Ricky Egeland | | NCAR HAO | Century-long Monitoring of Solar Irradiance and Earth's Albedo

thank you for coming to issue a cloaking today today we have Ricky Egeland from a trio and I’m Montana State University Ricky received his bachelor of science degree from university of minnesota in 2003 and after that he worked at CERN for seven years on software development for the compact muon solenoid project the CMS so he’s one of the three thousand-plus co-authors on the sahibs both some discovery paper actually because such an important paper i downloaded addenda as a 32 pages Ricky’s on 30th page a tricky and the University of Minnesota is on the thirtieth page it’s a pretty amazing effort there and after that he decided to look at something more visible and there’s nothing more visible than the Sun so he joined the solar group at Montana State University I got a Master degree in physics in 2013 he’s currently a PhD candidate at MSU and also a new Kirk fellow here at material working with Phil which also a co-author on this paper but feels a little bit under the weather today so hopefully he’s tuning in on web his research focuses during the thesis is a solar cycle sun-like stars magnetics cycle grand minimum and faint young Sun paradox and today he’s proposing a novel method for long-term monitoring of solar radiance and also the earth albedo thanks hun lee so yeah as I only mentioned i came to hio to study the solar cell our connection in particular the magnetic variation and solar and stellar dynamos and Phil come up with this idea that really makes the solar sailer connection concrete he wants as you’ll see the Sun it makes the Sun look like a star so this is this is really a connection home and the question that that we’re thinking about that we’re hoping to answer with this experiment is an important one and it’s a very critical to the mission of n car and of a jo it’s how how does the radiance of the Sun very on century long time scales and I’ll do a brief review of you know where we are with this question at the moment but it’s it’s it’s something that’s not very well known and I think we have a responsibility to try to get at this question for interest of climate science and we should be very grateful to the ancestors our predecessors in in solar physics for their diligence in making a 400-year observation of sunspots right and so if we did something if we started off today making similar observations we would have a good a much better understanding about this question and so the importance to climate comes in this in the sun’s role in radiative forcing which on this chart from the IPCC assessment is the one of the smallest slivers on the chart and so and this is a from forcing relative to 1750 so we’re definitely talking about century long timescales here it’s got a medium confidence rating and it’s got a value that is anywhere 0 2.1 so it’s has a hundred percent air bar on it which makes you think okay if that’s if that were a Gaussian standard distribution something like sixty five percent is in that range there’s a possibility that’s negative right so we’ll come back to that later so it plays a part in input for climate models and for the period before the Industrial Revolution this is the only the only game in town this is what’s driving the climate so people who are interested in in paleoclimatology climate studies are very interested in this in this question this is the space-based record from space-based radiometers of the of the total solar irradiance so all all wavelengths into one measure watts per meter squared at the earth what we can immediately see here is that there’s a good precision for any given experiment but low accuracy among the in Samba love these experiments so all of them are able to detect the point one two percent variation that goes in phase with the

solar cycle for the duration of an individual experiment but they’re absolute levels are sort of scattered more along the LOC percent range in this in its this plot recently it is sort of headed out by the source I instrument advances in understanding radiometers have have convinced the other experiments Virgo to come down from the previous standard value of 1365 meter squared down to this level of thirteen sixty and some missions that were launched since then are sort of in agreement to that accuracy but if you’re looking at the whole time scale you have the problem of tying them all together and this is what’s known as making a composite so based on some assumptions or some understanding on the degradation of these instruments you have to try to put them all on to the same scale so that you can have a longer times here of roughly 33 um and this is complicated by what’s known as the Akram gap so Akram of being one of the higher precision experiments there’s a couple of years where there’s no overlap and so that that hurts a lot when you’re trying to make these composites and for the variations that we’re looking for these sort of long-term variations those assumption the assumption that you make in putting the composite together we’re going to make a difference in sort of the long-term behavior that’s observed so this is from a review from Yeol 2014 where there they’ve taken the three major composites that are out there the the Akram the P Mod and they can’t even read the other 1i rmb i think it was so normalized the 2008 minimum so that it’s clearly you can clearly see the differences between them as one goes back in time so the the Akram in red increases from this minima to this minimum and comes back down and the P Mod composite sort of declines throughout this period and black line is a is not based on data but it’s actually a property model that’s the satire s which takes into account our understanding of what’s of what’s it’s an empirical relation i should say of what’s causing the variations in the total solar irradiance it breaks up the Sun in two parts there’s quiet sun there’s applause there sunspots you come up with empirical relations to how these