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This was an amazing project: they counted argon atoms about once per month—and remember, they were looking for a tiny handful of argon atoms in a massive tank of chlorine atoms. When all was said and done, Davis’ experiment, begun in 1970, detected only about one-third as many neutrinos as predicted by solar models! This was a shocking result because astronomers thought they had a pretty good understanding of both neutrinos and the Sun’s interior. For many years, astronomers and physicists wrestled with Davis’ results, trying to find a way out of the dilemma of the “missing” neutrinos.

Eventually Davis’ result was explained by the surprising discovery that there are actually three types of neutrinos. Solar fusion produces only one type of neutrino    , the so-called electron neutrino, and the initial experiments to detect solar neutrinos were designed to detect this one type. Subsequent experiments showed that these neutrinos change to a different type during their journey from the center of the Sun through space to Earth in a process called neutrino oscillation .

An experiment, conducted at the Sudbury Neutrino Observatory in Canada, was the first one designed to capture all three types of neutrinos ( [link] ). The experiment was located in a mine 2 kilometers underground. The neutrino detector consisted of a 12-meter-diameter transparent acrylic plastic sphere, which contained 1000 metric tons of heavy water. Remember that an ordinary water nucleus contains two hydrogen atoms and one oxygen atom. Heavy water instead contains two deuterium atoms and one oxygen atom, and incoming neutrinos can occasionally break up the loosely bound proton and neutron that make up the deuterium nucleus. The sphere of heavy water was surrounded by a shield of 1700 metric tons of very pure water, which in turn was surrounded by 9600 photomultipliers, devices that detect flashes of light produced after neutrons interact with the heavy water.

Sudbury neutrino detector.

Photograph of the Sudbury Neutrino Detector. The 12-meter diameter sphere is shown with the interconnected triangular support structures, as well as the matrix of photodetectors covering its surface.
The 12-meter sphere of the Sudbury Neutrino Detector lies more than 2 kilometers underground and holds 1000 metric tons of heavy water. (credit: A.B. McDonald (Queen’s University) et al., The Sudbury Neutrino Observatory Institute)

To the enormous relief of astronomers who make models of the Sun, the Sudbury experiment detected about 1 neutrino per hour and has shown that the total number of neutrinos reaching the heavy water is just what solar models predict. Only one-third of these, however, are electron neutrinos. It appears that two-thirds of the electron neutrinos produced by the Sun transform themselves into one of the other types of neutrinos as they make their way from the core of the Sun to Earth. This is why the earlier experiments saw only one-third the number of neutrinos expected.

Although it is not intuitively obvious, such neutrino oscillations can happen only if the mass of the electron neutrino is not zero. Other experiments indicate that its mass is tiny (even compared to the electron). The 2015 Nobel Prize in physics was awarded to researchers Takaaki Kajita and Arthur B. McDonald for their work establishing the changeable nature of neutrinos. (Raymond Davis shared the 2002 Nobel Prize with Japan’s Masatoshi Koshiba for the experiments that led to our understanding of the neutrino problem in the first place.) But the fact that the neutrino has mass at all has deep implications for both physics and astronomy. For example, we will look at the role that neutrinos play in the inventory of the mass of the universe in The Big Bang .

