How Many Stars are There in the Milky Way?

Artist's impression of The Milky Way Galaxy. Based on current estimates and exoplanet data, it is believed that there could be tens of billions of habitable planets out there. Credit: NASA

When you look up into the night sky, it seems like you can see a lot of stars. There are about 2,500 stars visible to the naked eye at any one point in time on the Earth, and 5,800-8,000 total visible stars (i.e. that can be spotted with the aid of binoculars or a telescope). But this is a very tiny fraction of the stars the Milky Way is thought to have!

So the question is, then, exactly how many stars are in the Milky Way Galaxy? Astronomers estimate that there are 100 billion to 400 billion stars contained within our galaxy, though some estimate claim there may be as many as a trillion. The reason for the disparity is because we have a hard time viewing the galaxy, and there’s only so many stars we can be sure are there.

Structure of the Milky Way:

Why can we only see so few of these stars? Well, for starters, our Solar System is located within the disk of the Milky Way, which is a barred spiral galaxy approximately 100,000 light years across. In addition, we are about 30,000 light years from the galactic center, which means there is a lot of distance – and a LOT of stars – between us and the other side of the galaxy.

The Milky Way Galaxy. Astronomer Michael Hart, and cosmologist Frank Tipler propose that extraterrestrials would colonize every available planet. Since they aren't here, they have proposed that extraterrestrials don't exist. Sagan was able to imagine a broader range of possibilities. Credit: NASA
Artist’s impression of the Milky Way Galaxy. Credit: NASA

To complicate matter further, when astronomers look out at all of these stars, even closer ones that are relatively bright can be washed out by the light of brighter stars behind them. And then there are the faint stars that are at a significant distance from us, but which elude conventional detection because their light source is drowned out by brighter stars or star clusters in their vicinity.

The furthest stars that you can see with your naked eye (with a couple of exceptions) are about 1000 light years away. There are quite a few bright stars in the Milky Way, but clouds of dust and gas – especially those that lie at the galactic center – block visible light. This cloud, which appears as a dim glowing band arching across the night sky – is where our galaxy gets the “milky” in its name from.

It is also the reason why we can only really see the stars in our vicinity, and why those on the other side of the galaxy are hidden from us. To put it all in perspective, imagine you are standing in a very large, very crowded room, and are stuck in the far corner. If someone were to ask you, “how many people are there in here?”, you would have a hard time giving them an accurate figure.

Now imagine that someone brings in a smoke machine and begins filling the center of the room with a thick haze. Not only does it become difficult to see clearly more than a few meters in front of you, but objects on the other side of the room are entirely obscured. Basically, your inability to rise above the crowd and count heads means that you are stuck either making guesses, or estimating based on those that you can see.

a mosaic of the images covering the entire sky as observed by the Wide-field Infrared Survey Explorer (WISE), part of its All-Sky Data Release.
A mosaic of the images covering the entire sky as observed by the Wide-field Infrared Survey Explorer (WISE), part of its All-Sky Data Release. Credit: NASA/JPL

Imaging Methods:

Infrared (heat-sensitive) cameras like the Cosmic Background Explorer (aka. COBE) can see through the gas and dust because infrared light travels through it. And there’s also the Spitzer Space Telescope, an infrared space observatory launched by NASA in 2003; the Wide-field Infrared Survey Explorer (WISE), deployed in 2009; and the Herschel Space Observatory, a European Space Agency mission with important NASA participation.

All of these telescopes have been deployed over the past few years for the purpose of examining the universe in the infrared wavelength, so that astronomers will be able to detect stars that might have otherwise gone unnoticed. To give you a sense of what this might look like, check out the infrared image below, which was taken by COBE on Jan. 30th, 2000.

However, given that we still can’t seem them all, astronomers are forced to calculate the likely number of stars in the Milky Way based on a number of observable phenomena. They begin by observing the orbit of stars in the Milky Way’s disk to obtain the orbital velocity and rotational period of the Milky Way itself.