different types of areas contribute to the total solar irradiance and it does a very good job of following these space-based measurements there’s still the discrepancies and you could imagine that if we have even longer time series that’s broken up from several different missions this problem may still remain going back to sensory long time scales like is considered in the IPCC report you must use these proxy models and you use proxies that get progressively worse as you go back in time so we have magneto grams you know for a good part of the 20th century necessary 21st century that’s that’s a good way to get the these areas then it goes back to the telescope area drawings & and so you can imagine it’s more and more difficult as you go further back in time to to trust the accuracy of these of these reconstructions but nevertheless there they are and this one predicts very small changes in the total solar irradiance so just measuring from the base of these minima here I picked out to sort of noticeable change level here one of them has a point Oh 3 and change going back to about 1900 so that’s roughly a century and a point 06 first change from the maunder minimum when sun spots disappeared from the Sun for some time now as you might imagine the the assumptions that you make when making one of these reconstructions can also have a large effect on the results so here’s another reconstruction from Shapiro atau that has much larger changes in the reconstructed variability

total solar irradiance variability so he’s got something like from the monitor minima a point four percent changed let’s I think that’s over a factor of 10 larger than the it’s almost a factor of 10 larger and here we’re getting close to a one percent change he goes back many millennia and so that’s I think that’s a similar change from his work it’s based on his assumption that what’s varying here is the quiet sun on long time scales he uses a 22-year average of quiet sun variation and he connects that to the the radioisotope variations taken from ice cores and as sort of the that modulates the amplitude of this proxy and he gets these large changes and he knows it’s very different from the other ones and he says in the conclusions the observational data do not allow to select in favor one of the proposed reconstructions therefore until new evidence becomes available we are in a situation where different approaches and hypotheses yield different solar forcing values so he sang there’s nothing you can do to throw this away well there’s been some looks at this one that from particular from Judge and Shapiro you even joined in on it that reduced it by factor of two there was been modeling work taking the Assumption seriously and they said no no there’s no way the years climate the Earth’s climate would have varied way too much in order for this to be true but you would really hope to sort of to eliminate those kinds of things using data another thing that’s it’s very important to the climate study is the spectral variation of the Sun and this was the source seemed surprised the measurement of spectral variability from the period of two thousand four to two thousand seven when the TSI was doing something like this so going from Maximum to minimum and be well while that the TSI was decreasing the visible and the infrared were increasing and the ultraviolet were decreasing by much more than was expected by one of these proxy models and and this was from hi Adele nature paper in 2010 and one of the conclusions from this measurement was this would put the the solar forcing a tan inverse relationship to the solar cycle so at cycle maximum you would have a relatively low forcing than at cycle minima and so you could imagine if the century-long history looks something like this then you would have a negative value right you wouldn’t you would have actually the earth a relative cooling effect on the earth due to the increase in activity sort of counterintuitive but that’s the measurement and here’s a here’s a plot from a cop and lean sort of summarizing the difficulties in measuring these these small changes very small changes so here’s the solar cycle variability that’s that’s at about close 2.1 percent point and this is a time on the on the bottom axis these angled bars here our degradation of instrument that may be happening over time and superimpose here are a couple of estimates of of the Sun coming out of the modern minimum these are from from reconstructions two different ones from from their earlier work and so this is sort of gives you an idea of what sort of sensitivities you would need in order to get at this and he says directly detecting these kinds of chains are either requires intrumental stabilities of point 0 0 1 percent per year and measurement nua t & or measurements having absolute accuracy uncertainties of 0 point 0 1 percent such a the planned future future mission so that measurements separated by several decades detect secular changes so I think you would really like to have both because if you imagine breaking up the time series you know there’s there’s no other standard for this measurement so how do you know when accuracy has been achieved and I think if the time series is broken you would sort of always be left with the question okay what was going on during the time that weren’t looking at it so the experiment i’ll be describing today really aims at measurement continuity and the inspiration for this experiment came

