The great American eclipse

August 21st: The Great American Eclipse


Next August 21st we will be able to watch the most expected total solar eclipse in recent times: the great American eclipse.


The band of totality will cross, diagonally from East to West , the United States of America. More than 100 million people will be able to witness the phenomenon live. NASA has already considered it the astronomical event of the year and is organizing all kinds of educational and informative activities during the day of the eclipse.


This astronomical event will be broadcasted live and through the website by STARS4ALL. The city of Mackay selected by NASA as an official Eclipse 2017 viewing site will be the spot selected for the broadcasting.


After approximately a year and a half since the last total eclipse of the Sun on March 9th, 2016, the shadow of the Moon will again touch the surface of our Planet on August 21st, 2017. It will be the “great American eclipse” as the band of totality will cross the country from the state of Oregon to South Carolina (see Fig. 2). The continental USA did not live a total eclipse since 1979. In April 2024 another total eclipse will cross the eastern part of the nation.



A group of astronomers, members of the STARS4ALL project, will travel to the state of Idaho (USA) to observe and relay live the event. The connection will take place at 4:00 pm Universal Time (One hour more in the Canary Islands, two more hours in central Europe and 10:00 am local time) on 21st August and the whole phenomenon can be followed through the web



STARS4ALL is a Collective Awareness Platform for the Promotion of the Dark Skies in Europe through Light Pollution Initiatives (LPI). LPIs are local or global working groups that fight against Light Pollution.


Why have astronomers chosen Idaho for the broadcast?


Miquel Serra-Ricart, the expedition leader, comments: “After the last eclipse in Indonesia, which was really difficult to observe due to the clouds, we are expecting the great American one. This time the cloud probability is lower and we will have two points of observation, so this will be the “safest” eclipse in the last few years. In fact, we had not had such favorable conditions during an eclipse since 2006, when we were watching from the Libyan desert.”


Picture 1.- Image of the Sun taken from Palu (Indonesia) on March 9th, 2016. The corona is symmetrical because the Sun was in a period of great activity. “Flares” of the chromosphere are also visible. High resolution.


Miquel, who belongs to the Instituto de Astrofísica de Canarias (IAC), is an experienced observer of eclipses and this will be his 14th expedition as leader (see His first one was in 1998 in the middle of the Atlantic: “We’ve been waiting for the big American eclipse for many years. The next important event like this will happen in August 2026 in Spain, where the band of totality will cross cities like A Coruña, León, Palencia, Valladolid, Zaragoza, Castellón and will finish in La Palma.”


Several TESS-W photometers developed by Universidad Complutense de Madrid (UCM) within the STARS4ALL project will measure the luminosity and temperature data during the eclipse. The data obtained will be available for educational activities and for any research purposes under open licenses.


The City of  Mackay Village (Idaho, USA) -which organizes the event “Totality on the Top of Idaho”- will participate in the broadcasting. Mackay has been selected by NASA as an official Eclipse 2017 viewing site.


The Sun eclipse will be broadcasted from the state of Idaho from two different locations to increase the probability of success. The first observation point will be located at Smiths Ferry -where the Moon’s shadow will reach the Earth’s surface first- and the coordination will take place from the town of Mackay where the event will begin about two minutes later.


At the same time UCM astrophysicists Jaime Zamorano, Jaime Izquierdo and Jesús Gallego will conduct the observation near the population of Cascade (Idaho), where they will take images of the solar corona and spectra of the chromosphere. These professors will be observing along with outstanding astronomers of the United States like James Lowenthal (American Astronomical Society and council liaison for the eclipse).


From Western Europe the final phase of the eclipse (partial phase) will be observable just at sunset on August 21th. If you are in Galicia (Spain) you will be able to witness a sunset with the solar disk slightly eclipsed by the Moon. It will be also possible to observe a partial eclipse from Paris, London, Dublin and Oslo. From Iceland the partiality will be more intense and the best place to observe the eclipse from Europe will be the Canary Islands, where the eclipse will be observed with greater intensity. From the Observatories of the Canary Islands the Moon will hide about 30% of solar disk during the sunset at the following hours:

Start Máximum Sunset
Roque de Los Muchachos Observatory 19:50:47 20:40:56 20:43
Teide Observatory 19:51:25  20:41:11 20:38

STARS4ALL is a project funded by the European Union H2020 Program under agreement number 688135. STARS4ALL involves 8 institutions (UPM, CEFRIEL, SOTON, ECN, ESCP Europe, IAC, IGB, UCM) from 6 different countries.


Three Spanish supercomputing centers, the Centro Extremo de Tecnologías Avanzadas (CETA-CIEMAT), the Consorci de Serveis Universitaris de Catalunya (CSUC) and the Instituto de Astrofísica de Canarias (IAC) will collaborate in the distribution of the retransmission of the web portal (


IAC contact: Miquel Serra-Ricart, IAC researcher,


Broadcasting channels

Mackay, Idaho (Solar image & comments)
Smiths-Ferry, Idaho (only solar image)



Circumstances of the Eclipse in Mackay, Idaho, USA (August 21, 2017).


Duration of Total Sun Eclipse: 1 minute 50 seconds


Local time = UT -6h

CEST time = UT + 2h

Canarian time = UT + 1h



Contacts Total Eclipse Sun Time (UT)
Start bias (C1) : 16:13:38.0
Total solar eclipse start (C2) : 17:30:20.3
Eclipse’s maximum: 17:31:26.6      
End of total eclipse (C3) : 17:32:33.0
End of partial eclipse (C4) : 18:54:54.4 

Picture 2. Total band (blue lines) of the eclipse of August 21, 2017 according to data provided by NASA (interactive map). The magenta point (GD, Greatest Duration) indicates the place where the duration of the eclipse will be maximum (2m 40s). The observation area of the Shelios 2017 expedition will be the state of Idaho (USA, see map expedition, red dots) photo NASA / Google