Welcome to the StarCast for the week of August 24th, 2025. I'm your host, Jay Shaffer, and with me is my co-host, Mike Lewinski.

How you doing, Mike? I'm great, how are you, Jay? Doing great. Let's take a look at some space weather from SpaceWeather.com.

Mike, what's happening with the sun over the next couple of days?

Well, Jay, there are a couple of far-side sunspots just behind the sun's eastern limb that are going to turn and face Earth in a few days. These regions have been active and have been sending CMEs into space. If they continue that activity, we will soon be in the line of fire. At this time, there is an estimated 35% chance of an M-class flare in the next 24 hours and a 45% chance of an M-Class flare in the next 48 hours. X-class flares are estimated only at a 5% chance. So, here in the mid-latitudes, our chance of an active aurora condition is about 10% for the next day, or 35% for one to two days out. Things get a little bit better when you're up at the high latitudes, with a peak chance of northern lights being around 50% in the 24 to 48-hour range.

So, what's up in the sky this week, Jay?

Well, yesterday morning at 2:08 AM Eastern Daylight Time, we had the new moon. You may have heard some hype about it being the Dark Moon, as if it were something super extraordinary. But, in fact, it was named that just because it's the second new moon that happened in the month of August. This week is a great week to observe the night sky, however, if your weather cooperates. It's a good time to observe the Andromeda Galaxy in the Northeast. The Milky Way is setting fairly early in the evening now, and if you wake up early in the morning, you will see in the pre-dawn sky a preview of the winter evening sky, with Orion, Sirius, and the Gemini twins all visible. Unfortunately, my forecast is for rain every night over the next few nights, so I won't be able to observe too much of that. So, now let's take a look at some space news. Mike?

In a significant astronomical discovery, researchers have announced the finding of a new tiny moon orbiting the ice giant Uranus. Provisionally named **S/2025 U1**, this moon was identified using images captured by the James Webb Space Telescope in February of this year. The discovery, announced August 19th, brings the total count of confirmed Uranian moons to 29. With an estimated diameter of only 10 kilometers, S/2025 U1 is one of the smallest known moons of Uranus and orbits the planet approximately every 9.6 hours. This marks the first moon discovery within our solar system using the powerful James Webb Space Telescope, highlighting its remarkable ability to detect faint objects that even NASA's Voyager spacecraft missed during its 1986 flyby.

Jay, what have you got?

Well, based on data from NASA's Dawn mission, a new study published in *Science Advances* suggests that the dwarf planet Ceres may have once had the necessary conditions to support microbial life. While there's no evidence that life ever existed there, researchers found that about 2.5 billion years ago, Ceres likely had a source of chemical energy in its subsurface ocean, which could have fueled microorganisms. This energy, along with the presence of water and organic molecules previously found, completes the three key ingredients for habitability. Although Ceres is now too cold to be considered habitable, this finding offers new insight into the potential for ancient life on similar icy bodies throughout our solar system.

So today, Mike and I are going to talk about Albert Einstein, the theory of relativity, and GPS satellites. Mike, why are these three things related?

Yeah, I'm glad you asked, Jay. I've been doing some background reading on relativity, and in particular, related to the speed of light for my presentation at the Crystal Dark Sky Festival next week. In my reading, I came across some discussion about GPS satellites and the way that Einstein's theories of special relativity and general relativity affect them. GPS is a constellation of about 30 satellites in orbit, and these satellites are continuously broadcasting their current time to ground-based receivers, such as we have in our cell phones or vehicle navigation systems.

Now, where relativity comes into play here is that Einstein's theory of **special relativity** says that objects that are moving through space at a greater speed experience a different passage of time than those moving at a slower speed. For example, if we could travel near the speed of light, time for us would pass much slower than time on Earth. So, satellites that are orbiting at a speed of approximately 8,700 miles per hour are ticking an extra 7 millionths of a second each day. Because the time signal from GPS is very important to being able to correctly calculate our position, we need to account for this. Atomic clocks on the GPS satellites need to subtract 7 microseconds every day.