from the the solar cellar community and this is the automated photometric telescope program are run by Tennessee State University at fairborn Observatory Lou Boyd are responsible for keeping the telescope going Greg Henry for the the output and analysis and these are very moderate modest telescopes measuring solar like variability of sun-like stars from the ground and so it’s it’s pretty impressive when you think about it the level of precision that they’re able to achieve going through the turbulent atmosphere and I’ll describe how that’s how that’s done in the following slides but these are about 80 centimeter telescopes they sit outside at fairborn Observatory in in Arizona and the measurement program goes like this so you pick a target that you would like to observe this is one that I’ve been working with recently HD 30 495 you find you define a group of nearby targets that you hope will be photometrically stable all right so these are going to be standard candles out in the sky which you are going to take the relative difference relative photometry measurements with respect to those you don’t know in the beginning whether they’re going to be stable or not so the only way is to start developing your time series and sort of check but the operation program goes like this you you measure your program star D and the comparison stars a through C 3 times per group 20 to 30 second integrations in these B&Y bands that are centered at a book 480 and 550 nanometers right near the peak of the output for the Sun and they’re interested in sun-like stars so it makes sense to choose these bands let’s see and then you take all of those measurements and the fundamental end product after the data produced is not absolute measurements with differences the three green differences are your program star D with respect to the stars that you hope are stable enough to get a highly precise relative measurement and the the dip is among those stars are used as a check to make sure that they are in fact stable so if one of these guys is varying strongly you’re going to see that variation in the relative measurements that involvement and okay so this is a this is a stellar photometry so we’re going to have to be talking in the language of astronomers which is magnitudes which is a strange scale that goes sort of backwards the brighter it is the more negative it is but it turns out this is what you need to keep in mind a milli magnitude change is about a point one percent variation okay and so here’s HD 304 I’ve ability I also plotted here is our the comparison stars so let’s start with the comparison stars the white squares are the mean subtracted differences of the two comparison stars that were left one of them was rejected because it was too variable it was found to be variable when you when you looked at it plotted with respect to the other you can see that they had one problem in common so you get rid of the common problem and the variation the mean subtracted variation of the difference between those two pins and stars is very flat so it has a year-to-year scatter of 0 point 0 7 percent and an uncertainty so in a yearly average all of this work is sort of using your Lea jizz that’s a very eight percent so those are the comparison stars were pretty sure that those are stable this actually shows that they’re stable now the difference of our target star is shown in the black lines here those are the seasonal averages again yearly averages with respect to the mean of those two so we’re using both of them at the same time and that’s that gives us the very nice variation we see here it’s varying by one point eight percent much larger than the Sun but they find in there and they’re in samba studies this is a not uncommon for very young fast rotating stars like this one the uncertainty and in a given seasonal mean very low the

point 0 six percent error bars can’t be seen so the green the green dots are the individual differences with respect to the comparison stars the black being are the seasonal averages and you can get a spectral information from this as well as to these two colors that are being measured one in the blue and one slightly yellow green if you take the difference of so there’s the difference between the colors of the differential magnitudes which is sort of a mouthful you get how this star varies in color as it goes through its its cycle here and we see as this star gets brighter it tends toward the blue and as it gets dimmer it tends toward the yellow so some spectral information is available in this but that star was much more active than the Sun what about a really sun-like star so here’s the solar twin 18s co which is which is photometrically and spectroscopically the the most sun-like star that’s been found to date and it’s part of this program its variation has been measured it’s slightly larger amplitude than the Sun Oh point one two percent and we got error bars on the on the seasons of point oh three percent so yes you can you can get at solar like the Sun if the Sun were out there for us to look at this program would be able to measure its its cycle variability and there’s the idea so let’s do it let’s put the Sun out there and and so that we can do differential photometry with respect to stable background stars we do that by a reflecting object into geosynchronous orbit the numbers so geosynchronous orbit means it’s going to stay above a latitude you know we hope for Perpetua tree this is the distance of that orbit we ran numbers like with a 4 meters sphere it would have an angular diameter of 20 milli arc seconds which is actually smaller than some of the stars in the sky so baitul juice is three times larger and angular diameter has been measured then then this would would appear it has a high albedo we use 2.9 and this gives it a magnitude of 10 so 10 magnitude object in the sky that’s reflecting sunlight okay and so we can directly apply the same techniques that worked for the stellar program so looking at the how we how we get some of these numbers on this is how you calculate the brightness of this object so it’s dependent on the on the magnitude of the Sun which is about negative point 27 it’s dependent on the proportional to how large the sphere is that’s the radius of the spear and its distance away from the as well as its its albedo so you you you know you would like to have a bright object right that’s of course easier to see and this is a it’s a parameter thats related to how it scatters light so what’s the distribution of angles of incoming light so we assumed a lambertian diffuser which