Is There an Unidentified Object Near the Horsehead Nebula?

[russ_watters]

TL;DR Summary

I captured something I can't identify near the Horsehead nebula over two nights. Looking for help identifying it.

As I mentioned in another thread, I'm imaging the Horsehead Nebula right now. On the evenings of 2/5 and 2/6 from suburban Philly between 6:30 and 9:00pm I captured an unknown object/phenomena about a half degree below and to the right of the horsehead (when oriented upright). It is 3 lights in a line, and it appears well-defined in green (2min exposures, f/5.25, scale 1.17 arcsec/pixel), barely in blue and not at all in red (Ha, 4min). At first I thought it was a rogue galaxy (they often appear unexpectedly in astrophotos) but then I realized it's moving. Not steadily, but apparently back-and forth. It's noticeable in a scale of a few minutes, but was still in almost the same spot a day later.

My Starry Night software shows no objects in the area (manmade, comets, asteroids, etc.). My leading theory is a relatively new geosynchronous satellite (body and two solar panels) that has just a bit of north-south drift. Other thoughts:

• It doesn't seem to be internal since they are point sources of light. That tells me "distant", small objects, not, say, internal reflections.
• The halo doesn't seem to match the star halos. I'm not sure what that could mean (its own cloud around it?).
• I haven't done any math on rates, directions or sizes yet.
• I was hoping other astrophotographers might take a look.
• I'm headed on vaca so I won't be able to analyze my photos more before next week.

Below are a downsampled photo of the scene (10 frames/20min, aligned and stacked on the "object"), a full scale zoom, and an obligatory preview of the overall work; just the red (Ha) data (the nebula is like 99% red anyway).

 

[DaveC426913]

I wasn't sure at first, the relationship between pics 1 (the object) and 3 (the Nebula), since neither is visible in the other. But I see they are of the same area of sky, as is apparent in this superposition:

Nothing appears in Stellarium either:

 

[DaveC426913]

I'm not sure Heavens Above shows GSO sats, so I'm looking at a list of them in Wiki.
https://en.wikipedia.org/wiki/List_of_satellites_in_geosynchronous_orbit

Can you tell us the alt-azimuth of the Nebula at the time of your observation?
[EDIT] Nevermind, I got it from Stellarium
From 1830: 132°Az 33°Alt to 2130: 189°Az 44°Alt

Thing is, as you say:

" it's moving. Not steadily, but apparently back-and forth. It's noticeable in a scale of a few minutes, but was still in almost the same spot a day later."

I'm not sure a GSO sat fits that bill. I can't think of any plausible reason a satellite would move back and forth over the course of a few minutes.

A couple of tests:
- is it still there tonight, in the same location?
- presumably the object disappears if your swing your scope off-target. That would confirm it's not a scope artifact.
- contact a buddy in your area to verify the sighting with his own scope

Shoot. Right. You can't do #1 or #2 cuz you're away.


(Any chance you live in the shadow of a radio tower or other tall structure? )

 

[collinsmark]

My Starry Night software shows no objects in the area (manmade, comets, asteroids, etc.). My leading theory is a relatively new geosynchronous satellite (body and two solar panels) that has just a bit of north-south drift.

That actually sounds pretty reasonable.

If it was only a single "dot", instead of 3, I might have guessed one of the following. Most of those listed below passed through the area you are looking, in your timeframe, but are a bit closer to the Great Orion Nebula, rather than the Horsehead, except for the two indicated. (Next time, try to narrow down the time a little better.)

SES-14
USA159 (DSP21)
AMAZONAS 5
TELSTAR 19V
AEHF-4 (USA 288) <== Good contender
VIASAT 2
STAR ONE D1
SXM-7
SBIRS GEO-4 (USA 273) <== Good contender

But the fact that you're seeing 3 "dots" could be an indication they're a set of new satellites -- as you suspected -- that were launched together in a batch, but haven't yet reached their final orbits yet. If that's the case, then my Stellarium software isn't going to be of much help (either Stellarium isn't showing the new sattelites yet, or if they are shown, they may have stale two-line element [TLE] data due to maneuvers).

===============

Before we conclude it's a set of geosynchronous sattelites (which I'm gussing they probably are), I do have to ask:

What type of telescope are you using for this target? I ask because certain types of telescopes are subject to reflections that produce what's described here (yes, even small, "point-like" reflections). Such reflections less likely if you are using a refractor, and more common for Newtonians or Cassegrain style scopes, particularly with open tubes -- optical tube assemblies (OTAs) that are made of struts but are otherwise open, as opposed to more traditional closed tube assemblies. But even closed tube assemblies can produce such reflections if the conditions are just right.