Estimates:

From what they have observed, astronomers have estimated that the galaxy’s rotational period (i.e. how long it takes to complete a single rotation) is apparently 225-250 million years at the position of the Sun. This means that the Milky Way as a whole is moving at a velocity of approximately 600 km per second, with respect to extragalactic frames of reference.

"This dazzling infrared image from NASA's Spitzer Space Telescope shows hundreds of thousands of stars crowded into the swirling core of our spiral Milky Way galaxy. In visible-light pictures, this region cannot be seen at all because dust lying between Earth and the galactic center blocks our view. Credit: NASA/JPL-Caltech
Infrared image of the Milky Way taken by NASA’s Spitzer Space Telescope. Credit: NASA/JPL-Caltech

Then, after determining the mass (and subtracting out the halo of dark matter that makes up over 90% of the mass of the Milky Way), astronomers use surveys of the masses and types of stars in the galaxy to come up with an average mass. From all of this, they have obtained the estimate of 200-400 billion stars, though (as stated already) some believe there’s more.

Someday, our imaging techniques may become sophisticated enough that are able to spot every single star through the dust and particles that permeate our galaxy. Or perhaps will be able to send out space probes that will be able to take pictures of the Milky Way from Galactic north – i.e. the spot directly above the center of the Milky Way.

Until that time, estimates and a great deal of math are our only recourse for knowing exactly how crowded our local neighborhood is!

We have written many great articles on the Milky Way here at Universe Today. For example, here are 10 Facts About the Milky Way, as well as articles that answer other important questions.

These include How Big Is The Milky Way?, What is the Milky Way?, and Why Is Our Galaxy Called the Milky Way?

Astronomy Cast did a podcast all about the Milky Way, and the Students for the Exploration and Development of Space (SEDS) have plenty of information about the Milky Way here.

And if you’re up for counting a few of the stars, check out this mosaic from NASA’s Astronomy Picture of the Day. For a more in-depth explanation on the subject, go to How the Milky Way Galaxy Works.

NASA News Too Depressing for a Headline

OK, I give up. I’ve sat here for about a half an hour trying to come up with a headline for this news piece. Actually, there are three different news items I’m combining into one article. One is fairly good news, the other two are very depressing.

First the good news: Today, the first major flight hardware of the Ares I-X rocket arrived in Florida to begin preparation for the inaugural test flight of NASA’s next-generation launch system. But amid this tangible event of moving toward the future comes bad financial news about the Constellation program. Congressional investigators have concluded that the Constellation program is likely to cost $7 billion more than budgeted if it is going to be ready to fly by its target date of March 2015. Without extra money, it could be delayed by 18 months or more.

At the same time another report concludes that NASA would need an extra $2 billion a year to keep its shuttle fleet flying beyond 2010, a measure which would shorten the gap where NASA wouldn’t have a human rated vehicle available for access to space. But doing so would hamper plans to convert a launch pad and other facilities for moon missions, likely delaying Constellation even more.

More money for either Constellation or the shuttle program is just not in NASA’s budget, and shifting money around from other programs “would be disastrous,” NASA shuttle program manager John Shannon said. “What we’re trying to do is find a path that continues to keep Americans flying on American vehicles, but does not mortgage the future of manned space flight,” he said. “We really have to step back and think very hard about what we want the future to look like, and make sure that we’re not going to make it something that is not achievable.”

I need ideas for a headline for this article. Readers — comments?

Both Republican presidential candidate John McCain and Democratic presidential candidate Barack Obama have said they would increase NASA’s budget by $2 billion to minimize the gap between shuttle retirement and the first piloted flights of Ares 1 rockets and Orion crew capsules. (This is being written before the election results are in.) But even that won’t be enough to solve all of the problems.

