Three of Jupiter’s Galilean moons caught in the sunlight

James Edgar

The moon and Uranus are just 1.8 degrees apart Aug. 1. Look in the northeast before dawn, near the Pleiades, which are just to the east of the pair. New moon is Aug. 8 (Lunation 1220). Aug. 10, the thin crescent of a 2.5-day-old moon is four degrees away from Venus in the western evening sky. Aug. 20 and 21, respectively, Saturn, then Jupiter, are four degrees north of our satellite. The moon is full Aug. 22, so Jupiter should still be nearby, making a possible photo opportunity.

Mercury is in superior conjunction Aug. 1, meaning it is on the opposite side of the sun from Earth. It doesn’t begin to appear until mid-month, but even then this is a poor apparition for northern observer. Mercury hugs the horizon at sundown, so disappears shortly after that. Mars is 0.1 degrees away Aug. 18. Even though the opportunity is slim, it might be worthwhile looking for this pair at sunset.

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Venus continues to rise in the west along with nearby Mars, but at the same time, the angle of the ecliptic becomes less, so that the planets appear to move eastward close to the horizon. Watch for the nearby moon Aug. 10.

Mars is similarly close to the horizon as it moves eastward among the stars of Leo, the lion. The bright star Regulus is just two degrees away from Mars on Aug. 1. A tight conjunction with Mercury can theoretically be seen Aug. 18, but a telescopic view during daylight hours might be the best option. If undertaken, be careful not to have the sun in the field of view. Even though the Red Planet is moving eastward, Earth’s more rapid motion makes it look like Mars is going westward. By the end of the month, the planet is lost in the sun’s glare.

Jupiter is in opposition on Aug. 19, meaning it rises at sundown, is directly south at midnight and it sets at sunrise – visible all night. The giant planet is also in retrograde motion, so moving westward through the stars of Aquarius into Capricornus. Aug. 15, a rare triple shadow transit occurs, where three of Jupiter’s Galilean moons are caught in the sunlight. The full moon passes four degrees to the south Aug. 21.

Saturn reaches opposition Aug. 1, when it is 74 light-minutes from Earth – a little over 13.4 million kilometres away. It, too, will be visible all night, just like Jupiter. And retrograding like Jupiter, but against the stars of Sagittarius.

Uranus is prograding until Aug. 20, when it stops, then begins retrograde motion. The blue-green planet is at its highest point (declination) since the 1960s.

Neptune rises in midevening, in retrograde motion in Aquarius, approaching a mid-September opposition.

The Perseid Meteors peak Aug. 12.

James Edgar has had an interest in the night sky allm his life. He joined The Royal Astronomical Society of Canada in 2000, was national president for two terms, is now the editor of the Observer’s Handbook, and production Manager of the bi-monthly RASC Journal. The IAU named asteroid 1995 XC5 “(22421) Jamesedgar” in his honour and he was recently awarded a Fellowship of the RASC.


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