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On November 11 we're in for a rare treat, as the innermost planet, Mercury, passes directly in front of the Sun for a few hours.
This event is called a transit, and for Mercury they happen only about 13 times in a century. (Transits of Venus are even more rare.)
The event will last about five and a half hours, during which Mercury's path will take it right across the middle of the Sun's disk. For observers in the Eastern U.S., the transit begins after sunrise, meaning you'll be able to view the entire thing. For the central and western U.S., the transit begins before sunrise, but there's enough time left as the Sun climbs up the sky for you to catch a glimpse before Mercury makes its exit.
Now remember, you should never look directly at the Sun without proper protection, as it can permanently damage your eyes. If you have a pair eclipse shades, those are okay for viewing the Sun, but Mercury is so small in comparison that it can be next to impossible to see a transit without magnification.
You should never look directly at the Sun without proper protection, as it can permanently damage your eyes.
Your best bet is a telescope with a certified sun filter, but other options include solar projection boxes and sun funnels. Plus, NASA's Solar Dynamics Observatory spacecraft will be sharing near-realtime images during the transit. Whatever method you choose, be safe when observing the Sun!
The next Mercury transit that will be visible in the U.S. isn't until 2049! So if you're in the States, you might want to make the effort to catch this special celestial event.
A more frequent type of transit you might want to check out is the regular dimming and brightening of the "Demon Star," Algol.
Found in the constellation Perseus, Algol is actually two stars orbiting each other, and they're oriented nearly edge-on such that, from our perspective, the smaller star regularly passes in front of the larger, brighter one, causing it to dim for about 10 hours at a time. This happens like clockwork, every 2 days, 20 hours, 49 minutes. You can find tables of these "minima," as they're called, in lots of astronomy magazines and websites.
To observe Algol's eclipses, find the date and time of a predicted minimum and start observing maybe an hour or two before that time. Take a look about every half hour (binoculars are really useful for this). Over a few hours following the minimum, Algol will slowly brighten back to its normal state.
At its normal brightness, Algol appears about as bright as the nearby star Almach, while at its minimum, it dims to around the brightness of its neighbor Gorgonea Tertia. So these two stars provide a helpful way to compare Algol's brightness throughout the night as you observe.
This Month's Moon Phases
Here are the phases of the Moon for November.
Nov. 12: Mercury Transit
During a transit, planets (either Mercury or Venus) appear as dark spots that seem to crawl across the surface of the Sun. Transits are much rarer than eclipses of the Moon. A Mercury transit occurs, on average, once every seven years. As for Venus, its next solar transit will not occur for another century, on December 11, 2117.
Not all transits are the same because the planets cross the Sun at different places, sometimes just grazing the Sun's outer edges. The 2019 Mercury transit is an especially good one because it will have a degree of separation of just 0.02 degrees (76 arcseconds). This means Mercury’s center will pass very close to the Sun’s center, making it a real treat for observers. (Arcseconds, denoted with quotation marks, represent the degree of separation between the planet’s center and the Sun’s center. For reference, one degree is about the width of your little finger at arm’s length. There are 3,600 arcseconds in one degree.)
- View the transit in near real time from NASA's SDO mission
- Mercury transit info from NASA-JPL Education
- Night Sky Network observing events Nov. 11
- Night Sky Network transit viewing info & certificate
Algol dims like clockwork every couple of days when the fainter of its two orbiting companion stars passes in front of the brighter one. This eclipsing binary star forms the winking eye of the snake-haired Gorgon, Medusa, in the constellation Perseus. It's located about 90 light-years away, and varies in brightness between magnitude 2.1 at its brightest, and magnitude 3.4 at its minimum.
Referring to a star or planet in the night sky, magnitude is the apparent brightness of the object as seen from Earth. On the magnitude scale, more strongly negative values mean objects are brighter, and more positive values mean objects are dimmer. For example, the brightest star in the sky, Sirius, has a magnitude of -1.46.
What Unites Planet Transits and Variable Stars
To bring together both the Mercury transit and the dimming of Algol, these events are both relevant to the way NASA finds and studies planets orbiting other stars, or exoplanets. Scientists look for the telltale dip in a star's light — like the dimming of Algol but way more subtle — that occurs when a planet transits across the face of its star — just like the transit of Mercury.
Learn more about exoplanets at https://exoplanets.nasa.gov
The sky charts presented here show a field of view of 90 degrees — that is, an area on the sky that goes from the horizon up to the top of the sky (also called the zenith).
Sometime around Friday, November 1, 2019 (2019-Nov-01 08:03 UTC with 4 days, 10 hours, 36 minutes uncertainty), Near Earth Object (2014 UC192), between 51 and 113 meters (166 to 372 feet) in size, will pass the Earth at between 6.4 and 60.2 lunar distances (nominally 32.8), traveling at 12.88 kilometers per second (28,800 miles per hour).
On Friday evening, November 1, 2019, the planet Saturn will appear to the upper left of the waxing crescent Moon. Later on Saturday morning, for parts of New Zealand and the southern Atlantic Ocean, the Moon will pass in front of Saturn, blocking it from view.
Sunday morning, November 3, 2019, is the end of Daylight Savings Time (for those parts of the USA that go on Daylight Savings Time).
On Monday morning, November 4, 2019, the Moon will appear half-full as it reaches its first quarter at 5:23 AM EST.
Thursday morning, November 7, 2019, at 3:37 AM EST, the Moon will be at apogee, its farthest from the Earth for this orbit.
On Monday morning, Nov. 11, 2019, the planet Mercury will be passing between the Earth and the Sun as seen from the Earth, called inferior conjunction.
Planets that orbit inside of the orbit of Earth can have two types of conjunctions with the Sun, inferior (when passing between the Earth and the Sun) and superior (when passing on the far side of the Sun as seen from the Earth). Mercury will be shifting from the evening sky to the morning sky and will begin emerging from the glow of the dawn on the eastern horizon by mid-November (depending upon viewing conditions).
November 12: The Next Full Moon
The full Moon after next will be Tuesday morning, November 12, 2019, at 8:34 AM EST.