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Moon Will Hit the 'Bull's-Eye' in Stellar Eclipse Sunday

A stellar eclipse will be visible from nearly everywhere in the United States and much of southern Canada on April 10. Continue reading →

A stellar eclipse will be visible from nearly everywhere in the United States and much of southern Canada this Sunday (April 10). Even skywatchers in Hawaii will be able to see the eclipse, although it will not be visible from Alaska.

The waxing crescent moon, 15 percent illuminated by the sun, will pass in front of the star that marks the angry orange eye of the constellation Taurus, also known as the Bull.

That star is Aldebaran, the 13th brightest star in the sky and certainly one of the more colorful ones. This eclipse is known to astronomers as a lunar occultation. As the moon orbits the Earth, it appears, from our perspective, to move slowly toward the east relative to the stars, at roughly its own diameter per hour. A waxing moon always leads with its dark edge as it moves along its orbit against the starry background. [The Best Night Sky of April 2016 (Sky Maps)]

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However, there is a catch: Across most of its viewing range, the moon will be crossing in front of the star during the daytime.

Some skywatchers may think that this will preclude them from seeing the occultation, but that's not necessarily so. While you certainly will not be able to see it with your unaided eye, if you're looking just prior to when it vanishes behind the moon, a good pair of binoculars or a small telescope should allow you to pick out Aldebaran against the blue daytime sky.

Of course, your ability to see it will be strongly dependent on your local weather. If, for instance, the sky is hazy or if there are thin or high clouds passing across your line of sight as Aldebaran is about to duck out of sight behind the moon, you probably will not see it. In fact, your first hurdle would be to locate the moon itself. It will be located about 50 degrees to the east (left) of the sun. Your clenched fist held out at arm's length measures roughly 10 degrees, so look for the moon approximately "five fists" to the left of the sun.

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If the sky in your area is deep blue - which usually happens after the passage of a cold front or storm system accompanied by rain to "cleanse" the sky of any clouds or haze - you have a better chance of observing this skywatching event.

And if you do glimpse Aldebaran in your binoculars or telescope, keep in mind that it will disappear behind the moon's unilluminated portion first. In deep twilight or darkness, you would be able to see the dark part of the moon approach the star by virtue of earthshine - that dark portion would be dimly lit with a bluish-gray hue. But in the daytime, it's completely invisible, so the star will suddenly seem to "click off" as if somebody had flipped a switch.

This table provides a listing for a dozen selected cities in the United States and Canada and the times when Aldebaran will disappear, and later reappear, from behind the moon. All times are in local daylight time, except for Honolulu. (Hawaii does not observe daylight saving time.)

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If you live near or along the Atlantic Seaboard, the occultation will take place close to the time of sunset. In fact, from the northeastern United States, the time that Aldebaran is due to emerge back into view (along the moon's bright edge) will take place after sunset in a twilight sky,making it a bit easier to see. And from the Canadian Maritime Provinces, both the disappearance and reappearance will occur after sunset.

Check out this table which provides listings for six selected cities in the northeastern United States and eastern Canada, and the times when Aldebaran will disappear and later reappear (after sunset) from behind the moon. The local time of sunset is included. All times are in local daylight time.

For those who are a bit more technically inclined, here is a link to the International Occultation Timers Association (IOTA) web page, which provides a map showing the region of visibility of the occultation, along with a comprehensive listing of times for nearly 600 locations in the United States, Canada, Mexico and the Caribbean. All times are in Universal Time (UT).

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Of course, once darkness falls across all of North America on Sunday evening, skywatchers will readily see Aldebaran plainly shining to the lower right of the moon - the moon will have "run over" the star a short time earlier.

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A stellar eclipse will be visible from nearly everywhere in the United States and much of southern Canada on April 10. The crescent moon will "run over" the star Aldebaran in the constellation Taurus.

SOHO, or the Solar and Heliospheric Observatory, just celebrated 20 years in space with a main goal of learning more about the sun's activity. The spacecraft has seen some neat things, including comets, planets and unexpected solar activity. Here,

based on a video recently produced by NASA

, are some of the more unusual things SOHO has witnessed.

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Because the planets periodically pass nearby the sun from SOHO's perspective, the spacecraft can see them in its viewfinder. They look a little overexposed because they are so bright (compared with the wispy clouds of plasma in the solar wind), but they still provide a unique view of our neighbors in space. This congregation pictured here took place in 2000 and includes Venus, Mercury, Jupiter and Saturn -- as well as a famous star cluster called the Pleiades.

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"Such congregations of planets are rare events, and they cannot be seen from the ground when close in the sky to the dazzling sun. But the LASCO C3 instrument on SOHO uses a mask to blot out direct sunlight, and it has a wide enough field of view (15 degrees) to take in the four planets in the same picture," the SOHO website wrote at the time.

Is that a snowstorm in space? No, it's actually energetic particles hitting the viewfinder of SOHO. These are caused by fast-moving protons coming from the sun, and you can see the view can get rather ... intense at times. This particular image happened in January 2012 during one of the strongest radiation storms since 2005. These storms are more frequent when the sun reaches its maximum, which last happened in roughly 2013-14.

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NASA is interested in these storms not only because they are awesome to watch, but also to monitor their effects on Earth. Solar storms can cause blackouts in radio communications, satellites and power lines if they are strong enough. Part of SOHO's role is to provide better predictions of the sun's activity and how Earth's environment will react to it.

SOHO was not designed to look for comets, but the sun happens to be a great place to look for them. The massive gravitational attraction of the star periodically pulls comets very close to its vicinity. Most of these so-called "sungrazers" do not survive their closest approach, called perihelion, but at least we can see their remains in pictures. Comet count so far? More than 3,000.

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This is a particularly spectacular example from 2003, when Comet NEAT made a close approach while the sun was quite active. "The LASCO pictures and movies of this comet are quite out of the ordinary, with a sizeable tail and a very bright (saturated) comet nucleus," the SOHO website wrote at the time. "We even got a nice coronal mass ejection (CME) off the west limb close to perihelion time, putting the icing on the cake!"

The sun has a fairly routine cycle of activity that lasts roughly 11 years between maximum and maximum. But it's not always a clear shot as to when you're going to see a big flare. In 2003, the sun became extremely active long after its expected peak in 2001, which shows us how much more scientists have to learn.

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"Some of the most intense activity that we saw was in the fall of 2003," said Joe Gurman, the U.S. project scientist for SOHO, in a NASA video posted on Twitter. "This was bit of a surprise as it was a couple of years after the maximum of the 11 year cycle."

Image: A spectacular coronal mass ejection erupts off the sun in 2003. At left is a planet.

This was a surprise discovery for SOHO. The spacecraft's observations reveal a sort of pulse that takes place during coronal mass ejections -- those particle-laden explosions from the sun. It's a neat find because it shows us more about how the inner workings of the sun create the activity that you can see in pictures of CMEs.

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"Think of an underwater explosion: you will get water forced upwards as a great spray, but you will also get a wave on the surface of the water that travels outwards from the explosion site," SOHO wrote on an educational website. "The waves on the sun are similar, although in this case the explosion occurs just above the surface rather than below it."

Image: A 2008 solar explosion caught up close by the TRACE spacecraft after first being spotted by SOHO.