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DrJoePesce

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Mar 31, 2020
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Happy Monday dear astronomy enthusiasts!

Given the great turnout on my previous AMA appearances, it looks like now you will have me here on a more regular basis!

I look forward to your questions and our continued discussions. And, as always, I will try to answer as many as I can (though there might be some I can't answer!).

In the meantime, keep looking up!

Dr Joe
 

rod

Oct 22, 2019
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Dr. Joe. I use a 90-mm refractor telescope with altazimuth mount and 10-inch Newtonain dob mount with Telrads on both. I checked my stargazing log (MS ACCESS DB) and 8 days out in Dec, 8 hours and since Jan-2022 thru this week, 14 days observing and some 18 hours logged. This includes solar observing using a safe, glass white light solar filter.

Do you get out much in stargaze and what type of equipment do you like? FYI, I am retired now for more than six years.
 
Nov 18, 2019
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Many thanks, Dr. Joe. May I repost my question from the previous week?

>DrJoePesce said:
>Thanks for the follow-up XinhangShen. My understanding (maybe incorrect) is that the
>GPS satellites' clocks are synchronized. I don't think they are synchronized with the
>ground clocks. I'll see if I can get someone better versed in this subject to weigh in.

I think that all the clocks including the ground clocks should be synchronized so that they all have the same time that can be used to determine the position. Some people argue that the clock on a satellite and the clock on the ground are synchronized only relative to the ground reference frame and not synchronized relative to the satellite reference frame. If it was true, then the difference between the clocks observed from the satellite would monotonically grow but can't be corrected because the clocks are still synchronized observed from the ground frame, which is obviously not the case on the clocks of the GPS.

I think, Lorentz Transformation is a redefinition of space and time (called relativistic time in the following) which is no longer the clock time, but a fake time without physical meaning.

In fact, Lorentz Transformation is mathematically equivalent to the following definitions:

t' = (1/γ)T' - (γv/c^2)X'
x' = γX'
y' = Y'
z' = Z'

where γ = 1/sqrt(1 - v^2/c^2), (X', Y', Z', T') is the Galilean spacetime of the inertial reference frame moving at speed v in the X-direction relative to aether, (x', y', z', t') is the relativistic spacetime of the same inertial reference frame. When v = 0, relativistic spacetime (x, y, z, t) becomes the same as Galilean spacetime (X, Y, Z, T).

Galilean spacetime follows Galilean Transformation:

T' = T
X' = X - vT
Y' = Y
Z' = Z

We can verify that the speed of light defined by Galilean spacetime follows Newton's velocity addition law, while the speed of light defined by relativistic spacetime is constant relative to all inertial reference frames:

C = X/T

C' = X'/T' = (X - vT)/T = X/T - v = C - v

c = x/t = X/T = C

c' = x'/t'
= (γX')/[(1/γ)T' - (γv/c^2)X']
= (X'/T')/[(1/γ^2) - (v/c^2)(X'/T')]
= C'/[(1 - v^2/c^2) - (v/c^2)C']
= (C - v)/[1 - v^2/c^2 - (v/c^2)C + v^2/c^2]
= (c - v)/(1 - v/c)
= c

That means, all what Lorentz Transformation does is to redefine spacetime.

Since the clock time Tc is defined by the number N of cycles of a physical periodical process:

Tc = N/k

where k is a calibration constant and equals 9,192,631,770 for a cesium atomic clock.

The clock times Tc and Tc' of two clocks attached to the inertial reference frames defined by Galilean spacetime (X, Y, Z, T) and (X', Y', Z', T') are

Tc' = N'/k = (T'/Τ' )/k = (T/Τ)/k = N/k = Tc

where the Galilean periods Τ and Τ' of the two clocks are the same because Galilean time is absolute.

This equation tells us that clock time is also absolute same as Galilean time.

