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Shooting star?

brrttpaul

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brrttpaul

brrttpaul

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Had a go last night kust left the camera run on the star adventurer, ended up with 300 photos which I tried stacking but not the best. Came across this as the camera was aimed at just to the right of Cassiopeia looks like a shooting star to me (which is what I was after). Found a few feint lines in all my subs but for some reason they didnt come out in the final stack even though I was on 100% stack. Any ideas how to combine shooting stars? I am using DSS

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Starman

Starman

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It's definitely not a Perseid and quite likely not a meteor either unfortunately. The profile of the trail looks like a flaring satellite. There are loads of these visible throughout the course of a night (not just Iridium Flares) and they do a great job of looking like meteors!

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Starman

Starman

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A gif? I assume this is a still, or from a sequence of stills? If so, I'm assuming a gif (and please feel free to correct me if I've misinterpreted what you're saying) will be an animation of the stills. If so, this will show a star field, then the streak appearing in one frame, then back to the star field. Is that correct?

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Starman

Starman

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A satellite flare could easily occur in a 10s period and the extremes of the trail could disappear from view so not be visible on the before and after frames. A typical meteor trail will either be straight of widen towards the end of travel caused by the meteoroid's bow shock encountering ever thicker atmospheric layers. It's uncommon for one to brighten and then fade demonstrably like I'd bring shown here.

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Starman

Starman

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Okay - let's deal with the speed of event first. You say it's a 10s exposure so we can assume that the trail is 10s worth of motion. That's not necessarily the case but there's a reasonable chance that it is. I've measured your trail length against the background stars and it's 8 degrees in length. Here's a shot of the ISS passing over head I got during a Perseid session back in 2013. I've measured the trail length for this shot and it's 29 degrees. This trail, because it maintains a reasonably constant brightness along its length can be assumed to represent the entire motion of the ISS during the course of the exposure. In this case the exposure was 30s. Apparent satellite motion across the sky varies with the angle made between the satellite, you and your zentih. If a satellite passes overhead then it appears to be travelling faster than when it's low down. This is something very evident with the ISS which appears to climb up from the west or southwest quite slowly, then gathers speed as it passes overhead. It then appears to take an age to disappear in the eastern half of the sky. 

So it's not unreasonable that in your 10s exposure, a satellite would appear to travel 8 degrees across the sky.

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Stu

Stu

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Fair point he most probably does, just find it strange that on another website it was a definate meteor. It really dont matter honestly

Well, that's just why you come to SGL, to get the best advice and opinion :)

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Starman

Starman

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Next, the shape. As a meteoroid passes through the atmosphere, if it's of average size - say the size of a grain of sand - then it will compress the air in front of it. The compressed air heats up (ram pressure) and at around 1700C material is vapourised off the front of the meteoroid. This material interacts with the gases in the atmosphere getting them excited. When they de-excite, they give off light and that's what causes the trail you see. As the particle passes down through the atmosphere, the density of atmosphere increases. The net result is that a photographed meteor trail will typically start thin and grow in thickness. It doesn't always do this and sometimes it'll stay relatively thin for the entire length. However, it's very unusual for a meteor to start thin, get bright and then thin down for a reasonable length. If there's something inside the meteoroid, such as a pocket of gas, when this is revealed due to the vapourisation process, this can cause the meteoroid to flare or fragment. Typically this will bring the trail to an end in a terminal burst - i.e. the trail will start thin, gradually thicken and then dramatically thicken. Alternatively, the meteor may exhibit a burst along its length but keep going. Although it sound like this could emulate what you've photographed, it tends not to look as regular. Your trail exhibits a gradual brightening and then a gradual dimming. In my experience, this is normally the profile of a flaring satellite.

Here's an example, a satellite with an initially relatively bright trail that flares and then fades back to the same brightness. It looks quite similar to a meteor with a terminal burst but I can assure you it's a satellite. A satellite may be so dim that it doesn't register on a photograph. If it then appears to flare up, it can just appear on one exposure but not be seen on the one before or after it.

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Starman

Starman

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Misidentification of meteors is pretty common to be honest. It's got worse over time because more people are trying to photograph them and there are more satellites up there which mimic them. I've seen quite a few images already, some put up by serious astronomical news sites, which show pictures of Perseid meteors which are nothing of the sort. I've been doing this a very long time so it's easy for me to identify things. I've also got tens of thousands of attempted 'meteor' photos. Many show satellites, and there are lots of different types to sort through. 

I've just done a piece on the Perseids which discusses the identification issues if you're interested. You can see it here: 

http://www.bbc.co.uk/programmes/articles/19xRzJcFNmgPNpR64Wwpr9s/how-to-watch-the-perseid-meteor-shower

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Uranium235

Uranium235

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I've just done a piece on the Perseids which discusses the identification issues if you're interested. You can see it here: 

http://www.bbc.co.uk/programmes/articles/19xRzJcFNmgPNpR64Wwpr9s/how-to-watch-the-perseid-meteor-shower

Thanks for posting this (and your other explanations), very informative.

Also, what people tend to forget is that using a camera is far more sensitive than the eye to these events - so misidentification is quite an easy thing to do for the inexperienced. Some parts of the sky are also more prone to satellite trails than others, on some occasions ive had six consecutive 15min subs ruined by these blighters :)

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barkis

barkis

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Yes, a good thread, and with some fine explanations, and demonstrations  given too.

Many of us reading this can probably consider ourselves a bit wiser now.

There's no substitute for experience  :smiley:.

Ron.

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