EPOD 20th - Observing the Moon on the Same Day from the Northern and Southern Hemispheres

September 17, 2020

Freitas Moon-Venus-Copenhagen-Mario(3)

Frietas Moon-Venus-Curitiba-SandroColetti (1)

Freitas-Twilight-20h45min-UTC-July-15-2018 (1)

November 2018 Viewer's ChoiceWe’re celebrating 20 years of Earth Science Picture of the Day during the month of September! Today’s photo features a popular EPOD from the past. Thanks to all of our followers (on the blog, Facebook, Instagram and Twitter) for supporting us. Thanks also to all of you who’ve submitted your photos. We’re most appreciative. This EPOD was originally published November 22, 2018.

Photographers: Mario Freitas; Sandro Coletti
Summary Author: Mario Freitas 

The shooting times of the pair of photos above differ by less than one hour, but their locations were more than 10,000 kilometers apart. During civil twilight on July 15, 2018, the same Moon-Venus conjunction was observed by amateur astronomers in Copenhagen, Denmark and Curitiba, Brazil. If we consider that both celestial bodies lie close to the ecliptic plane, the Earth’s roundness provides that the arc connecting Venus to the waxing crescent Moon appears almost horizontal in Copenhagen, but is strongly tilted upwards in Curitiba.

Fortunately, meteorological conditions were favorable for observing the sky at both locations -- shooting times were 20:44 for Copenhagen and 21:26 UTC for Curitiba. The simulation by Google Earth makes it clear that the way the Earth’s axis tilts allows twilight times to be simultaneous in both cities. Although they differ by 60 degrees in longitude and 80 degrees in latitude, the geodesic line between Copenhagen and Curitiba eventually coincides with the solar terminator. Note that the planet Mercury is also visible in second picture (at lower left of the Moon).