The Congressional Budget Office report listed several of problems facing the Ares I rocket and the Orion capsule, which NASA hopes will return astronauts to the moon by 2020. Among them are difficulties in developing an engine for Ares and a heat shield for Orion. “NASA has identified several problems associated with the Ares I that could delay successful development of the vehicle,” according to the 18-page report. Read the report here.

We’ve discussed all the issues previously on Universe Today, including intense shaking on liftoff, and concerns that Ares could crash into the launch gantry.

NASA officials said they were studying the report. But agency managers insist the program is on track.

At a news conference NASA held last week to counter reports of Constellation’s problems, Steve Cook, Ares project manager said, “The Ares I rocket is a sound design that not only meets the high safety standards required for a manned spacecraft, it is within budget, on schedule, and meets its performance requirements with margin.”

So what’s the real story? I’m not certain anymore. I desperately want to believe that the media (is that me, too?) overblowing the problems and NASA isn’t just looking through rose colored glasses. But the bad news keeps coming from all fronts.

NASA’s options other than the Ares appear limited.

One proposed option would extend the current space shuttle flight schedule through 2012, using the giant external fuel tanks and other hardware NASA has already planned to build. A second option calls for NASA to build more fuel tanks and hardware to keep flying three shuttle missions per year until 2015.

The CBO report also cautioned that the cost of more shuttle flights could only hurt Constellation under NASA’s limited budget.

Even by throwing more money at Constellation, the investigators also don’t think that NASA could speed up Constellation’s development, at least in the near term. They said NASA told them that “additional funding can no longer significantly change” the March 2015 target date of a first launch.

Even so, the Orlando Sentinel reports that NASA is looking at radical changes in the program to see if it can speed up development.

According to former astronaut Eileen Collins, currently a member of the NASA Advisory Council, one option under consideration would eliminate features needed to go to the moon and turn it a simple craft that could ferry crew and cargo to the space station. That would mean further delays for the real reason for Constellation: returning to the moon.

I thought we had some good news about Constellation last week. But this seems depressing. Too depressing for a headline.

Sources: NASA, Orlando Sentinel, Florida Today

Alan Stern Resigns From NASA

174142main_alan_stern.thumbnail.jpg

Alan Stern has stepped down as NASA’s Associate Administrator for the Science Mission Directorate. No word on Stern’s reasons for leaving, or why such an abrupt departure, but the timing suggests it could be related to the erroneous announcement that funding for the Mars Rovers would be cut. Stern is seemingly highly respected and very popular among mission scientists and designers, and Stern had pledged to toe the line about mission spending and cost overruns. There are conflicting reports whether Stern will continue as Principal Investigator for the New Horizons mission to Pluto, but it would be very surprising to see him leave the mission to which he has devoted most of his career.

Stern had only been with the Science Mission Directorate for about a year but during that year Time Magazine named Stern as one of the 100 Most Influential People in 2007.

Continue reading “Alan Stern Resigns From NASA”

Space Program At Risk, Panel Says

vision.thumbnail.jpg

A panel of 50 space experts met recently to discuss NASA’s current direction with its Vision for Space Exploration. While the conference, “Examining the Vision: Balancing Science and Exploration” was seemingly billed as forum for discussing alternatives to the moon/Mars vision, attendees endorsed NASA’s current direction and then concluded what anyone with an eye on NASA already knew: NASA isn’t receiving adequate funds in line with the grand goal of sending humans to Mars.

The panel of scientists, engineers, and former astronauts and NASA administrators concluded that NASA is on the right path with its objectives of going to the moon as a stepping stone to reach Mars, but those goals are in danger because of chronic underfunding to the US space program.

“The nation’s space program is in peril,” said Stanford Professor Scott Hubbard, former director of NASA’s Ames Research Center, and an organizer of the conference. “You simply cannot continue doing more with less and meet these goals. That is a fact. This workshop achieved a consensus that NASA’s resources have not been commensurate with its mandated missions of exploration and science.”

