Search found 17 matches

by Alnilam
Sat May 07, 2016 3:18 pm
Forum: The Observation Deck: Latest Sky Photography
Topic: Submissions: 2016 May
Replies: 173
Views: 309546

Re: Submissions: 2016 May

Mars retrogradation loop (partial) I am french and I hope that you will excuse my poor English. Since February, I took (relatively) regular pictures of Mars to reveale its retrogradation loop. In fact, the retrogradation started on April 18th and will end on July 2nd. But to have a complet go/back/...
by Alnilam
Fri Apr 13, 2012 8:41 am
Forum: The Bridge: Discuss an Astronomy Picture of the Day
Topic: APOD: A Dust Devil of Mars (2012 Apr 13)
Replies: 27
Views: 3949

Re: APOD: A Dust Devil of Mars (2012 Apr 13)

"...warm, rising air currents...". Is there "air" on Mars ??? ;o)
by Alnilam
Wed May 04, 2011 7:46 am
Forum: The Bridge: Discuss an Astronomy Picture of the Day
Topic: APOD: Celestial Trails over Greece (2011 May 04)
Replies: 31
Views: 6229

Re: APOD: Celestial Trails over Greece (2011 May 04)

More of "time-lapses" in this video are not very natural : it is obvious that the changing sky is added on a still image of landscape, otherwise trees or flowers must be shaked by the wind. It is very different in the last sequence with the flag. I suppose that this choice was made to avoi...
by Alnilam
Thu Feb 24, 2011 7:48 am
Forum: The Bridge: Discuss an Astronomy Picture of the Day
Topic: APOD: Star Size Comparisons (2011 Feb 22)
Replies: 131
Views: 39276

Re: APOD: Star Size Comparisons (2011 Feb 22)

@ alNilam: Wouldn't the name actually be "an Nilam"? There should be assimilation of the "l" of the article "al" to the first consonant of "Nilam". Thank you for your interest in my pseudo. We have a good book about arabian names of stars (in French of course...
by Alnilam
Tue Feb 22, 2011 8:55 am
Forum: The Bridge: Discuss an Astronomy Picture of the Day
Topic: APOD: Star Size Comparisons (2011 Feb 22)
Replies: 131
Views: 39276

Re: APOD: Star Size Comparisons (2011 Feb 22)

Hello Ann ! The pseudo "Alnilam" is realy inspired by the Orion belt : it's the first asterism that I noticed when observing the sky during winter evenings when I was walking from the school bus stop to my home (long, long, long ago...). And then I decided to learn more about stars and con...
by Alnilam
Tue Feb 22, 2011 7:39 am
Forum: The Bridge: Discuss an Astronomy Picture of the Day
Topic: APOD: Star Size Comparisons (2011 Feb 22)
Replies: 131
Views: 39276

Re: APOD: Star Size Comparisons (2011 Feb 22)

Ooouuupppsss ! One more :

If planets rotations could be corrected, please use their proper own speed (ex.: Moon about 27 days, Mars and Earth about 1 day, Jupiter and Saturn about 10 hours, and Sun about 25 days).
by Alnilam
Tue Feb 22, 2011 7:21 am
Forum: The Bridge: Discuss an Astronomy Picture of the Day
Topic: APOD: Star Size Comparisons (2011 Feb 22)
Replies: 131
Views: 39276

Re: APOD: Star Size Comparisons (2011 Feb 22)

I'm french and I hope you will excuse my poor English. :wink: Few comments about this video : - why all planets except Uranus ? - why all planets with their atmosphere and Venus without ? (giant planets would be very strange without their huge atmosphere !!!) - almost all planets rotate in the wrong...
by Alnilam
Tue Nov 03, 2009 9:01 am
Forum: The Bridge: Discuss an Astronomy Picture of the Day
Topic: Pleïades and California (2009 Nov 3)
Replies: 12
Views: 1940

Pleïades and California (2009 Nov 3)

250 full moons betwen them ?!? It's almost a third sky (125°) !
I checked it in my favourite sky maps software : it's about 13°, so... "only" 25 full moons.

http://apod.nasa.gov/apod/ap091103.html
by Alnilam
Wed Aug 05, 2009 3:59 pm
Forum: The Bridge: Discuss an Astronomy Picture of the Day
Topic: APOD: A Triple Sunrise Over Gdansk Bay (2009 Aug 04)
Replies: 338
Views: 49720

Re: Cause of Triple Sunrise (APOD 2009 August 4)

To geckzilla and others :

