith, space facing port. This marked the first spacecraft docking at Poisk.

Earlier STS 130 article by Ken Kremer from KSC

STS 130 flight pressing forward to launch as NASA resolves coolant hose leak

STS-130 Shuttle flight facing delay due to Payload technical glitch

Shuttle Endeavour Rolled to Pad; Countdown to the Final Five Begins

Tranquility Module Formally Handed over to NASA from ESA

Posted on by universetoday

Apollo 11 Pictures

Apollo 11 Crew Photo. Credit: NASA

Here are some Apollo 11 pictures; of the crew, the spaceships and the Moon landing.

Here’s a picture of the Apollo 11 crewmembers. On the left is Commander Neil Armstrong, the first person to walk on the Moon. In the middle is Command Module Pilot Michael Collins, and then Lunar Module Pilot Buzz Aldrin on the right.

Saturn V

This is a picture of the Saturn V rocket. This was the booster that carried Apollo 11 from the Earth to the Moon. Over the course of the Apollo program, NASA launched a total of thirteen Saturn V rockets.

Lunar Module

Here’s a picture of the Apollo 11 Lunar Module “Eagle”. This is the spacecraft that the astronauts used to descend from lunar orbit down to the surface of the Moon.

Lunar Experiments

Here’s a picture of Buzz Aldrin standing on the surface of the Moon during Apollo 11. You can see an experiment in front of Aldrin designed to detect “moonquakes”. And then there’s the Eagle Lunar Module in the background.

US Flag on the Moon

Here’s a picture of Aldrin standing beside the US flag placed on the Moon. There’s no wind on the Moon, so there’s a metal support bar holding up the flag.

Once they returned from the Moon, the crew of Apollo 11 were put into quarantine, in case they brought back any kind of lunar bacteria or viruses. This turned out to be unnecessary, and didn’t happen for future missions.

We’ve written many articles about Apollo 11 for Universe Today. Here’s an article about the astronauts reflecting back on their experience at the 40th anniversary, and here’s another look at the Apollo 11 landing site from lunar orbit.

If you’d like more info on Apollo 11, check out NASA’s 30th anniversary site here, and here’s the 40th anniversary page.

We’ve also recorded an episode of Astronomy Cast about the Apollo 11 missions. Listen here, Episode 114: The Moon, Part 2.

Posted on by Jean Tate

Atomic Mass Unit

Faraday's Constant

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Believe it or not, there are actually several atomic mass units … however, the one that’s standard – throughout chemistry, physics, biology, etc – is the unified atomic mass unit (symbol u). It is defined as 1/12 (one-twelfth) of the mass of an isolated carbon-12 atom, in its ground state, at rest. You’ll still sometime see the symbol amu – which stands for atomic mass unit – but that’s actually two, slightly different, units (and each is different from the unified atomic mass unit!) … these older units are defined in terms of oxygen (1/16th of an isolated oxygen-16 atom, and 1/16th of an ‘average’ oxygen atom).

As it’s a unit of mass, the atomic mass unit (u) should also have a value, in kilograms, right? It does … 1.660 538 782(83) x 10-27 kg. How was this conversion worked out? After all, the kilogram is defined in terms of a bar of platinum-iridium alloy, sitting in a vault in Paris! First, it is important to recognize that the unified atomic mass unit is not an SI unit, but one that is accepted for use with the SI. Second, the kilogram and unified atomic mass unit are related via a primary SI unit, the mole, which is defined as “the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12“. Do you remember how many atoms there are in a mole of an element? Avogadro’s number! So, work out the Avogadro constant, and the conversion factor follows by a simple calculation …

The Dalton (symbol D, or Da) is the same as the unified atomic mass unit … why have two units then?!? In microbiology and biochemistry, many molecules have hundreds, or thousands, of constituent atoms, so it’s convenient to state their masses in terms of ‘thousands of unified atomic mass units’. That’s far too big a mouthful, so convention is to use kDa (kilodaltons).

Find out more on the (unified) atomic mass unit, from the Argonne National Laboratory, from the International Union of Pure and Applied Chemistry, and from the National Institute of Standards and Technology (NIST).

Learning to Breathe Mars Air and Mini-Detector Could Find Life on Mars or Anthrax at the Airport are two Universe Today articles relevant to the atomic mass unit.

Energy Levels and Spectra and Inside the Atom are two Astronomy Cast episodes related to the atomic mass unit.

Sources:
Wikipedia
Newton Ask a Scientist
Wise Geek

Posted on by Jean Tate

Antineutrino

IceCube neutrino detector.

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The antineutrino (or anti-neutrino) is a lepton, an antimatter particle, the counterpart to the neutrino.