The panel did say, however, that NASA should focus more on sending humans to Mars instead of building large bases on the moon. But also, former astronaut Kathryn Thornton said before the meeting, she felt the best way to get to Mars was going there directly. But the meeting changed her mind, she said, and she now believes there are benefits to using the moon as a way station, such as scientific research and testing rocket hardware and infrastructure.

Alternatives such as going to asteroids was discussed, but not endorsed by the panel. Also of interest is that the panel said science is not the major motivation for human spaceflight.

But the panel concluded that any human ventures out of low earth orbit should be international in nature. “The next administration should make the human spaceflight goal an international venture focused on Mars–both to bring in more public support and to sustain the program politically,” said Louis Friedman, Executive Director of The Planetary Society.

In particular the attendees agreed to the following statements:

  • It is time to go beyond LEO with people as explorers. The purpose of sustained human exploration is to go to Mars and beyond. The significance of the Moon and other intermediate destinations is to serve as steppingstones on the path to that goal.
  •  Bringing together scientists, astronauts, engineers, policy analysts, and industry executives in a single conversation created an environment where insights across traditional boundaries occurred.
  •  Human space exploration is undertaken to serve national and international interests. It provides important opportunities to advance science, but science is not the primary motivation.
  • Sustained human exploration requires enhanced international collaboration and offers the United States an opportunity for global leadership.
  •  NASA has not received the budget increases to support the mandated human exploration program as well as other vital parts of the NASA portfolio, including space science, aeronautics, technology requirements, and especially Earth observations, given the urgency of global climate change.

The panel gathered privately on Feb. 12-13, 2008 to discuss space policy options facing the new US administration that will take office in January 2009, and may offer more recommendations in the future.

Original News Sources: New Scientist, Planetary Society Press Release

Memorial Service Honors Columbia Astronauts

080201_columbia_crew.thumbnail.jpg

Five years ago, family members of the STS-107 space shuttle crew were waiting at the Kennedy Space Center to hear the double sonic boom that would announce the arrival of the Columbia shuttle returning home from its mission to space. But the sonic booms never came; there was only silence. Today, at the Space Mirror Memorial at the NASA Kennedy Space Center, NASA officials, astronauts and families of the Columbia crew paid tribute to all astronauts who have lost their lives, and called for NASA to continue to learn from the tragedies.

Evelyn Husband Thompson, wife of STS-107 commander Rick Husband said that each of the families are recalling what they went through five years ago in public or private ways. Families of Ilan Ramon and Willie McCool are in Israel for a memorial service there, while the families of Dave Brown, Laurel Clark, Mike Anderson and Kalpana Chawla are privately remembering the accident.

The astronauts were returning home from a successful flight when the shuttle broke up on re-entry.

Husband-Thompson, who remarried just three weeks ago said, “Life does go on, and even though we never know what life is going to bring us, there is hope for tomorrow.”

Eileen Collins, who commanded the STS-114 return to flight mission two years after the Columbia accident said that, personally, this was a difficult day for her, and that it was hard to describe the experiences of the past five years.

“I can’t properly put it into words, but our purpose here today is to honor and respect, remember and learn,” she said. Collins said that she has changed because of the accident, and now realizes that spaceflight is even more difficult and hazardous than she originally believed.

“Everyday requires constant attention to detail,” she said.

Remembering the crews of Columbia, Challenger, and Apollo 1, NASA Associate Administrator for Space Operations Bill Gerstenmaier said, “All astronauts who have sacrificed their lives are pioneers and role models who refused to shy away from seemingly impossible challenges.”

Gerstenmaier spoke frankly about loss and NASA’s mistakes.

“This is a tough time of year for our agency as we pause and remember the loss of our co-workers and friends, and the failure of our engineering design. We feel the deep ache of regret,” he said. “Our memories serve to dedicate ourselves to reducing the risks associated with the hostile environment in which we fly. We must continually challenge our assumptions and test our designs. Only with this attitude can we hope to not be surprised by another tragedy.”

