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Thread: Astronomy

  1. #61
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    Tyson is the guy who has the TV programme on space. He was a colleague or student of Carl Sagan. The first post (Spacecraft behaving Badly) is fascinating. I look forward to reading more. It argues that Newton's theory of gravity which is one of the taken-for-granted "facts" of space travel doesn't apply once the crafts (in this case Pioneer I and II) leave the solar system.

  2. #62
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    Tyson's article interested me in questioning Newton's laws of gravity beyond 15 AU from the sun where Einstein's modifications were no longer relevant. Also, if Newton's laws of gravity are the problem what does that do to the supposed existence of dark matter and energy? I thought those were based upon missing matter and energy assuming Newton's laws were correct.

    I wonder if there is information about this from Voyager 1? http://en.wikipedia.org/wiki/Voyager_1

  3. #63
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    Yes, I wondered about that, too. I've re-read the voyager 1 link you provided, and I am still confused. There is no mention of drifting similar to Pioneer, but a lot of other stuff like passing the heliopause, termination shock, and passed the heliosheath and both V1 and V2 are now in interstellar space. heading towards other galaxies. Taking 300 years to reach the Oort Cloud where comets are born, and take 30,000 (!) years to pass through it.

    Perhaps they don't know where the probes are with any accuracy to show that there has been or has not been any drift.

    The whole thing is just too mind-boggling to understand.

  4. #64
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    Your initial link got me thinking about dark matter/energy and it looks like there are people questioning whether the evidence that seems to call for the existence of dark matter is really evidence that the laws of gravity are not as simple as we assumed. http://en.wikipedia.org/wiki/Dark_matter

    I was looking for the crescent moon I saw a couple days ago and realized that things change quickly. The moon has lost that lovely crescent shape. I will have to wait until next month to get the photo, if the skies are clear and I don't forget.

    I also read that in the first weeks of January Venus and Mercury will be in conjunction, that is, they will set at the same time.

  5. #65
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    As I understand Dark Matter it is light travelling away from the viewer at a speed faster than light, being sucked into a hole. But it is very theoretical, much like Schrödinger's Cat, a concept that, however much I try to grasp, eludes my understanding.

    Yes, astronomy can be very frustrating. Here we have had blue skies during the day but it clouds over by dusk or even earlier, and it has been like this for a week or more, staying cloudy until it is light and the stars can't be seen. I still have not managed to use my binoculars as I had hoped...

  6. #66
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    I just found an extensive and very interesting Wikipedia article on it, and it reports that they solved the question with fair certainty in 2012. I find it fasinating how much interest there was in it, and the different proposed explanations. Tyson's article builds suspense very well.. With all of the factors involved, all of the different temperatures, instruments, and everything else, it took them until 2012 to account for the anomaly completely.

    It appears a certain amount of the article was written before the issue was settled, so some of the parts about possible explanations are a history of it, for example:

    The asymmetrical radiation of heat remains a prime suspect, as presented at the second ISSI meeting in Bern, February 2007. A presentation at the APS April 2008 meeting suggests that differential heating may account for as much as one third of the observed acceleration.[39]
    Yesterday my best guess was drag - dust and what not, but nope.

    Drag
    The cause could be drag from the interplanetary medium, including dust, solar wind and cosmic rays. However, the measured densities are too small to cause the effect.
    and another one, what you mentioned Dream-

    Observational or recording errors
    The possibility of observational errors, which include measurement and computational errors, has been advanced as a reason for interpreting the data as an anomaly. Hence, this would result in approximation and statistical errors. However, further analysis has determined that significant errors are not likely because seven independent analyses have shown the existence of the Pioneer anomaly as of March 2010.[43]

    The effect is so small that it could be a statistical anomaly caused by differences in the way data were collected over the lifetime of the probes. Numerous changes were made over this period, including changes in the receiving instruments, reception sites, data recording systems and recording formats.[9]

    Meetings were held...

    A meeting was held at the University of Bremen in 2004 to discuss the Pioneer anomaly.[61]

    The Pioneer Explorer Collaboration was formed to study the Pioneer Anomaly and has hosted three meetings (2005, 2007, and 2008) at International Space Science Institute in Bern, Switzerland to discuss the anomaly, and discuss possible means for resolving the source.[62]

  7. #67
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    Nikolai, that was very interesting, after just a quick read. I didn't think to search in Wiki for it. I need to read this a couple more times to digest it properly.