However, general relativity changes this because gravitational mass also affects the passage of time. Clocks on Earth tick more slowly than those that are farther away, such as on GPS satellites. So, this adds microseconds each day to a GPS atomic clock. They must add 45 microseconds back due to the lesser effect of gravity on the satellite than on the ground station. So, we're subtracting 7 microseconds and adding 45 back, which means that GPS clocks don't tick over to the next day until they have run a total of 38 microseconds longer than comparable clocks on Earth. There are estimates that if the GPS clocks were not adjusted to accommodate both special and general relativity, there would be a drift of something like 10 kilometers per day of accuracy. The problem being that, of course, that 38 microseconds would get added day after day after day, and so the drift would presumably become much longer.

The full story there is a little bit more than we're going to get into today because that 10 kilometers of distance is actually assuming that at least three of the four satellites that we get a fix from have not made the correction because all of the satellites are basically going to have the same offset of time. It would change the amount of drift that we would experience. And I just want to say, before we jump into the rest of our discussion about relativity here, that GPS time accuracy is very important for observational astronomy. We have constellations of telescopes in different parts of the Earth that are doing VLBI, or very large baseline Interferometry. These disparate telescopes are using GPS signals to more accurately coordinate observations of very, very distant objects simultaneously. This has been compared to, in some cases, on the moon being able to pick out an individual on Earth in terms of the accuracy of these observations.

While GPS allows ground-based telescopes to do very precise observations of very distant objects, it's also very useful for other satellites for spacecraft. We're able to save quite a bit of money on the amount of instrumentation we use when we're launching a rocket with payloads because GPS provides such excellent location information. The last thing I'll say is that GPS is also essential for the science of geodesy, which is making very accurate measurements of the Earth. Before we had GPS constellations, we were using quasar signals with disparate ground-based receivers. And knowing the frequency of that quasar signal, we could calculate the accurate shape of the Earth based on differences in the signal's arrival at ground-based stations, so there's just a whole host of very interesting applications that emerge out of GPS for Earth sciences, for astronomy, for agriculture, for safety. The fact that our cell phones are able to get our location so accurately, so quickly, it's not just that there are GPS satellites, it's that there are GPS satellites that are highly corrected and correlated with the internet, and the internet really expanded the ability to provide very precise location from GPS signals. So with that, Jay, let's turn it back over to the clock and train thought experiment.

So yeah, Mike, so Einstein had come up with his general theory of relativity, he further refined that as the **special theory of relativity**, which you spoke about earlier, which talks about time dilation. And so how that came to be was Einstein reportedly had made a thought experiment where he imagined himself on a train pulling away from a train station and looking at the clock at the train station. If you can kind of expand your imagination so that he could constantly look at that clock as the train pulled away, and that train, if it was pulling away at the speed of light, then the photons striking the clock's face and reflecting out toward Einstein's eye on the train would also be moving at the speed of light. And since he was moving away from the clock at the speed of light, the clock hands would never appear to move. Because he would be seeing the same photons that were reflected from the face of the clock constantly, as he was moving through space at the speed of light. And you can also think about this analogy a little bit, like bullet time in *The Matrix*. When Neo was able to slow himself down, or speed himself up, relative to the speed of a bullet, he was able to basically slow that bullet down, or at least the perception of that bullet being slowed down. And so that's basically how time dilation works in Einstein's special theory of relativity.

And then, if I may talk a little bit about, again, you talked about the separation in his **general theory of relativity**, which deals more with gravity. So, in his theory of general relativity, he had the thought that gravity would bend spacetime. In other words, if light from a distant star passed through a strong gravity field, it would actually bend that light from that star, and so it would bend around the massive object. And so he put that out in his general theory of relativity, and during the total solar eclipse of September 21st, 1919, a team of Australian astronomers and physicists, including Professor William Ernest Cooke, set out on a remarkable expedition to Wallal, Western Australia. Their goal was to photograph the stars near the sun's eclipsed disk, a critical test for Einstein's groundbreaking theory of general relativity. The theory predicted that the sun's massive gravity would warp the fabric of spacetime, causing the light from distant stars to bend around and appear shifted from their normal positions.  With specialized cameras and precise timing—no GPS at that time, actual stopwatches—the team captured a series of photographic plates during the fleeting moments of totality. Their measurements confirmed the predicted shift, providing the pivotal evidence that supported Einstein's revolutionary ideas and fundamentally changed our understanding of gravity in the universe. So, both these things are interacting, both the theory of general relativity and the theory of special relativity. And so, if you want to expand upon that a little bit more, Mike?