NASA Adminstrator Mike Griffin said, “American’s don’t quit. We’ll never quit. But today we remind ourselves that not quiting can have high costs. Today, we celebrate the people who bore those costs and the people who remain behind them. We don’t forget, we never forget, we can’t forget, we won’t forget.”

Original News Source: NASA TV

“Across the Universe” Day for NASA and Beatles Fans

goldstone-tour1.thumbnail.jpg

NASA will use its Deep Space Network to transmit a song across the universe. And fittingly, the song is “Across the Universe” by the Beatles. On Feb. 4 at 7 pm EST, the song will be beamed towards the North Star, Polaris, located 431 light years away from Earth, and will travel across the universe at 186,000 miles per second.

Former Beatle Paul McCartney thinks this is a great idea. “Send my love to the aliens,” he said in a message to NASA.

If there are any beings near Polaris, they’ll hear the song in about 431 years.

The song’s transmission will commemorate the 40th anniversary of the day The Beatles recorded the song, as well as the 50th anniversary of both NASA’s founding and the beginning days of the Beatles. Two other anniversaries also are being honored: The launch 50 years ago this week of Explorer 1, the first U.S. satellite, and the founding 45 years ago of the Deep Space Network, an international network of antennas that supports missions to explore the universe.

Feb. 4 has been declared “Across The Universe Day” by Beatles fans to commemorate the anniversaries. As part of the celebration, the public around the world has been invited to participate in the event by simultaneously playing the song at the same time as the transmission by NASA.

John Lennon’s widow, Yoko Ono, characterized the song’s transmission as a significant event. “I see that this is the beginning of the new age in which we will communicate with billions of planets across the universe,” she said.

Even though radio and television signals on Earth ‘leak’ out into space all the time, hopefully NASA can use this event to generate enthusiasm and promote awareness of its history, as well as its plans for future missions.

Additionally, this is a chance for the public to learn more about the Deep Space Network, NASA’s incredibly reliable system of radio antennas that is critical in supporting lunar and planetary exploration. The DSN is used for tracking of spacecraft, sending telemetry and commands, and for deep space navigation. Learn more about the DSN here.

Original News Source: NASA Press Release

NASA Astronaut Survey: No Launch Day Drinking

shuttlelaunch.thumbnail.jpg

A NASA survey of astronauts and flight surgeons released on January 23, 2008 turned up no evidence of launch day drinking by flight crews, contradicting an earlier report by a health care panel that disclosed two instances of drunken astronauts. NASA surveyed 87 of all 98 astronauts as well as all 31 flight surgeons. None reported seeing a crew member heavily drinking alcohol on launch day, or within 12 hours of liftoff.

However, the anonymous survey did find one report of “perceived impairment” in an astronaut during the days preceding launch, which was later was traced to an interaction between prescription medication and alcohol. That astronaut was ultimately cleared for flight and launched into space.

“We really never understood from the beginning exactly what might have led to the comment in the health care report,” said Ellen Ochoa, deputy director of Johnson Space Center and a former shuttle astronaut. “We’ve tried to run it to ground. We haven’t uncovered anything. I don’t know of any issues associated with alcohol before flight.”

The healthcare report was conducted in mid-2007 in the wake of astronaut Lisa Nowak’s arrest. Nowak, who traveled from Houston to Florida to confront another woman about a romantic rivalry involving another astronaut, was arrested for attempted kidnapping and burglary with assault. She has yet to stand trial.

NASA established a panel of aerospace medicine experts, led by U.S. Air Force Col. Richard Bachmann, Jr., to look into astronaut mental health. The panel, citing unidentified sources, reported heavy drinking by two astronauts right before launches; one before a shuttle launch and another prior to the launch of a Russian Soyuz rocket. The panel reported that the flight surgeon’s concerns about the astronauts’ impairment were supposedly overruled by management, which created an atmosphere where both astronauts and flight surgeons were reluctant to report improper conduct.

