Astronomy for the layman; Light of the night sky

But National Association of educational broadcasters with the cooperation of the California Academy of Sciences and radio station KPFA in Berkeley presents a program in the recorded series astronomy for the layman on today's program. Leon the son of a lecturer in astronomy at the Morrison Planetarium of the academy and John Hopkins an inquisitive layman discuss light of the night sky was oh Diable light. Mr. Hopkins begins the discussion. Leon I'd like to branch out tonight and ask you something which in a sense isn't isn't truly astronomical optional. Further afield in our discussion of the atmosphere I notice that if one goes outdoors on a clear moonless night it isn't really dark not like inside a closet. Is this star light or weird Where does this light come from. The light of the night sky is the various sources the stars of course do give us some light. The Milky Way in particular is a band of very faint illumination caused by the combined light

from medians of very distant stars. The planet Venus if it's in the sky and they give so much light as to actually cast a shadow. That of course requires being in an otherwise dark place to see this. So we may attribute a small amount of light to just the objects other than Sun and Moon which may be in the sky when we observe the mention I just made of the sun and moon reminds me of what is said to be an old Russian joke. Yvonne asked his school teacher or was asked by his school teacher which is the more important the sun of the moon. To which Yvonne said of course the moon and the sun shine in the daytime when it's light but the moon shines at night when the light is needed. Well I was one of them will. I didn't realize that Venus could actually produce a shadow.

Yes I have seen it on one occasion and I have heard of other people being able to see it. Well there are other causes for light at night. The Aurora. It is always visible to some extent. Now that doesn't mean that we can actually go out and see an aurora display but there is a general glow in the sky called the light of the night sky which is persistent which varies in intensity but it's always there. I want to kill you just after twilight when there is still a good deal of radiant energy being dispersed in the very high atmosphere where they sun's rays have only recently left atoms and molecules are radiating light energy which they have been receiving during the day. Well this if it is directly. Responsive to the sun would be true at any latitude I know the URL displays are chiefly high nor high latitudes I guess Southern as well as northern.

But if it's just due to the solar radiation then that would be available. The equator just as much as the poles. Oh yes absolutely. The only reason that the aurora is more prominent in the polar regions is simply that when a very bright a raw display comes forth it is due to the convergence of a lot of charged particles which are coming in from space from the sun actually. And as these approached the earth they were drawn in along the lines and they have a force of years field. And they plunge in a ring that's centered about the geomagnetic poles and within this ring on the earth Iran displays are very intense and very frequent. Well them if. If whenever the earth became magnetize the poles that happened to be OWN would more moderate latitude say latitude 30 something like that then the displays would be down in

this part of the world. Oh yes the predominance of the raw displays in the north polar regions and south polar regions is simply a consequence of the fact that the geomagnetic pole that is the place where the magnetic field of the earth is strongest at the surface and comes through at the surface happens to be not so very far from the north geographic pole. Well I say not so very far the June 8 poll is on the north west coast of Greenland. This by the way is not the same as the one at a pole or the pole toward which the compass points. That's in the Hudson Bay region. There is a slight positional difference. But all of these things are in the Arctic regions. This is just a consequence of the fact that the negative axis of the earth differs by a few degrees rather than say 90 degrees from the axis of the Earth's rotation has nothing to do them with the fact that the Northern Lights occur the light of the or all displays occur in cold places.

Now that is just incidentally auroral display occur in they very rare a fight atmosphere 100 or more miles above our heads. And this in this region the temperature is quite cold at least it would be cold measured by a thermometer. Now the ordinary kind. But that's an interesting point. I have before me here a very interesting chart which was published in the Scientific American back in 1989 January issue is a double page affair that gives a sort of a cross-section of the Earth's atmosphere. We talked about that in a previous program member John and some of the information we discussed then is presented here such as the chemical composition. But what I'm looking at is the cross-section of the auroral zone the auroral zone starts just above where the meteorites first become visible. That is to say that about 80 miles high. And then it goes away on

up to an altitude of more than 300 miles and it was in this great range. The soft and glowing light will appear which we see on the earth and called the Aurora. And along this side of this chart is a scaled up temperature starting at 50 degrees Fahrenheit at the surface of the earth and we find in the auroral zone temperatures fall away from three hundred fifty up to twenty five hundred degrees Fahrenheit. This would cause some surprise and insofar as you and I would feel quite chilly up there. It's known technically as a kinetic or rather an excitation temperature its temperature that is based upon the way that the atoms in the molecules are giving light. And this is not the same as we would obtain by plunging some ometer inside of a cup of coffee or something of that kind.

