Starship Asterisk*

The featured image was taken earlier this year from Las Campanas observatory in Chile over the Andes Mountains in Argentina

johnnydeep wrote: ↑Tue Mar 30, 2021 10:50 pm

Chris Peterson wrote: ↑Tue Mar 30, 2021 9:19 pm

johnnydeep wrote: ↑Tue Mar 30, 2021 8:37 pm

Makes sense. But do we know how long the exposure is? I couldn't find it stated anywhere. Also, I did follow one of the links to https://www.flickr.com/photos/pennstate ... 17/sizes/l, which shows multiple entire sprites forming within the span of a single millisecond:

Click to view full size image

This would mean that the entire scene of the APOD could potentially be only a few milliseconds, no?

I didn't find the exposure length. But it was clearly taken with an ordinary commercial digital camera, and I have enough experience taking nighttime images with that kind of equipment to know that we're looking at an exposure time on the order of 10 seconds. Those submillisecond images required image intensifiers and other exotic equipment.

So, would that mean the sprites have a long life after forming and look very much the same over several seconds? (Though the millisecond sequence pic shows that multiple sprites can indeed form and evolve very quickly.) Or are the sprites very short lived, and we are only seeing multiple sprites in the APOD pic merely because multiple ones have come and gone during the (long) exposure?

Chris Peterson wrote: ↑Tue Mar 30, 2021 9:19 pm

johnnydeep wrote: ↑Tue Mar 30, 2021 8:37 pm

Chris Peterson wrote: ↑Tue Mar 30, 2021 8:18 pm

As this is a long exposure (seconds or tens of seconds) of a phenomenon that lasts no more than milliseconds or tens of milliseconds, then yes... we're seeing the entire sequence beginning to end, both directions, captured in a single frame.

Makes sense. But do we know how long the exposure is? I couldn't find it stated anywhere. Also, I did follow one of the links to https://www.flickr.com/photos/pennstate ... 17/sizes/l, which shows multiple entire sprites forming within the span of a single millisecond:

Click to view full size image

This would mean that the entire scene of the APOD could potentially be only a few milliseconds, no?

I didn't find the exposure length. But it was clearly taken with an ordinary commercial digital camera, and I have enough experience taking nighttime images with that kind of equipment to know that we're looking at an exposure time on the order of 10 seconds. Those submillisecond images required image intensifiers and other exotic equipment.

johnnydeep wrote: ↑Tue Mar 30, 2021 8:37 pm

Chris Peterson wrote: ↑Tue Mar 30, 2021 8:18 pm

johnnydeep wrote: ↑Tue Mar 30, 2021 7:50 pm

Yes, very cool image. One question: both the text and the WikiPedia article say that:



So, are we seeing both the downward moving balls of ionization AND the smaller upward moving balls here?

As this is a long exposure (seconds or tens of seconds) of a phenomenon that lasts no more than milliseconds or tens of milliseconds, then yes... we're seeing the entire sequence beginning to end, both directions, captured in a single frame.

Makes sense. But do we know how long the exposure is? I couldn't find it stated anywhere. Also, I did follow one of the links to https://www.flickr.com/photos/pennstate ... 17/sizes/l, which shows multiple entire sprites forming within the span of a single millisecond:

Click to view full size image

This would mean that the entire scene of the APOD could potentially be only a few milliseconds, no?

Chris Peterson wrote: ↑Tue Mar 30, 2021 8:18 pm

johnnydeep wrote: ↑Tue Mar 30, 2021 7:50 pm

APOD Robot wrote: ↑Tue Mar 30, 2021 4:11 am Red Sprite Lightning over the Andes

Explanation: What are those red filaments in the sky? They are a rarely seen form of lightning confirmed only about 30 years ago: red sprites. Recent research has shown that following a powerful positive cloud-to-ground lightning strike, red sprites may start as 100-meter balls of ionized air that shoot down from about 80-km high at 10 percent the speed of light. They are quickly followed by a group of upward streaking ionized balls. The featured image was taken earlier this year from Las Campanas observatory in Chile over the Andes Mountains in Argentina. Red sprites take only a fraction of a second to occur and are best seen when powerful thunderstorms are visible from the side.

Yes, very cool image. One question: both the text and the WikiPedia article say that:

sprites are actually clusters of small, decameter-sized (10–100 m or 33–328 ft) balls of ionization that are launched at an altitude of about 80 km (50 mi) and then move downward at speeds of up to ten percent the speed of light, followed a few milliseconds later by a separate set of upward moving balls of ionization.

So, are we seeing both the downward moving balls of ionization AND the smaller upward moving balls here?

As this is a long exposure (seconds or tens of seconds) of a phenomenon that lasts no more than milliseconds or tens of milliseconds, then yes... we're seeing the entire sequence beginning to end, both directions, captured in a single frame.

johnnydeep wrote: ↑Tue Mar 30, 2021 7:50 pm

APOD Robot wrote: ↑Tue Mar 30, 2021 4:11 am Red Sprite Lightning over the Andes

Explanation: What are those red filaments in the sky? They are a rarely seen form of lightning confirmed only about 30 years ago: red sprites. Recent research has shown that following a powerful positive cloud-to-ground lightning strike, red sprites may start as 100-meter balls of ionized air that shoot down from about 80-km high at 10 percent the speed of light. They are quickly followed by a group of upward streaking ionized balls. The featured image was taken earlier this year from Las Campanas observatory in Chile over the Andes Mountains in Argentina. Red sprites take only a fraction of a second to occur and are best seen when powerful thunderstorms are visible from the side.

Yes, very cool image. One question: both the text and the WikiPedia article say that:

sprites are actually clusters of small, decameter-sized (10–100 m or 33–328 ft) balls of ionization that are launched at an altitude of about 80 km (50 mi) and then move downward at speeds of up to ten percent the speed of light, followed a few milliseconds later by a separate set of upward moving balls of ionization.

So, are we seeing both the downward moving balls of ionization AND the smaller upward moving balls here?

APOD Robot wrote: ↑Tue Mar 30, 2021 4:11 am Red Sprite Lightning over the Andes

Explanation: What are those red filaments in the sky? They are a rarely seen form of lightning confirmed only about 30 years ago: red sprites. Recent research has shown that following a powerful positive cloud-to-ground lightning strike, red sprites may start as 100-meter balls of ionized air that shoot down from about 80-km high at 10 percent the speed of light. They are quickly followed by a group of upward streaking ionized balls. The featured image was taken earlier this year from Las Campanas observatory in Chile over the Andes Mountains in Argentina. Red sprites take only a fraction of a second to occur and are best seen when powerful thunderstorms are visible from the side.

sprites are actually clusters of small, decameter-sized (10–100 m or 33–328 ft) balls of ionization that are launched at an altitude of about 80 km (50 mi) and then move downward at speeds of up to ten percent the speed of light, followed a few milliseconds later by a separate set of upward moving balls of ionization.

Also, please note that the Discuss link points to the APOD of March 28.

The clouds and thunderstorms could be behind (below) that line of hills. ?

jks wrote: ↑Tue Mar 30, 2021 4:23 am Wow, a stunning image!

Also, please note that the Discuss link points to the APOD of March 28.