Ask Me Anything AMA with Dr Joe - Feb. 7th

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DrJoePesce

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Mar 31, 2020
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Hi Joe,
Is there any data on other solar systems in the Milky Way that define the angle between their local ecliptic and the ecliptic of the Milky Way? In order for us to get maximum view of exoplanets transiting in front of their local sun, doesn't their solar system ecliptic need to be parallel to the Milky Way ecliptic? Our solar system ecliptic is at about 60 degrees to the Milky Way ecliptic so wouldn't only a tiny portion of the Milky Way be able to see any of our solar system planets transiting in front of the Sun? Are there other possible explanations for the transits we observe in other systems, such as sun spots?
thanks
Hi mmm. Stars and their surrounding planets can form in any orientation, randomly. As you point out, to see a transiting planet (that is the planet is between its sun and us, and we see it as it moves across the disk of the star), we (Earth, planet, and its sun) need to be aligned. Even though planet orientation is random, there are lots of stars/planets, so we can potentially see lots of transits. (Note, the ecliptics don't need to line up, we just need to see the orbit edge-on, in whatever orientation that is.)

Note that, for the vast majority of the planetary systems, we don't actually SEE the planet moving across the star. Rather we measure the dip in the star's brightness as the transiting planet blocks some of the star's light from our view. We can get time information too: The dip in brightness lasted 3 hours, or whatever, which is, of course, the time it took for the planet to move across the disk of the star from our vantage point. Measuring that time can give us orbital information about the planet. It's really an interesting way to learn a lot about these exoplanetary systems.

Now stars vary in brightness for many reasons that have nothing to do with transiting planets, including, as you point out, because of star spots. That's why we need to understand the host star as well as possible: Is that type of star known to have lots of star spots, how does its brightness vary (level of brightness and over how long)? Etc. Then we attempt to eliminate all the non-planet possibilities. One way is by observing multiple transits: If they are always exactly the same length of time, and the same amount of brightness reduction, and they occur regularly, the likelihood the brightness variation is caused by a transiting planet is increased. For example, star spots would not cause brightness variations of exactly the same amount and length of time and occurring every 6 months (say).
 
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As you know, the spectrometer is an instrument that allows us to break light into its consituent parts (like a prism does to white light, creating a rainbow of light). The spectum them tells us where the electromagnetic emission peaks in wavelength: a red star is going to have light from all visible-light wavelengths, but is brighter in the red than in the blue. And vice versa for a blue star. This information is useful: it tells us the color, and from that we infer surface temperature) and many other things. A spectrum can also tells what elements might be present in the astronomical object, to measure redshift (hence distance), etc.
Uh oh, you're addressing the one area I know a few things of interest.

Yes, the cooler "red" stars are far stronger in the red portion of the spectrum, and vice versa for the hotter "blue" stars. As you imply, all stars emit all the colors of the spectrum. But, surprisingly, some who should know better have claimed the Sun is white because it emits all the colors of the spectrum, without recalling that all stars emit all the colors, even the red and blue stars as you mention.

As a result of this combination of colors, the red stars will not normally have a saturated red color, nor the blue stars be a deep blue, but bluish-white instead.

Some exceptions: The T-class objects are cool enough where their molecular emissions can produce a limited variety of color, including one I recall having a crimson color. Carbon stars also can be stronger in red that will favor a more rich color red. The variation in the human eye can make a difference here as well. I see most "red" stars as orange (e.g. Betelgeuse), but at least one other person I know sees some of these as red. Our atmosphere can also redshift colors if the particle counts are high.

Regarding spectrometer use, are there SED's in the visual range for early accretion disks? I assume that for the earlier disks, we could not see them due to their placental cloud's interference.

A couple of things... and 2) the solar spectrum peaks around 5700A/570nm, meaning the Sun should have a slight greenish cast, though likely overwhelmed by brightness (not having been to space I can't answer this!).
:) [570 nm would be a peak for a 5084K BB.]

