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For the next couple of weeks, go out in cloudless skies fifteen minutes after sunset, and for the next forty-five minutes look west and just above the horizon to view a rare event. The bright object is the planet Venus. At 'one o'clock', two-fingers thickness at arm's length to the right, the dimmer object is planet Mercury, the planet closest to the sun at 88 million miles.

99% of the human race has never purposely viewed Mercury as it rarely gets very far from the horizon.  For people living away from the equator with longer twilight, it is lost in the glow.

Get out the glass and binoculars will reveal two round objects, not point-of-light stars. Venus may have a slight yellow tint. Mercury is waning like our moon and is slowing shrinking to less than full.

For the best of reasons this is the rarest of events, only duplicated by total solar eclipes. 

As you look west, place yourself in time and spce. You are standing on the Earth  near a north-south line where you are slipping into darkness as the planet rotates. Imagine the proximate location of the sun below the hoizon. Earth, Venus and Mercury are lined up. Earth-size Venus is obviously closer than moon-size Mercury and it is easy to imagine this moment their curving orbit around the sun.

It's not a flat two-dimesional sky for you now. That's the point.

It's a a three dimensional sky. Earth, Venus and Mercury are chasing each other in their orbits. Watch night-to-night and their positions will change amplifying the effect.

You might not know that both Venus and Mercury show phases similar to our moon.

But wait! There's more!!

At sunset, March 18, our moon will be seen in between the two.

Although a lifelong sky-watcher that subscribes to Astronomy, I am unaware of the last time this all lined up for we viewers on Earth.

While I suspect this event will be also noted on news Internet sites the event day, I will remind every one March 18.

Do. Not. Miss.


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