<p>The ISS maximum brightness is reported at about -5.9, sometimes -6.
I guess you could technically estimate it analytically by considering how much light it receives, but I imagine that would be messy to get accurate.</p>
<p>Here you can see an archived version of the original fact sheet by heavens-above, where the maximum is given as -5.7: <a href="https://web.archive.org/web/20090705134152/http://heavens-above.com/satinfo.aspx?SatID=25544" rel="nofollow noreferrer">https://web.archive.org/web/20090705134152/http://heavens-above.com/satinfo.aspx?SatID=25544</a></p>
<p>I believe whoever came up with the -5.9 value simply observed the ISS when it's best lit by the sun and the Earth is in perihelion (closest to the sun in its orbit).</p>
<p>Personally, I've only seen the ISS once, the night of 29/04/22 when it shined at -2.4.</p>

CC BY-SA 4.0
2022-07-12T11:39:32.627Z
Could you lead me with a link to that -6 claim? How did the person prove it's -6? Hell, how did they even know what's -6 when watching the flying station?
longtry
CC BY-SA 4.0
2022-07-12T20:41:16.167Z
Here you can see an archived version of the original fact sheet by heavens-above:
https://web.archive.org/web/20090705134152/http://heavens-above.com/satinfo.aspx?SatID=25544
Marco Leonardi
CC BY-SA 4.0
2022-07-12T21:23:40.023Z
@longtry it's a very good question! Wikipedia [says it's about -4](https://en.wikipedia.org/wiki/International_Space_Station#Sightings_from_Earth) Looking at [heavens-above FAQ](https://heavens-above.com/faq.aspx) and finding "How do you estimate the brightness of a satellite?" The paragraph answer ends "...For this reason, our magnitude estimates should only be treated as a rough guide, and the actual brightness you see could be considerably more or less than this."
uhoh
CC BY-SA 4.0
2022-07-14T14:57:05.417Z
Personally, I've been noting  every  Heavens Above prediction for the ISS for my location since April 3, 2018.  At about 41.6° N, the brightest pass peak magnitude prediction in my records is -4.0, which happened three times in 2018.
notovny
CC BY-SA 4.0
2022-07-12T09:00:29.667Z
2022-07-12T21:17:13.873Z
2022-07-12T21:17:13.873Z
Marco Leonardi
<p>Heavens-above indicates that this evening, it will fly almost over my head (79°) with a sizzling magnitude of -3.9. What is the maximum brightness it can have?</p>
<p>Is there a formula to calculate its lowest magnitude, theoretically?</p>

CC BY-SA 4.0
2022-07-12T03:45:46.003Z
If you're in the right place at the right time, you could catch a flare from the solar panels, which would increase its brightness many times over. https://astroengine.com/2009/05/01/space-station-flare-captured-on-film/
Greg Miller
CC BY-SA 4.0
2022-07-12T11:38:00.850Z
Ah yes, you mention makes me realize that I did see an ISS glare before. A minus -2 or more subtraction to the predicted brightness in totally achievable.
longtry
<amateur-observing><artificial-satellite><magnitude><brightness><iss>
What's the brightest magnitude that the ISS can appear from Earth's surface?
longtry
# What's the brightest magnitude that the ISS can appear from Earth's surface?

(Asked by: username_0 on 2022-07-12)

Heavens-above indicates that this evening, it will fly almost over my head (79°) with a sizzling magnitude of -3.9. What is the maximum brightness it can have?

Is there a formula to calculate its lowest magnitude, theoretically?

**Tags:** amateur-observing, artificial-satellite, magnitude, brightness, iss

> **Comments:**
> **username_1**: If you're in the right place at the right time, you could catch a flare from the solar panels, which would increase its brightness many times over. https://astroengine.com/2009/05/01/space-station-flare-captured-on-film/  
> **username_0**: Ah yes, you mention makes me realize that I did see an ISS glare before. A minus -2 or more subtraction to the predicted brightness in totally achievable.  

---

## 1 answers

### Answer by username_2 on 2022-07-12. Score: 3

The ISS maximum brightness is reported at about -5.9, sometimes -6.
I guess you could technically estimate it analytically by considering how much light it receives, but I imagine that would be messy to get accurate.

Here you can see an archived version of the original fact sheet by heavens-above, where the maximum is given as -5.7: <https://web.archive.org/web/20090705134152/http://heavens-above.com/satinfo.aspx?SatID=25544>

I believe whoever came up with the -5.9 value simply observed the ISS when it's best lit by the sun and the Earth is in perihelion (closest to the sun in its orbit).

Personally, I've only seen the ISS once, the night of 29/04/22 when it shined at -2.4.

> **Comments:**
> **username_0**: Could you lead me with a link to that -6 claim? How did the person prove it's -6? Hell, how did they even know what's -6 when watching the flying station?  
> **username_2**: Here you can see an archived version of the original fact sheet by heavens-above: https://web.archive.org/web/20090705134152/http://heavens-above.com/satinfo.aspx?SatID=25544  
> **username_3**: @username_0 it's a very good question! Wikipedia [says it's about -4](https://en.wikipedia.org/wiki/International_Space_Station#Sightings_from_Earth) Looking at [heavens-above FAQ](https://heavens-above.com/faq.aspx) and finding "How do you estimate the brightness of a satellite?" The paragraph answer ends "...For this reason, our magnitude estimates should only be treated as a rough guide, and the actual brightness you see could be considerably more or less than this."  
> **username_4**: Personally, I've been noting  every  Heavens Above prediction for the ISS for my location since April 3, 2018.  At about 41.6° N, the brightest pass peak magnitude prediction in my records is -4.0, which happened three times in 2018.  

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