Starship Asterisk*

The time needed to evapourate a black hole of one proton mass, due to Hawking radation, is given by: 5120 2 π² G² M³ / (h c² c²) G = 6.67E-11 [Nm²/kg²], M = 1.67E-27 [kg], h = 6.62E-34 [Js], c=3E8 [m/s] That is approximately: 1E4 x 1E1 x 40E-22 x 5E-81 / (6E-34 * 81E32) = 200E-98/500E-2 = 4E-97 s Fo...

Porrima, δVirginis Thanks, Henk! But which is it? Porrima (gamma virginis / γ Vir) or Auva (delta virginis / δ Vir) :?: Excuse. γ Virginis The other question: since it is still daylight here (monitor of 10 years old), i only see one, about the same height in the image as γ Virginis, at a distance f...

bystander wrote:But there is a fourth, fainter white dot. What is it?

Porrima, δVirginis

I don't think they have had any collisions, yet. They only have one beam circulating. But don't worry, if they do create a black hole, we'll probably never know about it. No collisions yet, indeed. And we will probably never know whether a black hole is created. The amount of 'material' circulating...

A few pixels may have a significantly higher dark current rate. With a long enough exposure, these pixels will saturate. <snip> Sometimes hot pixels are isolated, and sometimes they are part of a small cluster of pixels with similar characteristics. Chris, is this due to localized chemical impuriti...

Chris Peterson wrote:The point sources are hot pixels- defects related to the CCD.

Chris, what precisely are hot pixel defects? I heared about pixel defects, single pixels, which do not work. Do hot poixel defects occur in groups of about 10 adjacent circular or square elements?

From left to right, exposure times are 60, 90, 120 secs. shot with Canon 400D(stock) with a 75-300 F/4.5 with a 2x tele-converter shooting at F/5.6. Tracked using a Celestron CG-5ASGT In support of Chris Pettersons analysis, the dark object itself is stationary during the exposures. The dark blob i...

Doum wrote:Some change in 30 sec, other in 2 to 5 minutes.

With the help of makc and Doums description i know now that the images the BBC was showing, were probably real-time. Sometimes processes are shown in a 'fast forward' pace, like clouds speeding in the sky.

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Thanks.
 Henk

In today's APOD, we see the arc of Anthe, but the background has numerous star trails which seem to trace different trajectories, one is even curved. Why is this? FranksHobbies asked a similar question. I was a little puzzled by the quote that Indigo_Sunrise included, especially: The long exposure ...

I think that it would be catastrophic if the ice shelves in Antarctica suddenly broke off and melted (although I'm a little uncertain that it would happen in a day, and then sea levels rise in a day. It would probably happen over periods a decade that the sea level would rise). I calculated about a...

http://www.youtube.com/watch?v=icugqEEOgkg Most of the individual clips here were each taken over about a 10 minute period to give you an idea of how much they were moving in real time. Unfortunately i can not display these clips, since they are Flash format. Is it safe to assume that 1 minute is t...

I noticed it said that Dwingeloo 1 is a member of the Local Group. I thought it was a member of the Maffei 1 Group? Welcome Hrundi to the forum. You are right. The wikipedia on Dwingeloo I reports that it is a member of the Maffei 1 subgroup. It is classified as SB, so a barred spiral, as BMAONE23 ...

Except, it doesn't appear to me that we see a double period. There is a 2.6 hour main cycle, and that pair of plateaus which are 6 hours apart. The earlier published light curves from the same instrument show only the 6 hour cycle, and the analysis I've seen indicates no other periodicity. Did some...

G'day folks, Yesterday evening (20080907) the BBC had a topic about Norway and Svalbard. Some images of aurora were shown. From the images one could not get an good idea of the time scale of the fluctuations, since the images could have been sped up considerably. The aurora looked like curtains slow...

I'd be interested in seeing some discussion about why the light curve in the presentation looks so different. Thought experiment. Take a cylinder (soda can), paint it white and let it rotate around an axis, perpendicular to the symmetry axis. Let some light shine on it, e.g. from the back side of t...

Do you know of any descriptive text to go along with the presentation you link? Unfortunately not. The webstreaming of the press conference, well its gone. See http://www.esa.int/rosetta or i'm missing a player. In a later (September 6th) article on the ESA website an e-mail address is mentioned fo...

I kinda expected there would be some attitude instability. But the flyby video indicates that this body doesn't tumble. Wonder why? Did you see the presentation of H. Uwe keller ? On page/sheet 5 a light curve is drawn. The horizontal scale is in Modified Julian Date and the vertical scale is the &...

G'day Art, The Metop WV 6.2 micron band is equivalent to the GOES 7.0 micron with the Metop grey/black corresponding to the GOES red/black color. Great, now i known where to look for. "Red or blue" was the question and it's definitively red/black. These both represent the dry regions just ...

As someone who has spent a career observing the earth from satellites (including having designed this opaque water vapor channel ) Art, can you give me a clue how i can recognise the jet stream in your images? Im used to B/W watervapour images, in which the jet stream is predominantly dark (black) ...

How would the evening sky look like in a cluster? Todays APOD gives us an impressioin. But how realistic is it? If stars are visible during daylight, as in the APOD, they must be at least of magnitude -5. The distance between the stars must be considerable smaller than in the neighbourhood of our su...

neufer wrote: <<[Mozart's] title, Così fan tutte, is often translated as "Women are like that [i.e., fickle]". >>

"All do such things"

Cosi : this way, that particular action
fan : do, act (plural of fare)
tutte : all (plural of tutto)

Regards,
 Henk

I simply meant that if you made a simple drawing of the 2D case, it should become pretty clear how a retroreflector works. But I can do that: http://www.cloudbait.com/misc/corner.gif Thanks Chris, now i see it. During the Apollo flights i heared about these reflectors but i never understood how the...

G'day Chris, It's simple to see why it works if you first consider the 2D case. The only rule you need is that the angle of incidence equals the angle of reflection. Snell's law deals with refraction, which isn't involved here. It is not my intention to be rude, but the phrase "It is simple to ...

The reflectors are arrays of corner prisms, aka retroreflectors . These cannot help but to send reflected light back along the same path it entered on. In the wiki i can read that it differs from a plane mirror. It is a constellation of three perpendicular perfectly flat reflecting planes. The reas...

G'day Art, You quoted the wiki on the reflectors on the moon. More specifically: the accuracy which was improved to near mm accuracy. That means that the time of flight must be accurate to 10 ps, (100 GHz being 3 mm). The time of flight is about 2.5 s, so a remarkable accuracy. That has rizen a few ...