What triggered my interest in this topic actually was an article in a magazine by an astronomer in the NE who made this argument for green. Phil Plait also noted that the Sun's color wasn't established within mainstream. [I can imagine solar physicists laughing at this given all their white projections, and all these are mainly post blue extinctions by our atmosphere (again Rayleigh scattering). These white, unfiltered projections demonstrably negate any yellow argument! :)]

But using the spectral irradiance data from SOHO and others (SORCE was my source :)) a better fit is 5850K. What you may not know is that the Sun's variation from a BB puts the peak energy distribution well within the blue band, 479.4 nm from one data set. This seems to surprise a lot of people who are comfortable using BB models, apparently. Below is a plot using data that had a peak closer to 450nm, IIRC. Regardless, the peak energy for the Sun is always blue. :)



Even more surprising, however, is found by using the better modeling for vision, namey a photon flux density distribution. As one amateur told me regarding "flashing" the ISS one night - "It's all about photons!" :)

To convert to photon flux, we simply use E= hv, which means the blue end has more energy per photon, thus the distribution number of the "blue" photons will be much less when using a photon distribution plot, as seen here:



The Sun's photon flux profile is almost flat, which is why the Sun is just a white star. It not only has all the colors, but they are all about equal in distribution, which is the key to any color determination. Even the limb isn't yellow, as illustrated by my McMath-Pierce solar projection image you can see in my Avatar (the RGB plastic pieces are there to verify color accuracy).

If you get in the mood for something zanny/goofy within astronomy, you might enjoy The Color of the Sun - Revelation (part 3 of 3). [However, you might not, so caveat emptor. ;)]
 
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Jzz

May 10, 2021
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By the way, you say that a photon travels forever: If the photon doesn't interact with anything, it could travel forever. In reality, it will lose energy as the universe under it expands (i.e., redshift; and this is what the cosmic microwave background radiation is), and it's more likely an individual photon will not travel forever because it will be absorbed by gas, dust, other stars, retinas, etc.
Thank you Dr. Joe, your comments are greatly appreciated. However, as always I have a few questions, I have challenged the assumption that the CMBR exists. I reproduce that post for you:
What is the Cosmic Microwave Background Radiation? And what does it mean?
View: https://www.youtube.com/watch?v=P_deJsiCNSk&t=4s

"Firstly, let me just say that I loved this talk, I appreciated the detail that went into explaining the concept of the CMBR. But then, it is incredible to think that the Universe is filled with unimaginably huge clouds of hydrogen. It is even more incredible to imagine that those massive, massive clouds of hydrogen are absolutely quiescent, in terms of signal activity, when just picking up a pencil displaces trillions upon trillions of electrons. Venturing further along this path is the strange coincidence that the CMBR almost exactly matches up with the hydrogen emission spectrum. The CMBR was never the faint relic radiation that is described, in fact it often set up a howl on old radio sets, it was a brawny, strong signal that was incredibly hard to get rid of. Today, radio reception is so sophisticated that the CMBR is hardly ever heard in any of the communication devices that we use. So there are two main questions arising from the concept put forward in the video. The first is why does the CMBR radiation so strangely mimic the hydrogen emission spectra? The second question that comes to mind when watching this video is this; when matter is made up of 99.999999999999% of empty space and believe me that percentage is important when calculating the mass in the Universe and when every act from walking to being stopped from walking through walls is governed by electromagnetic interactions, how is it possible to ignore emissions that these hydrogen clouds might (must!) be emitting? The CMBR is not relic radiation from the Big Bang. The CMBR is very much an indication of the present distribution of matter in the Universe.


Surprisingly, the OP loved this comment.
 

rod

Oct 22, 2019
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What a profound question Jzz, and one on many levels. I love questions like this because there are so many things to talk about.

First of all: In extremely dark conditions, with the Milky Way directly overhead, you CAN read by the light of the stars. I've been fortunate to have done so many times (especially in the dark skies at our observatories in Chile). It is a spectacular, unforgettable, and moving experience.

But those dark skies necessary to do this are rapidly disappearing because of light pollution. Many (most?) of my astronomy students have never seen the Milky Way because of light pollution. How sad....

There are solutions to light pollution, and many are being enacted. See, for example, https://www.space.com/39787-light-pollution-problem-you-can-help.html

In other areas, what you ask is deeply insightful and is what's known as "Olbers' Paradox": Why is the night sky not bright (like the surface of a star)? But to ASK this question you have to make some assumptions: The universe is uniform and infinite. In such a universe (uniform and infinite), everywhere you look you will see a photon from a star (no matter how far away it is). In this case (ol' Heinreich Wilhelm Olbers would argue), the universe should be uniformly bright.

The simple answer is that the universe isn't uniform and infinite.

