What is responsible for this year’s natural spectacle is the comet with the scientific name C / 2020 F3 (NEOWISE) that can be seen throughout the night in our latitudes in the second half of July. It happens only four to five times a century that such an impressive comet can be observed in the sky. Or perhaps one should say “can still be observed”? Artificial light sources, for instance street lamps and advertising lights, result in an increasingly brighter night sky above large cities like Vienna. The contrast with celestial objects such as stars and comets is increasingly lost and they become paler. This phenomenon, also called light pollution, has almost quadrupled in Vienna since the last strikingly bright comet C/1995 O1 “Hale-Bopp” in 1997. While NEOWISE can still be seen with the naked eye over Vienna, this might no longer be possible in a decade or two.
 
Increasing light pollution destroys valuable night habitats
“The comet may best be observed far from big cities and artificial light sources,” says Christoph Goldmann, an astronomer and educator at the Natural History Museum Vienna. The last areas in Austria with a natural night sky, such as the surroundings of the Dürrenstein Wilderness Area in Lower Austria and the Kalkalpen National Park in Upper Austria, are particularly suitable in this regard. “In some places natural nights without light pollution may still be found, and these make it possible to experience the beauty of the comet phenomenon to its full extent,” adds Goldmann. In order to ensure that these places, which are enormously important as “night habitats”, are preserved for the future, the project “Conservation of Dark Sky Habitats”, coordinated by the Natural History Museum Vienna, is fully committed to the preservation of these last islands of natural night. In order to illustrate the importance of a dark sky for comet observation, one of the project partners, the Kuffner Observatory Association, has calculated the difference in the quality of observation using measurements of night sky illumination. In the center of Vienna the contrast of the comet is reduced to 1/25, on the outskirts to 1/14. In protected “starlight oases” away from cities, the contrast is still reduced to 1/4 of the impressive spectacle one would enjoy in the natural sky.
 
 
Observation strategies for maximum comet viewing pleasure
The best conditions for observing the comet are in the days leading up to July 31 in an area in Styria that extends roughly from Wildalpen in the east to Lachtal near Oberwölz in the west at altitudes higher than 1,000 m. There, the comet can already be observed towards the northwest as a blurry spot with a tail in the late evening twilight. In July this is about an hour after sunset, at around 9:45 p.m. Up until the end of July, owing to the comet’s relative proximity to the Earth, the tail is so large that it does not fit into either normal telescopes or binoculars. The best observation strategy is therefore to look at the sky with no optical aids. The visibility period for the naked eye is expected to end when the moonlight increases in late July. After that, the comet can be found again in the western sky roughly from August 7 to 25, but then preferably with binoculars. The last period of visibility is expected from September 3 to 25. At that point the comet, which will have become smaller because of its much greater distance from Earth and Sun, will also fit well into telescopes and can be found in the southwest. It is important to have the right viewing point with a low horizon and to adjust your eyes well to the dark. For this purpose, you should not look at light sources such as street lights or cell phone displays for at least half an hour, or even up to an hour beforehand, in order to enjoy the full comet experience.
 
Do it yourself: open comet science (citizen science)
Take the opportunity to evaluate the quality of the sky. To do this, follow the instructions on http://sternhell.at (How many stars can we still see?) and report how you saw the Little Dipper (Ursa Minor). The summer comet also enables you to conduct a unique experiment: measuring the comet's tail with the naked eye under different conditions in July.
 
Instructions:
1.) Wait facing the sunset (NW) until the comet begins to emerge. The later and darker the better.
2.) Measure the length of the comet's tail with your hand and extended arm:
+ A fist width corresponds to 8°
+ A thumb width corresponds to 2°
+ The little finger of the outstretched hand corresponds to 1°
3.) Send a text with the length of the comet's tail in degrees immediately after your observation or with an indication of the time and position (GPS or nearest location) to +43-(0)664 23 00 336 or send an email to Verein@Kuffner-Sternwarte.at
 
You can find the results at http://sternhell.at and http://Kuffner-Sternwarte.at
 
The project “Conservation of Dark Sky Habitats”
In spring 2019, an interdisciplinary team set out on a two-year process of developing new nature education opportunities for the perception of nature by night and measures against light pollution based on current scientific studies. With a series of events for the general public, an advisory service for local authorities as part of the project and a management concept for protected areas, the project is designed to make a major contribution to raising awareness and preserving natural night habitats and their endangered biodiversity. Partners of the Natural History Museum Vienna in the project are the Umweltdachverband, the E.C.O. Institute for Ecology, and the Kuffner Observatory Association. The project is being funded with over € 220,000 by the Austrian government (BMLRT) and the European Union within the framework of the Austrian program for rural development 2014 to 2020 (program LE 14-20) in cooperation with the BMK.
 
Conservation of Dark Sky Habitats Project:
https://www.nhm-wien.ac.at/forschung/projekt_lebensraum_naturnacht
 
Partners in the project:
Natural History Museum Vienna (coordination): https://www.nhm-wien.ac.at
E.C.O Institute for Ecology: https://e-c-o.at
Umweltdachverband GmbH: https://www.umweltdachverband.at (German only)
Kuffner Observatory Association: http://kuffner-sternwarte.at (German only)
 
In cooperation with:
Austrian Federal Ministry for Climate Action, Environment, Energy, Mobility, Innovation, and Technology (BMK) https://www.bmk.gv.at/en.html
 
Sponsor:
ELER: https://ec.europa.eu/agriculture/rural-development-2014-2020_de
Austrian Federal Ministry of Agriculture, Regions, and Tourism (BMLRT): https://www.bmlrt.gv.at/english/