In the new survey, however, conducted in August-December 2007, astronauts and flight surgeons indicated they were not afraid to raise concerns of flight safety, and they felt there is a healthy relationship between astronauts and doctors. But a small number of respondents acknowledged that some astronauts still feel they could lose out on a space assignment if they expressed concerns.

The astronaut survey was conducted and analyzed using both NASA specialists and external academic experts to ensure the study’s validity. “The response rate of the survey was 91 percent, a rate well above what you would normally expect in a survey,” Ochoa said. “That indicates the seriousness with which astronauts and flight surgeons approached this survey.”

The survey focused four areas: the relationship between astronauts and flight surgeons regarding openness of communication, level of trust, and understanding of safety responsibilities; concerns with raising and responding to issues of flight safety and/or crew suitability for flight; knowledge and implementation of policies and procedures detailing astronaut performance and crew assignment; and determining if there was personal knowledge of a US astronaut presenting a risk to flight safety due to alcohol use on launch day.

The 12-hour ban on drinking, which originally an “unwritten rule” is now standard policy. A new astronaut code of conduct is being written, as well.

Dr. Richard Williams, NASA’s chief health and medical officer said that NASA is in a better position today than it was a year ago to detect serious behavioral health problems facing astronauts, and to intervene before it’s too late.

Original News Source: NASA News Release

Should NASA Overhaul Its Vision?

vsfe_ship.thumbnail.jpg

Is the moon really “so yesterday?” An article in the Jan. 18 issue of Aviation Week and Space Technology reported that a group of influential people in the space community will meet in early February to discuss alternatives to NASA’s current Vision for Space Exploration of returning to the moon to prepare for future missions to Mars. But a subsequent letter to the editor in AWST written by Planetary Society President Lou Friedman and Scott Hubbard of Stanford University tried to put the brakes on any notion that the group has already come to a consensus that NASA’s VSE should change direction and destination.

In the letter, Friedman and Hubbard state that the article created “the misperception that the workshop we are organizing at Stanford University has already decided upon a new path for the human and robotic exploration of space. We wish to make it clear that the purpose of the workshop is to examine critically the Vision for Space Exploration in order to prepare for future space policy considerations in a new Administration and new Congress.”

The Aviation Week article reported that the purpose of the February meeting is “to offer the next U.S. president an alternative to President Bush’s ‘vision for space exploration’–one that would delete a lunar base and move instead toward manned missions to asteroids along with a renewed emphasis on Earth environmental spacecraft.”

But Friedman and Hubbard’s letter said, “This point of view is undoubtedly the personal opinion of some participants – but such an opinion is neither a premise nor a presumed outcome of the workshop.” Instead, they said, the workshop will address a many issues of space exploration and the workshop has no predetermined conclusions.

“We have deliberately included a wide range of participants with disparate views, including those who would maintain the status quo. We personally do not know what the conclusions of the workshop will be – or even if there will be a definitive consensus,” said Friedman and Hubbard.

Examining the current Vision is surely a good idea. A Business 101 rule is that once a plan is put into action, you should always stay on top of changing conditions and adjust your plan accordingly, constantly updating and improving. Should NASA consider missions to asteroids instead of the moon? Will going to asteroids get us to Mars more quickly, or is the moon a good, safe place to get our space legs back before moving on?

Hopefully the group meeting at Stanford University in February, as well as the upcoming new political administration in the US, will examine the VSE with open minds, considering both human and robotic missions, and without political agendas.

Another Business 101 tenet is that communication is vital to success. It’s good to see that space exploration is something people are talking about.”

Original News Source: Planetary Society Press Release

NASA Wants Your Opinion on the Lunar Lander

206407main_jsc2007e113282_lo.thumbnail.jpg

NASA’s Constellation Program has released an announcement that they are looking for people to evaluate the design of the Altair spacecraft that will land on the moon. So if you work in the science community or in a related industry, NASA wants your opinion. What they are looking for are evaluations of the current developmental concept for the Altair lander and the safety improvements that have been proposed, as well as recommendations for industry-government partnerships.