When you. Start to give that temperature range the first temperature you mentioned I believe was 350. I thought. Frank I thought you're going to say three hundred fifty below zero. But then when you got to twenty five hundred I knew it couldn't be below zero because temperatures don't go that far below in the very rarefied atmosphere of the earth. So they find this strange inversion of the temperature and they search in this way starting from 58 degrees Fahrenheit on the average surface of the earth dropping to minus 60 degrees in the stratosphere climbing a little you know one of the layers of the stratosphere and then dropping again. And then in the boundary line between the stratosphere and the I own a sphere technically where these are already and other radiation effects occur. The start temperature starts to climb and so far as this picture shows anyway it just keeps on going. Well I don't want to take you or us too far from that but this year

when you spoke of the temperature not being well being you know different since then on top of a cup of coffee the. This then is not the kind of thing it's going to worry. Spaceships trying to get out there. I've heard some talk that this it was so hot out there that the spaceship would melt and that sort of thing. But you've sort of given these people and I haven't you. Well the thing you have to understand is that what makes what would make the space ship warm would be a contact with something that had a considerable amount of heat otherwise known as calories within it and a near vacuum cannot hold any any calories. It has no calorie content. However we must be careful to realize that the radiation of the sun freed from the filtering effect of the dusty atmosphere here at the surface of the Earth would be quite efficient in warming up say black surface. So we wouldn't want to have a dead black surface pointed in the direction of the sun. That would

lead to a very high temperature at the skin of the ship and the other hand if the surface were a reflector like polished metal. The temperature would go. Down quite far. Of course this is one way of controlling the temperature of a rocket ship just turn alternately in the dark side of the light side toward the sun. When you spoke of a dark body that was in line with what I was going to ask you know actually I was suppose the thermometer an ordinary thermometer bulb. We're all wrapped in black cloth or something like that would it then read these temperatures that you have mentioned you know well it would read a temperature which is in the vicinity of zero as far it would depend upon your distance. It can be calculated a lot the temperature of such a black body held at the Earth's distance from the sun might be. And as I recall. It's not far from zero on the Centigrade scale. So the temperature out there is just. It's not either kind of temperature it's not what

a black body would be and it's not what the Earth actually is not what a thermometer would read. No it's measured by the behavior of the atoms in the rarefied gas and so we see the aurora light is not due to heat in the ordinary sense it's due to the emission of light. By atoms or molecules that have absorbed radiation from the sun. Energy from the sun for a long time was a puzzle but these might be for no gases and chemical laboratories cause to glow by various means would give the same spectrum lines. But some time ago two scientists at the in the physics department at UCLA. Investigated this phenomenon in very low pressure gases and using special meth and were able to reproduce them of the spectrum lines observed in the Aurora. And it turns out that the Aurora light is due to the atomic oxygen and nitrogen and molecular oxygen and nitrogen. But in a condition that is hard to duplicate for the

density is so low and the concentration of ultraviolet light from the sun is so high that the atoms power might say packed with energy and release energy in a way that is not easily reconciled with ordinary conditions around us. But it has been done and we are quite confident of this analysis. I'm surprised that both atomic and molecular oxygen will be present in the same place since. Equal volumes of them would be half what the other does would have half the density of the other. So I'm going to have a gravity gravitational gradient. Should I keep the molecular oxygen close to the Earth's surface closer. It's fairly certain that there's considerable circulation in the atmospheric layer so there would be a good mixing. However this atomic or molecular oxygen and nitrogen condition is a sort of a transient thing. The molecule of oxygen or nitrogen might meet up with a highly energetic. The quantum of ultraviolet light coming from the sun which

would split apart a molecule only have two atoms to atoms might come together and the same time not be in the presence of energetic quantum of ultraviolet light and they would combine to form a molecule and so this will go on and depending upon whether the energy resides in the atomic call molecular gaseous state why the auroral spectrum would be a little different. The lights are beautiful I myself have never seen them but I've seen some very large beautiful colored pictures in a National Geographic issue of November in 1907. There was an excellent article called unlocking the secrets of the Northern Lights by Professor Garth line of Cornell who runs a neural research station in northern New York where by the way they get some nice arole displays. And in this article there are beautiful pictures of the Aurora showing the characteristic yellow and yellow green and red and colorations. These assume fantastic shapes looking like great bursts of

