Coming soon... Satellite forecasting

[admin]

This is just an intro to a feature that will be making a debut in the next update to SharpCap 4.2 Beta - a satellite forecasting tool to give you an idea of how likely you are to get passing through each frame depending on your location, time and where you are looking...

It turns out that the number of satellites that you might see depends on time, date, location and the direction you are looking in a remarkably complex way. For example there are nearly 5000 starlink satellites that orbit with an orbital inclination of about 53.2 degrees. If you are significantly north of 53 degrees then you just won't be affected by those satellites. Even here at about 51.6N, if you are looking into the northern sky below about 60 degrees of altitude, you are looking 'under' those satellites - where your line of sight reaches the altitude of the satellites is beyond their orbital limit of 53.2 degrees so they are not affecting you.

On the other hand, where that group of satellites reach their latitude limit of 53.2 degrees, their orbits are roughly E-W, so they spend longer at those latitudes than at other latitudes, meaning you get a band with higher density across the sky near the turnaround point.

On top of that, the altitude that your view direction intersects with the orbit of the satellites has to be calculated. In some parts of the sky, that intersection point might be inside the Earth's shadow, meaning that the satellites will not be reflecting significant amounts of light and will be invisible.

The sort of plot you will get looks like this...

Screenshot 2026-05-11 140021.jpg (245.25 KiB) Viewed 644 times

Think of this as like a planisphere view of the sky - as if you are looking up at the sky - with North at the top. The colours show the chances of one or more satellites being in a frame based on the set exposure, field of view, time, date and location - ranging from below 1% (grey, purple, blue) to 50 to 100% (orange to red). The plot shown is for the equinox when the variations across the sky are very pronounced. Image a target in the west and you have a high chance of getting satellites (20% or more), but in the east of the sky it is significantly lower - 5 to 10% or less. Note that in this screenshot, the sun's position is 22 degrees below the horizon - astronomical darkness.

SharpCap shows the familiar constellation outlines, the mount position and the sun/moon on this plot to make orientation/interpretation easier.

The calculations are based on the orbits of (currently) about 14,000 satellites in low and mid orbits. SharpCap is not calculating the position of each satellite individually, but instead divides them into groups with similar orbital characteristics. SharpCap is calculating for about 100 different groups that between them total about 96% of active satellites in those orbits.

I'm still fine-tuning both the way the data is displayed in the plot on the right and how you control the calculations (changing date, time, location, etc) on the left. Even with the current basic setup, you can step forward in time by 1hr or 15min at a time, meaning you can work things out like waiting to image a target until later in the evening when it will be in an area with less satellites, or imaging in a different part of the sky in the earlier part of the evening.

comments welcome,

Robin

[Gfischer]

Robin,
Great idea those satellites drive me crazy. The current satellite detection tool helps a lot. This will help avoid the problem areas.

Thank you

[admin]

This feature is now available to try out in an updated beta version of SharpCap 4.2 (https://www.sharpcap.co.uk/sharpcap/sha ... p-4-2-beta)

Screenshot 2026-05-15 153655.jpg (285.37 KiB) Viewed 563 times

There are a few changes to the original screenshot above, including better support for night mode, adding the sun and moon to the plot when they are above the horizon (including moon phase) and an indication box showing whether it is day/dusk/night as well as the solar elevation readout.

If you have a camera and mount open when you start the tool, some of the adjustments on the left will be auto set for you - i.e.

* The exposure will come from the current camera exposure
* The FOV will be set from the camera FOV if known (via plate solving or pixel size/focal length)
* The lat/long will be set from the mount observer location

If the camera or mount are not open when you activate this tool, SharpCap will use previously used values or try to find some default values for these settings.

I am planning on a 'timeline' feature for a particular target next - something that will show how the satellite chances for a target vary over the next 12 hours or so as the night progresses and the target moves across the sky.

cheers,

Robin

[Opmc73]

Hi Robin,

What I do generally is to have stellarium opened in a session and survey if satelittes displayed in stellarium will cross my field of view (area of the camera) . If yes then I return in SC and I pause the stacking and restart once the satelitte as gone.

