by Mara Johnson-Groh for GSFC News
Greenbelt MD (SPX) Mar 21, 2017
The movements of the stars and the planets have almost no impact on life on Earth, but a few times per year, the alignment of celestial bodies has a visible effect. One of these geometric events - the spring equinox - is just around the corner, and another major alignment - a total solar eclipse - will be visible across America on Aug. 21, with a fleet of NASA satellites viewing it from space and providing images of the event. To understand the basics of celestial alignments, here is information on equinoxes, solstices, full moons, eclipses and transits:
On these days, there are almost equal amounts of day and night, which is where the word equinox - meaning "equal night" in Latin - comes from. The equinox marks the onset of spring with a transition from shorter to longer days for half the planet, along with more direct sunlight as the sun rises higher above the horizon. In 2017, in the Northern Hemisphere, the spring equinox occurs on March 20. Six months later, fall begins with the autumnal equinox on Sept. 22.
Full Moon and New Moon
The time between full moons is about four weeks - 29.5 days to be exact. Halfway between full moons, the order of the three bodies reverses and the moon lies between the sun and Earth. During this time, we can't see the moon reflecting the sun's light, so it appears dark. This is the new moon.
As mentioned above, the plane of the moon's orbit around Earth isn't precisely aligned with the plane of the Earth's orbit around the sun so, from Earth's view, on most months we see the moon passing above or below the sun. A solar eclipse happens only on those new moons where the alignment of all three bodies are in a perfectly straight line.
When the moon blocks all of the sun's light, a total eclipse occurs, but when the moon is farther away - making it appear smaller from our vantage point on Earth - it blocks most, but not all of the sun. This is called an annular eclipse, which leaves a ring of the sun's light still visible from around the moon. This alignment usually occurs every year or two, but is only visible from a small area on Earth.
On Aug. 21, a total solar eclipse will move across America. While lunar eclipses are visible from entire hemispheres of Earth, a total solar eclipse is visible only from a narrow band along Earth's surface. Since this eclipse will take about an hour and a half to cross an entire continent, it is particularly important scientifically, as it allows observations from many places for an extended duration of time. NASA has funded 11 projects to take advantage of the 2017 eclipse and study its effects on Earth as well as study the sun's atmosphere.
But such transits also offer a way to spot new distant worlds. When a planet in another star system passes in front of its host star, it blocks some of the star's light - making it appear slightly dimmer. By watching for changes in the amount of light over time, we can deduce the presence of a planet. This method has been used to discover thousands of planets, including the TRAPPIST-1 planets.
Washington (UPI) Feb 25, 2017
The sky above parts of Earth's Southern Hemisphere will be illuminated Sunday in a "ring of fire" during the first solar eclipse of 2017, NASA said. The annular eclipse will be mainly visible near parts of the Southern Hemisphere, including Chile, Argentina and Angola. Unlike a total solar eclipse, an annular eclipse happens when the moon is too far from the Earth to obscure the sun com ... read more
Sun and Earth at NASA
Solar Science News at SpaceDaily
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