# What could have made a satellite appear to move side to side while near the horizon?

Yesterday while coming out of a restaurant my wife and I noticed what appeared be a satellite passing quite high in the sky. Based on the location, time, and brightness this appears to have been a passing of the GEOS 3 Rocket. What made this unusual is that when it got low (perhaps 25-30 degrees off the horizon) it suddenly appeared to dart side to side (over 15 degree sweeps) multiple times over perhaps a second, while continuing its general western trend, before vanishing.

Since this all happened rather quickly I had to estimate the distances after the fact using my hands and what few reference points were available. It is certainly possible that it was lower in the sky than my estimate as that is always a tricky part to judge. I'm quite certain of the sweep distance but an answer that could explain a smaller sweep could still be very useful.

What could cause a satellite to appear to move side to side in this fashion?

• This sounds like the guys over at space exploration SE could help you better with... – AtmosphericPrisonEscape Feb 13 '17 at 3:09
• Could well be atmospheric turbulence -- same source that causes those ripples when looking down a very hot beach or road at a distant object. – Carl Witthoft Feb 13 '17 at 16:19
• @CarlWitthoft the OP says 15 degree sweeps side to side while at an altitude of at least 25 degrees above the horizon. There is no atmospheric physics that can do that. None. Not even close. – uhoh Feb 13 '17 at 16:29
• @uhoh yes, I'm well aware that that's a huge swing. Notwithstanding, at near-horizon viewpoints ugly stuff happens. We've all seen pix of a setting sun where the sun is fully "split." Since the OP was observing without tools, I'm taking that "15-degree" estimate with a large grain of salt. (And, yes, IAAAOP (adaptive-optics physicist) :-) – Carl Witthoft Feb 13 '17 at 16:33
• @CarlWitthoft OK, but that's a good 2 order of magnitude grain of salt. The total refraction of the Earth's atmosphere near the horizon is less than one degree at an altitude of 1 degree, and it's vertical. Physically possible variation in that mean angle are even smaller, and once again, vertical. – uhoh Feb 13 '17 at 16:40

Your link shows estimated magnitude, and it gets quite dim when it gets close to the horizon.

above: from heavens-above, (from url: lat=52.2681&lng=-113.8112)

As a spacecraft in low earth orbit appears to approach the horizon, the line-of-sight distance from it to you can change from a few hundred to a few thousands kilometers, which is why the brightness in your table changes so much.

The path in the sky shown in the link is going to be almost vertical (reaches 70 degrees). Wikipedia says GEOS-3 is a satellite put into orbit in 1975. These days there is a big effort to de-orbit the "leftovers" so they burn up in the atmosphere (space junk mitigation) but back then it was common for each launch to leave other stuff up there for decades or longer.

Wikipedia says the COSPAR-ID for the actual GOES-3 satellite is 1975-027A. That means it was the 27th internationally recognized launch in 1975. "A" is assigned to the GEOS-3 satellite itself, but if you look up 1975-027 in the satellite catalog (SatCat) at Celestrak.org you can see there are were four other objects associated with the launch being tracked. One of them has burned up, but the others are still there.

You can double check if 1975-027B is the one that your link is talking about. Anyway, since they are so old, none of them is capable of a spectacularly sudden engine burn and change in orbit. So I'd have to say that whatever you did see, it isn't associated with the GEOS-3 launch.

Another point to consider; if you just coming out of a restaurant, the chances are low that you could see a 5th magnitude object. Near the horizon the apparent speed would be much slower than that of a satellite overhead.

• Yes an engine burn like that would have been impossible even for an actual functional rocket. The brightness doesn't match up perfectly with what we saw but my understanding is it's not uncommon for the predicted brightness on heaven-above to be off the mark particularly for odd objects like left over rockets. While your answer is very informative it doesn't make an argument for what could have caused the appearance of movement that we observed. – Ceribia Feb 13 '17 at 5:29
• Actually a satellite with flat surfaces - especially solar panels - can deviate quite a bit brighter than expected if the angle is just right. But it's an interesting question how a relatively smooth cylinder, covered in diffuse white paint could do that. It could get dimmer, but I'm not sure if a rocket body can get substantially brighter. Even end-on, the end of a tank would likely be rounded rather than flat, but I'll try to find out if a rocket body has the same "flare" vocabulary as a satellite, it's an interesting question. – uhoh Feb 13 '17 at 6:33
• @uhoh I've updated my question with some timing information. There's no need to, "walk the OP back into science", as I've always been quite firmly there. – Ceribia Feb 13 '17 at 17:01
• @uhoh Fist at arms length is what I was using to estimate, and 25-30 seems pretty much right. It is possible buildings were throwing me off true horizon or something like that, amateur observer and all. No heavy blurring that I recall but can't rule it out. City is mostly light business and residential where I was looking so a large vent seems unlikely but can't rule it out. Winter weather is something I've considered but haven't been able to find much good info on. As a one off event it seems like the answer is going to be more, "It could have been this or this", rather than, "this for sure" – Ceribia Feb 13 '17 at 21:53
• (cont'd) GOES3 orbits with a perigee of about 22,200 km. Even if it were directly above (when it's closest to you), if it were moving in a 15-degree arc in <1s, that would mean it was traveling at about 0.02c. Thinking about turbulence, were you seeing it above the restaurant by chance? They might have had an exhaust from their kitchen causing significant turbulence with the cold air. Also, could you add time and location info? – nflemming2004 Feb 14 '17 at 4:30