Cosmic Light Pollution
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"This is a good week to wake up early and see the planets," agrees astronomy professor George Lebo. "Mercury, Venus, Jupiter and Saturn are all emerging from the Sun's glare in the eastern morning sky, and they're about to form some outrageous groupings."
Above: Artist Duane Hilton's rendering of Venus, Saturn and the slender crescent Moon on July 17, 2001, when the three will gather together in the eastern pre-dawn sky.
The show begins on Friday the 13th -- a lucky day for stargazers -- and continues for a week with can't-miss highlights on July 15th, 17th and 18th.
Around 4:30 a.m. local time on Friday, July 13th, Venus, Saturn, and the red star Aldebaran will form a compact equilateral triangle hovering 25 degrees above the eastern horizon. How high is that? If you hold your clenched fist at arm's length it spans an angle about 10 degrees wide. So, you can find the celestial threesome about two and a half "fists" above the horizon.
The brightest member of the grouping, Venus, is so brilliant it's often mistaken for an airplane or a UFO. But if you stare at Venus for a few moments you'll see it doesn't blink, twinkle, or move abruptly like a spacecraft -- it really is a planet! Venus glares so because it's close to Earth and its global clouds reflect much of the sunlight that falls on them. Yellow-hued Saturn is 10 times wider than Venus, but 50 times dimmer in Earth's night sky because Saturn lies in the outer solar system. Aldebaran, even more distant at 71 light years, is a giant reddish-colored star 40 times wider than the Sun that could swallow 40 billion Venus-sized planets.
If you're a parent showing giant Aldebaran to your kids, you might wish to mention that the fiery-red eye of the constellation Taurus is also a far-out tourist destination. NASA's venerable Pioneer 10 spacecraft is headed in the general direction of Aldebaran -- and due to arrive in that part of the Galaxy two hundred thousand years from now.
Before sunrise on Sunday, July 15th, Venus and Saturn will have a close encounter of their own. The pair will be separated by just 0.7 degrees -- about the width of a pinky finger held at arm's length. It will be a spectacular sight with or without magnification. View the planets through a modest telescope and you'll see that their globes are both 17 arcseconds wide. Venus will appear as a bloated half-planet (like our Moon, Venus has phases), while Saturn with its rings tilted alluringly toward Earth will provoke exclamations of pleasure from first-time telescope viewers.
Left: The eastern sky before dawn on July 17th as viewed from mid-northern latitudes. Click to.
Dark-sky observers will see something that day that their city cousins won't: cradled in the arms of the crescent Moon will appear the ghostly outline of the full Moon, a dim glow that astronomers call "Earthshine." Earthshine is sunlight that bounces off our planet and then falls on the Moon, gently illuminating its night side. A crescent Moon with Earthshine is regarded as one of the most delicate and beautiful sights in the night sky.
Right: The eastern sky before dawn on July 18th as viewed from mid-northern latitudes. Click to.
Spotting Mercury on July 18th is good practice for July 19th, when sky watchers with an unobstructed horizon can see something truly extraordinary, but only if they know where to look. On that morning, even as the sky begins to glow with the rising Sun, Mercury and the whisker-thin crescent Moon will converge and seem to touch.
What a sight!
And what better way to begin the day? The coffee drinkers among us might still fire up the coffee pot after the Sun rises. But before dawn, you can't beat waking up with a dose of dazzling planets!
Editor's note: This story was written with northern hemisphere sky-watchers in mind, but the planets will put on a show in the southern hemisphere, too. If you live south of the equator, turn the star charts in this story upside down and keep an eye on the eastern sky before local dawn. The planets will be just as dazzling in your part of the world.
July 10, 2001
presented by ThursdaysClassroom.com
These lessons and activities for 6th to 12th grade classrooms are based on the Science@NASA news story "Morning Coffee and Planets"
- Discussion Questions: These lively questions might inspire your students to wake up before dawn. [lesson plan] [activity sheet]
- Hands Up!: One of the most useful tools for navigating the sky is right by your side -- your hands! In this activity students will explore the daytime horizon, measuring the angular size of features they see there. It's great preparation for a night of stargazing. [lesson plan] [activity sheet: for older kids or for younger kids] [A Handy Hand-out]
- Sky Orienteering: OK, so the planets are putting on a show...where should you look? This simple lesson introduces kids to the cardinal directions around their house so they'll know how to find the planets in mid-July. [lesson plan]
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Jupiter - Learn more about the biggest planet in our solar system.
Saturn - the second-largest planet orbiting the Sun is arguably the most beautiful. Even a small telescope reveals its enchanting rings.
Mercury - Fiery Mercury never strays very far from the Sun.
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