  8. #68
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    That article on the Pioneer anomaly, http://en.wikipedia.org/wiki/Pioneer_anomaly, made me wonder even more about dark matter. Here is the part about gravitation that caught my attention:

    It is possible that deceleration is caused by gravitational forces from unidentified sources such as the Kuiper belt or dark matter. However, this acceleration does not show up in the orbits of the outer planets, so any generic gravitational answer would need to violate the equivalence principle (see modified inertia below). Likewise, the anomaly does not appear in the orbits of Neptune's moons, challenging the possibility that the Pioneer anomaly may be an unconventional gravitational phenomenon based on range from the Sun.

    If there is no anomaly in Neptune's moons, then there is no need for dark matter to make those orbits perform as predicted. Does that mean there is no dark matter in our solar system?

  9. #69
    Jai Keshava NikolaiI's Avatar
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    I am not sure, YesNo.

  10. #70
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    I started looking around the internet and apparently this problem has already been raised: http://www.technologyreview.com/view...ing-in-action/ It looks like there isn't much of any dark matter in the solar system, but apparently on a large scale it is needed to make the gravitational laws work.

    Either the gravitational laws are accurate but the calculation of the amount of visible mass is off by a factor of 5 to 10 or so or the gravitational laws are more complicated than originally believed. Perhaps both. Of course, perhaps there is dark matter out there.

    Edit: I just thought of something that I remember reading from Rupert Sheldrake's books. Newton's law of gravity F = G*(m1*m2/r^2) may have a problem because G ("big G") may not be a constant. When we are looking at galaxies we are seeing them as they were in the past and big G may have been different then. Here are the recent results of trying to calculate big G: http://www.scientificamerican.com/ar...te-slide-show/

    If the value of big G is dependent upon time then one should be able to see galaxies with certain mass behaving differently but similarly for those the same distance from us. That would be one way to test and possibly falsify the conjecture that big G changes with time.

    Edit 2: Although the day was bright and warm with a clear sky, the evening sky is covered with clouds.
    Last edited by YesNo; 11-29-2014 at 08:52 PM.

  11. #71
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    Quote Originally Posted by YesNo View Post
    Edit 2: Although the day was bright and warm with a clear sky, the evening sky is covered with clouds.
    YesNo: did the end of this get cut off unfinished? I might have said something along these lines re my frustration over conditions when I can use my binoculars. Or is it nothing to do with that?

  12. #72
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    Yes, I wanted to say that I was having the same problem you were having. Yesterday I expected the sky to be clear because it was a nice warm day with few clouds. I could even see the moon half illuminated as I walked through the forest preserve and got some pictures of it with my phone through the trees. That was around 2 pm. Toward evening the clouds came in, just as you described.
    Last edited by YesNo; 11-30-2014 at 09:45 AM.

  13. #73
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    I guess one of the things I am learning is patience. Not easy trying to try out new equipment.

  14. #74
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    When I was a young child I used to like to tell people, "Patience is a virtue, and virtue is its own reward, so we should all just sit and wait for that reward to come." But all kidding aside, anticipation can heighten pleasure It will be that much prettier when you can use it on a clear night.

  15. #75
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    I'm still practicing patience since last night was cloudy again, but I think Wednesday may be just right. I don't know what I'm looking to see, perhaps just to convince myself that the constellations in Patrick Moore's book are really out there.

    I also searched for dark energy and dark matter. It seems they are ad hoc solutions to two different problems. Dark matter attempts to explain why spiral galaxies do not fall apart and dark energy tries to explain why the universe is expanding. They do fit the solutions to the current problems perfectly as seen from the cosmic microwave background, but that is what an ad hoc solution is supposed to do. Since there is no need for dark matter in our solar system and the Andromeda galaxy is heading toward us, not away, they make me wonder.

    In my wanderings in the internet forest, I found a blogger, Miles Mathis, who doesn't like this dark stuff either. He reminded me of Eliezer Yudkowsky who believes in many worlds. They are both very literate, that is, they are both likely to convince me if I don't watch out. I wonder if I'll be disagreeing with Mathis as much as Yudkowsky the more I read him.
    Last edited by YesNo; 12-01-2014 at 07:56 AM.

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