In special relativity, the clock times Tc and Tc' of two clocks attached to the inertial reference frames defined by relativistic spacetime (x, y, z, t) and (x', y', z', t') can be calculated by:

N' = t'/𝜏'
N = t/𝜏
t' = t/γ
𝜏' = 𝜏/γ

Tc' = N'/k = (t'/𝜏')/k = (t/𝜏)/k = N/k = Tc

where N', t' and 𝜏' are the number of cycles, elapsed relativistic time and the relativistic period of the moving clock, respectively, N, t and 𝜏 are the number of cycles, elapsed relativistic time and the relativistic period of the stationary clock respectively.

This equation tells us that clock time is Lorentz invariant and thus is still absolute and independent of the reference frame, which confirms that the property of the clock time (i.e. the absoluteness of the clock time) won't change with the change of the definition of time. Thus, the relativistic time is no longer the clock time but a meaningless mathematical variable.

Therefore, based on such a fake time, special relativity is wrong and so are all relativistic spacetime based theories including the Big Bang theory.
 
Feb 12, 2022
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Happy Monday dear astronomy enthusiasts!

Given the great turnout on my previous AMA appearances, it looks like now you will have me here on a more regular basis!

I look forward to your questions and our continued discussions. And, as always, I will try to answer as many as I can (though there might be some I can't answer!).

In the meantime, keep looking up!

Dr Joe
Hello Dr joe. I am really interested in research arrears for Ph D in this field of astronomy
 
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Oct 23, 2019
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Hello Dr Joe, thanks for being there to answer our questions.
My question to you today is about Nasa Voyager 1 and 2 missions.
Why did they send voyager 2 before voyager 1? One would think that they would have logically sent voyager 1 first, what would be the reason that they didn't, I'm sure there's a perfectly good reason.

"From the NASA Kennedy Space Center at Cape Canaveral, Florida, Voyager 2 was launched first, on August 20, 1977; Voyager 1 was launched on a faster, shorter trajectory on September 5, 1977."
 
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Apr 5, 2021
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Hi Joe

is it possible to have a combined (planet wide) optical telescope similar to EHT radio telescope which pictured a black hole, and would we then be able to look at nearby star systems and their planets with similar resolutions of EHT image?

Thanks
 
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Jzz

May 10, 2021
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Many thanks, Dr. Joe. May I repost my question from the previous week?

>DrJoePesce said:
>Thanks for the follow-up XinhangShen. My understanding (maybe incorrect) is that the
>GPS satellites' clocks are synchronized. I don't think they are synchronized with the
>ground clocks. I'll see if I can get someone better versed in this subject to weigh in.
Xinhang shen: Are you aware that the GPS system does not use and has never used Special relativity to calibrate the GPS system? Anyone trying to calibrate the 4 satellites needed to calibrate the GPS would have his work cut out, since any observer viewing a source of light, which is what technically radio-signals are, would each record a different distance and time. Therefore, each of the 4 satellites in the air and the station on the ground would be recording a different time and distance. An unacceptable situation! Therefore, I repeat, Special Relativity has not been and could not be used, unless it is attempted by SR fanatics, in the GPS. Instead, just adjusting the transmission for the normal changes is enough to ensure the required accuracy.

Now, this requires some attention be paid to the fact that according to SR times and distances do actually change for each observer. If this were not the case there would be instances where the speed of light is exceeded, as for instance when a space ship travels a distance measured as 10 light years from earth at 0.9 c. The time taken for the spaceship to reach a destination 10 light years away according to an observer on earth would be 11.11 light years approx. But for an observer on the space ship the time taken to complete a distance of 10 light years appears to be only 4.77 years! t‘ = t x sqrt (1- v² /c²) So, if the clock on the spaceship is measuring time properly according to an observer moving with the clock, how can we account for the fact that the observer on the ship seems to cover a distance of 10 light years in 4.77 years, which would imply that they’re traveling at a speed of 2.08c? That absolutely cannot be true. For one thing, one of the implications of relativity is that nothing can travel faster than c, the speed of light in vacuum. c is the ultimate speed limit in the universe. For another, two observers will always agree on their relative velocities. If the person on the Earth sees the spaceship moving at 0.9c, the observer on the spaceship agrees that the Earth is moving at 0.9c with respect to the spaceship (and because the other planet B is not moving relative to the Earth), everyone’s in agreement that the relative velocity between the spaceship and planet is 0.9c.