In such a universe, you CAN have sight lines without photons coming to your retina. That is, there are places we can look and not see light from any source. Since this is the case for quite a few "sight lines", the night sky is dark.
Olbers' paradox - Wikipedia
 
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Jzz

May 10, 2021
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Jzz, you might want to compare an actual H emission spectrum to the near-perfect blackbody emission spectrum of the CMBR. These two are extremely different.
Helio : Two points, firstly have you thought about how huge these hydrogen clouds are? A single cloud could contain hundreds or thousands of galaxies like the milky way. They are also very homogeneously constituted (I.e. , mainly hydrogen) so any radio signal would have strong black body characteristics. Second if these huge clouds did emit, which they must do given all the activity in the Universe. Why don't we hear it as a clear signal. Like the CMBR for instance?
This is just an aside: but when you look at your reply in a disinterested way, don't you think you could be putting a spin on it to point in a desired direction?
 
Helio : Two points, firstly have you thought about how huge these hydrogen clouds are? A single cloud could contain hundreds or thousands of galaxies like the milky way. They are also very homogeneously constituted (I.e. , mainly hydrogen) so any radio signal would have strong black body characteristics. Second if these huge clouds did emit, which they must do given all the activity in the Universe. Why don't we hear it as a clear signal. Like the CMBR for instance?
I think your best answer here will come from our host scientist.

This is just an aside: but when you look at your reply in a disinterested way, don't you think you could be putting a spin on it to point in a desired direction?
No spin, just science. What spin do you see? H-emission spectrums are beyond question. The CMBR spectrum is beyond any resonable question. These both give us solid objective evidence to allow us to draw a comparison.

Hydrogen is tricky within clouds, so much so that astronomers look to CO emissions instead. Ionized hydrogen, of course, does allow detection, but that is only the silver lining. :)
 

rod

Oct 22, 2019
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Jzz and Helio. https://forums.space.com/threads/the-big-bang-what-really-happened-at-our-universes-birth.53947/

This has a number of threads on the CMBR and cooling rates used. There are reports indicating that certain objects with redshifts can be mapped to the cooling rate for the CMBR originating at some 3,000 K or higher than as the universe expands (4D space, not 3D space), the CMBR drops to near 3 K today. One problem I see, the redshift plots can be setup on a spreadsheet using MS Excel and a graph shown. Very limited number with low redshifts so far (e.g. 0.1, 3.0, 6), thus the cooling rate becomes a very large extrapolation from limited number of data points documented. The CMBR redshift is postulated to be some 1100 or so today say compared to a galaxy or quasar with redshift of 3.0. Using cosmology calculators, this indicates the universe radius as observed from Earth only about 41 million light years, e.g. LAMBDA - Calculators (nasa.gov) when the CMBR light was released or created in the origin model.

Plenty is going on to make the CMBR work as used in the BB model today, including inflation is needed. George Gamow and Ralph Alpher calculated a background glow of about 51 K originally and we would see a very lumpy CMB today as 4D space expands, without inflation tossed in. I look at inflation like MS releasing various security patches to fix problems that arise :)
 
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Jzz

May 10, 2021
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Jzz and Helio. https://forums.space.com/threads/the-big-bang-what-really-happened-at-our-universes-birth.53947/

This has a number of threads on the CMBR and cooling rates used. There are reports indicating that certain objects with redshifts can be mapped to the cooling rate for the CMBR originating at some 3,000 K or higher than as the universe expands (4D space, not 3D space), the CMBR drops to near 3 K today. One problem I see, the redshift plots can be setup on a spreadsheet using MS Excel and a graph shown. Very limited number with low redshifts so far (e.g. 0.1, 3.0, 6), thus the cooling rate becomes a very large extrapolation from limited number of data points documented. The CMBR redshift is postulated to be some 1100 or so today say compared to a galaxy or quasar with redshift of 3.0. Using cosmology calculators, this indicates the universe radius as observed from Earth only about 41 million light years, e.g. LAMBDA - Calculators (nasa.gov) when the CMBR light was released or created in the origin model.

Plenty is going on to make the CMBR work as used in the BB model today, including inflation is needed. George Gamow and Ralph Alpher calculated a background glow of about 51 K originally and we would see a very lumpy CMB today as 4D space expands, without inflation tossed in. I look at inflation like MS releasing various security patches to fix problems that arise :)
Yes,quite a bit going on. Not meaning to sound contentious (and sounding very contentious). I also have questions about SR and frames of reference. All these red- shifts are calculated using SR. The point is that with every frame of reference experiencing a different time and distance in order for the speed of light to be constant. ( a little thought will go to show that this must be true) . Where is there scope for causality and sentient life forms? Bob and Jack and Mary might be OK as illustrations but what if you have a 1000 spaceships all travelling at near light speeds? 1000 different frames of reference and different distance and times for the same bit of space. A 1000! different times and places for the same bit of space. How can causality exist? This a number bigger than the number of atoms in the Universe and with only a 1000 participants.
 

