Posted on by Jean Tate

What is Alpha Radiation?

Alpha radiation is another name for the alpha particles emitted in the type of radioactive decay called alpha decay. Alpha particles are helium-4 (4He) nuclei.

Radioactivity was discovered by Becquerel, in 1896 (and one of the units of radioactivity – the becquerel – is named after him); within a few years it was discovered (Rutherford gets most of the credit, though others contributed) that there are actually three kinds of radioactivity, which were given the exciting names alpha (radiation), beta (radiation), and gamma (radiation; there are some other, rare, kinds of radioactive decay, the most important being positron, or positive beta). Rutherford (with some help) worked out that alpha radiation is actually the nuclei of helium … by allowing alpha radiation to go through the thin walls of an evacuated glass tube, and later analyzing the gas in the tube spectroscopically).

Some fun facts about alpha radiation:

* alpha radiation is the least penetrating (of alpha, beta, and gamma); typically it goes no more than a few cm in air

* like all kinds of radioactive decay, alpha decay occurs because the final state of the nucleus (the one decaying) has a lower energy than the initial one (the difference is the energy of the emitted alpha particle, both its binding energy and its kinetic energy)

* alpha decay involves both strong and electromagnetic interactions (or forces), unlike beta and gamma decay

* the key to the specifics of alpha decay is the quantum effect called tunneling; Gamow worked this out, in 1928

* only heavier nuclides can undergo alpha decay; the lightest are light isotopes of tellurium

* alpha radiation played a star role in the development of our understanding of the nature of atoms … Rutherford, in 1909, aimed a beam of alpha radiation at a piece of thin gold foil, and counted the number of particles which were deflected at each angle; from this he deduced that the atom has a very small nucleus (with all the positive charge, and nearly all its mass).

For more background on alpha radiation, check out the Jefferson Lab’s What are alpha rays? How are they produced?.

There are many ways alpha radiation can turn up in Universe Today articles; for example, in NASA May Have to Revamp Science Plans Without RTGs, alpha radiation is essential to RTGs; and in Opportunity Rover Sidelined by Charged Particle Hit, alpha radiation is what’s used to help determine the elemental composition of samples.

Nucleosynthsis: Elements from Stars and Cosmic Rays are two Astronomy Cast episodes which also cover alpha radiation.

Source: Wikipedia

Posted on by Jean Tate

Sirius B

Not a black dwarf ... yet (white dwarf Sirius B)

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Sirius B is the name of the fainter, smaller, less massive star in the Sirius binary system (the brighter, larger, more massive one is Sirius A, or just Sirius). It was hypothesized to exist almost eighteen years before it was actually observed!

Details: Bessel – yep, the guy who Bessel functions are named after – analyzed data on the position of Sirius (Bessel was the one who first observed stellar parallax), in particular its proper motion, and concluded – in 1844 – that there was an unseen companion star (the same principle used to infer the existence of Neptune, around the same time). In 1862 Alvan Clark saw this companion, using the 18.5″ refracting telescope he’d just built (quite a feat; Sirius B is ~10 magnitudes fainter than Sirius A, and separated by only a few arcseconds).

Sirius B is a white dwarf, one of the three “classics”, discovered to be white dwarf stars in the early years of the 20th century (Sirius B was the second to be discovered – 40 Eridani B had been found much earlier, and Procyon B was also hypothesized by Bessel (in 1844) though not observed until much later (in 1896)). It is one of the most massive white dwarfs so far discovered; its mass is the same as that of the Sun (approximately). Like all white dwarfs, it is small (it has a radius of only 0.008, compared with the Sun’s, which makes it smaller than the Earth!); like most seen so far, it is hot (approx 25,000 K).

Sirius B was likely a five sol B star as recently as 60 million years ago (when it was, coincidentally, approximately 60 million years old!), when it entered first a hydrogen shell burning, then a helium shell burning, stage, shed most of its mass (and enriching its companion with lots of ‘metals’ in the process), and shrank to become a white dwarf. There is no fusion taking place in Sirius B’s degenerate carbon/oxygen core (which makes up almost all of the star; there is a thin, non-degenerate, hydrogen atmosphere … this is what we see), so it is slowly cooling (it cools so slowly because it has such a small surface area).

Packing such a large mass into such a small volume means that Sirius B’s surface gravity is huge … so great in fact that it serves as an excellent test of one of the predictions of Einstein’s theory of General Relativity: gravitational redshift (this was first observed in the lab in 1959, by Pound and Rebka). The most recent observation of this gravitational redshift was by the Hubble, in 2005, as described in the Universe Today article Sirius’ White Dwarf Companion Weighed by Hubble.

