APOD: Asteroids in the Distance (2013 Feb 10)

Comments and questions about the APOD on the main view screen.
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APOD: Asteroids in the Distance (2013 Feb 10)

Post by APOD Robot » Sun Feb 10, 2013 5:07 am

Image Asteroids in the Distance

Explanation: Rocks from space hit Earth every day. The larger the rock, though, the less often Earth is struck. Many kilograms of space dust pitter to Earth daily. Larger bits appear initially as a bright meteor. Baseball-sized rocks and ice-balls streak through our atmosphere daily, most evaporating quickly to nothing. Significant threats do exist for rocks near 100 meters in diameter, which strike the Earth roughly every 1000 years. An object this size could cause significant tsunamis were it to strike an ocean, potentially devastating even distant shores. A collision with a massive asteroid, over 1 km across, is more rare, occurring typically millions of years apart, but could have truly global consequences. Many asteroids remain undiscovered. In fact, one was discovered in 1998 as the long blue streak in the above archival image taken by the Hubble Space Telescope. Further, just last year the 50-meter wide asteroid 2012 DA14 was discovered that will pass inside the orbit of Earth's geosynchronous satellites this coming Friday. A collision with a large asteroid would not affect Earth's orbit so much as raise dust that would affect Earth's climate. One likely result is a global extinction of many species of life, possibly dwarfing the ongoing extinction occurring now.

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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by gratefulguy » Sun Feb 10, 2013 5:31 am

With very limited knowledge of astronomy, I ask the group's indulgence in wondering if the other (shorter) blue lines indicate other asteroids and are the yellow lines just an artifact of the imaging process, or do they denote movement of some other type of object?
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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by Ann » Sun Feb 10, 2013 6:26 am

gratefulguy wrote:With very limited knowledge of astronomy, I ask the group's indulgence in wondering if the other (shorter) blue lines indicate other asteroids and are the yellow lines just an artifact of the imaging process, or do they denote movement of some other type of object?
Thanks to all who bring this website to us.
I'm not the person you should be asking about this, but I remember reading about this image when it was first published as the Hubble Heritage Image of the Month. I seem to remember that the caption that went with the picture back then commented on the shorter blue and yellow lines. But now that I checked Hubble Heritage (and found that the picture was originally published on March 4, 1999), I couldn't find any information in the caption about the short lines.

However, I do think I remember that I have read about these short lines, and I think they are the products of various high-energy particles and possibly little grains of space dust whizzing by. They are "noise", if you like. I think almost all Hubble images originally contain these little streaks. The streaks have to be "cleaned off" before the picture can be published.

By the way, why are most of the streaks so blue? Well, it's because this picture was made using only two filters, 606 nm and invisible infrared at 814 nm. (I believe that the orange filter can also be described as "clear", meaning that it detects all visible light.) The objects detected by the orange or visible filter are shown as blue, and the objects detected by the infrared filter as red. Yellow objects are detected by both the infrared and the orange filter.

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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by stephen63 » Sun Feb 10, 2013 1:35 pm

What does it indicate when the asteroid has such a curved path?
Ann is correct. Those little squiggly lines are cosmic ray hits. Its quite a nasty environment for humans up there!

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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by neufer » Sun Feb 10, 2013 2:14 pm

stephen63 wrote:
What does it indicate when the asteroid has such a curved path?
You are observing the curved path of the Hubble, itself, in its orbit.

(Think of the apparent motion of trees in front of a fixed full moon as observed from a car or train.)
http://hubblesite.org/newscenter/archive/releases/1998/10/text/ wrote:
<<The Hubble images capture an asteroid as a long trail produced by its motion across the camera's field of view. The trails appear like the streaks of light found on photos taken at night of speeding cars with their headlights on. In Hubble's case, asteroid trails show a unique curvature due to the continuously shifting position of the telescope as it orbits the Earth. This effect, known as parallax, allowed Evans and Stapelfeldt to determine distances and sizes for the asteroids spied by Hubble. A similar parallax effect is the key to depth perception in human vision: our eyes are set apart so that we can see three dimensionally.

"Asteroid trails observed by the Hubble telescope are usually curved because the telescope travels in a curved low- Earth orbit," Stapelfeldt says. "By precisely measuring the shape of the trails, we can solve for the distance to each asteroid at the time it was observed. It isn't possible to do this using a stationary telescope on the ground.">>
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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by neufer » Sun Feb 10, 2013 2:23 pm

Click to play embedded YouTube video.
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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by Messican » Sun Feb 10, 2013 2:36 pm

Tomorrow's picture; What's a scupture?