For the distance travelled (inverse of Lorentz gamma used for time dilation and length contraction is 0.43). Since 10 light years = 9.46 x 10^13 km. Distance as measured on space ship is 0.43 x 9.46 x 10^13 = 4.0 x 10^ 13 Km. Therefore, the distance travelled as seen by the space ship is not 9.46 x 10 ^13 Km. but only 4.0 x 10^13 Km. So, distance is velocity multiplied by time and we know the velocity and time measured by the observer on the spacecraft is 0.9c and 4.8 years. This implies that they measure a distance for the trip of 4.0 light-years, much smaller than the 10 light-year distance measured by the observer on the Earth.
 
Nov 18, 2019
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Xinhang shen: Are you aware that the GPS system does not use and has never used Special relativity to calibrate the GPS system? Anyone trying to calibrate the 4 satellites needed to calibrate the GPS would have his work cut out, since any observer viewing a source of light, which is what technically radio-signals are, would each record a different distance and time. Therefore, each of the 4 satellites in the air and the station on the ground would be recording a different time and distance. An unacceptable situation! Therefore, I repeat, Special Relativity has not been and could not be used, unless it is attempted by SR fanatics, in the GPS. Instead, just adjusting the transmission for the normal changes is enough to ensure the required accuracy.
Many thanks, Dr. Joe for your very detail explanation. Do your words above confirm that the clocks on the GPS satellites are synchronized relative to all reference frames (the reference frames of all satellites and the ground frame) to show the same absolute time, which means clock time is absolute and SR's claim that time is relative is wrong?
 

DrJoePesce

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Hello All - I'm here but have been having some technical issues: I didn't see any posts until about 5 mins ago, and thought I was here all alone!

I see that's not the case and will get to your questions ASAP!

Dr Joe
 
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DrJoePesce

Verified Expert
Mar 31, 2020
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417
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Dr. Joe. I use a 90-mm refractor telescope with altazimuth mount and 10-inch Newtonain dob mount with Telrads on both. I checked my stargazing log (MS ACCESS DB) and 8 days out in Dec, 8 hours and since Jan-2022 thru this week, 14 days observing and some 18 hours logged. This includes solar observing using a safe, glass white light solar filter.

Do you get out much in stargaze and what type of equipment do you like? FYI, I am retired now for more than six years.
Thanks Rod – It's great what you doing - keep it up! Sadly I haven’t observed with my own equipment for quite a number of years. Of course I was observing with other instruments, but also I’ve been doing other parts of astronomy that doesn’t involve direct research: At the moment, I’m helping to foster the research of others in the field. And communicating those terrific results in fora like this!
 
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DrJoePesce

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Mar 31, 2020
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Hello Dr joe. I am really interested in research arrears for Ph D in this field of astronomy
Hello bringen, that’s fantastic! Tell me more. Are you a student? Wanting to change careers? In any case, a lot of math and physics background is going to be necessary. The main (traditional) path for Ph.D. astronomers is in academia conducting research. But Ph.D. astronomers are everywhere: the education provides background that makes astronomers good problem solvers so I see them in all sorts of fields outside of astronomy.

Tell me more and I can provide more specifics.
 
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DrJoePesce

Verified Expert
Mar 31, 2020
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417
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Hello Dr Joe, thanks for being there to answer our questions.
My question to you today is about Nasa Voyager 1 and 2 missions.
Why did they send voyager 2 before voyager 1? One would think that they would have logically sent voyager 1 first, what would be the reason that they didn't, I'm sure there's a perfectly good reason.

"From the NASA Kennedy Space Center at Cape Canaveral, Florida, Voyager 2 was launched first, on August 20, 1977; Voyager 1 was launched on a faster, shorter trajectory on September 5, 1977."
Thanks for the question Virgo. I have to say that I don’t know the deep history of this. I do know that, even though Voyager 1 was launched second, it was on a faster and shorter trajectory to Jupiter, so arrived first. This may be why it was named Voyager 1 and why it went 2nd, but this is just speculation on my part. Maybe a reader with more direct experience with the program will chime in.
 