Actually, there are three distinct antineutrinos, called types, or flavors: electron antineutrino (symbol ̅νe), muon antineutrino (symbol ̅νμ), and tau antineutrino (symbol ̅ντ).

Beta Decay which produces electrons also produces (electron) antineutrinos. Wolfgang Pauli proposed the existence of these particles, in 1930, to ensure that beta decay conserved energy (the electrons in beta decay have a continuum of energies) and momentum (the momentum of the electron and recoil nucleus – in beta decay – do not add up to zero); Enrico Fermi – who developed the first theory of beta decay – coined the word ‘neutrino’, in 1934 (it’s actually a pun, in Italian!). It would be a quarter of a century before the (electron) antineutrino was confirmed, via direct detection (Cowan and Reines did the experiment, in 1956, and later got a Nobel Prize for it).

Another Nobel Prize – for Leon Lederman, Melvin Schwartz, and Jack Steinberger, in 1988 – came from experimental work in the 1960s which showed that muon antineutrinos are not the same as electron antineutrinos.

And in 2002, Davis and Koshiba shared the Nobel Prize (with Giacconi, for work in x-ray astronomy) for their detection of cosmic antineutrinos (a 40-year task!), which lead to the discovery of flavor oscillations (in which an antineutrino of one kind changes into another – electron antineutrino to muon antineutrino, for example).

Are neutrinos their own antiparticles? No … but perhaps there is an as yet undiscovered kind of neutrino that is (called a Majorana neutrino)? So β– (electron) decay produces antineutrinos (lepton number is conserved: 1 + (-1) = 0), and β+ (positron) decay produces neutrinos.

No Guide to Space article would be complete without some ‘Further Reading’, would it? KamLAND (the Kamioka Liquid-scintillator Anti-Neutrino Detector) is a wonderful place to start! For one of the greatest physics detective stories of the 20th century, check out my idol John Bahcall’s webpage. Applied Antineutrino Physics (Lawrence Livermore National Laboratory) – great stuff there too.

You won’t find ‘antineutrino’ in many Universe Today articles … but you’ll find plenty on neutrinos! That’s OK … remember that it’s very common to use the word ‘neutrino’ in a generic sense, one that includes the meaning ‘antineutrino’. Some examples: Neutrino Evidence Confirms Big Bang Predictions , Seeing Inside the Earth with Neutrinos, and Do Advanced Civilizations Communicate with Neutrinos?

Two Astronomy Cast episodes give you more insight into the antineutrino, Antimatter, and The Search for Neutrinos.

Sources:
Stanford University KamLAND
Wikipedia

Posted on by Fraser Cain

Universe Today Guide to the Messier Objects



Well, Tammy’s done it again. Remember the Universe Today Guide to the Constellations? Well now Tammy has completed another monster volume. The Universe Today Guide to the Messier Objects. This is a guide to all 110 Messier Objects, from M1 (the Crab Nebula) to M110 (a satellite galaxy to Andromeda), and everything in between.

In addition to descriptions of the individual Messier Objects, there’s also a nice introduction to the Messier Objects, a guide to doing a Messier marathon, and suggestions for stretching your Messier marathon out to a week.

If you’ve got any questions, comments or feedback, please let us know. I’m sure there are going to be some bugs in there.

Thanks. And thanks again to the wonderful Tammy Plotner for grinding through this monster project.

M1 – M2 – M3 – M4 – M5 – M6 – M7 – M8 – M9 – M10 – M11 – M12 – M13 – M14 – M15 – M16 – M17 – M18 – M19 – M20 – M21 – M22 – M23 – M24 – M25 – M26 – M27 – M28 – M29 – M30 – M31 – M32 – M33 – M34 – M35 – M36 – M37 – M38 – M39 – M40 – M41 – M42 – M43 – M44 – M45 – M46 – M47 – M48 – M49 – M50 – M51 – M52 – M53 – M54 – M55 – M56 – M57 – M58 – M59 – M60 – M61 – M62 – M63 – M64 – M65 – M66 – M67 – M68 – M69 – M70 – M71 – M72 – M73 – M74 – M75 – M76 – M77 – M78 – M79 – M80 – M81 – M82 – M83 – M84 – M85 – M86 – M87 – M88 – M89 – M90 – M91 – M92 – M93 – M94 – M95 – M96 – M97 – M98 – M99 – M100 – M101 – M102 – M103 – M104 – M105 – M106 – M107 – M108 – M109 – M110

P.S. If you want to use any part of this information for any reason whatsoever, you’ve got my permission. Be my guest. Print them off for your astronomy club, turn it into a PDF and give it away from your site. Republish the guides on your own site. Whatever you like. All I ask is that you link back to Universe Today and the specific page, so people can find out where it came from.