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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by neufer » Sun Feb 10, 2013 2:54 pm

Messican wrote:
Tomorrow's picture; What's a scupture?
  • It's a scup sculpture.
http://en.wikipedia.org/wiki/Scup wrote:
Image
<<"Scup" is a shortened form of a Narragansett word like mishcùppaûog. The scup, Stenotomus chrysops, is a fish which occurs primarily in the Atlantic from Massachusetts to South Carolina. Another English name for the fish, paugie, is a shortening of the same word which simply removes the other side of it. Along with many other fish of the family Sparidae, it is also commonly known as porgy. Scup grow as large as 18 in and weigh 3 to 4 lb, but they average ½–1 lb. In the Middle Atlantic Bight, scup spawn along the inner continental shelf. Their larvae end up in inshore waters, along the coast and in estuarine areas. At two to three years of age, they mature. Scup winter along the mid and outer continental shelf. When the temperature warms in the spring they migrate inshore. They are fished for by commercial and recreational fishermen. They are a fine fish to eat because of their light flavor and are sometimes called panfish. Popular methods of cooking include but are not limited to frying, broiling and baking.>>
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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by Chris Peterson » Sun Feb 10, 2013 3:16 pm

neufer wrote:
stephen63 wrote:What does it indicate when the asteroid has such a curved path?
You are observing the curved path of the Hubble, itself, in its orbit.

(Think of the apparent motion of trees in front of a fixed full moon as observed from a car or train.)
Of course, the path of the asteroid is curved, as well. It isn't visually apparent in such a narrow field (although it could probably be measured instrumentally), but the actual curve is a convolution of the fast orbital motion of the telescope and the slower orbital motion of the asteroid.
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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by stephen63 » Sun Feb 10, 2013 3:25 pm

Tomorrows APOD? I knew I'd make it sooner or later! :lol2:
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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by Chris Peterson » Sun Feb 10, 2013 3:36 pm

Ann wrote:By the way, why are most of the streaks so blue? Well, it's because this picture was made using only two filters, 606 nm and invisible infrared at 814 nm. (I believe that the orange filter can also be described as "clear", meaning that it detects all visible light.) The objects detected by the orange or visible filter are shown as blue, and the objects detected by the infrared filter as red. Yellow objects are detected by both the infrared and the orange filter.
Since the cosmic ray rate is statistically uniform, we could even count the number of events collected in each of the two exposures, and use that information to infer the relative exposure times used for each. That is, if there were twice as many blue streaks as yellow, we'd know that image made through the filter mapped to blue was exposed twice as long as the image made through the filter mapped to yellow.

(I don't think that the mapping used here was blue and red, but rather cyan and yellow. It is the white objects that were detected by both filters. Where did you find information on the filters used for the two exposures?)
small_asteroidI_before_after.jpg
BTW, this image is also available in its calibrated form, with the cosmic ray hits removed.
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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by bystander » Sun Feb 10, 2013 4:01 pm

Chris Peterson wrote:(I don't think that the mapping used here was blue and red, but rather cyan and yellow. It is the white objects that were detected by both filters. Where did you find information on the filters used for the two exposures?)
I think the information she used was from the mapping in the Hubble Heritage image which does not appear to be the same as was used in the HubbleSite image, although it appears to be a lot closer to your calibrated image
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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by geckzilla » Sun Feb 10, 2013 4:06 pm

It ends up looking cyan and yellow because both filters used are combined 50/50 to produce the green channel.
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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by Chris Peterson » Sun Feb 10, 2013 4:16 pm

geckzilla wrote:It ends up looking cyan and yellow because both filters used are combined 50/50 to produce the green channel.
Right, which is just the mechanism used to map the two images to cyan and yellow. That's why we see no red, no blue, and no green in the image.
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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by Beyond » Sun Feb 10, 2013 4:59 pm

Chris Peterson wrote:
geckzilla wrote:It ends up looking cyan and yellow because both filters used are combined 50/50 to produce the green channel.
Right, which is just the mechanism used to map the two images to cyan and yellow. That's why we see no red, no blue, and no green in the image.
Which is why i don't try to figure out and keep track of filters and wave lengths. It gives me a headache :!: I'm just not photo-astrologically minded. I just look at the pretty pictures. :lol2:
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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by Chris Peterson » Sun Feb 10, 2013 5:17 pm

Beyond wrote:Which is why i don't try to figure out and keep track of filters and wave lengths. It gives me a headache :!: I'm just not photo-astrologically minded. I just look at the pretty pictures. :lol2:
Well, in an image like this there's no need to know the specifics of the filters used, and little need to know the specifics of the color map used. But it is necessary to understand that this is a stack of two images, each mapped to a different color, or much of what we see becomes impossible to interpret.
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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by stephen63 » Sun Feb 10, 2013 5:24 pm

Chris Peterson wrote:Where did you find information on the filters used for the two exposures?
http://hla.stsci.edu/hlaview.html#Inven ... 2CGHRS&ds=
This is the exposure name: hst_05092_5m_wfpc2_f606w_wf
It was a 1000s exposure. 606nm filter(the one that captured the asteroid)

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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by neufer » Sun Feb 10, 2013 5:36 pm

Chris Peterson wrote:
neufer wrote:
stephen63 wrote:
What does it indicate when the asteroid has such a curved path?
You are observing the curved path of the Hubble, itself, in its orbit.