Questions & Answers

why the dark side of moon never face us? because moon dont rotate? why tho
Rishabh Reply
im in 8th standard and my school teach us nothing about astronomy but i want to be an astronomer so i study from youtube and apps like this but sometimes i get language problems
Rishabh
dark**
Glory
side**
Glory
The Moon does actually rotate. It takes 27 days for the Moon to make a full rotation. Because it takes it so long and the Earth is rotating around the sun, it seems like the Moon is pretty much standing still. That's called "synchronous rotation".
steveh259
I ment to say "The Earth is orbiting around the sun"
steveh259
Tidal Locked.....
Adam
***svs.gsfc.nasa.gov/4442
Collins
thats cool
Gospel
ya gives you a look at how the moon orbits around us too and a perspective of how fast we are going. also gives the moon phases for the year! enjoy 😁
Collins
yes you are absolutely correct, it just like something like the milk of heaven
Subhasish
the far side of the moon is not the dark side of the moon.
Shawn
what phases of the moon occurs when spring tide?
Florence Reply
the moon has a 28 day cycle. you can download a moon calander or follow the pattern and make your own calendar. 1st full moon of the year 21/22nd Jan, its also a blood moon and a wolf moon. if this info helps at all. 😊
Collins
***svs.gsfc.nasa.gov/4442
Collins
How to determine the velocity of light?
PARTHIB Reply
using this formula c=1/√absolute permeability×absolute permittivity of free space i.e. c=1/√8.854×10^-12×4π×10^-7~3×10^8ms^-1
Vidyashankar
what is mean by Big Bang
block Reply
What it means by Big Bang is how the world was made and came in to exist
Glory
The Big Bang Is The Best Explanation For What We See Around Us, And For The Origin Of The Universe, All Our Evidence Points To The Big Bang Theory..... And Was Proposed By A Belgian Priest.....
Adam
if the big bang theory is really true than i would like to know what exploded and where did it came from and where did the energy came from and where come from for the matter to expand into amd where did the organization come from and where did the information come from.........
Gospel
Some say that on the otherside of the singularity was a black hole. They say that at the other end of all black holes is another universe. Hence the multiverse. It's all theoretical at this point but less than a 100 years ago people believed that there was only 1 galaxy in the universe. So why
Rafael
should there be only 1 universe?
Rafael
universe.
Rafael
is astronomy a hard subject to learn because i want to be an astronomer
FNAF Reply
No it not it just takes time and effort to learn
Glory
if your already interested/observing, your already an astronomer ! The more you look and read the more you'll learn.
Collins
I want to become a scientist but my knowledge is very low. How I can improve my knowledge?
Wwe
any form of science courses, there's free crash course channel on you tube. I've learned alot from this channel. covers most topics, science: biology chemistry physics, astronomy, ranges to anatomy, history and many many more. it's a never ending subject!
Collins
suggest a channel as a example
Wwe
CrashCourse is the name of the channel and there is a picture of an apple. look through their play lists. They will have other related channels they follow also.
Collins
thank you so much
Wwe
your very welcome
Collins
Why are they so far away that their light takes hundreds of millions of years to reach us on earth?
LadyCatTM Reply
what is comets , astroids ,
Sumit Reply
comets are broken pieces of dust frozen debris Asteroids are big soiled pieces of Ice that burst into flames when it in to earth's atmosphere
Glory
hi, I am yamini, I am in class 8 but very much interested in astronomy and go to NASA, what are the subjects in which I can master and lead to NASA.
yamini Reply
Hello Yamini, Im Ken and I'm avery intrested in joining the NASA too. Is nice to meet you.
Ken
very*
Ken
nice to meet u ken
yamini
What I know about the subjects is that you have to be a master on science and math, also if you know about aviation is better too
Ken
I read that the Russian language is very important, is not a requirement but it's like an extra point!
Ken
yeah like physics, chemistry and maths, they are my most favorite.
yamini
than you can go free of cost
Arush
Yes, That's right!
Ken
how
yamini
Oh! Free of cost?
Ken
hello yamini nice to meet you
Burak
wow from NASA ur so lucky
FNAF
hello yamini nice to meet you
block
what is time
Abdul Reply
Time is relative
mrunal
pls elaborate
sakshi
the clear defination.I know that.
Abdul
In planet mars there the life exits or not and is there water there
Eshwarsa Reply
see till now nothing can be found as u know that the curiosity rover has struck in mars
Maya
It has been proven that there are water molecules on Mars but not enough that most lifeforms could thrive upon.
Ariana
There are huge amounts of water in the ice caps and under the surface. The surface and chemistry indicate that Mars had cosiderable amounts of water on its surface in the past.
Julius
what is your opinion about the theory of Vedas about modern physics..
Manish Reply
i think in some ways vedas are also correct but not everytime
Maya
I agree
sakshi
hmm even I agree
Samuel
Is there any patened theory about time relativitg in growth and development?
donot Reply
some astronomer's says that there is no alien exist but why search for extra terrestrial intelligence center is established
Eshwarsa Reply
No One Knows That For Absolute Fact, The Universe Is Too Huge To Have Any Type Of Idea About What Exist In The Far Reaches Of Our Universe.....
Adam
Check Out The Drake Equation.....
Adam
their should be aliens as like ours there would be another planet
Maya
which could have existed life on it
Maya
adam i want to ask a question
Maya
can kepler 1st law be applied on all the planets of the universe
Maya
hello, anyone home?
Denise
guys listen we cannot ever find aliens because our technology is not that great.we don't know whether they exist or no because our universe is very large . Just for an example;even if we spot out aliens we cannot reach there because lot of time must have been passed and before us reaching there
Samuel
what if their species or existence might get vanished our have been extinct!! getting my point
Samuel
sjskskfhjkkktewqqw and try?
Lanika Reply
what is this ?
Samuel
hi I am Samuel from India mumbai
Samuel
nice to meet you
Samuel
thats my question, what is this?
penzias and wilson's a discovery of the cosmic microwave background is a nice example of scientific serendipity-something that is found by chance but turns out to have a positive outcome
Jacqueline Reply

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Source:  OpenStax, Astronomy. OpenStax CNX. Apr 12, 2017 Download for free at http://cnx.org/content/col11992/1.13
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