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Two dumb questions
Hi;
Dumb question #1: It is my understanding that about 4 billion years ago the moon was much closer to the earth than today (correct ?). and as a result of bumping into dust/asteroids etc. it has gradually lost energy and therefore moved AWAY from the earth. My intuition tells me that as the moon looses energy/momentum it should be less able to resist earth's gravity, and therefore move NEARER to the earth. Why is my intuition wrong? Dumb question #2: I live in Quebec City Canada, which is somewhere around the 47th parallel. Since that is far north of the Tropic of Cancer (the most northerly height of the sun in late June) I had always just assumed that the sun would ALWAYS be south of east in the morning, and south of west in the evening. Recently I noticed that that does not appear to be the case. In late June, if I draw a line pointing to the sun first thing in the morning, and another just before the sun goes down, the interior angle is a lot less than 180 degrees. It appears that this angle is about 150 degrees on the NORTH side of my house. This makes no sense to me and is beginning to drive me insane. I assume I am seeing the sun north of east/west in the morning/evening, but why? Cordially; Friar Broccoli Robert Keith Elias, Quebec, Canada Email: EliasRK (of) gmail * com Best programmer's & all purpose text editor: http://www.semware.com --------- I consider ALL arguments in support of my views --------- |
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Dear Friar Broccoli:
"Friar Broccoli" wrote in message ps.com... Hi; Dumb question #1: It is my understanding that about 4 billion years ago the moon was much closer to the earth than today (correct ?). and as a result of bumping into dust/asteroids etc. it has gradually lost energy and therefore moved AWAY from the earth. This "moving away" stuff *requires* energy/momentum... not the loss of it. My intuition tells me that as the moon looses energy/momentum it should be less able to resist earth's gravity, and therefore move NEARER to the earth. Why is my intuition wrong? It isn't. The recession of the Moon is largely driven by the Earth's tides. Angular momentum is transferred from the Earth to teh Earth-Moon system, in much the same way a miner panning for gold can radially accelerate water in his pan. By slightly shifting the center of mass. Dumb question #2: I live in Quebec City Canada, which is somewhere around the 47th parallel. Since that is far north of the Tropic of Cancer (the most northerly height of the sun in late June) I had always just assumed that the sun would ALWAYS be south of east in the morning, and south of west in the evening. Recently I noticed that that does not appear to be the case. In late June, if I draw a line pointing to the sun first thing in the morning, and another just before the sun goes down, the interior angle is a lot less than 180 degrees. It appears that this angle is about 150 degrees on the NORTH side of my house. This makes no sense to me and is beginning to drive me insane. I assume I am seeing the sun north of east/west in the morning/evening, but why? Nearer the geographic North pole, the Sun never sets in the summer. Your assumption of "less than 180 degrees" is incorrect. Be OK for a flat-earther, though. ;) David A. Smith |
#3
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"N:dlzc D:aol T:com (dlzc)" N: dlzc1 D:cox
wrote in message news:qjeAe.25726$Qo.4513@fed1read01... .... It isn't. The recession of the Moon is largely driven by the Earth's tides. Angular momentum is transferred from the Earth to teh Earth-Moon system, in much the same way a miner panning for gold can radially "tangentially" not radially... accelerate water in his pan. By slightly shifting the center of mass. Sorry about that... David A. Smith |
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Thanks to Llanzlan Klazmon and "N:dlzc D:aol T:com (dlzc)"
(how do you get David Smith from that?) for your useful responses. N:dlzc D:aol T:com (dlzc) wrote: This "moving away" stuff *requires* energy/momentum... not the loss of it. Glad to hear it. The recession of the Moon is largely driven by the Earth's tides. Angular momentum is transferred from the Earth to teh Earth-Moon system, in much the same way a miner panning for gold can radially accelerate water in his pan. By slightly shifting the center of mass. I didn't understand this till I read "Llanzlan Klazmon" comment: The movement of the Moon away from the Earth is caused by transfer of angular momentum from the Earth's rotation to the Moon's orbit. Right now I still don't REALLY understand, but I'm pretty sure that I will get it after reflecting on the earth's rotation and tides for a few days/weeks. Nearer the geographic North pole, the Sun never sets in the summer. Your assumption of "less than 180 degrees" is incorrect. Be OK for a flat-earther, though. ;) This definitely has not sunk in yet, but this gives me a new way of trying to visualise the situation. Again I should get it after more reflection. If I fail, I will add acceptance of a flat earth to the fundamental tenants of the Broccolist faith. Thanks again; Cordially; Friar Broccoli Robert Keith Elias, Quebec, Canada Email: EliasRK (of) gmail * com Best programmer's & all purpose text editor: http://www.semware.com --------- I consider ALL arguments in support of my views --------- |