I had to ask, just to rule out low-hanging fruit.

===================

I'm not sure a GSO sat fits that bill. I can't think of any plausible reason a satellite would move back and forth over the course of a few minutes.

@DaveC426913, I interpret @russ_watters OP as saying that the motion is noticiable over a few minutes, not the whole period. I think he said that the period is about a day, since the objects were in approximately the same location the following day.

For clarification, there's a difference between "geostationary" and "geosynchronous."

All geostationary sattelites have an orbital inclination of zero, i.e., they're directly above Earth's equator. Geostationary sattelites appear to be stationary with respect to the background stars with respect to azimuth and altitude/elevation [and will always be right near the celestial equator*] when viewed from the Earth's surface. But geosynchonous sattelites (as opposed to geostationary) don't need to have an inclination of exactly zero. If they don't, then when viewed from the ground here on the suface of Earth, they will oscillate North and South [centered approximately around the celestial equator] with a period of 1 sidereal day** (approximately one solar day). So you can expect them to be in about the same place at a given time of day, from one day to the next (more-or-less). @russ_watters observations seem to fit that.

*(A bit south of the celestial equator for latitudes in the northern hemisphere, and a bit north of the celestial equator for latitudes in the southern hemisphere. This is of course due to parallax.)

**(The oscillations are not exactly one sidereal day either, because the orbit will precess a little bit. But it's pretty close is my point.)

[Edit: made some minor clarifications and corrected a mistake.]

 

[collinsmark]

Btw, I can't immediately verify it with my own scope because I'm in some sort of "atmospheric river" (as it's being called) and will be for the next few days.

 

[collinsmark]

My leading theory is a relatively new geosynchronous satellite (body and two solar panels)

Oh, it can't be one object (one body and two attached solar panels).

Three separate geosynchronous satellites relatively close to other, maybe. Some rocket launches include multiple satellites in the payload, so this isn't out of the question, although it is unusual for geosynchronous satellites.

But it can't be just one big satellite that you're observing -- not without it zipping across the sky really quickly because it's in low earth orbit (LEO).

At the distances we're talking here (geosynchronous orbits) we're not going to make out any detail whatsoever with a backyard telescope. Even something as large as the ISS couldn't be much more than a couple of pixels at that distance.

 

[russ_watters]

@collinsmark

A few responses:

• The time is what it is: 7-9pm give or take a few min. The object was visible the entire time as far as I can tell remember from a quick flip through the subs.
• The scope is an Explore Scientific 127mm apo refractor.
• Geo orbit; right, what I don't know is how much or little oscillation there is for geosynchronous. Miles? Thousands of miles? And is geostationary absolutely perfectly stationary?
• Regarding the size; good point: geo isn't leo; it's much further away.
• And yes, discernable motion over a few minutes, not a full period oscillation.

 

[collinsmark]

@collinsmark

A few responses:

• The time is what it is: 7-9pm give or take a few min. The object was visible the entire time as far as I can tell remember from a quick flip through the subs.
• The scope is an Explore Scientific 127mm apo refractor.
• Geo orbit; right, what I don't know is how much or little oscillation there is for geosynchronous. Miles? Thousands of miles? And is geostationary absolutely perfectly stationary?
• Regarding the size; good point: geo isn't leo; it's much further away.
• And yes, discernable motion over a few minutes, not a full period oscillation.

[boldface mine]

Hi @russ_watters

But was in roughly the same location, more-or-less, relative to the Horsehead nebula, for the duration of 7-9 PM? I mean, was it in the field of view of your Horsehead Nebula image for the whole 2 hours?

If so, it's/they're not geosynchronous satellites. Given your field of view of Horsehead nebula, a geosynchrous satellite would have drifted from one edge of frame to other in about 6 minutes or so.

Recall that geosynchronous satellites keep roughly constant altitude and azimuth, but not constant right ascension (RA) (and drift a slight bit in declination as discussed earlier). Even geosynchronous satellites drift relative to the background stars (albeit much slower than low-earth-orbit satellites).

So if it was in the field of view of the Horsehead nebula the whole time, no it's not a geosynchronous satellite.

