Starship Asterisk*

Perseid Meteors Over China

Explanation: Comet dust rained down on planet Earth earlier this month, streaking through dark skies in the annual Perseid meteor shower. While enjoying the anticipated space weather above Zhangbei Prairie, Hebei Province, China, astronomer Xiang Zhan recorded a series of 10 second long exposures spanning four hours on the night of August 12/13 using a wide angle lens. Combining frames which captured 68 meteor flashes, he produced the above composite view of the Perseids of summer. Although the sand-sized comet particles are traveling parallel to each other, the resulting shower meteors clearly seem to radiate from a single point on the sky in the eponymous constellation Perseus. The radiant effect is due to perspective, as the parallel tracks appear to converge at a distance. The next notable meteor shower may be the Orionids in late October.

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I know a few kids I am showing this to...........

Let's see, over four hours the earth rotates by sixty degrees; therefore, each of the 68 frames that were combined was rotated as needed to compensate for earth's rotation, so that the patterns of stars from different frames overlapped correctly. That leaves a puzzle: Why is the silhouette of a tree in the bottom right corner so sharply delineated?

Guest wrote:Let's see, over four hours the earth rotates by sixty degrees; therefore, each of the 68 frames that were combined was rotated as needed to compensate for earth's rotation, so that the patterns of stars from different frames overlapped correctly. That leaves a puzzle: Why is the silhouette of a tree in the bottom right corner so sharply delineated?

The tree is a single exposure layered with the sky shot. Probably.

Yeah, the only thing kept between the shots are the meteors and one nice photo is used as the background. It's an artistic representation of the meteors that fell during that time period.

The light from the metors all seem pretty uniform visually. I wonder how much difference a spectra of the light would differ from shower to shower?

Spectacular Job...4 hours of work that really paid off...

:---[===] *

Ron-Astro Pharmacist wrote:The light from the metors all seem pretty uniform visually. I wonder how much difference a spectra of the light would differ from shower to shower?

Here's an interesting page on the history of meteor spectroscopy, and another on a recent spectroscopic study of the Leonid meteor shower. Apparently meteor spectra contain emission lines from elements both in Earth's atmosphere and in the meteoroid, and differences are seen even between meteors in the same shower.

Thanks Anthony- I'll learn about meteor spectroscopy as soon as I can get out of warp speed from staring a this picture too long.

stephen63 wrote:

Guest wrote:Let's see, over four hours the earth rotates by sixty degrees; therefore, each of the 68 frames that were combined was rotated as needed to compensate for earth's rotation, so that the patterns of stars from different frames overlapped correctly. That leaves a puzzle: Why is the silhouette of a tree in the bottom right corner so sharply delineated?

The tree is a single exposure layered with the sky shot. Probably.

I suppose this is the same technique to get an analemma. I mean, first you get the analemma, and then you layer the single landscape shot. Is this ok?

I suppose this is a similar technique to get an analemma. Is it ok?

Similar, but not the same. An analemma is a composite of many photos taken from the same location at the same time of day on different days pointing the camera in the same direction. For the meteors, the subject is moving across the sky as the planet rotates so the compositing process presents different challenges. Disclaimer: I have never done either so I am just giving my best guess about how I think I would go about it. I guess it is not necessary to track the radiant but it might be convenient.

geckzilla wrote:Yeah, the only thing kept between the shots are the meteors and one nice photo is used as the background. It's an artistic representation of the meteors that fell during that time period.

And the stars, of course. The foreground shot may not be purely artistic. Depending on how dark it was, that may be a longer exposure of the same field, which would also help bring out more stars.

There are two ways of making a shot like this. One is to have the camera fixed, and rotate the images when they are stacked. The other is to have the camera on a tracking mount. With a wide angle lens, the latter is preferred, since lens distortion is amplified by image rotation. You can see quite a lot of radial distortion in this image, which suggests that the images were rotated, not the camera.

Ron-Astro Pharmacist wrote:The light from the metors all seem pretty uniform visually. I wonder how much difference a spectra of the light would differ from shower to shower? :?:

Most meteor showers are produced by cometary debris, which is probably more uniform in composition than asteroidal debris.

Instrumentally, there is quite a bit of spectral variation between sporadic (non shower) meteors. Most of this isn't so obvious visually, where apparent color is more often determined by atmospheric emissions, which in turn are determined by temperature and altitude.

I'm currently at a pair of meteorics conferences, and there are several talks about meteor spectra derived from some new instruments, which are allowing a lot of new data to be collected (in the past, there was only limited information on meteor spectra, which is very difficult to collect). If anything interesting about shower spectra is presented, I'll report it back here.