Other Universe Today stories about Sirius B include White Dwarf Theories Get More Proof, and this 2005 What’s Up This Week one.

Astronomy Cast has two episodes related to Sirius B, Dwarf Stars, and Binary Stars.

References:
http://www.solstation.com/stars/sirius2.htm
http://en.wikipedia.org/wiki/Sirius

Posted on by Abby Cessna

When Was Saturn Discovered

Saturn. Image credit: Hubble

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Saturn was one of the five planets visible to the naked eye that have been known to exist for thousands of years. The Ancient Greeks knew about the planet and named it after their god of agriculture – Kronos. That may be due to the planet’s golden color, which is similar to wheat. The planet later became known as Saturnus or Saturn, which was the Roman equivalent of Kronos. Saturn was the most distant of the five planets that can be seen with the naked eye. The Romans and Greeks were not the only ones who knew about Saturn. In Hindu culture, it was one of the nine Navagrahas, which are the main celestial bodies that are supposed to have influence over people’s lives. Saturn was known as Shani and was the Judge of the planets. The Chinese and Japanese termed it the earth star; their classification was based on the five elements. To the Ancient Hebrews, Saturn was known as Shabbathai.

Although people have known about Saturn for thousands of years, discoveries have still been made about the planet more recently. No one knew that Saturn had rings until the 1600’s. Galileo discovered them with his telescope in 1610, but he did not know what these were either. Thus they remained a mystery until 1655 when the astronomer Christian Huygen figured out that they were planetary rings.

Additionally, Saturn’s moons were discovered over a period of time. Christian Huygen discovered Titan, which is Saturn’s largest moon. Giovanni Domenico Cassini discovered four moons – Iapetus, Rhea, Tethys, and Dione. In 1789, the astronomer William Herschel discovered two more moons – Mimas and Enceladus. In 1848, British scientists discovered a moon called Hyperion.

We have learned much more about Saturn with the use of probes. To date, scientists have discovered 60 moons around Saturn. In 1979, Pioneer 11 flew by the planet and took photos. In 1980, the Voyager 1 probe took images of the planet and its largest moon, Titan. Voyager 2 also gathered information and showed scientists changes in the planet’s ring system. They also discovered gaps in the rings.

In 2004, Cassini-Huygens extensively studied the Saturn system. It brought back detailed data about both Titan and Saturn.  Scientists believe that the information that Cassini gathered has shown them proof of geysers on Enceladus that have eruptions of liquid water. Scientists were also able to discovere another ring of Saturn in 2006 due to photos that Cassini had taken.

Universe Today has articles on how long does it take Saturn to orbit the Sun and interesting facts about Saturn.

If you are looking for more information, try discover Saturn or Saturn.

Astronomy Cast has an episode on Saturn.

Reference:
NASA

Posted on by Ken Kremer

Clock Ticking for Shuttle Atlantis on Critical Resupply Mission

Editor’s Note: Ken Kremer is in Florida for Universe Today covering the upcoming Atlantis launch attempt.
As the shuttle enters its final year of operation, the countdown clock is ticking towards blast-off of Space Shuttle Atlantis and her six man crew at 2:28 PM EST on 16 November 2009 towards the International Space Station (ISS) I am reporting from the Kennedy Space Center (KSC) Press site to witness the STS 129 launch and provide on-site coverage for readers of Universe Today. The weather is gorgeous here at KSC with clear blue skies and moderate temperatures.

NASA managers unanimously declare Atlantis is “Go” for launch after reviewing all flight and hardware issues according to Mike Moses (left), director of Shuttle integration at a KSC press briefing. Shuttle Launch director Mike Leinbach (center) said “We are right on the money with the launch countdown. Cryogenics are being loaded into the shuttle fuel cells”. Weather officer Kathy Winters (right) predicted a 90 percent chance of favorable weather at launch time on November 16. Credit: Ken Kremer
NASA managers unanimously declare Atlantis is “Go” for launch after reviewing all flight and hardware issues according to Mike Moses (left), director of Shuttle integration at a KSC press briefing. Shuttle Launch director Mike Leinbach (center) said “We are right on the money with the launch countdown. Cryogenics are being loaded into the shuttle fuel cells”. Weather officer Kathy Winters (right) predicted a 90 percent chance of favorable weather at launch time on November 16. Credit: Ken Kremer

Shuttle weather officer Kathy Winters forecasts a 90 percent chance of favorable weather conditions at launch time on Monday. That drops to 70 percent favorable in the event of a one day scrub to Tuesday November 17 and just 40 percent “Go” on Wednesday. Two days after launch, Atlantis will rendezvous with the ISS and link up with the stations six person crew.