light sunbursts. Curtains hung in the sky flickering. Now they have caused a great deal of comment on All in all times. It's interesting to note some of the reactions that people of olden times have had to the Aurora as noted in the excellent article by Professor dark line that I just mentioned. He says here the Book of Maccabees parts of which are included in some versions of the Bible describe what is believed to have been in Iraq and it came to pass that through the whole city of Jerusalem for the space of 40 days there were seen horsemen running in the air in gilded Rayment and armed with spears like bands of soldiers and horses set in order by Ranks running one against the other with the shakings of shields and a multitude of men and helmets with drawn swords and casting of darts and glittering of golden armor and of harnesses of all sorts. Often the aurora is mistaken for a great fire burning in the distance. An old

account from Roman times says that under to bury a Caesar the cohorts ran together in aid of a colony of Dia as if it were in flames. An Associated Press dispatch from London describing a brilliant aurora display in England and Europe January 25th 1938 said the ruddy glow led many to think half the city was ablaze. The Windsor fire department was called out in the belief that Windsor Castle was a fire below bathing snow clad mountain tops in Austria and Switzerland. It was a beautiful sight but firemen turned out to chased nonexistent fires. Well you see this isn't anything to do with people. Such a long time ago either. And I notice here is a report that involves Pearl Harbor in 1041 just before Pearl Harbor. Some people in Washington DC seeing analog display which is rare so far south thought it was a new weapon being cried out by the army or searchlight helping to repel a surprise attack by the German air force.

People who don't know the cause of the Aurora think that there are reflections of light from the snow capped in the northern countries not realizing during the best displays that the long night up there and there is no light to reflect off the snow capped. In Old Norse Stein's they thought that when the Northern Lights flashed of all cures for the writing of Aha. So in the legend and partly in science all down the years we find many strange ideas about the Aurora which are only recently cleared up by the identification of the spectrum with the radiation of atomic nitrogen and oxygen. Your mention of the fact couldn't possibly be reflection of light because at that time of year in the winter there was no light to be reflected. Makes me think of another possibility of light at night which of course I'm sure is a real possibility and that is in the summer time in northern latitudes

the sun just doesn't get very far below the horizon. Yes that of course is just Twilight which we talk about when we spoke of the atmospheric effects on astronomical observation there they like coming from just below the north point of the horizon. I would if you was in the air above us but that is merely reflected sunlight and shows no was no difference in its spectrum. Well in the present situation with the North Magnetic Pole where it is in the auroral displays in the north this sort of leaves the equator out to the people to equator have any kind of a source of sky light. Well and aside from any general light of the night sky they have I think a very fine opportunity to see something with very few persons seen or even know exists. I never heard about it's called was a Dayak a light. It's no good if you live in the city you just waste your time trying to see it. But if any of our listeners are at a distance sufficient that they do not have any city lights to interfere in their

sky then they look to the west just after twilight ends. I figure an hour after sunset when the sky would be otherwise quite dark. There is a great diffuse wedge of light standing in the West as a broad base and tapers up 30 or 40 degrees. This is difficult to see. You have to go out and be away from lights for 15 or 20 minutes so that your eyes become used to the faint blue mini. Wiley's the Dayak a light can be generally seen after twilight in the tropics at all times of the year. Here in the north latitudes the best occasions are in the spring after sunset and in the fall before sunrise. The reason for this is something as follows. The equator of the sky cuts our horizon at a constant angle depending on our latitude. This angle is the same at all seasons of the year and all

times of the night. But the eclipse pic or apparent path of the sun along which there's a diopter light seems to stretch and makes an angle of twenty three and a half to agrees with the equator and therefore depending on the time of the evening or morning and season of the year the ecliptic will cut our horizon at a steep or not so steep angle and in the cases I just mentioned the ecliptic will cut the horizon at the steepest possible angle and there give us our best view of the Dayak a light. And this is a strange thing it's been reported down through the years but very unscientifically it was thought to be some strange kind of a twilight and nobody knew quite what. And it wasn't until about 100 years ago that anyone took the trouble to make any kind of how we say scientific observations.

And it was a chaplain on the US team for a good Mississippi in the year 1853. This gentleman Reverend George Gilman was on a trip to Japan and before we left he had talked with some astronomers and learned that there was this the Kuder light in the sky. None of this would die of the light because it lies along the direction of the zodiac on either side of the sun. But nobody knew much about it and an astronomer suggested it Reverend Jones far from artificial lights way out at sea and lots of time on their hands might get a good view of this. And he made a careful record. And as a result of his observations and careful description it was pretty well established that the best explanation for this light is simply a swarm of billions upon billions of little tiny specks that are going about the sun in individual orbits spaced between the Sun itself and the Earth's orbit. And as we look in toward the sun

