Tag Archives: satellite

Physicists disagree


Getting back to our satellites—traveling around Earth at 17,000 miles per hour, a satellite’s time slows down, according to Einstein. Also according to Einstein, since gravity is weaker up where the satellites are, time moves a little faster. If that’s the case, wouldn’t a satellite’s GPS signal be inaccurate?

As I researched this question online, I got 2 answers to it: yes and no.

Yes. The satellites’ times slow down, but those amazing scientists who put the satellites up there in the first place cleverly adjusted their signals to compensate for it. Each satellite carries an atomic clock and sends a time & location signal at the speed of light, slightly adjusted (through programmed computer chips) for Einstein’s Special Theory. The clock takes into consideration both the slowing down because of speed and the speeding up because of weak gravity.


No. The satellites’ times slow down, but since they’re all zooming along at 17,000 miles per hour, all their times will be slowed down by the same ratio. So, it doesn’t matter. If all the satellites’ times agree with each other, the GPS system will be accurate. Or, the slowing down is cancelled out by the speeding up caused by weak gravity, so it’s what they call a ‘wash.’ Or, Einstein’s theories are a bunch of baloney so we shouldn’t pay any attention to them.
View at Medium.com

Um. I don’t know what to say here, gang. As you must be aware, I’m just some shmo who is learning as I write this. If you put me on the spot for which is the right answer, I’m going with the bloggers who have better proofreading/grammar skills and citations. If any of my loyal readers want to chime in, please do!

UPDATE: Regarding a satellite’s time difference because of relativity, our indefatigable physics consultant, Ms Physics, says:

Infinitesimal difference, yet a difference. You need to approach the speed of light 3.0 x 10^8 m/s (670,616,629 mph) to have a significant difference. Any way John you remember the precision of the Cesium clock, these differences would really become significant in GPSA calculation using General Relativity predicts that the clocks in each GPS satellite should get ahead of ground-based clocks by 45 microseconds per day.

A microsecond is one-millionth of a second. https://www.simetric.co.uk/si_time.htm

This is why I stick to drawing pictures and let others do the heavy brain-work.

I borrowed parts of this composition for my sketch. I removed the horses and put everybody in lab coats.

Back to the beginning of The Western Civ User’s Guide to Time & Space

Just a second

Before I got side-tracked into digital clocks and watches, we were talking about satellites and the Global Positioning System. I mentioned that the satellites that send us navigational signals need to have an incredibly accurate clock aboard. Even a second’s difference in time between satellites’ clocks would change significantly your GPS data—and give you the wrong location.

So you’re thinking, “Well, Manders, those quartz crystal clocks lose or gain only 15 seconds a month. That seems pretty accurate to me. How you gonna improve on a system that measures 32,768 oscillations per second? How you gonna do that? How?”

To which I reply, with a rueful smile, “My friend, there is another clock yet to come, whose sandals the quartz crystal clock isn’t fit to lace. I speak of a clock that loses only one second every 100 million years!”


Back to the beginning of The Western Civ User’s Guide to Time & Space

Satellites and hamster balls

Satellites are useful for a whole bunch of purposes: talking on your cell phone; keeping an eye on the weather; broadcasting television and radio stations; seeing what your enemy is up to in times of war; communicating with people when there’s an emergency…but you probably guessed why I decided to talk about satellites.

Satellites serve the same purpose the stars did for Galileo and Maskelyne. They give you information you need to find your location on Earth. Satellites communicate with the Global Positioning System (GPS) on your phone or in the car. They constantly send out 2 bits of information: time and distance.

Most satellites orbit fairly close to the Earth, like 11,000 miles above its surface. When a satellite sends out information, its range is like a sphere—the satellite in its sphere is like a hamster in a hamster-ball.

Well, maybe not exactly, but you get the idea.

These spheres overlap. In fact, we want 3 or 4 satellite spheres to overlap. If you’re looking at your GPS device, satellites are telling it when you’re within their spheres.

So if you’re in the overlap of 2 spheres, you have a general idea where you are.

A third sphere makes that overlap even smaller, right? The smaller the overlap, the more accurately you know your position.

Then there’s a fourth sphere: Earth. You’re inside that overlap, and on the surface of the Earth.


trilateration noun

: the measurement of the lengths of the three sides of a series of touching or overlapping triangles on the earth’s surface for the determination of the relative position of points by geometrical means (as in geodesy, map making, and surveying)

triangulation noun

1 : the measurement of the elements necessary to determine the network of triangles into which any part of the earth’s surface is divided in surveying broadly : any similar trigonometric operation for finding a position or location by means of bearings from two fixed points a known distance apart

While the satellites are telling your GPS device where they are, they’re also zipping along at hundreds of miles an hour. Their positions change from second to second. All 3, 4 or 5 satellites need to tell you their positions at the exact same moment or it doesn’t work. They need a clock that’s even more accurate than Harrison’s chronometer.

https://thesciencegeek.org/2017/01/29/gps/                                                               mmmmmmmm


Back to the beginning of The Western Civ User’s Guide to Time & Space

Man-made moons

Okay, remember back when we talked about how Galileo thought that we could use the moons of Jupiter as a clock, and their location would help us find our location on Earth? Or how about when Nevil Maskelyne figured we could use the positions of the stars and planets to find out where we are—if we know what time it is?

Maskelyne put in a ton of night-time hours charting the courses of the stars and planets. How much easier it would have been if the heavenly bodies just told him where they are. Well, guess what? Right now, as you sit there eating your frooty kibble, there are over 19,000 moons—man-made satellites—orbiting the Earth that we shot up into space. Every last one of ‘em sends back a constant signal telling us where exactly it is, and the time.


This site shows you where every satellite is right now—https://maps.esri.com/rc/sat2/index.html
Quickie overview of satellites for kids with a charming young lady and a puppet constructed 10 minutes before showtime—https://www.youtube.com/watch?v=03pZdYVacaM