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Ddear Friar Broccoli:
"Friar Broccoli" wrote in message oups.com... Thanks to Llanzlan Klazmon and "N:dlzc D:aol T:com (dlzc)" (how do you get David Smith from that?) for your useful responses. The "d" is for David. The other three letters are for my wife and kids. N:dlzc D:aol T:com (dlzc) wrote: This "moving away" stuff *requires* energy/momentum... not the loss of it. Glad to hear it. The recession of the Moon is largely driven by the Earth's tides. Angular momentum is transferred from the Earth to teh Earth-Moon system, in much the same way a miner panning for gold can radially accelerate water in his pan. By slightly shifting the center of mass. I didn't understand this till I read "Llanzlan Klazmon" comment: The movement of the Moon away from the Earth is caused by transfer of angular momentum from the Earth's rotation to the Moon's orbit. Right now I still don't REALLY understand, but I'm pretty sure that I will get it after reflecting on the earth's rotation and tides for a few days/weeks. Sounds like an excellent plan! If you drink coffee, and you think about it, get down to the last ounce in the cup. See if you can get the coffee to "whirl around" in the cup without using a spoon. Earth's tides have a center of mass that very slightly leads the Moon in its orbit (the "leading" is caused by the ocean's momentum, which tends to pretty much follow the Earth around). When the tides move around like this (very slightly counter to the Earth's rotation), it tends to apply a braking torque to the Earth. The tides boost the Moon's orbit, while slowing the Earth's rotation. Nearer the geographic North pole, the Sun never sets in the summer. Your assumption of "less than 180 degrees" is incorrect. Be OK for a flat-earther, though. ;) This definitely has not sunk in yet, but this gives me a new way of trying to visualise the situation. Again I should get it after more reflection. If I fail, I will add acceptance of a flat earth to the fundamental tenants of the Broccolist faith. Thanks again; Good luck. Llanzlan Klazmon's response should lead you in the right direction. David A. Smith |
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To Friar
To really appreciate what is happening beyond the illusion of sunset and sunrise and equatorial orientation to the Sun it is best to order things according to their correct properties. First things first - the earth's axial orientation is more or less constant over the course of a year,you can check this by the North star Polaris - http://homepage.mac.com/tarashnat/as.../0001-08a.jpeg As the Earth's polar axis is fixed to Polaris ,it follows that the Earth's Equator at 90 degrees to the axis will also remain fixed - http://www.qrg.northwestern.edu/proj...quator-45s.gif What causes the seasons is not axial tilt to the Sun or orbital plane but the change orientation of the Earth in its orbit around the Sun,it stands to reason as the Earth as a whole does not tilt (see Polaris) so something else has to cause the illusion. It was a decision by 17th/18th century cataloguers to furnish the Earth with an axial tilt property to the Sun for their agenda in trying to solve the Longitude problem and it will drive you insane if you are not careful enough to escape the bluffing and blustering. It may be initially difficult to see things from a changing orbital orientation passing through a fixed Earth orientation as the main factor in seasonal differences but it certainly is worth the effort for the alternative is just slightly better than a flat Earth i.e. a hemispherical Earth like this description where axial tilt to the Sun is attributed as a cause - http://www.schoolsobservatory.org.uk...easonsanim.htm There is an enormous difference between recognising Keplerian orbital changes passing through fixed axial orientation and the inferior view of axial tilt to the Sun. |
#7
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"Friar Broccoli" wrote in
ps.com: Hi; Dumb question #1: It is my understanding that about 4 billion years ago the moon was much closer to the earth than today (correct ?). and as a result of bumping into dust/asteroids etc. it has gradually lost energy and therefore moved AWAY from the earth. The movement of the Moon away from the Earth is caused by transfer of angular momentum from the Earth's rotation to the Moon's orbit. This comes about through tidal interaction and has nothing to do with dust/asteroids etc. BTW the Moon's orbit has greater energy than when the semi-major axis was less than it is now. Note that this also means the period of the Earth's rotation is slowing lengthening. i.e the day is slowly getting longer. My intuition tells me that as the moon looses energy/momentum