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DrJoePesce

Verified Expert
Mar 31, 2020
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Hi Joe

is it possible to have a combined (planet wide) optical telescope similar to EHT radio telescope which pictured a black hole, and would we then be able to look at nearby star systems and their planets with similar resolutions of EHT image?

Thanks
Hi suneritz, optical interferometry (multiple telescopes operating as one; like EHT does in the radio part of the electromagnetic spectrum) is absolutely possible. But it’s more difficult (because of the shorter wavelengths of visible light compared to radio light).

Radio interferometers can use time stamping of the data stream to line up the observations from individual radio telescopes. Optical interferometers need to use optical fibers to insert a time delay to the collected photons as they travel to the instruments, to synchronize individual telescopes in the array. This is difficult and tricky. The European Very Large Telescope (VLT) in Chile does this, but the telescopes are relatively close together. Doing it from space would be better but is even more difficult. Bottom line: it’s possible but much more difficult than conducting interferometry in the radio part of the EM spectrum. Also, for supermassive black holes at least, radio wavelengths penetrate the gas and dust in galaxies, better than visible wavelengths, so we can see deep into their nuclear regions where the supermassive black holes are found.
 
Apr 5, 2021
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Thanks Joe. From your experience what's the pros and cons of a career in Planetary astronomy, is it what's trending these days or could you recommend another branch of Astronomy which is in demand? What about Data Science path. Thanks
 
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DrJoePesce

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Thanks Joe. From your experience what's the pros and cons of a career in Planetary astronomy, is it what's trending these days or could you recommend another branch of Astronomy which is in demand? What about Data Science path. Thanks

Thanks for the question and the interest suneritz. You know I love all of astronomy, so my opinion is that someone wanting to go in the field professionally should do what they want to do, no matter what the fashions of the day are. It is true that fields enjoying more “popularity” than others will have a larger, maybe more vibrant, community with which to work. But because astronomy is in discovery space (as I say often) -- meaning there are still new things to discover and explore in all subfields -- it kind of doesn’t matter what you do. So follow your heart.

Having said that, planetary astronomy is big now, not only because of the large-scale exploration taking place in our own solar system, but also because of the research on planets beyond our solar system (exoplanets) that is going from strength to strength.

Are you considering such a career?
 

DrJoePesce

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Hey Dr. Joe!

Do we know why the Sun (and solar system) oscillates above and below the galactic plane?

-Wolf sends

P.S. Happy Friday!
Hey Wolfshadw, good to see you here. And thanks for the good wishes on Friday! It was a great day.

You are referring to the fact that our solar system doesn’t always orbit in the plane of the galaxy (like a car on a racetrack), but goes above and below, so as we make our roughly 250-million-year orbit around the galaxy we “bob” up and down. I think this is probably just due to the gravitational interactions acting on the gas/dust cloud from which we formed 4.5 billion years ago. It might have been caused by gravitational interactions with other members of the star cluster in which the solar system spent its earliest days (almost certainly the Sun was not alone in a stellar nursery). Or it could have been caused by gravitational interactions (with other galactic objects) well after formation that torqued the solar system’s orbit.

Incidentally, there are some thoughts that mass extinctions on Earth are caused by our orbit: as the solar system goes down (or up!) through the denser parts of the galaxy’s disk, there might be interactions with exploding stars, other material, etc., that affect life on Earth. There is no definitive connection of extinctions to the orbit, however.
 
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DrJoePesce

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Dr Joe:

When do you think humanity will make first contact with aliens?
What a cool question Cehunt. And one that could get me in trouble, as my answer will be in the digital realm forever!

Rather than tell you 5 April 2063, let me say this. I think life is everywhere, in its most simple forms at least. So, one answer to your question could be “soon”: I think we will find microbial-like lifeforms (directly or indirectly) within our lifetimes.

Intelligent life is probably less likely, though probable. But distances are vast, making communication and travel difficult (certainly for us, maybe not for a super-advanced species). While we might discover intelligent life indirectly (by observing their communications, say), I think direct contact is highly unlikely. And, in either case, probably not within the next 50-100 years.
 

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