September 2000: The Gegenschein
Riccardo Balestrieri with his son Elio (9), Bruno Caprile and Marco Fulle climbed Stromboli on the night of 27./28. September 2000 with (heavy!) astronomical equipment able to track on stars for hour-long exposures. Here we present the results of this volcano-astronomical night spent on Pizzo, together with other astronomical photos taken from the «Crocetta» (close to Stromboli's cemetery) and from the Giulian Alps for comparison. The aim of the expedition was to photograph the faintest and most elusive object in the sky, the Gegenschein. Thanks to a perfect night with no wind at all (necessary to obtain good very long exposures), the aim was reached, thus confirming that Stromboli has one of the darkest skyes in Europe. To give a sense of the perspective, camera lens focal lengths are given (i.e. f=28mm). As usual, the pictures on this page link to larger photos. In order to maintain accurate, point-like star images, little image compression had to be used, which lead to unusually big file sizes (100 to 250 KB).
28 September 2000, 01:20-02:10 UT (50 min exposure), f=50mm f/2, Elite 400, from Pizzo. We reached Pizzo after midnight, when the sky was dominated by the magnificent constellation of Orion. Note on the left the brilliant red «Rosetta Nebula». The following three images are only enlarged sections of the image above.
The three stars of Orion's belt are the center of the faint red nebula of «Barnard's loop». The lower left star of the belt excites the red «Horse Head Nebula». Below, the well known Orion Nebula is overexposed.
Another faint and giant red nebula surronds the star Lambda Orionis. Betelguese shines in bright orange at lower left center. On the left, the external arm of our Galaxy shines with thousands of young blue stars.
In the second half of the night sporadic meteors reach maximum frequency. Therefore long exposure photographs commonly capture some of them. This reminds us that we were here not to study constellations and nebulae, but dust of our Solar System.
26 September 2000, 21:00-21:40 UT (40 min exposure), f=16mm f/2.8 (fish-eye photo, diagonal = 180°), Elite 400, from «Crocetta» (covering the sky in the upper left corner), Stromboli. The summer Milky Way spans from Aquila up to the Perseus Double Cluster. On the lower left tourists descend the volcano after an evening trip with the local guides. Three red paths of airplanes cross Cygnus, Lyra and Vulpecula (this is the only defect of Stromboli's night sky...).
28 September 2000, 01:20-02:10 UT (50 min exposure), f=16mm f/2.8, from Pizzo, Stromboli. The Winter Milky Way from Deneb (in the steam reddened by the volcano's eruptions) to Procyon (upper right corner). On the top the Hyades, Pleiades, Jupiter (right) and Saturn (left). Below them, the red «California Nebula» borders the Milky Way. On the right, the morning zodiacal light above the Calabria horizon (lower right corner) crosses Cancer (with the Praesepe Cluster) and Gemini.
28 September 2000, 00:20-01:10 UT (50 min exposure), f=16mm f/2.8 (fish-eye photo, diagonal = 180°), Elite 400, from Pizzo, Stromboli. This wide angle view covers the sky from Orion (left) to Aquarius (right), with Jupiter and the Hyades (left) and Saturn and the Pleiades (right) in Taurus. The Gegenschein is the wide bright blob between Pisces and Cetus, exactly in the antisolar point of the sky. The horizon is marked by the Sicily lights and Salina Island (right).
21 October 2000, 20:20-20:55 UT (35 min exposure), f=16mm f/2.8 (fish-eye photo, diagonal = 180°), Elite 400, from Mt. Matajur, 1325 m.a.s.l. After a month, the Gegenschein has moved into Aries, following the Sun's apparent annual motion. Here it is barely visible, showing that the sky above the Alps is less suited to astrophotography than that of Stromboli (Trieste city lights in the lower right corner). The Winter Milky Way crosses the top of the image from Auriga (left) to Cygnus and Delphinus (right).
21 October 2000, 21:00-21:45 UT (45 min exposure), f=16mm f/2.8 (fish-eye photo, diagonal = 180°), Elite 400, from Mt. Matajur. This photo shows that light pollution from aeroplanes is a common problem in wide angle astrophotography. The longer exposure makes the Gegenschein evident. Orion rises from the eastern horizon.
21 October 2000, 21:50-22:10 UT (20 min exposure), f=16mm f/2.8 (fish-eye photo, diagonal = 180°), Elite 400, from Mt. Matajur. This is not an aurora but simply a jet stream in the upper atmosphere. It causes high cirrus clouds which soon put an end to our investigation of the Gegenschein which requires a perfectly uniform, dark sky.
23 October 2000, 19:45-20:35 UT (50 min exposure), f=16mm f/2.8 (fish-eye photo, diagonal = 180°), Elite 400, from Mt. Matajur. After two days we take advantage of a perfect night. This view spans from rising Orion (lower left corner) to Delphinus (upper right corner). The Gegenschein is in the lower center of the photo. Above it are the Andromeda Galaxy and the Cepheus Milky Way (top).
23 October 2000, 21:40-22:10 UT (30 min exposure), f=16mm f/2.8 (fish-eye photo, diagonal = 180°), Elite 400, from Mt. Matajur. After two hours the Gegenschein has rotated in the photo frame which proves that it is not a camera or film artifact. The darker sky above Slovenia (horizon on the left) compared to Italy's (right) allows us to glimpse the red nebula of Lambda Orionis.
Our whole Solar System is embedded in a cloud of dust released both by asteroids during their mutual collisions, and by comets during the development of their dust tails. Due to complex interactions between dust and solar radiation, all this dust collapses towards the Sun building up an ellipsoidal cloud centered on our star. Its density increases towards its center. When we look in a direction between the solar and the antisolar point we can see the sunlight reflected by this dust. This is the Zodiacal light, which is obviously brighter close to the Sun. The cause of the Gegenschein is more subtle, because it is not due to a real increase of dust density. It is an apparent effect due to the so-called radiation backscattering: particles of sizes close to the wavelength of light reflect light backwards much better than in all other directions (strictly speaking, the forward scattering is even stronger but, in the case of Solar System dust, it is hidden by the sunlight). The same light backscattering is the origin of the Brocken (Stromboli LiveCam image) effect in common fog.