it should be less able to resist earth's gravity, and therefore move NEARER to the earth. Why is my intuition wrong? See above. Dumb question #2: I live in Quebec City Canada, which is somewhere around the 47th parallel. Since that is far north of the Tropic of Cancer (the most northerly height of the sun in late June) I had always just assumed that the sun would ALWAYS be south of east in the morning, and south of west in the evening. No. The extreme case is at the poles where the Sun doesn't set at all at the height of summer. Recently I noticed that that does not appear to be the case. In late June, if I draw a line pointing to the sun first thing in the morning, and another just before the sun goes down, the interior angle is a lot less than 180 degrees. It appears that this angle is about 150 degrees on the NORTH side of my house. This makes no sense to me and is beginning to drive me insane. I assume I am seeing the sun north of east/west in the morning/evening, but why? The Earth's axis is tilted a little over 23 degrees to the 'normal' of the ecliptic. The ecliptic is the plane of the Earth's orbit about the Sun, which is thereby tilted at a little over 23 degrees to the plane of the Earth's equator. On the day of the northern Summer soltice, the Sun's declination is a bit over 23 degrees North of the equator. It's just a bit of projective geometry. Download a skycharting program and explore. Klazmon. Cordially; Friar Broccoli Robert Keith Elias, Quebec, Canada Email: EliasRK (of) gmail * com Best programmer's & all purpose text editor: http://www.semware.com --------- I consider ALL arguments in support of my views --------- |
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To Klazmon
Your explanation is basically derived from the cataloguers of the 18 th century who found it necessary to explain away the Equation of Time by bringing in an inapprorpriate analemmatic feature based on Equatorial orientation to the Sun.The EoT has nothing whatsoever to do with daylight/darkness asymmetry or the solstice which denotes the hemispherical extremes of that feature but most continue to bluff and bluster,up to and including Nasa. http://imagine.gsfc.nasa.gov/docs/as...s/980116c.html In will not make sense to have the Earth's axis tilt to the orbital plane to generate that illusion of the Sun passing at higher elevations during the summer (hemispherical term) so the other option is to ignore axial orientation and Equatorial orientation altogether and concentrate on the Earth's orbital motion and orientation. Here is what the Earth's faster motion taking an inner heliocentric orbital circuit looks like against the motion of Jupiter and the slower and outer moving Saturn http://www.opencourse.info/astronomy...turn_retro.gif This takes care of the great Copernican insight and how the early heliocentrists understood the heliocentric system and it is as exciting today as it was back then. Now as for orbital orientation as changing over an annual orbit - This graphic gives a rough idea of the planet's orientation to the Sun generating a division between planetary sunlight and planetary shadow (which we call 'night'),for convenience any old analogy will do - http://www.phschool.com/science/scie...strange_01.jpg The great error in explaining seasonal changes for the entire planet and at once ! is that the real cause is not to be tempted into explaining axial tilt variations against the orbital plane but by the altering of orbital orientation in a longitudinal way for only two times during an annual orbit at the Equinoxes will the orbital orientation align with the polar terrestial axial longitudes with a maximum variation at noon. Go ahead and try it,it works far better than axial tilt to the Sun/orbital plane for it removes the need for spliting the Earth into seperate hemispheres and will get rid of that nasty 17th century analemmatic maneuver which causes the problem. *http://www.bodley.ox.ac.uk/cgi-bin/i...x.x.54 .x.336 |
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Friar Broccoli wrote:
It is my understanding that about 4 billion years ago the moon was much closer to the earth than today (correct ?). and as a result of bumping into dust/asteroids etc. it has gradually lost energy and therefore moved AWAY from the earth. No, it has gained energy from the Earth by means of tidal forces, vaguely like 'pumping' a playground swing higher and higher by shifting your centre of gravity in synch with its period. In return the rotation of the Earth has been slowed, so that our day is longer than it used to be. My intuition tells me that as the moon looses energy/momentum it should be less able to resist earth's gravity, and therefore move NEARER to the earth. Why is my intuition wrong? If the Moon did experience a net loss of energy its orbit would indeed tend to contract, but see above. I live in Quebec City Canada, which is somewhere around the 47th parallel. Since that is far north of the Tropic of Cancer (the most northerly height of the sun in late June) I had always just assumed that the sun would ALWAYS be south of east