The new moon occurs July 2, at 3:16 p.m. EDT (1916 GMT), and will offer up a total solar eclipse that will cross South America from just south of Buenos Aires to the city of La Serena, Chile.
When the moon is directly between the Earth and sun, we call that the new moon. This happens about every 29.5 days, at which point the two bodies share the same celestial longitude, an alignment also called a conjunction. (Celestial longitude is a projection of the Earth's own longitude lines on the celestial sphere).
Usually the illuminated side of the moon is facing away from Earth at the new moon, so it is not visible to ground-based observers. This time, the moon will pass in front of the sun, and the result is an eclipse.
During a solar eclipse the moon's shadow isn't visible all over the Earth. The shadow of a spherical object makes a conical shape, and it's in that region where the sun's light is blocked. The moon is just far enough away from the Earth that the tip of the cone touches the Earth's surface, creating a total solar eclipse. Sometimes the moon is just a bit further away, and the effect is an annular eclipse, in which the sun makes a thin ring, or annulus, around the moon.
This total solar eclipse will be visible along a track that runs roughly northeast across the South Pacific, before turning southeast and crossing South America. The shadow will first touch the Earth 1,180 miles (1,900 kilometers) east of New Zealand's North Island, according to Eclipsewise.com. Observers in Rarotonga, in the Cook Islands, will see the sun rise on July 2 at 7:17 a.m. local time with the sun already partially eclipsed by the moon; maximal eclipse in Rarotonga is at about 7:52 a.m., when about half of the sun will be covered by the moon. The eclipse ends at 8:53 a.m.
Other islands that will get close to, but not quite, a total eclipse are Rikitea in French Polynesia, where the eclipse will start at 8:01 a.m. local time. Maximum eclipse there will be at 9:17 a.m., when the sun will be 96 percent obscured by the moon. The eclipse ends at 10:45 a.m. On Pitcairn Island, the eclipse starts at 9:07 a.m. local time and reaches a maximum at 10:27 a.m., when eclipse watchers will see 97 percent of the sun's light blocked. The eclipse ends at 11:58 a.m. local time there.
The eclipse track will run northeast until it reaches a point almost due north of Easter Island. The partial eclipse over Easter Island starts at 11:48 a.m. local time. Maximum eclipse is at 1:21 p.m., but the moon will cover less of the sun than in French Polynesia – about 75 percent. The eclipse ends at 2:54 p.m. local time.
The moon's shadow then turns southeast, and at 3:22 p.m. local time touches the city of La Serena in Chile. Totality starts at 4:38 p.m. and will last for 2 minutes and 18 seconds. The eclipse ends at 5:46 p.m.
The next stop will be Argentina, where the eclipse track moves through the provinces of San Juan, La Rioja, San Luis, Córdoba, Santa Fe and Buenos Aires. In the city of San Juan (capital of the eponymous province) the eclipse will start at 4:26 p.m. local time and totality will begin at 5:40 p.m. Totality will only last about 36 seconds. From Argentina, the sun will be setting as the eclipse ends; sunset in San Juan is at 6:42 p.m. while the eclipse ends at 6:46 p.m.
Further east, the town of Bragado will experience a 1 minute 12 seconds of totality. The eclipse starts at 4:33 p.m. local time and totality begins at 5:42 p.m. Sunset is at 6:01 p.m., and the eclipse ends 40 minutes later. So, the moon will still be blocking a substantial portion of the sun when it sets, making for some dramatic photo opportunities.
In Buenos Aires itself, the eclipse will begin at 4:36 p.m. It won't be an official total eclipse – the total coverage of the sun will be 99.72 percent. Maximum eclipse is at 5:44 p.m. and sunset is 10 minutes later.
What if you can't get to South America? You can still watch the eclipse remotely via a number of webcasts, and there will be plenty of planets and constellations to observe in lieu of an eclipse.
For Northern Hemisphere skywatchers in the wee hours of July 2, Venus will be visible at about 9 degrees above the horizon in New York City by about 4:30 a.m. local time, an hour before sunrise (at 5:29 a.m. local time). At 9 p.m., a half hour after sunset, lucky observers might be able to catch Mercury, though from New York it will only be about 7 degrees above the horizon by then, and the planet sets by 9:39 p.m. Mars will also be low in the western sky.
Jupiter, meanwhile, will be the constellation Ophiuchus, just above Scorpius. At 9 p.m. it will be about 20 degrees above the southeastern horizon, and observers in mid-northern latitudes will see the bright star Antares just to the right of the planet. With a clear horizon all of the Scorpius constellation will be visible until the wee hours of the morning. By 8:50 p.m. local time, Saturn, which is in Sagittarius, will rise as well, and it too will be visible in the southern sky for the rest of the night as it doesn't set until 6:05 a.m. local time.
You can find out exactly when the sun, moon and planets will be visible from any specific location using timeanddate.com's visible planets calculator.
Leo and Virgo will both be high in the eastern sky in the evening, and by 10 p.m. local time Lyra, Cygnus and Aquila will be high enough that the whole Summer Triangle asterism will be visible. The Summer Triangle consists of Vega (Alpha Lyrae), Deneb (Alpha Cygni) and Altair (Alpha Aquilae). By midnight all three are near the zenith and offer good views of the Milky Way from a dark-sky site.
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