(Think of the apparent motion of trees in front of a fixed full moon as observed from a car or train.)
Of course, the path of the asteroid is curved, as well. It isn't visually apparent in such a narrow field (although it could probably be measured instrumentally), but the actual curve is a convolution of the fast orbital motion of the telescope and the slower orbital motion of the asteroid.
Convolution isn't quite the right word. Combination, conflation... :?:

Correction: Think of the apparent motion of Ents in front of a fixed full moon as observed from a moving car or train.
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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by Chris Peterson » Sun Feb 10, 2013 5:46 pm

neufer wrote:Convolution isn't quite the right word. Combination, conflation... :?:
Actually, I think its the most technically accurate word, since we are looking at a curve described by a new function created by the mathematical convolution of two other functions (one describing the motion of the HST, and one by the motion of the asteroid). However, the other words you suggest are also descriptive of what's going on, in a less mathematical sense.
Correction: Think of the apparent motion of Ents in front of a fixed full moon as observed from a moving car or train.
Perfect. I was thinking of the path of distant headlights as seen from a moving train, but your imagery is much nicer.
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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by neufer » Sun Feb 10, 2013 6:57 pm

Chris Peterson wrote:
neufer wrote:Convolution isn't quite the right word. Combination, conflation... :?:
Actually, I think its the most technically accurate word, since we are looking at a curve described by a new function created by the mathematical convolution of two other functions (one describing the motion of the HST, and one by the motion of the asteroid). However, the other words you suggest are also descriptive of what's going on, in a less mathematical sense.
Convolution generally implies some sort of universal smearing out such as an exact global cluster image as convolved (i.e., smeared out) with the tiny Airy disk (+ diffraction spikes) of the Hubble (or, unfortunately, the ugly Response Function of the original miss-focused Hubble). :arrow:

Today's APOD blue streak is simply the locus of image points of a moving (and relatively local) asteroid as observed by a moving Hubble.
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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by Chris Peterson » Sun Feb 10, 2013 7:14 pm

neufer wrote:Convolution generally implies some sort of universal smearing out such as an exact global cluster image as convolved (i.e., smeared out) with the tiny Airy disk (+ diffraction spikes) of the Hubble (or, unfortunately, the ugly Response Function of the original miss-focused Hubble).
Convolution is essentially the operation of combining two functions to produce a third (there is a rigorous mathematical definition which involves an integral transform). Filters (like the one you describe in an imaging case) are one example, but convolution extends to many areas besides imaging.
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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by bystander » Sun Feb 10, 2013 7:38 pm

neufer wrote:Correction: Think of the apparent motion of Ents in front of a fixed full moon as observed from a moving car or train.
I don't think they had cars or trains in Middle Earth, maybe from the back of a Great Eagle or a fast horse.
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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by Beyond » Sun Feb 10, 2013 9:36 pm

Chris Peterson wrote:
Beyond wrote:Which is why i don't try to figure out and keep track of filters and wave lengths. It gives me a headache :!: I'm just not photo-astrologically minded. I just look at the pretty pictures. :lol2:
Well, in an image like this there's no need to know the specifics of the filters used, and little need to know the specifics of the color map used. But it is necessary to understand that this is a stack of two images, each mapped to a different color, or much of what we see becomes impossible to interpret.
EXACTLY!! I don't interpret anything. I just look at the pretty pictures. Hey, i used to refer to Orion as a kite. Now it's Orion, a not too good a kite. :lol2:
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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by DavidLeodis » Mon Feb 11, 2013 12:01 pm

gratefulguy wrote:With very limited knowledge of astronomy, I ask the group's indulgence in wondering if the other (shorter) blue lines indicate other asteroids and are the yellow lines just an artifact of the imaging process, or do they denote movement of some other type of object?
Thanks to all who bring this website to us.
Hi gratefulguy. :)

In information about the image in Hubble NewsCenter release STScI-1998-10 dated March 9 1998 it states "Numerous orange and blue specks in this image...were created by cosmic rays, energetic subatomic particles that struck the camera's detector." The full release (split into several webpages) is available through the "above archival image" link in the explanation.

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Re: APOD: Asteroids in the Distance (2013 Feb 10)

Post by neufer » Mon Feb 11, 2013 1:47 pm

neufer wrote:
Chris Peterson wrote:
Of course, the path of the asteroid is curved, as well. It isn't visually apparent in such a narrow field (although it could probably be measured instrumentally), but the actual curve is a convolution of the fast orbital motion of the telescope and the slower orbital motion of the asteroid.
Convolution isn't quite the right word. Combination, conflation... :?:
  • va(t)= position vector of the asteroid

    ve(t)= position vector of the Earth

    vh(t)= position vector of Hubble [ = (vh(t)-ve(t)) + ve(t) = (Hubble orbit) + Earth orbit ]

    vah(t)= [va(t)-vh(t)] = relative position vector of asteroid vis-à-vis Hubble

    n= unit Hubble pointing vector (in celestial coordinates).

    Pn(t) = n x (n x vah(t))/(n ⋅ vah(t))
    where Pn(t)= path vector of the asteroid in the Hubble(/camera obscura) image plane.
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