is sort of a ideal case but it makes it scatters all angles equally and it makes Q about 1.5 and then it depends on the phase angle and the phase angle is going to change every day and at night this thing is going to be full right so this is the this is the phase angle it’s the angle between the Sun the observer on earth and the geosphere so you put up an opposition he’s right here and then we took a look at how how big does the geosphere need to be in order to get you know some things that we would like for the observation so this is so if you assume a point oh five percent rms photon noise in these in these photometers you want integration times to be short so you can do lots of observations then this this sort of sets a limit depending on the the width of your of the band that you’re observing this this sets a limit on the diameter of the geosphere and the diameter of your telescope so there’s sort of a cost-benefit analysis implicit in this do you want to make huge telescopes for this program or do you want to put a huge speak out there in the geosynchronous orbit so we chose a sort of a middle ground for a four meter geosphere in the strom gun bans gives us something like a 1.5 meter telescope which is simple that’s a small telescope by

today’s standards so first question you might ask can you really put something into geosynchronous orbit and expected to stay there forever and the answer turns out to be yeah actually it’s not too bad so this is a some simulations from freezed in a tell in 1992 taking a look at integrating orbits for geosynchronous objects using the gravitational potential that all of the from the earth all of the non spherical components largest being the equatorial bulge but he took it everything that he had available at the time and the gravitational attraction due to the move into the Sun and so he he knew numerically integrated the absolute and obtain solutions like this finding that up for any geosynchronous orbit the worst-case radial excursions are about 50 kilometers or changes in the semi-major axis it’s about plus or minus 2 kilometers changes in the e centricity which conspired to make this about 50 kilometer change in radial distance what varies oh one of the most important things for this concept is is is it going to stay in the same longitude it’s going to move away from observatories so it turns out if you if you put it there are certain stable longitudes at these two positions 75 East and 105 degrees west about which these orbits will oscillate so if you put it at one of those longitudes it will oscillate very close to it it’ll stay above you the inclination is a problem so this simulation is from a is it started from an inclination of zero so this is a special case of geosynchronous this is the geostationary it’s the kind that you know really doesn’t move at all or it stays on the equator but if you were unpowered it would oscillate all the way up to what is that 14 Greed’s inclination come back down there’s it’s not really doing a discontinuity here but actually this other parameter is changing the right ascension and so it sort of oscillates there and so that would be a problem what else oh this this fact of 50 kilometer excursions has been tested in practice there are actually abandoned satellites out there that are tumbling around unpowered and they fall within the bounds that he calculated so the problem of the the huge inclination changes can be solved because actually there’s a plane about which those orbits oscillate as well it’s an in plane of the orbit which about which they ought that’s a 7.3 degrees inclination and when he started the the numerical integration from there there’s a much smaller amplitude in the changes over the century something like 1.3 degrees so this is a very stable orbit and the reason that this stable exists he’s got a nice picture that appeals simply to Newton’s second law it’s the it’s a balance between the the attraction of the equatorial bulge and the the Sun and the moon which are out out there in the ecliptic plane time integrated the force is roughly cancel out so there’s that’s why the stable plane exists yeah this is proposed as a better alternative for graveyard orbits instead of just putting them into a higher orbit if they were in this plane objects would have less relative velocity to each other there’d be less chance for collisions and things like that so where are these stable longitudes well they’re in very good very good location to actually one of them cuts right through the American Southwest where there are many well established observatories one of them being fair born in fact was right up right above boulder and there’s you know a lot of them depending on how far east west you’re you’re willing to go to make these observations now you’re it did you don’t want to you don’t want to be at the sort of a observe this thing at an angle because you don’t want to compound the effects of air mass the reason that the differential method works so well at getting rid of the problems with air mass is because they keep the stars close together right so they’re looking at roughly the same air mat through the