and when the sun is shielded by our horizon we see light being reflected from this zone of space. And just like so many little planets infinitesimal in size all reflecting a little bit of light and these give the total effect known as the Dayak light are these particles similar let's say two very small meteors. Yes yes they are just infinitesimal own and meteors there might be a few particles in the vicinity in fact I'm quite sure a few of them would make respectable meteorites if they hit the earth. But the general makeup of it is simply fine dust which is scattered in the plane of the solar system that is approximately the plane of the Earth's orbit on both sides of it and out about as far as the earth's orbit and probably beyond two but the SO Diable band which is supposed to go all the way around and not just. Either before the sunrise or after the sunset is extremely difficult to see and I myself have never

seen as a viable band. While I have seen was a Gaika light and exactly opposite the sun is supposed to be a region where the little particles are all reflecting very efficiently and they are. This causes the comfort glow or begin to shine. This I have never seen and it is supposed to be quite difficult to observe. This then would be just after sunset in the East would be the gate. If you saw me and said I could light in the West me a very broad X-Treme think patch of light just opposite the sun. You more or less answered my next question to you. That was about the extent of this cloud of dust particles. With the people on Mars. I was a Haikal height. Yes yes they would. Although it would be it would appear smaller that it's a more concentrated and closely to the sun and therefore more difficult to observe the total amount of light might be a little greater But I think

not because it's so far as I know it suppose that the particles which comprise of the Dayak light are largely confined within the orbit of the earth. The greatest percentage of reflected light comes from inside the Earth's orbit. Well and by the same token it was the night the light would be even brighter I suppose on Venus. Yes and it would be just amazing I suppose from Mercury where it would be seen in a dark black sky since the. Planet Mercury has no atmosphere and would seem to go right down to the sun. The fact that leads me to recall that it was a dyke of light is thought by some to be merely the outward extension of the sun's corona. The Sun at Eclipse time shows this beautiful her halo of pearly light around it which is known by its spectrum to be partly

reflected sunlight and partly emitted light from atoms. And then the spectrum of these what I call light has been obtained and is found to correspond or reflected sunlight so portions of that of the corona must be physically quite similar to portions of the as a DI Collider So it is thought that there is possibly a gradation in June 954 there occurred a total eclipse of the sun whose path of totality started with the sun rising in Eclipse near northeastern Nebraska. Then through Canada labrador cross Greenland the Scandinavian countries parts of Europe and then down into the Near East where the eclipse was total at sunset. In India. Now just before the eclipse the sun rose as would be the case in the Rocky Mountains near Denver. There was

apparently a fine opportunity to check this matter of the transition between the Corona Light and the Dayak a light that is at the time the sun was totally totally eclipsed. It was below the horizon but the outer streamers of the corona and of the Dayak the light would be just over the eastern horizon. And so astronomers planned to take photographs and photoelectric recordings and all sorts of light sensitive measuring devices to establish just what kind of light was there and how one grated into another. This was a unique opportunity and the hopes ran high. Unfortunately the weather at the time was not of the best and results if any will be rather hard to interpret. But the astronomers who tried this problem though doubtless planned to do it again at the next opportunity.

And eventually we may have the answer to the question what intimate relation if any is there between the outer corona and the acolyte. Well not from pictures I've seen only on the corona is what some call it right good I suppose but a rather irregular sort of glow around the sun. Then when one looks in the West after sunset to look for there's a dicho light. Is it rugged too or is it a fairly smoothly outlined band. It made it into a pyramid. Yes it has a wedge shaped appearance the broad base toward the sun and the apex the way the outline is diffuse but I wouldn't say it was jagged. The coronal screamers and maybe something a little different than the extension of the Dayak alight. The point being however that there is a transitional of finely divided and very sparse material starting with the sun and going outward. And just how it drains from coronal conditions into the Dayak all

light conditions is something we would very much like to know. There's a direct the light is so little known that even amateur astronomers without very much equipment can add something to our knowledge. There was a fine series of observations made by a seafaring man on the ships back in the beginning of our century a ship which is going from regularly from Sydney Australia to Vancouver B.C. And he published a nice series of observations and then just recently last year a captain Ghent Dutch and member of the Dutch merchant marine officer rather reported his observations of over 40 years duration on his voyage is and his observations every quite detail and regard is very valuable. I think we can say that if anyone wants to learn anything about the Dayak alight the first thing is to get a job at sea.

You've been listening to a discussion between Leoni Sellon a lecturer in astronomy at the Morrison Planetarium in San Francisco and John Hopkins an inquisitive layman on light of the night sky was oh Diable light the series of astronomy for the layman was recorded at radio station KPFA in Berkeley with the cooperation of the California Academy of Sciences. This is the end of the network.