Could it be possible to do something like this automatic in the future , reading the satelittes trajectory as stallarium does, estime if it will cross the field and pose or reject the frame if satelittes assumed in it ?

kind regards
Olivier

[admin]

Are you able to track all 14000+ active satellites in Stellarium at once? I did consider that approach but rejected it as for a number of reasons:

* Likely to consume massive amounts of CPU resources to calculate everything - that problem will get worse as we get more satellites launched
* Relies on up-to-date TLE data which would need to be updated regularly - with old data the predictions could easily be rubbish
* Prone to errors if your lat/long co-ordinates aren't exact - that won't affect general target finding/tracking, but could easily mean that the calculated positions of satelllites in the sky doesn't match the real observed positions.

So you can see I rather think this is unlikely to be an 'easy to use' and robust approach - that's why I went for the more statistical approach of estimating the chance of a satellite in view in different areas of the sky and (hopefully) guiding people to image in the areas where there are less visible satellites. If you've looked at the latest 4.2 update with the observability plot in the target selection window, you can see that this includes a graph showing how the satellite chances change over the course of the night for a particular target, so you can pick your time of observation to coincide with a minimum chance of satellites.

cheers,

Robin

[carlomuccini]

Hi

I'd prefer a system to automatically delete the frame with the satellite trail.
I've never been able to use the current feature.

If I need to capture an object at a "prohibited" latitude, I shoot anyway and manually discard the frames with the satellite trails, which can be two or three at most in a fifteen-minute shot.
It's a pain to sit in front of the monitor for hours keeping an eye on the passing satellites.
This would be an important, if not indispensable, feature for me.

Carlo

[admin]

Hi,

it's actually a tricky one - I have known for some time that the current satellite trail removal is hard to use, since the adjustment of the sensitivity settings is difficult.

However, the same problem applies to a feature that would try to detect the satellite trails and exclude that frame from the stack - how to adjust the sensitivity so that it finds satellites but doesn't do false detection on the actual target you are trying to capture (it turns out that globular clusters are quite good at false triggering the satellite trail detection...)

A good way to solve that sensitivity adjustment problem would be a big step forward

cheers,

Robin

[carlomuccini]

Hi
certainly the human eye is much better than any algorithm!

I understand that detecting the trail is not at all trivial, but it would be one of the key functions of the program, given the growing trend of satellites in orbit.

It's certainly useful to know if satellites will be passing over a certain area at a certain time.
For some time now, I've been spending my evenings in front of the monitor checking for satellites and removing them if necessary.
I usually take 15-second exposures, saving them in livestacking every 15 minutes.

Detection could also be semi-automatic.
SC detects a probable satellite and suggests removing it yes/no, with the default being yes.
If I image a globular cluster (I understand the problem !) disable automatic detection.

Thanks anyway for all the great work you're doing and that keeps us all entertained every evening we get the telescope out!

Carlo

[Jean-Francois]

Hello,

The calculation if a satellite is in the sky is relative simple. But you need to have the TLE data very up to date.
You want not only the position, but a precise timing when a satellite is passing in the telescope field of view.

But ... the most difficult will be the calculation of the estimated magnitude of the satellite.
It depends if it is illuminated by the sun (OK, that is still "simple" to calculate).
The problem is a "small-white" satellite will reflect more light than a "large-black" satellite.
In addition ... some part of the satellite reflects more than other depending on the sun-satellite-observer angles.

So ... from the +14000 objects in orbit, a lot will be present in the field of view, but not visible or fainter as other.

I do not think that the TLE data contains the size and albedo of the satellites.
You can calculate the distance to the observer, but it will be difficult to estimate the magnitude and so the intensity of the trace on the image.
In detail ... 2 satellites with the same magnitude in the sky will have not the same effect on the image ... if they have different speed.
If one is 10x speed as the other, then the trace of the slow satellite will be 10x brighter on the image as the rapid satellite.

Regards,
Jean-Francois

[Opmc73]

Hi

I'd prefer a system to automatically delete the frame with the satellite trail.
I've never been able to use the current feature.

If I need to capture an object at a "prohibited" latitude, I shoot anyway and manually discard the frames with the satellite trails, which can be two or three at most in a fifteen-minute shot.
It's a pain to sit in front of the monitor for hours keeping an eye on the passing satellites.
This would be an important, if not indispensable, feature for me.

Carlo

Sit in front of the monitor was what I was doing also to unstack satelitted pictures. Now I have abandonned that and when there are satelittes I restack my frames with Siril using its rejection of pixel based on Generalized Extreme Studentized Deviate. It removes most and often all satelittes .

Now this is a pitty to have sharpcap doing stacked fits and to have to redo the stack afterward just because more and more satelittes are present.