roughly the same air mass in close succession under the hopes that the atmosphere doesn’t change too much now they do get rid of some data when when there is atmospheric variation but so you’re hoping to subtract away in the difference the problems due to the atmosphere there’s also an eastern hemisphere stable longitude so you could imagine why not put two up we can have a sort of east-west competition to measure this the best so what would it look like what would what would it look like in the night sky so here’s a long exposure photograph from Pitt from bill livingston at Kitt Peak where you can see these little white dots those are geostationary satellites and so geostationary satellites are they’re powered so they have propulsion to keep them into place because you don’t want to have your customers going out on the roof every night and you know trying to get the TV station right so they’re really in the same spot and so there’s for reference here these are stars streaking by during this exposure this one’s Rigel and this purple streak is the Orion Nebula that’s about 2.8 degrees apart so what would geosphere look like not like one of those dots but like a big figure eight so its inclination is going to mean that throughout the 24-hour period it’s going to be changing declination in in the in the celestial spheres changing its its altitude in the sky if the if the East centricity isn’t perfect there’s going to be a little width to this and it’s going to follow this figure eight pattern if you had a very low eccentricity this would follow something like a straight line here’s a nice animation i found on wikipedia for a japanese japanese gps system that would be an inclined to do secret bits with three satellites such that at any given time one of them would be above Japan and so a vector going from the surface of the earth to the position of one of these satellites in there inclined orbit traces out this analemma is figure eight pattern so that’s what the juice to your orbit would look like and that takes us to the first problem you’ve got bright stars passing behind geosphere all the time this is a source of noise you want to be the brightness of geosphere very precisely and not not things passing behind us fear so yeah you got something like 15 arcseconds cosine declination motion of these stars so passing through the sky one way you might get around this is by putting three photometers in the focal plane so that at the integration of geosphere which stays in the in the primary photometer and the stars are passing by you have an estimate of the flux that’s passing behind you sphere both before and after so say you could do a subtraction from the signal right other complications to the observation program so in a six-hour night geosphere is going to move six hours in right ascension across the celestial sphere its position at local midnight it’s going to move one degree per day or one fifteenth of an hour hour a per day so geosphere will only be next to a background star you will only be able to observe it x2 a background star for about 90 days given the 6-hour night so that means unlike the apt program which you know each target star had one group of comparison stars geosphere would need to have many comparison stars ok this is both a blessing and a curse a larger in Samba gives you more stars to throw away they turn out to be variable but it does give you a lot more to keep track of so in what follows I’m imagining a single one of these robotic apt telescopes trying to observe over and over again geosphere and so the observe a chemise so here’s jus sphere moving through part of its analemma during a single night and since we won’t want to make sure we’re doing the compared where we’re doing the photometry with comparison stars that are nearby we have a radius for which we would want comparison stars in the group so I’ve got a 15 degree radius here and as you as g 0 sphere moves through the night it’s moving through different

groups or observing geosphere with respect to its groups and many times as we can every single night and 15 days laters about to later the earth is going to get you know different position in its revolution on the Sun it’s going to change the sky around and geosphere is going to lose this group gained a group over here so that’s what the observationally now the question how do you achieve the precision that’s necessary for for observing these secular changes in the in the solar variability well the answer is by measuring it over and over and over and over again taking average and getting the benefit of 1 over root and reduction in the variances so a single measurement is a difference between geosphere your target and a comparison star with routine with repeated measurements the variances add so there’s there’s the solar variance and we’re interested in and there’s the variance that’s due to our comparison starts not being perfectly stable if we have a group of n comparison stars we get a 1 over n reduction of the variance of the comparison stars for that group and so what we’re really doing it for any single group is taking the the difference between the flux from geosphere versus the the average group so the average of flux of geosphere versus the group so it’s an average difference giving you that one over N you do that m times as many times as you can in the night and you will get a 1 / MN reduction in the in the variance do the comparison stars which is really it’s the it’s the the stars are part of your instrument so you want to reduce the noise of these so getting as many measurements as you can is what helps you accomplish that so just adding up how much time you would have to take using a hundred second integration I think it’s too long a sort of conservative you would get something like 11 point four hours with numbers like this which is too long because we really only have an hour for for these things but it gives you an idea what you need to play with in order to to make this observation program so you want to get a bigger telescope and reduce this questions like that so with one good group and n good nights in a year you get to put end in the fraction of the standard deviation annually so averaged through the year this is the sort of standard deviation of the comparison stars that you would get assuming pretty good comparison stars and this number comes out of Henry’s work from from the program so the Stars this could do exist there are lots of them especially when you go to magnitude he actually looks at writer stars and that gives you for a single group of a standard deviation of point 0 0 2 percent this would be a broken time series because as I said you could only look at one group for 90 days out of the year now if you want to have a continuous time series and not leave any part of not leave the Sun unobserved for any part of time you’ve got to develop a ladder