If it was in the field of view the whole time, then I would suspect it's a reflection, perhaps Alnitak, caused by something in your telescope's optical train.

The fact that it's filter dependent might be a clue. What type of camera and filter holder are you using?

The scope is an Explore Scientific 127mm apo refractor.

That's a good quality telescope right there.

Geo orbit; right, what I don't know is how much or little oscillation there is for geosynchronous. Miles? Thousands of miles? And is geostationary absolutely perfectly stationary?

Yeah, it can be thousands of miles away from the plane of Earth's equator. A geosynchronous satellite will pass through the plane twice in approximately one sidereal day, making the period approximately one sidereal day (23 hours, 56 minutes, 4 seconds).

But here's the thing. Your scope is tracking on the background stars while the geosynchronous satellites are staying in roughly the same place relative to the ground on Earth, more-or-less. That means that your scope will track right past them.

As such, from the coordinate system of the background stars (i.e., the Horsehead nebula), you should expect geosynchronous satellites to drift at a rate of approximately 15 degrees per hour (i.e., the same rate at which the background stars seem to move across the sky, from our perspective).

If something isn't moving very fast relative to the background stars, it really is something very far away (like farther away that geosynchronous orbit, i.e., asteroid or comet) or it's a reflection of something that is, such as maybe Alnitak reflecting off of various components in your optical train.

 

[Vanadium 50]

I'm hardly an expert, but isn't it low in the sky to be geosynchronoius?

Geosync is 22000 miles above the equator, and you're 2700 miles nprth of the equator. So it should be high in the sky, not low, right?

 

[collinsmark]

Here's a test for reflections. It's something you can do when you get back from vacation.

1. Set up your scope in roughly the same configuration as before, and reproduce the situation as best you can (same target [Horeshead Nebula] same framing, same filters, same exposure time, etc.) I'll assume here that you can reproduce the same three dots again.
2. Keeping all else the same, adjust your framing a little. Slew the scope such that Alnitak is a little bit closer to the center of the frame, but not exactly at the center of the frame -- it should still be off the to side at least a little.
3. Did the three dots change position appreciably relative to the rest of the Horsehead Nebula? If so, it may be a reflection.
4. Try it again with a different framing. If you find that the three dots are almost always opposite Alnitak, then it's definately a reflection, probably some sort of lens flare issue. But even if the three dots are not always opposite Alnitak, but still change position as a function of your framing, it's a reflection.

 

[collinsmark]

I'm hardly an expert, but isn't it low in the sky to be geosynchronoius?

Heisync is 22000 miles above the equator, and you're 2700 miles nprth of the equator. So it should be high in the sky, not low, right?

It depends on your latitude. The celestial equator is the same angle from the zenith in one direction as your latitude is in the other. Then, one must also adjust a little for paralax, when accounting for geosynchrous satellites.

For eample, when Russ took the images near Philadelphia (latitude about 40 deg N), his celestial equator would go from East to West, about 40 degrees south of the the zenith. (That's about 50 degrees above the horizon, at the meridian.)

And due to paralax, most of the geostationary and geosynchrous satellites will be roughly around -6 degrees of declination, more or less.

That places the geosynchonous sattelites at approximately 44 degrees above the horizon if they happen to be near the meridian. If they're not near the meridian, they'll be closer to the horizon (lower in the sky) than that.

 

[Vanadium 50]

I think my point is that one should run the numbers. I believe Alnitak (isn't that the nearest bright star) is almost due south of Russ, so an expert - not me - could probably figure out pretty quickly.

I'm also thinking about Alnitak, Mintaka, Rigel and Sirius. They are all very bright in the UV (maybe even the top 4) - the green color is making my wonder if something is fluorescing. It looks like a star because it is - just in the wrong place and wrong color. A long shot, I know. But the color is saying it's not thermal, and probably not a reflection of something thermal.

 

[collinsmark]

I think my point is that one should run the numbers. I believe Alnitak (isn't that the nearest bright star) is almost due south of Russ, so an expert - not me - could probably figure out pretty quickly.

Alnitak is the bright star in Russ's images. By that I mean the really, really bright one on the left, right there in the images that Russ took (to the left of the horsehead, just above of Flame Nebula).

The Horsehead Nebula, along with Alnitak, was due south of Russ at exactly 20:39:49 (8:39 PM and 49 seconds) on the day of 2024-02-05. At other times that night it was either east of South or west of South. Remember, the Earth is rotating, even if the geosynchronous satellites are revolving along with it.