“Atlantis is ready to go. There was a unanimous vote to proceed with the launch countdown” declared Mike Moses, Shuttle Launch integration manager at a KSC press briefing. The primary goal is to deliver nearly 30,000 pounds (15 tons) of critical spare parts and cargo to the International Space Station (ISS) which cannot be transported by any other existing launch system besides the Space Shuttle. This third Utilization and Logistics shuttle flight for the ISS is designated as ULF-3.

Another top objective for Atlantis is to bring home ISS Expedition 20 and 21 crew member Nicole Stott after three months stay in space. Stott is the final astronaut scheduled to use a space shuttle as a taxi to and from the ISS and thereby will increase Atlantis crew size to seven during reentry.

The path forward was cleared when the launch of an Atlas 5 rocket was scrubbed in its final stages in the early morning hours of November 14 and subsequently delayed until after the STS 129 launch. This avoided a potential conflict on the Air Force Eastern Range which requires a 48 hour turnaround to reconfigure tracking and support systems between launches.

My view of the Vehicle Assembly Building (VAB) adjacent to the Kennedy Space Center Press Center. Shuttles are prepped for flight inside the rectangular box shaped buildings at left (near water tower) known as the Orbiter Processing Facility (OPF). At right see the Launch Control Center (LCC). Ares 1 rocket gantry under construction with tall crane to right of VAB. Credit: Ken Kremer
My view of the Vehicle Assembly Building (VAB) adjacent to the Kennedy Space Center Press Center. Shuttles are prepped for flight inside the rectangular box shaped buildings at left (near water tower) known as the Orbiter Processing Facility (OPF). At right see the Launch Control Center (LCC). Ares 1 rocket gantry under construction with tall crane to right of VAB. Credit: Ken Kremer

The cargo bay is loaded with two spare gyroscopes, two nitrogen tank assemblies, two pump modules, an ammonia tank assembly and a spare latching end effector for the station’s Canadian built robotic arm. Atlantis’s crew will conduct three spacewalks during the nominal 11 day flight to transfer the spare parts from the payload bay and install them onto the station’s external structures.

Since my last trip here for the STS 125 Hubble repair mission in May 2009, (also conducted by Atlantis) historic changes are rapidly unfolding at the launch pads and environs of the Kennedy Space Center. Launch Pad 39 B has been transferred to the Ares rocket program and been structurally transformed in such a manner that it can no longer support shuttle flights. STS 129 is only the 6th remaining shuttle flight before marking the end of the space shuttle era.

The entire future of US human space flight hangs in the balance as NASA awaits a decision by President Obama which will determine the US destiny in space for decades to come. Following the issuance of the Augustine commissions blue ribbon report outlining a range of future exploration options for NASA, the continuation of the Ares 1 rocket program and NASA goals to return human footsteps to the moon are in serious doubt as the out year NASA budgets have been significantly cut.

Posted on by Ken Kremer

Atlas Launch halted by ORCA; Shuttle Atlantis Next in Line

(Editor’s Note: Ken Kremer is in Florida for Universe Today covering the current launch attempts of the space shuttle and Atlas) Image caption: The Atlas 5 will orbit the commercial Intelsat 14 communications satellite. This photo shows upper portion of rocket and umbilical cord connections leading from mobile launch platform to the decaled 4 meter wide white colored payload fairing and Centaur upper stage. The flight is designated as tail number AV-024. Credit: Ken Kremer

Shortly after midnight on Saturday November 14 the launch of an Atlas 5 rocket poised  at Complex 41 and bathed in xenon lights was suddenly halted when engineers discovered a power dropout with the ORCA, or Ordnance Remote Control Assembly.

Atlas 5 rocket sits atop mobile launch platform at launch pad at Complex 41, Cape Canaveral, Florida on a cloudless day just a few hours prior to the scheduled post midnight launch on 14 November 2009. Note lightings masts at left and Vertical Integration Facility at right where rocket components are assembled. Credit: Ken Kremer
Atlas 5 rocket sits atop mobile launch platform at launch pad at Complex 41, Cape Canaveral, Florida on a cloudless day just a few hours prior to the scheduled post midnight launch on 14 November 2009. Note lightings masts at left and Vertical Integration Facility at right where rocket components are assembled. Credit: Ken Kremer

The Atlas was due to blast off at 12: 48 AM EST into the cloudless and calm sky above Cape Canaveral, Florida carrying the commercial Intelsat 14 communications satellite into orbit.  I was observing from the Kennedy Space Center press site along with other media representatives as weather conditions were near perfect and gremlins intervened.   My vantage point at KSC provides a clear and direct view to the base of the Atlas rocket and launch pad.