of these these comparisons group star groups that are adjacent to one another so the difference of comparison star for with respect to a base comparison star one is going to be something like taking to the show measurements in some areas are going to add up so it makes the the precision word if you again assume that all of the comparison terms of a roughly similar variants so that you can just do the sum you get to j minus one there and so we’re looking at longitude bands across the celestial sphere we used about 25 of them in our in our calculation of enstars over n nights that you can do the group to group comparison in order to build this this scale this large yearly ensemble which would have which I’d have compares that starts table 2 point 0 2 percent so this is the basis of which you would measure the geosphere and if you want to do better than that and you have to start averaging over years and why not we’re interested in long-term variations the the space-based radiometers are already doing an excellent job of getting rotation scales and rotation scale variants and a great deal

of precision the advantage here is the duration and shouldn’t be afraid to average by 25 years really wanted to get this number down so the problem of stable comparison abundances is sort of summarized in this chart from from Henry 1999 for the apt program so basically you find that hot o-type stars like a and F have a low percentage of being greater than this variable variability in year-to-year means so these are the ones that you would sort of at the outset want to be looking at in order to build your in Samba stable comparison stars now again some of them are going to turn out to be variable you’re going to want to have a vort you want to have more comparison stars in your program at the start and you expect to finish with so we’re thinking about something like 250 to 300 stars maybe you would want to have White’s that I don’t know to start out with and just to make sure that you that you end up with a stable group now the other big problem can you really put something into space and expect its albedo to stay the same so some problems that my compy our oxidation ought to be negligible at this distance there’s just not a lot of oxygen out there so 1 to 10 of atoms per centimeter cube micrometeorite peering there’s not a lot of data on on cratering out in geosynchronous orbit but in low-earth orbit there have been measurements on such things as the solar panels of mere things like that and extrapolating their results you know the earth is sort of acting like a shield and we came up with a point four five percent change in cratered area from micrometeorites per century which is not negligible it would it would be a change in albedo if you had if you started with a an ish and initial albedo of a knot and the albedo of a crater is B and this K is here is your rate it would change the albedo by less than 0.5% but that’s already you know a level of that you would be concerned about so did you do maybe you could try to pre crater it before launch if it starts out fully cratered and a new crater comes in you know you would expect to have to reduce that change photo chemical changes so what should you make it made out of such that the x-rays and the UV light don’t basically age the surface change the albedo like my old Super Nintendo that the plastic trim so you might want to use a simple you wouldn’t make it out of Super Nintendo plastic you would make it out of something simple like a metal alloy or crystal so that the the impacts would be reduced from this high energy radiation maybe you could pre burn it before launch if you if you felt confident enough that you know what the how it would change over time but really what would be the best is in situ monitoring of the changes in albedo from something like ground-based lasers so the the geosphere will be in eclipse twice per year so the sunlight contribution will be gone and now would be the time that you would even try to get at monitoring the variations in its albedo and so adding this to the the slew of instruments on on Greg crops Greg cops chart here geo spheres yearly 1 Sigma variants to the to the comparison stars would fall here which gives us an expectation that you would be able to measure variations of the type that that are being discussed here the the Shapiro’s variation is something like here so that one you should be able to find out more easily depending on what the sun’s actually doing this problem is either very difficult to very hard we really don’t know because until you do the measurement you don’t know um Engineering considers and so we are talking what should you make it out of not really sure how do you launch a Demeter and inert object into a specific orbit we really haven’t looked into that how is expensive is it going to be to launch geosynchronous object you you could help if it would expand so you can launch something small that blows up you probably don’t want it to be inflatable because I wouldn’t expect that to be stable over a century but a rigid structure like this Hoberman sphere here that’s in the movie might be just the