Jzz

May 10, 2021
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Helio. Just an aside really. When Penzias and Wilson were given the task of eliminating static from radio sets, they had a very definite frequency to tune into. Is the implication then, that this set of frequencies has been so refined with passage of time that it is possible to separate the CMBR signal from all the other signals. I find it hard to believe. A much better candidate for relic radiation from the big bang would be dark matter. Dark matter has all the properties of being relic radiation. The very first photons. Look at any atomic clock, it uses microwave frequencies to cause electrons within the caesium atom to oscillate at 9,192, 631,770 cycles per second. The fact that electrons can oscillate at such high frequencies goes to show that frequency of a photon is real and not an imaginary number to help determine photon energy. This illustrates that the photon to electron ratio is massive on the order of 10^8 photons per second! Dark matter might be relic light left over from the Big bang, these photons have such low energies (about 10^-40 J) that for all practical purposes they don't exist, (i.e., they are not acknowledged by the laws of conservation) . Dark matter photons lost energy as the Universe expanded. Hence the very low interaction ton with matter , no atom could have any possible use for photons of such low energies. Hence matter moves through dark matter as if it doesn't exist and vice versa. Dark matter being relic light also explains how electromagnetic radiation can propagate through dark matter without any opposition.
 
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Jzz

May 10, 2021
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Is Special Relativity, correct?

Dr. Joe Pesce, I found your remarks on the expansion of the Universe very intriguing. To my own mind it seems to me that using SR to calculate anything, especially the red-shift and the expansion of the Universe, is not right. Here is the reason why:
The question to be asked is “Is Special Relativity Correct in its assumptions?” Special Relativity presents the novel and strange theory that both time and space are mutable, they can change according to from where they are viewed. To illustrate this aspect, look at Einstein’s famous thought experiment of a train. Imagine for a moment that there is a light on top of the train that can be viewed by observers in all directions. Say there are 4 observers to begin with. Observer A is sitting inside in the middle of the train. Observer B is standing behind the train, Observer D is standing in front of the train and observer E is on the platform. As the train moves each observer sees the following:
  • Observer A sees the light as stationary as he is moving with the light.
  • Observer B sees the light as travelling more slowly towards him (i.e. minus the speed of the train moving away from him.)
  • Observer D sees the light moving faster towards him (i.e., speed of light + speed of train.)
  • And Observer E sees the light travelling a greater distance than the observer on the train.
According to Einstein, the speed of light should remain constant for all of these observers, regardless of their frame of reference. Therefore, it should not be possible that Observer D standing in front of the train sees light moving faster towards himself nor should it be possible for observer B to see light moving at a slower speed toward himself or for E on the platform to observe that light travels a longer distance.
The way in which Einstein resolves this problem is to state that for Observer D time dilates and lengths expand in such an exact way as to keep the speed of light constant. For observer B at the back of the train lengths contract and time expands, so that even if light travels a longer distance towards himself, the speed at which it travels remains constant, the same applies to observer E on the platform.
Now imagine that each of these observers is moving, now each of these 4 observers should experience light travelling at different rates but because time dilates and lengths contract and expand for each of them the speed of light remains constant. Therefore, the combined possibilities of these four frames of reference works out to 4! (four factorial) or 24 possible combinations. Hence my contention that if 1000 space ships are travelling at near the speed of light (to and from the same destination) the number of possible combinations that these space ships would see would be 1000! (Thousand factorial) a number greater than all the number of atoms in the whole of the Universe. For space to be split (and these are actual splits not imagined ones) to such an extent not only negates causality it also makes impossible for sentient life forms to exist.
Imagine now, the existence of an aether, (i.e., a medium) now the speed of light remains constant for all observers regardless of their own motion, the motion of the source of the light or of the observer. The speed of light would remain constant because it is travelling through a medium and its speed is governed solely by the properties of the medium and nothing else. No need for space to contract or expand, or for time to dilate, the speed of light remains constant as a function of its manner of propagation. The existence of a medium would also provide a fixed frame of reference.
 
Nov 19, 2021
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Any movement of an observer relative to a source of light is accounted for by time dilation and Lorentz contraction, as you pointed out earlier. The speed of light as measured by them will remain constant.
Michelson-Morely disproved the existence of aether.
 
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