Starting in the southern sky after sunset on the evening of July 20, the growing moon is positioned three degrees above the bright Jupiter. The two objects will cross the sky together until Jupiter departs at 1
Credit: Starry Night Software
On Friday, the 49th anniversary of one of mankind's greatest achievements is committed: Apollo 11 the first moon landing. Astronomer Neil Armstrong set foot on the lunar surface on July 20, 1969, at 10:56 pm Eastern Time, when 600 million people watched on television worldwide, and said, "This is a small step for humans … a giant leap for humanity. " If you were alive then, you've undoubtedly seen or heard radio coverage of this amazing event.
And if you had gone out that evening and looked at the sky, you would have seen the moon appear as a broad crescent, 35 percent illuminated by the sun. Almost a dozen degrees to the right you would have seen a very bright, silvery-white object that imitates a star but does not wink – instead, with a steady glow. That would have been the planet Jupiter.
Now, rewind 49 years to the present. On Friday night (July 20), assuming your sky is reasonably clear, you can see the same two celestial objects that were so prominent in the night sky almost half a century ago: the moon and the planet Jupiter. [Exploring the Apollo Moon Missions Using Mobile Apps]
About an hour after sunset, the striking sky duo can be seen in the southwestern sky, about halfway up the horizon to the point directly above it (called Zenith). The moon, which is only one day after the first quarter phase – 63 percent illuminated by the sun – will be just above Jupiter at a distance of about 3.5 degrees.
As we have already mentioned, your clenched fist measures about 10 degrees at arm's length, so the distance between Moon and Jupiter will be about one third of the fist.
When the moon is at or shortly after the first quarter-phase, as it will be on Friday, we get the best views of the lunar landscape along the sunrise-sunset line or the terminator. Around those times when the moon is half-lighted or half moon-shaped, these features, which are close to the terminator, stand out in sharp, clear relief. With a telescope with small optical power (20x to 40x magnification) or even with good binoculars we can then see a wealth of details on the lunar surface.
In a telescope, Jupiter is also a major attraction, best seen in the early evening when it is still high and its image is reasonably quiet. And his four bright moons are always playing. They appear like little stars, though two of them are really bigger than our own moon. You can watch them changing their positions from hour to hour and from night to night.
If you look at Jupiter on a Friday night with a small telescope or even a pair of binoculars, you will see at least three and possibly all four of these large satellites. The number depends on where you are and when you are looking. In the eastern US, as soon as it gets dark, you see two moons flanking Jupiter on both sides: Io and Ganymede on one side and Europe and Callisto on the other.
At 11:06 EDT, Ganymede will disappear from view as it is darkened by Jupiter's shadow. This moon will gradually reappear, starting at 12:52 EDT (9:52 am Pacific Time), with all four satellites in sight again. But only an hour later, Europe will disappear for a few hours as it passes behind Jupiter's disk.
So, on the Jubilee Night of the First Moon Landing, as you enjoy the sight of Jupiter near the Moon, remember that there are up to four other moons visible with little optical help.
And if it is cloudy that night? Well, I apollo-gize.
Joe Rao is a lecturer and guest lecturer at the New York Hayden Planetarium. He writes about astronomy for Natural History Magazine, the Farmers Almanac, and other publications, and he's also a meteorologist in front of the camera for Verizon FiOS1 News in New York's Lower Hudson Valley. Follow us @Spacedotcom Facebook and Google+. Original article on Space.com