But as Russ mentioned, the image was taken over the course of 2 hours or more. The Horsehead Nebula (and Alnitak) were not due south the entire time.

That said, several known geosynchronous satellites did in fact pass through the general area that was being imaged during that 2 hour period, from Russ's perspective here on Earth. That much is confirmed. However, any one of these satellites would have been in and out of the field of view within a few minutes. So if these three dots persist longer than that, they're not from [geosynchronous] satellites.

I'm also thinking about Alnitak, Mintaka, Rigel and Sirius. They are all very bright in the UV (maybe even the top 4) - the green color is making my wonder if something is fluorescing. It looks like a star because it is - just in the wrong place and wrong color. A long shot, I know. But the color is saying it's not thermal, and probably not a reflection of something thermal.

Don't forget, each of the lens elements and filters have anti-reflective (AR) coatings and are strongly wavelength dependent. Some wavelengths might make it through and some may not depending on the nature of the AR coatings, regardless of the thermal nature of the source.

Given the information I have as I write this, my #1 suspect at this point in time is a lens flare caused by Alnitak. Notice in the image that Alnitak is opposite the three dots, assuming the central axis of the optical system is in the center of the image. This is indicative of lens flare reflections.

I'm not 100% certain, but if I was a betting man that's where I would put my money at this point in time. The three dots are reflections of Alnitak off of varius lens elements in the system. Each of the three dots could correspond to a different lens element reflection path.

Lens flares have a typical characteristic that the flare is opposite that of the bright source. If the source is to the upper right, the flare is to the lower left. Change the pointing such that the bright object is at the bottom of the frame, the flare will move to the top of the frame.

This is consistent with Alnitak being on the left of the frame, and the three dots being on the right of the frame.

The Explore Scientific 127 APO is an air spaced doublet, meaning their are two lens elements in the objective. Unless Russ has the Explore Scientific 127 FCD100 version, in which case it is a triplet with 3 lenses in the objective. I'm also assuming that Russ is using either a focal reducer or at least a field flattener, and in either case, that's another few lens elements. The point is that there are many lens elements in Russ's system. There's also a filter which fits in there too somehow. There's a lot of potential for reflections and lens flares.

And look at how bright Alnitak is in the image. It could be because of the stretch, but yeah, Alnitak is the bane of all astrophotographers. It gets everybody in the end because we all love the Horsehead and Flame nebulas.

So could it be another star besides Alnitak (such as Mintaka, Rigel, etc.)? 'Could be. But my money's on Alnitak. It's in exactly the right location to cause a lens flare, if those three dots are in fact caused by reflections.

Anyway, further testing might clear this up once Russ gets back from vacation.

I could also try to survey the area with my telescope if the sky clears up, but that doesn't look likely for at least a little while.

[Edit: Something that leads me away from the lens flare hypothesis however, is the three dots line up perpendiculary to the line connecting the center-axis and Alnitak. I would have expected them to line up horizontally in the image (everything in one line), not vertically as they are. So, I'm still scratching my head a little on this one. It could be because of lens element misalignment/poor colimation, but Explore Scientific makes pretty good scopes, so I'm hoping that's not the culprit.]

 

[Vanadium 50]

Alnitak is the bane of all astrophotographer

Wait a few million years. I promise it won't be there anymore.

 

[russ_watters]

[boldface mine]

Hi @russ_watters

But was in roughly the same location, more-or-less, relative to the Horsehead nebula, for the duration of 7-9 PM? I mean, was it in the field of view of your Horsehead Nebula image for the whole 2 hours?

Within maybe 10-20 arcsec the entire time. Not moving much.

If so, it's/they're not geosynchronous satellites. Given your field of view of Horsehead nebula, a geosynchrous satellite would have drifted from one edge of frame to other in about 6 minutes or so.

Ugh, of course. Dumb mistake. So, being almost stationary with respect to the stars would be pretty strange. Even comets and asteroids move faster than what I imaged.

If it was in the field of view the whole time, then I would suspect it's a reflection, perhaps Alinak, caused by something in your telescope's optical train.

The fact that it's filter dependent might be a clue. What type of camera and filter holder are you using?

Perhaps, but it doesn't seem quite perpendicular to Alnitak....much less in a line away from it. Camera is a Zwo Asi1600 and their filter wheel.