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Re: Star gazing
SierraNevada #41095 11/27/14 04:47 PM
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I agree. And to think that we've uncovered it in the Whitney Zone although the rest of the nation hasn't realized this discovery yet!

Re: Star gazing
Whitney Fan #41096 11/27/14 09:02 PM
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Steve C Offline OP
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Ok, Dave Clock says it is his copyright symbol. Once I enlarged the picture, it is pretty clear. Now I am looking for the symbol in the other pictures. smile

                       

He shared another with the copyright more obvious:


Re: Star gazing
Steve C #41099 11/28/14 01:22 AM
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By the way, his website has some spectacular pictures.

David Clock Photography

Interesting point made by SierraNevada regarding geosynchronous satellites and their figure 8 "wobble". Web pages discuss this and mention that the satellites need to occasionally fire rockets to keep their position steady, due to gravitational effects of the sun and moon.

One thing I can't find in the discussions is the effect of the moon's gravity on the satellites. It would seem that those satellites would be pulled back and forth by their position relative to the moon, similarly to the way the ocean's tides oscillate. In fact, the figure 8 wobble's north and south oscillation can be explained by the satellite's orbital plane being at some angle to the equator's plane. But isn't the width of the figure 8 caused by the gravitational oscillations due to the moon?

Here's a youtube video that shows timelapse pics of the earth over 8 days: http://youtu.be/tvsW2aGq2QU

Re: Star gazing
Steve C #41100 11/28/14 07:35 AM
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The Earth's pull is probably just that much stronger. Most people think you get into space and there is no gravity which isn't true. At the altitude the International Space Station orbits the gravity is about 10% less than it is on you right now.

Re: Star gazing
RoguePhotonic #41101 11/28/14 08:55 AM
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Observing Geostationary Satellites

In fact most geostationary satellites are really geosynchronous. Having mean motions between 0.9 to 1.1 revolutions per day they are allowed to drift across a box before corrections are made by on board thrusters. The size of this box is dictated by mission requirements. For example the box for a TV broadcast satellite is determined by the beamwidth of the reception dishes used.

The drift from the ideal position arises due to anomalies in the Earth's gravitational field, at this altitude atmospheric drag is not a consideration. The gravitational influence of the Moon provides an out-of-plane force too, which gradually increases the orbital inclination towards that of the Moon about the Earth (which itself varies between 18 and 29 degrees). The satellite now tends to describe a figure-of-eight ground track; ground controllers aim to restrict this to the box mentioned earlier given that enough orbit-keeping fuel remains. This wandering has been allowed to grow unchecked in the case of a few communications satellites in order to provide better coverage of the polar regions which is otherwise poor (from the poles a geostationary satellite would almost graze the horizon). Net connectivity to US research stations in the Antarctic was achieved in this manner.

Unlike objects in low Earth orbit, geostationary satellites are visible throughout every night of the year, only entering the Earth's shadow for up to 70 minutes per day, around a couple of weeks either side of each equinox. During the same period the satellite tends to brighten over several days, twice a year, when the satellites orientation favors the 'beaming' of the Sun in the direction of the observer.

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