Some pictures published here are quite strange in they ray-tracing !!! :(

Don't forget the reflection rule : the angle of reflection is equal to the angle of incidence ! :shock:
by Alnilam
Wed Aug 05, 2009 8:34 am
Forum: The Bridge: Discuss an Astronomy Picture of the Day
Topic: APOD: A Triple Sunrise Over Gdansk Bay (2009 Aug 04)
Replies: 338
Views: 49720

Re: Cause of Triple Sunrise (APOD 2009 August 4)

In French we says "un dessin vaut mieux qu'un long discours" (about : "a simple drawing is better than long tellings"), so I tried to verify if the theory of multiple same images of the sun could be right, on the picture itself. I take a copy of the "second sun" (becaus...
by Alnilam
Wed Aug 05, 2009 8:00 am
Forum: The Bridge: Discuss an Astronomy Picture of the Day
Topic: APOD: A Triple Sunrise Over Gdansk Bay (2009 Aug 04)
Replies: 338
Views: 49720

Re: Cause of Triple Sunrise (APOD 2009 August 4)

To owlice :

I confirm that there is realy a reflection of the "second sun" on the sea surface. Look at the above picture (I ajusted the contrast +60%).
by Alnilam
Wed Aug 05, 2009 7:56 am
Forum: The Bridge: Discuss an Astronomy Picture of the Day
Topic: APOD: A Triple Sunrise Over Gdansk Bay (2009 Aug 04)
Replies: 338
Views: 49720

Re: Cause of Triple Sunrise (APOD 2009 August 4)

To luchio : My opinion is that your picture (I gained the same) demonstrate that there is obviously reflections in the picture and it's a great probe for the window theory. But I think that the "gohst image" is not a reflection of the balcony because the distance between them isn't consist...
by Alnilam
Wed Aug 05, 2009 7:45 am
Forum: The Bridge: Discuss an Astronomy Picture of the Day
Topic: APOD: A Triple Sunrise Over Gdansk Bay (2009 Aug 04)
Replies: 338
Views: 49720

Re: Cause of Triple Sunrise (APOD 2009 August 4)

To drollere : Why guess about the dynamic of the camera and the reflection ratio of a window ? Just mesure it ! With PhotoShop, I mesured the brightness of several points in the picture : three for each sun image as illustrated on the picture above. Black point in the limbe, blue point in the top cl...
by Alnilam
Tue Aug 04, 2009 8:40 pm
Forum: The Bridge: Discuss an Astronomy Picture of the Day
Topic: APOD: A Triple Sunrise Over Gdansk Bay (2009 Aug 04)
Replies: 338
Views: 49720

Re: Cause of Triple Sunrise (APOD 2009 August 4)

To Green1 : Your picture is very interesting for me : by duplicating the initial sun image, you noticed also the dupication of its reflection on the sea surface but you don't remark that the sun "wings" (parts of the front clouds over-expoded) are too, and very much brighter. There is no s...
by Alnilam
Tue Aug 04, 2009 11:09 am
Forum: The Bridge: Discuss an Astronomy Picture of the Day
Topic: APOD: A Triple Sunrise Over Gdansk Bay (2009 Aug 04)
Replies: 338
Views: 49720

Re: Cause of Triple Sunrise (APOD 2009 August 4)

I'm not convinced by the last schema because the distance between the two glass layers is too large compared with the distance between the window and the focus point of the camera (the CCD chip) ! Before reading this post, I was just comparing the distance of the sun images in the APOD picture and o...
by Alnilam
Tue Aug 04, 2009 9:49 am
Forum: The Bridge: Discuss an Astronomy Picture of the Day
Topic: APOD: A Triple Sunrise Over Gdansk Bay (2009 Aug 04)
Replies: 338
Views: 49720

Re: Cause of Triple Sunrise (APOD 2009 August 4)

The "hourglass reflection" leads me to watch at the sea surface and my conclusion is quite different ! The "second sun" produces it's own reflection on the sea surface. It's obvious when the picture is lightened. So the "second sun" is far in the background, not a foreg...
by Alnilam
Tue Aug 04, 2009 8:17 am
Forum: The Bridge: Discuss an Astronomy Picture of the Day
Topic: APOD: A Triple Sunrise Over Gdansk Bay (2009 Aug 04)
Replies: 338
Views: 49720

Re: Cause of Triple Sunrise (APOD 2009 August 4)

I'm French and I hope you will excuse my poor English. In my opinion, the reflection trough a double glass windows is not the right explanation of this view. If you look at the first picture (in the APOD), it's obvious that the second and third suns (fainter and fainter) are behind the dark cloud/mi...