Two hemispheres sky

Two photographers, two hemispheres, one sky. The view to the night sky is limited by our Earth, meaning in one time at one place we can only see a half of the starry spheric view, the second one is below the horizon. But what if – apart from travelling away from Earth – there is a way to complete the whole view. Then it could look like this. Of course, some (better precise) planning is needed to make it happen. You have to think about what follows what and when is the time of view following the other view from the other hemisphere. Me and my friend, great TWAN photographer Juan Carlos Casado, focused on specific part of the year, when from two major observatories of almost same latitude, but opposite ways from equator, the column of the zodiacal light appears almost upright over the horizon. While mine view from ESO La Silla Observatory was taken in April (2016), Juan made it happen to capture the northern part from IAC La Palma Observatory on February (2020). Both views, sitched together in one, finally reveal the whole night sky scene around, using Earth’s horizon to block the bright sun from the view. Here are some of more interesting facts:

• Both observatories lie at altitude about 2400 meters and latitude 29 degrees (La Palma north, La Silla south)
• Southern part (La Silla) was taken on 13 April 2016, morning (a month after vernal eqionox). Northern part (La Palma) almost perfectly to fit – evening of 20 February 2020 (month before vernal equinox)
• On northern part (Casado) can be seen prominent reddish airglow from OH radicals, which is mostly visible after dusk, southern one (Horálek) shines with green (oxygen) airglow of which visibility is favorable also in mornings before dawn.
• Same equipment gave same resolution and same spectral sensitivity so HII regions are visible in both images. For both views were used modified Canon 6D cameras, 24mm lenses, f2.2, ISO 10000 and 15s exposures stitched to panorama. Most prominent HII regions are, of course – Gum nebula (behind MAGIC telescope), Barnard’s Loop, Orion Nebula, Rosetta Nebula, California Nebula, Heart and Soul… (Casado, north), Lagoon Nebula, Cat Paw Nebula, Rho Ophiuchi region, Carina Nebula, North America… (Horálek, south)
• In this time of year the 2 northern and 2 southern galaxies, except the Milky Way, are visible to naked eye in dark sky (in Casado’s La Palma view Andromeda galaxy and Triangulum galaxy, in Horálek’s one from La Silla the Magellanic clouds)
• Gegenschein can be seen as well – as a faint both-hemispheres belt 180 deg. away from Zodiacal Light columns
• Domes of one of world’s largest telescopes can be seen: Grand Telescopio Canarias (Casado, behind MAGIC telescope) and ESO 3.6 Telescope (Horálek, behind dome of New Technology Telescope)

The images would not have been taken without support of ESO – European Southern Observatory, IAC – Institute of Astrophysics of the Canary Islands and TWAN – The World At Night. Full credit of all images is Petr Horálek/ESO, Juan Carlos Casado/IAC/TWAN.

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