[OT]: SOHO LASCO C3 image.

[Sunil G.R.]

Slightly off topic from the current Lovejoy comet discussion.

1) Why is the image from center towards top right is not proper?

2) If we see the current gif of LASCO C3, there are many bright dots too getting appear and disappear. What are they? The lines could be meteors though.
http://sohowww.nascom.nasa.gov/data/LATEST/current_c3.gif

Regards,
Sunil.

On Thu, Dec 15, 2011 at 7:24 PM, Amar Sharma <amar_u...@yahoo.com> wrote:

This is getting hair raising by the moment (indeed for me).I hope all of you are also keeping a track of this thread and the SOHO LASCO C3 link: http://sohowww.nascom.nasa.gov/data/realtime/c3/512/ Sometime in a couple hours the comet should be visible in the LASCO C2 f.o.v of SOHO: http://sohowww.nascom.nasa.gov/data/realtime/c2/512/ I have been visiting the C3 link sparsely but periodically (for nearly 24 hours now) and have seen the comet uprise from the bottom end of the field to 1/4th way up. The next 12 hours will be crucial. Sad that it will be peak nightfall for us when it will get much closer for the action. Here is another news article about Lovejoy: http://www.esa.int/esaSC/SEM3HD8XZVG_index_0.html I am not fully prepared yet mentally, but one part of my brain is asking me to attempt for it -visually !!! Not feasible any possible way, since when the Sun rises it will be less than One degree close to the Sun! Then there will sure-shot be the thick clouds. I dont have a solar filtered scope or binocular too. :-( <chuckle> If there was a total solar eclipse and a comet like this, that would have been something... </chuckle> Happy comet-on-screen watching!

[Aditya Ravi]

Hi All,

          I am not expert on SOHO things but I will share with you what all I know. Sunil the answer for the first question of yours is that when the LASCO C3 images are taken one of the arms of the camera protrudes out and this blocks the light from that area. Hence you are seeing a blackish thing on the top right corner of the image.

The second question of yours those lines aren't meteors. I used to think the same as you. But now I am enlightened from a person the logic behind why they aren't meteors. It is pretty simple, it is impossible for meteors to move with that immense speed. You can compare the speed of these lines with respect to the comet lovejoy itself and see how unreasonable it is. What those lines  are i still don't know. I suspect them to be cosmic rays or something. Will do some research on it and get back to you on it. :)

Regards,

Aditya Ravi.

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[Amar Sharma]

1) Thats a good reply, Aditya, to the first question on the black streak off-shooting at 1 'o' clock position, which I personally dont have a clue about. A little read-up about SOHO should give in most answers. 2) (a) The several dots all through the picture are - stars. The SOHO coronograph (instrument used to block sunlight so it can render surroundings of the Sun visible). (b) Sunil, anything streaking in life, intuitively feels like a meteor. But lets analyze the simple scenario here. As Aditya mentioned earlier, the blue outer circle is the blocking coronograph, the white inner small circle is the actual Sun's representation. And you know its diameter - 14 lakh kilometers. Keep this always for reference. Visually putting, the comet's total length is atleast 5 times the diameter of Sun which means ~70 lakh kilometers!! Secondly, SOHO is a spacecraft out in space (please wikipedia or google for its distance). When these are the parameters set, how can the flying streaks be meteors which are an earthly phenomenon?? And if the immensely long comet itself is moving at so many tens of thousands of kilometers per hour, the streaks have to be plainly artifacts. They cant move at some tens of lakhs of kilometers per second as appears! Hope only the handful of us are not the spectators to this celestial show...

--- On Thu, 12/15/11, Aditya Ravi <adityar...@gmail.com> wrote:

Hi All,           I am not expert on SOHO things but I will share with you what all I know. Sunil the answer for the first question of yours is that when the LASCO C3 images are taken one of the arms of the camera protrudes out and this blocks the light from that area. Hence you are seeing a blackish thing on the top right corner of the image. The second question of yours those lines aren't meteors. I used to think the same as you. But now I am enlightened from a person the logic behind why they aren't meteors. It is pretty simple, it is impossible for meteors to move with that immense speed. You can compare the speed of these lines with respect to the comet lovejoy itself and see how unreasonable it is. What those lines  are i still don't know. I suspect them to be cosmic rays or something. Will do some research on it and get back to you on it. :)

[Rakesh Nath]

Hi Sunil

I am not sure what you mean by top right but if you are talking of the blocked out region out of the coronagraph then it is the arm that holds the coronagraph in place.

Also the white dots are background stars. These are seen because of the enormous amount of light blocked off by the coronagraph. Also remember the brightness of the sky on earth is because of atmosphere and not the sun.

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Regards
        Rakesh Nath  
"It is far better to grasp the Universe as it really is than to persist in delusion, however satisfying and reassuring." Carl Sagan

[Amar Sharma]

Got the exact answer to Sunil's question, from one of SOHO's webpages. Copying the same: ************* In the LASCO C3 (blue) images, you can also see the "pylon" (or "occulter arm") which is the arm that holds the disk in place in front of the LASCO C3 telescope. Visible all over the LASCO C2 and C3 images are hundreds of tiny white dots and streaks. Most of the dots are stars, all of the streaks are cosmic rays (noise). Here's how to tell them apart: Stars: In the LASCO images, stars always move from left-to-right, always horizontally and always at the same speed as one another. There are usally between 15 and 40 stars visible at any one time in LASCO-C2, and hundreds in LASCO-C3. They are very easy to spot if you look at a sequence of three or more images. Cosmic Rays: Cosmic rays are noise (white dots, blobs and streaks) created in the images by energetic particles striking the cameras in the telescopes. Cosmic rays get reported as comets more often than real comets do! So it essential to learn how to distinguish them from something that is real. Cosmic rays are completely random -- they can, and do, appear absolutely anywhere in the images and they only appear once. They are most commonly just dots, but they are also occasionally blobs or streaks. Some are very faint, but most are quite bright. Some even saturate the camera and cause the large horizontal spikes we often see on planets and bright stars.