“By soliciting ideas and suggestions from industry and the science community, NASA hopes to foster a collaborative environment during this early design effort,” said Jeff Hanley, the Constellation Program manager. “Such collaboration will support the development of a safe, reliable and technologically sound vehicle for our crews.”

All you have to do is write a proposal and submit it to NASA by jumping through the various hoops found here. NASA expects to award contracts for the studies of the Altair spacecraft in the first quarter of 2008. A total of $1.5 million is available for awards. The maximum individual award amount is $350,000. The contract performance period is six months.

In NASA-speak, proposals are due “30 days from the issue date of Jan. 11.” By my calculations, that is February 10, which is a Sunday, an odd day to have a proposal due since most of NASA’s offices are closed. Maybe its a subtle hint to get your proposals in early.

The Altair spacecraft will bring four astronauts to the lunar surface, and missions are currently scheduled to begin late in the next decade. NASA plans call for establishing an outpost on the moon through their lunar missions beginning no later than 2020.

The Constellation Program, based at NASA’s Johnson Space Center, Houston, manages the Altair Project for NASA’s Exploration Systems Mission Directorate. Constellation is developing a new space transportation system that is designed to travel beyond low Earth orbit. The Constellation fleet includes the Orion crew exploration vehicle, the Ares I and Ares V launch vehicles and Altair human lunar lander.

Find more information about the Constellation Program here.

Original News Source: NASA Constellation Program Press Release

Ulysses Passes Over Sun’s North Pole

ulysses_spacecraft.thumbnail.jpg

Continuing on its epic journey around the Sun, Ulysses has reached the Sun’s north pole just in the nick of time. In fact, its timing couldn’t be better, just as the Sun begins “Solar Cycle 24”. The probe is in a unique orbit, passing over the solar north and south poles, out of the ecliptic plane of the solar system, giving it an unprecedented view of parts of the Sun we cannot observe on Earth. “Graveyards for sunspots” and mysterious coronal holes lurk in these regions and Ulysses will be perfectly placed, directly above.

The joint NASA and ESA Ulysses mission has been a resounding success in its 18 years of operation since launch on board Space Shuttle Discovery (STS-41) in October 1990. The intrepid spacecraft was helped on it’s way by a gravitational assist by the planet Jupiter which flung it over the poles of the Sun. Quietly travelling in a perpendicular orbit (space missions and the planets usually orbit around the Sun’s equator), Ulysses has been measuring the distribution of solar wind particles emanating from latitudinal locations for one and a half orbits.

As Ulysses passes over the north polar region, the Sun will be observed during a period of minimum activity at this location for the first time. The poles of the Sun are of particular interest to scientists as this is where the fast solar wind originates from open magnetic field lines reaching into space. The dynamics of solar material in this location provides information on how the Sun interacts with interplanetary space and how the solar wind is generated. Observing the solar wind at “solar minimum” will be of massive interest as it may provide some answers as to why the solar wind is accelerated hundreds of kilometers per hour even when activity is at its lowest.

Just as Earth’s poles are crucial to studies of terrestrial climate change, the sun’s poles may be crucial to studies of the solar cycle.” – Ed Smith, Ulysses project scientist, NASA Jet Propulsion Laboratory.

The dynamics of low altitude magnetic fields in polar regions are also a focus for interest. As 11-year solar cycles progress, sunspot population increase near the solar equator. As the magnetic field is “wound up”, sunspots (and their associated magnetic flux) drift toward the poles where they slowly disappear as the old magnetic field sinks back into the Sun, quite accurately described as sunspot graveyards. Understanding how this cycle works will help to reveal the secrets of the solar cycle and ultimately help us understand the mechanisms behind Space Weather.

Source: NASA Featured News