NASA/JPL | What’s Up for March 2017: Red Star Aldebaran, Planetary Crescents
On March 4 the first quarter moon passes between Earth and the star Aldebaran, temporarily blocking our view of the star. This is called an occultation. The occultation begins and concludes at different times, depending on where you are when you view it.
The event should be easy to see from most of the U.S., Mexico, most of Central America, the Western Caribbean and Bermuda. Observers along a narrow path from Vancouver, British Columbia, to Hartford, Connecticut, will see the moon “graze” the star. The star will disappear and reappear repeatedly as hills and valleys on the moon alternately obscure and reveal it.
As seen from Earth, both Mercury and Venus have phases like our moon. That’s because they circle the sun inside Earth’s orbit. Planets that orbit between Earth and the sun are known as inner or inferior planets.
Inferior planets can never be at “opposition,” which is when the planet and the sun are on opposite sides of Earth.
But inferior planets can be at “conjunction,” which is when a planet, the sun and Earth are all in a straight line. Conjunction can happen once when the planet is on the opposite side of the sun from Earth and again when it’s on the same side of the sun as Earth. When a planet is on the opposite side of the sun from Earth, we say it is at “superior conjunction.” As the planet moves out from behind the sun and gets closer to Earth, we see less and less of the lit side. We see phases, similar to our moon’s phases.
Mercury is at superior conjunction on March 6. A few weeks later, the planet emerges from behind the sun and we can once again observe it. By the end of March we’ll see a last-quarter Mercury. On April 20 Mercury reaches “inferior conjunction.”
Brilliant Venus is also racing toward its own inferior conjunction on March 25. Watch its crescent get thinner and thinner as the planet’s size appears larger and larger, because it is getting closer to Earth.
Finally, look for Jupiter to rise in the East. It will be visible all month long from late evening until dawn.
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