in the morning, and south of west in the evening. You seem to be mixing up two different phenomena: the height of the Sun at noon, and the displacement of sunrise and sunset from due east & west (and from their 'nominal' solar times of 6h00 and 18h00) respectively. Recently I noticed that that does not appear to be the case. In late June, if I draw a line pointing to the sun first thing in the morning, and another just before the sun goes down, the interior angle is a lot less than 180 degrees. It appears that this angle is about 150 degrees on the NORTH side of my house. This makes no sense to me and is beginning to drive me insane. I assume I am seeing the sun north of east/west in the morning/evening, but why? Well, it's a little hard to explain without diagrams (you could probably find some by Googling), but let's start by picturing an observer on the geographic equator. The great circle running from east to west via the zenith, perpendicular to the horizon, is called the "prime vertical", and from 0° latitude this coincides with the celestial equator. So when the Sun is at 0° declination, on the vernal equinox for example, it rises due east, passes straight overhead at noon, and sets due west. As the Sun's declination increases over the next three months, its path remains parallel to the prime vertical but creeps northwards, so that its rising, culminating, and setting points are all in the northern half of the sky. Now imagine that the observer is a little north of the geographic equator. Although the celestial equator and his prime vertical still meet on the eastern and western horizons, the former now appears to be tilted slightly southward (by an angle equal to his latitude), so that on the vernal equinox the Sun, although rising and setting due east and west, at noon culminates south of the PV. As the spring progresses and the Sun moves northward, its culmination point approaches the zenith at the same pace as was observed from the GE; meanwhile the sunrise and sunset points are also shifting, but here the tilt of the CE makes them move north faster than they did there. To understand why, imagine looking eastward at 0600 solar time. The Sun's north declination places it not only north of due geographic east, but above the horizon as well, because celestial north no longer coincides with geographical north, being elevated by an angle equal to the latitude (the north celestial pole has the same altitude above the north horizon). So the Sun has already risen and its path, still parallel to the CE, is tilted; likewise at solar 18h00 it hasn't set yet, and the day has become longer than 12 hours. On a certain date the noon Sun will reach the zenith; from then through the summer solstice it will spend the entire daytime in the northern half of the sky. The further north the observer goes, the later this date of zenith culmination, and the Tropic of Cancer is the latitude where it falls on the summer solstice. From anywhere north of this point the noon Sun is always in the southern half of the sky -- but note that during the summmer it still crosses the PV twice a day, rising and setting on the north side. Moreover the increased latitude exaggerates the displacement, making the inequality of day and night more pronounced. As we get into the higher temperate latitudes the CE has become closer to the horizon than to the PV; the summer sun rises and sets at a shallow angle, a long way north of east and west, making for long twilights and short nights. At the Arctic Circle an extreme situation is reached; the CE is 'depressed' so far that on the summer solstice the Sun's diurnal circle only touches the north horizon instead of dipping below it. From the North Pole the CE coincides with the horizon; since the Sun's path is (as always) parallel to the CE, its altitude doesn't change appreciably all day. I've gone on longer than I intended, but to sum up the northward displacement of sunrise and sunset in summer *increases* with latitude; while in the tropics the relative length of day and night doesn't change very much, and the path of the Sun never strays very far from the PV, in temperate latitudes the difference between day & night, and accordingly the difference between the lengths of the portions of the Sun's diurnal arc lying above & below the horizon, become quite large. Everything I've said can be applied to the situation in winter, _mutus mutandis_. -- Odysseus |
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Friar Broccoli wrote:
It is my understanding that about 4 billion years ago the moon was much closer to the earth than today (correct ?). and as a result of bumping into dust/asteroids etc. it has gradually lost energy and therefore moved AWAY from the earth. My intuition tells me that as the moon looses energy/momentum it should be less able to resist earth's gravity, and therefore move NEARER to the earth. Why is my intuition wrong? Others have answered this, but for a nice picture, look at http://www.talkorigins.org/faqs/moonrec.html Steve Carlip |
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