Accurate ISS pass times- who is correct?

Hi all,
In trying to determine when the ISS passes over my house, I am noticing a discrepancy between the two sites I normally use to get the pass times; here and Heavens-Above. Below are extracts from both sites; anyone know which is really correct and why one is so far off?

ISS Fan Club data
12Mar09 00:07:58
12Mar09 01:40:42
12Mar09 03:16:39
12Mar09 04:53:37
12Mar09 06:29:42
12Mar09 08:04:56
12Mar09 09:40:47
13Mar09 00:33:11
13Mar09 02:08:02
13Mar09 03:44:47

Heavens-Above data
12 Mar 02:32:32
12 Mar 04:06:57
12 Mar 05:43:50
12 Mar 20:35:35
12 Mar 22:10:07
12 Mar 23:48:00

They are both calculated for the same location in south New Jersey. Any thoughts appreciated.
I suspect the data from here is more accurate, but I'm not sure.


mwrobison – Wed, 2009 – 03 – 11 07:54

Thanks for ISS passes. They

Thanks for ISS passes. They will help us.

Submitted by jasonglades on Wed, 2009-05-13 11:23.

ISS & STS-119

Hi all, trying to track if the ISS and Shuttle are passing over our skies tonight in the UK.Going to various differet sites like and Heavensabove and they give me a diagram with a circle around my village what does this circle mean????On this website the circle covers a bit of the UK and most of France ect??Bit confussed???Please help. :)

Submitted by Stars and Moondust on Tue, 2009-03-17 12:40.

iss pass times


So what times tonight (17 may) can we expect to SEE the iss/shuttle?

what time in BST?


Submitted by g1dra on Sun, 2009-05-17 11:31.

From I4GEI (Italy)Only

From I4GEI (Italy)

Only today did I read your question.

The small circle on your site may be the ISS footpoint (i.e. the point directly below the ISS) and the large circle the footprint (i.e. the area on the ground from which ISS is visible. The footprint depends on the height the object is orbiting. I estimate the ISS circle about 1500 km radius.

As for providers of pass-times I use (and cross-check) "Heavens Above" and "Calsky". I find them very accurate. The latter has a lot of configurable options.
Never forget that the ISS is now and then unpredictably boosted upwards to recover height lost due to atmospheric drag, with a consequent variation of time schedule.

Submitted by I1GEI on Fri, 2009-05-01 08:33.

Pass Times

I finally did the checking and the problem is that this site (ISS Fan Club) uses UTC/ ZULU time, while Heavens Above converts it to my local time, just as Wade and others mentioned. I had not noticed that in the past. So, *I'm* the doofus here, not the software!
Thanks for the assistance from all...hope to see the STS & ISS flying in close formation sometime during this mission and if I could make a contact while they are flying overhead together, that would be great!


Submitted by mwrobison on Mon, 2009-03-16 08:18.

Pass times

Thanks everyone- I'll give the sites you mentioned a try. And, unless I completely messed up downloading the pass times for my original question, I *did* use the same home location. That's why I was so puzzled over the results! I'll re-do the comparison and post if I get different results...


Submitted by mwrobison on Thu, 2009-03-12 20:09.

pass times

Hey Mike,

One thing to be careful of when using two different sites to calculate passes for your area are that one site may be providing times in UTC and the other may be providing times in your local time zone. Heavens above is extremely accurate for my QTH, but it is listed in CST, while orbitron and other programs and sites frequently provide results in Coordinated Universal Time (UTC).

Hope this helps.


Submitted by N0TEL on Sun, 2009-03-15 12:58.

Pass times

Thanks, Wade. I'll check that out.


Submitted by mwrobison on Sun, 2009-03-15 21:10.

Want times ?

I would say the reason for the discrepancy, is that the times quoted, are from different "Home" locations, rather than your location ? Say, the page site location ?

I downloaded an English program called Satscape. It is free, and you can download keps whenever you like, or leave it timed to do it automatically. I have always found that the predictions are pretty spot on for accuracy.

This software can be found at :

Once installed, all you have to input (check the boxes), for the satellites that you want to watch, as well as your coordinates. It is important that these be fairly accurate, and they can be ascertained, by say Google Earth, or something similar.Once that is done, the program puts your location on the main map, as "Home" and you are away.

Good luck

Submitted by VK7BBW on Thu, 2009-03-12 11:29.

Pass times

Orbitron and ISS fan club don't agree.I used other sites and I think the ISS site is wrong.


Submitted by Paul KB8CMW on Thu, 2009-03-12 05:54.

Pass times

I use AMSAT. So far the one that is closer to accurate for my location.

AMSAT Pass Data

Submitted by Robin Warren on Thu, 2009-03-12 10:00.

Spring Forward

It seems a lot of these errors started at the time change.

Be sure your computer has the correct UTC first and then your local time zone.


Different programs handle UTC and offset differently. I try to use the system time instead of leting each tracking program do its own thing. Make sure each tracking program is set correctly for your method of operation.

I founds errors on my system. Once fixed, they are all about the same for viewing or pass times.


Submitted by gfenisey on Mon, 2009-03-16 00:03.

Tracking on this site is correct

gfenisey is right.

This site is using GMT, if the other system is using localtime (like heavens-above usually does) you might get confused.
Another thing to consider is that I am showing every single pass, starting at zero elevation. Some programs (like heavens-above) might have an offset that shortens the length of each pass and also might prevent some other passes to be shown completely.
I doubled check and for my location (New York City) and tracking is working perfectly.
There still are some bugs on the graphic interface that I am aware of. I will fix them asap.

Alain WW3WW

Submitted by alain on Tue, 2009-03-17 17:10.

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