Well, Jay, I think just the two things that come to mind at the start of your segment, you mentioned that he refined general relativity into special relativity, but actually, special relativity was published in 1905, and general relativity came along in 1915, so four years before that solar eclipse experiment. So, in some ways, general relativity was the refinement. My interest in this topic goes toward the nature of the speed of light, which was really sort of a mystery until Einstein tackled this. There were different theories accounting for it, but how light moved the way that it moved. The thing that has just fascinated me and is going to be part of my presentation next Saturday is that photons don't experience the passage of time at all. So all of the movement of light happens through space and none of it through time. We talk about a light year, the distance that light travels in a year, but that's entirely from our perspective. If you could ask a photon about its journey from Alpha Centauri to the Earth, it would say that there was no journey, that it was always on Alpha Centauri, or leaving at Alpha Centauri and arriving at Earth, and that was its only experience, a sort of an eternal now. So, photons don't get old, which I think is just super fascinating.

We have these thought experiments about what would happen to us as we traveled near the speed of light and how that would affect our experience of time, but something that I don't hear talked about as often is how that would affect our mass. In my research here, I ran across the explanation that objects that travel at the speed of light become infinitely massive and therefore require infinite energy to move. So, you can't have infinite energy, even if you could have infinite mass, and therefore, we will never travel at the speed of light, and probably not even very close to the speed of light, because the closer we get, the more massive we become. So there is just a diminishing available energy to further accelerate our motion. So, every now and then, somebody says, "Oh, science, we know so little, surely we'll figure out a way to break the speed of light," but I don't think that's going to happen. Maybe we'll develop wormhole technology and be able to travel vast distances in short periods of time, but it won't be because the spacecraft that we send through the wormhole is actually traveling at or near the speed of light. It will be because we're taking a shortcut, and just as you wouldn't say, taking a shortcut around the block, you traveled at 600 miles an hour. No, you just cut through the backyard, and your speed was what your speed was. Just taking a shortcut, so that's kind of where my mind has been. I've also spent quite a bit of time learning about how photons are transmitted into neurochemical energy in the brain. I think that the last little kind of fun fact that's really a digression here is that the retinas of our eyes are not optic nerves that connect to our brain, they actually are our brain—the part of our brain that sits outside of the skull. And so, when you look up at the stars and that light that has traveled so many light years to reach the retinas, that's starlight just colliding with your brain.

Yeah, and so, we should note that photons are massless, and so that is why they can travel at that speed. Exactly. Secondly, I just wanted to, I had a thought here, and maybe you have the answer to it, is when we say that a photon is absorbed, what happens to that photon? Is it transformed into something else?

Yeah, so when the photon strikes the retina, it is typically absorbed by a protein, a specialized protein called an opsin. For example, rhodopsin is the protein that lives in the rods in the retina. The rods are the part that give us our night vision. They don't sense color, but they do sense light. The absorption of the photon in that protein basically changes its structure. And so, that energy in the photon is converted into both mechanical energy and heat energy. So, all cases of photons being absorbed are the transformation of one form of energy, of light, into a different form of energy of kinetic energy, basically. For all practical purposes, kinetic energy is heat. It's the motion of atoms that makes heat, so light turns into motion, which is a form of heat.

Yeah, and of course, my living off-grid, like you and I do, we are also dependent upon photons to convert themselves to electrons to provide us with our electricity to allow us to be able to broadcast podcasts, for example.

 So that's our discussion about Einstein, the theory of relativity, and GPS satellites. We want to thank all of our listeners for checking out this podcast. Please be sure to comment, like, and subscribe, and let us know what you'd like to hear more about. You can also check out our website at WildernessVagabonds.com, Skylapser.com, and if you'd like to help us out, you can buy us a coffee at [buymeacoffee.com/skylapser](https://buymeacoffee.com/skylapser). The intro music is "Fanfare for Space" by Kevin MacLeod from the YouTube Audio Library. From the Deep Sage 9 Observatory, this is Jay Shaffer and Mike Lewinski, wishing you all clear skies.