# Why is there lightning where there are no clouds? [closed]

Recently my family and I went onto the balcony to observed the stars in the night sky. We started to see flashes in the sky and we realized that it was lightning (non-fork lightning). I looked around to find the clouds but there was not a cloud in sight. It was just a clear night sky.

Please help me to understand this phenomena. Why was there lightning with no clouds? Was it really lightning? Please excuse my ignorance of the matter.

• A lightning can travel away from a cloud and then hit the ground (crh.noaa.gov/pub/ltg/crh_boltblue.php) Mar 12, 2015 at 23:56
• Weren't they meteorites? Mar 13, 2015 at 0:30
• @Sofia No we don't get them much in the southern hemisphere.
– user71793
Mar 13, 2015 at 1:47
• @Mindrus also in Sth Hemisphere, and have seen the occasional meteorite. It could have been a high altitude discharge of some sort / more exotic forms of lightning, though I wouldn't think you could actually see those from the ground. Mar 13, 2015 at 1:57
• It's not unusual to see "heat lightning" in the evening, on the horizon, especially in flat areas. This is from storms that, from that distance, are not visible. Mar 13, 2015 at 3:06

## 2 Answers

I sort of doubt the blue jet explanation by Xeren is probable (although it is a possibility). It's just too rare and too faint.

Much more likely, it's lightning far away near the horizon. Just because there are no clouds doesn't mean the light wont scatter. Sunlight makes the sky very bright blue during the day, and in the brief moment when lightning strikes, it's very bright - bright enough to make the scattered light visible. Usually, it's cloudy anyway, and you mostly see the lightning-illuminated clouds. But in the rare occasion, when you're far enough from the storm to have clear sky above you, the entire sky will still flash when a lightning strikes far away - could be 100km or more, could even be below the horizon, so you're not even in the line-of-sight with the bolt.

It sounds like you may have seen a Blue Jet. I don't know if you can see these with the naked eye at ground level but the article linked seems to imply that you may be able to.

Assuming a spherical earth of 3,960mi radius and 24,900mi circumference, you can work out how far something needs to be along the surface of the earth before you can't see it over the horizon judging by its height alone:

$$d = \frac {24900} {2\pi} \arccos \frac {3960} {3960+h}$$

For $h = 12$ this is about 196 miles, which seems a bit too far for it to have been conventional lightning absent there being any visible clouds.

That article says that blue jets occur in the region of 25-30mi up in the atmosphere. Assuming 20mi up, without knowing how far from the horizon this was observed, the storm / source could have been as far as 253 miles.

I'm afraid that without knowing the angle from the horizon at which this phenomena was observed, it's really hard to say more than this.