The scrub was called less than half an hour before the scheduled liftoff time and after propellant loading of the first and second stages had been successfully completed.   Engineers will need to troubleshoot the cause of the temporary power interruption to the ORCA electronics component which is used to control the critical flight events on the Atlas booster.

Technicians must obtain access to the electronics box within the rocket and remove it for further investigation of the technical glitch.  Since there is no access at the pad to gain entry and accomplish this task, the Atlas vehicle must be rolled back off the pad about 1800 feet and into the 30 story tall Vertical Integration Facility.  Therefore the launch team executed the standard detanking of propellants to safe the rocket following the scrub.

Atlas 5 rocket at sunset surrounded by 4 lightening masts at pad 41. Multiple tanks of compressed gaseous nitrogen at 4800 psi in foreground. A technical glitch with the ORCA electronics unit critical for flight control forced a scrub for what would have been the 19th flight of an Atlas 5. Credit: Ken Kremer
Atlas 5 rocket at sunset surrounded by 4 lightening masts at pad 41. Multiple tanks of compressed gaseous nitrogen at 4800 psi in foreground. A technical glitch with the ORCA electronics unit critical for flight control forced a scrub for what would have been the 19th flight of an Atlas 5. Credit: Ken Kremer

Atlas 5 rocket at sunset surrounded by 4 lightening masts at pad 41. Multiple tanks of compressed gaseous nitrogen at 4800 psi in foreground. A technical glitch with the ORCA electronics unit critical for flight control forced a scrub for what would have been the 19th flight of an Atlas 5. Credit: Ken Kremer

The launch is being conducted for Lockheed Martin Commercial Launch Services by United Launch Alliance (ULA).  A new launch date has not been set at this time, a ULA spokesman told me.   As a result of the postponement and rollback, the STS 129 flight will proceed without delay as the countdown clock is ticking towards blast off on November 16 according to NASA officials.

Just hours before the planned Atlas liftoff, I visited pad 41 on a special media tour for close-up photography and remote camera set up.  The twilight sun was setting to the west behind the mighty bronze colored rocket topped by a white colored nose cone which protects the valuable satellite payload from aerodynamic forces as it pierces through the atmosphere.

Ken Kremer with the Atlas launch vehicle at Pad 41 which will fly in the 431 configuration with 3 solid rocket boosters attached to the first stage and a single engine white colored Centaur upper stage. The Atlas 5 was rolled out to launch pad on Nov 12. Note tracks at center. The Intelsat satellite is encapsulated in a 4 meter wide extra extended payload fairing. A similar Centaur stage impacted the moon as part of the LCROSS mission.
Ken Kremer with the Atlas launch vehicle at Pad 41 which will fly in the 431 configuration with 3 solid rocket boosters attached to the first stage and a single engine white colored Centaur upper stage. The Atlas 5 was rolled out to launch pad on Nov 12. Note tracks at center. The Intelsat satellite is encapsulated in a 4 meter wide extra extended payload fairing. A similar Centaur stage impacted the moon as part of the LCROSS mission.

Ken Kremer with the Atlas launch vehicle at Pad 41 which will fly in the 431 configuration with 3 solid rocket boosters attached to the first stage and a single engine white colored Centaur upper stage. The Atlas 5 was rolled out to launch pad on Nov 12. Note tracks at center. The Intelsat satellite is encapsulated in a 4 meter wide extra extended payload fairing. A similar Centaur stage impacted the moon as part of the LCROSS mission. See my LCROSS photos here.

Posted on by Fraser Cain

How Far Away is Pluto From the Sun?

The Pluto system seen from the surface of Hydra. Credit: NASA

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How far away is Pluto from the Sun? Pluto’s average distance from the Sun is 5.9 billion km or 3.7 billion miles.

But Pluto actually follows an elliptical orbit around the Sun. Sometimes it’s much closer to the Sun, and other times it’s further away. At its closest point, Pluto measures only 4.4 billion km from the Sun. This is close enough that a thin layer of frost evaporates from its surface, becoming a thin atmosphere around the planet. And then as it continues its journey around the Sun, Pluto gets colder again and this atmosphere refreezes onto the planet. It continues to travel out to a distance of 7.4 billion km from the Sun.

Astronomers use another method of measuring distances in the Solar System called the astronomical unit. 1 astronomical unit or AU is the average distance from the Earth to the Sun; approximately 150 million km. So we can use this to describe Pluto’s distance from the Sun. At its closest point, Pluto measures 29.7 AU. And then at its furthest point, Pluto is 49.3 AU.

