Re: Astronomy Picture of the Day

[Gianni Ferrari]

Perhaps because of my bad English I have not understood completely the explanation of the beautiful image.    However in  my opinion the photo doesn’t  represent a  single sequence of photos but separate sequences of images of the Sun, of the Moon, of Venus and Jupiter while they are rising and in the following instants. Subsequently the photos of these four sequences have been overlapped and fused in an single image, together with the photo of the landscape. In other words the author has made : a sequence for the Sun after dawn with very short exposure times  ; a sequence for the Moon in a period at least 1.5-3 hours before down  ; a sequence for Venus few hours before the rising of the Sun and one for Jupiter while it was rising in a whatever  time of the night.   Each series lasts around 2 hours.   There are different reasons for this conviction : -         it is not possible to photograph Venus or Jupiter  after two hours from the rising of the Sun . -         The Moon is waning and there are still at least 2-4 days before  the new Moon. Under these conditions the Moon is from 24 to 40 degrees from the Sun and therefore she cannot be so near to the Sun as in the photo. Under these conditions the Moon rises around 1.5-3 hours before the Sun.  -         The brightness of the Sun is hundreds of thousand times that of the full Moon and therefore a photo where we want to see the Sun’s disk must be taken with a very closed diaphragm and with very short exposure time. In a photo taken under these conditions the Moon cannot be visible. Photos with the Moon and the Sun are practically impossible: they could be made only at dawn but the Moon would be New and therefore not visible. -         Same arguments for Venus and Jupiter   -         I don't remember  such a narrow conjunction among Venus, Moon and Jupiter, but this  perhaps is caused by my age  (not too young  :-)  ). Toward the end of the sequence the three bodies are at a  distance of a small fraction of the Lunar diameter : obviously  in the case that there was a single sequence.   The displacement of the Moon in comparison to Venus and to Jupiter doesn't have to deceive.  The moon moves in comparison to the stars of around 12 degrees in one day and therefore of one diameter in an hour. For this reason , while the photos were taken, the Moon is shifted of around two diameters, in comparison to the stars.   In the sequences in which Venus and Jupiter are been photographed there is not this move and therefore if we overlap the different sequences we see that the moon  has changed  her place  in comparison to Venus and Jupiter.   I remind that that the snaps are, in each sequence,  at a distance of 6 minutes among them.    In my opinion, supposing that the same equipment has been used without any movement, the different parallel arcs of  the ecliptic described by the images of Sun, Moon, etc.   are due to the different celestial Latitude of the celestial bodies in the day in which the sequences were taken. In this case from the measures of these celestial Latitudes one  would be able, with a lot of patience, to try to calculate the period in which the photos have been made – if they have been taken  in a period of few days.    But perhaps the author has introduced an artificial shift among the images during the overlapping with the purpose to separate and not superimpose the different celestial bodies.  :-)    Best Gianni Ferrari