ticket and in fact the Navy NRL Navy Research Laboratories has a guy working on on something like this to put an expandable steel structure in low-earth orbit in order to use it as a laser ranging target and a radar target so for calibration purposes for their equipment so there’s there’s some nice overlaps there between at least the mechanical requirements some other applications of the geosphere earth albedo variations so if if you don’t look at geosphere at opposition at midnight but instead when it’s at an angle with respect to the earth it’s going to be it’s going to be catching some earth light right and so a contribution of its of its brightness will be due to the earth and then you could use the same differential photometry techniques to do century-long monitoring of Earth albedo changes for that side of the earth that use fears on I already mentioned the radar application maybe they would be interested in shooting radars and lasers at it in fact we want them to shoot lasers at it too because you need a very precise range because as I said the the the distance is going to change by something like 50 kilometers and that’s going to be you know a magnitude change in its brightness so you have to constantly no to a great precision where geosphere is at actually in their in their proposal they said you would get they would get centimeter precision of its of its position so yeah that’s that’s really good you could maybe use the Sun in an astronomy a bit more use the Sun as a as a standard start which isn’t done because you can’t use the same instrumentation currently to look at the Sun and look at the the stars in the majority of cases and then you would get a large catalog of boring star that you could you could you know study why are they so flat do they stay flat over century it would answer other questions as well so here’s the conclusions the geosphere program could provide a measurement of spectral or spectral irradiance variations so of course you’re only looking at things that are going through the Earth’s atmosphere invisible wavelengths with sufficient precision to monitor secular variations 20 point 0 0 2 percent the stable orbit allows ground-based observations infinitely and this is the key feature it’s capable there forever anyone who’s at the rate longitude can do observations on it for as long as they want to the measurements should be of interest to the solar and climate variability commune communities these it’s addressing unanswered questions both in the long term variability of the of the Sun and also it you can get spectral measurements then I have that on this slide yeah I did I blew right over that uy variation so you is in is a narrow medium range band in the ultraviolet which is sort of where the maximum of the sim variation was was shown why was sort of at its minima so in relative short order you would be able to confirm this that measurement from the ground so these measurements should be of interest and if the interest is strong there’s a lot of work to be done that’s all thanks or Ricky well there’s some limitations to what kind of mirror show can make how why I spectral range you can reflect well and you also have different degradation of the of the mirrors as function of wavelength so how large a chunk of spectra to envision your you’re talking about the reflection of geosphere yeah okay well the baseline that we were using is from the apt program they only look at be and why I think just looking at those two bands would would be a great place to start there’s a lot to compare to for one thing although i did mention the you banned um and the other thing is i don’t think it matters that the albedo be high for you know extremely high for these things if if the albedo turns out to be if it doesn’t reflect well in a given band it just means that you have to integrate longer from the ground which you know that’s a limitation as well you want to avoid but i don’t think it would be the end of the

world if it weren’t particularly white what you do want to monitor TSI and you have spectral variability 00 co TSI okay only spectral well I do yeah sure but it’s just not possible you can’t it’s not going to come through the atmosphere so there’s you cannot do TSI with this sure but then you run into the same problem that they don’t survive on sort of decade long time scales so you you wouldn’t get the century-long I’m serious from that either put up a new space telescope and then you have calibration problems again and so these sun-like stars that you want to compare to they similarly similar enough that you don’t have to worry about changes in the Earth’s atmospheric composition affecting the spectra differently well so change it would be changes within the band that you’re observing that the telescope vessel changes on a 24 the Strom gun bands which are about 20 nanometers wide yeah it could be that could be an issue I’m not sure to what degree that would that would be an issue um so so you I’m thinking if they’re identical spectra a change in ozone will affect them identically but if they have slightly different spectra right and then the ozone will preferentially attenuate one of those lines and it’ll it appear as if it’s a change in in the brightness so both one thing okay now now that I thought about this better so you’re talking about changes in the ozone it’s going to affect your observation of both the geosphere and the end the comparison star and as long as it affects them in the same way subtract so ok I minced that you said it could be used to mop or the Earth’s albedo how do you differentiate between the you know radiation from the Sun and ALB you know yeah you would have to solve them simultaneously it would probably be a pretty hairy conversion problem but all may be doable and the mullions obviously a reflector is that because it’s too bright to be used for this purpose uh yeah the moon has sort of funny reflecting properties due to its due to its cratering so the the moon at different phases the changes in its in its its its brightness aren’t linear so it’s a tricky object because of it because of that so yeah other people we’ve we’ve so we’ve seen some work where people have you know tried to do this kind of thing with the moon with with other planets with Uranus they have seasons and things that that make that difficult so those efforts haven’t been successful to detect solar variation even if you observe it at opposition it is there not sufficient amount of light going through the Earth’s atmosphere that that’s going to be a pollution your measurement if it affects both the star and the target in the same way it’s will subtract out and what so you’re talking about brightness from I’m talking about I’m talking about light going through the Earth’s atmosphere and hitting your geosphere yeah I guess I don’t know about that e no more questions well let’s thank Ricky again