We have written many articles about Pluto for Universe Today. Here’s an article about why Pluto isn’t a planet any more, and here are some pictures of Pluto.

If you’d like more info on Pluto, check out Hubblesite’s News Releases about Pluto, and here’s a link to NASA’s Solar System Exploration Guide to Pluto.

We’ve also recorded several episodes of Astronomy Cast about Pluto. Listen here, Episode 64: Pluto and the Icy Outer Solar System.

Posted on by Nancy Atkinson

Water on the Moon

Artist concept of the Centaur and LCROSS heading towards the Moon. Credit: NASA

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Water has long been suspected to exist in the permanently shadowed polar craters on the Moon, and now the LCROSS impact has allowed scientists to make a direct and definitive finding of this precious resource in a place NASA and other space agencies are considering exploring with human expeditions. Many say this could be a game-changing discovery for the future of lunar science and exploration. Unlike the previous announcement in September of water on the Moon, where water exists diffusely across the moon as hydroxyl or water molecules adhering to the surface in low concentrations, this new discovery could mean underground reservoirs of water ice. “There is too much water to be just absorbed in the soil,” said Anthony Colaprete of the LCROSS mission at Friday’s press conference. “There has to be real solid ice there. You could melt it and drink it.”

But could you really drink it? “Well, not if it has methanol in it. We need to sort out the flavor of the water,” said Colaprete, “meaning we need to find out if it is water, ice, or vapor. We still need to do that math.”

Colaprete said from the amount of water the spectrometers on the LCROSS spacecraft detected, initial indications are it is ice. However, Colaprete added that the impacting Centaur upper stage didn’t hit appear to hit something hard and frozen, from the images of the crater.

If someone was walking on the Moon and was able to walk in Cabeus crater where the impact took place, would the regolith there look different compared to other places on the Moon? “That’s a good question – and we’ve been talking about that,” Colaprete said. “It would be an interesting place to walk around. With our near infrared camera we can relate the the data to what the human eye can see, and try to understand what the terrain looks like. We never saw the crater floor before impact, but now we can see what the floor looks like.”

Did they find anything else in the plume created by the impact? “We’re seeing a lot of stuff,” Colaprete said. “I think there’s a little bit of everything. We’re seeing other emission lines in the spectroscopic data we haven’t completely identified. We’re still working on those — I don’t know what all else is in there just yet. We’ve been focusing on the water quest so far.”

As to whether they’re seeing any organics, the team couldn’t yet say definitively. Colaprete said they are seeing compounds similar to those seen previously in asteroids and comets.

“This is only another snapshot in time of our understanding of the moon,” said Mike Wargo, NASA’s chief lunar scientist, ” and we’ll be continuing to work to get more details on the water and everything else. We’re not done yet.”

Posted on by Nancy Atkinson

The Artist of Apollo 12


40 years ago today, Apollo 12 launched on their mission to the Moon. On board was Pete Conrad, Dick Gordon and Alan Bean. Bean is a gifted artist who has shared his experiences on the Moon like no other astronaut has through his paintings, which offer a unique look at both real and imagined events during all the different astronaut’s moonwalks. (Check out his website to see a gallery of his amazing artwork.) And enjoy this great interview that Miles O’Brien did recently with Alan Bean.

NASA also has an interactive Apollo 12 feature.

Posted on by Fraser Cain

How Far is a Light Year?

X-Ray image of Proxima Centauri. Image credit: Chandra

A light year is a standard of measurement used by astronomers to describe huge distances in the Universe. The nearest star is 4.22 light years away. The center of the Milky Way is about 26,000 light years away. But how far is 1 light year? A light year is the distance that light travels in a single year. And light travels fast.

1 lightyear is 9,460,730,472,580.8 kilometers.

Need some other measurements? A light year is 5,878,625,373,183.6 miles. And a light year is 63,241 astronomical units (1 astronomical unit, or AU is the average distance from the Earth to the Sun).

But a light year isn’t the largest measurement tool astronomers have. That’s a parsec. 1 parsec = 3.26156 light years.

We have written several articles about measuring distance for Universe Today. Here’s an article about the speed of light, and an article about a device that makes radio waves go faster than the speed of light.

If you’d like more information on light years, here’s an article about what a light year is and how it’s used, and here’s a cool video that shows you how far a light year is.

We’ve also recorded an episode of Astronomy Cast about different tools for measuring distance in the Universe. Listen here, Episode 10: Measuring Distance in the Universe.