Crescents dazzle after dusk in March night skies

What’s up in Oak Bay's night skies for for March 2017?

What’s Up for March 2017?

The moon hides red star Aldebaran and crescents dazzle after dusk.

On March 4 the first quarter moon passes between Earth and the first-magnitude star Aldebaran, temporarily blocking our view of the star. This is called an occultation.

The occultation begins at 8:04 p.m. PST and concludes at 8:39 p.m.

The event should be easy to see from most of the U.S, Mexico, central America, the Western Caribbean and Bermuda …  and from here in at Cattle Point DARK SKY Star Park. Here you’ll be able to watch the red star Aldebaran just disappear behind the unlit side of the moon and reappear on the lit side, just barely sliding behind the moon’s northern limb.

Observers here in B.C. along a narrow path from Ladysmith on Vancouver Island through Vancouver to Hartford, Connecticut will see the star “graze” the moon. It will disappear and reappear as the hills and valleys on the moon alternately obscure and reveal it.

You can get more specific timing information from the International Occultation Timing Association at occultations.org/aldebaran/2017march/

March starts off with the crescent moon and Venus unmistakably similar in appearance.

As seen from Earth, both Venus and Mercury 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 a planet and the sun are on opposite sides of Earth. Only planets that orbit farther from the sun than Earth does can be at opposition.

But inferior planets can be at “conjunction,” which is when Earth, a planet and the sun are all in a straight line.

Conjunction can happen in two situations: once when a 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 – so that the sun blocks our view of it — we say it is at superior conjunction. If we could see the planet exactly at superior conjunction, the side facing Earth would be fully lit by the sun, like a tiny full moon.

As the planet moves around its orbit and gets closer to Earth, we see less and less of the lit side. We see phases, similar to our moon’s phases.

The first recorded observations of the phases of both Venus and the moon were telescopic observations by Galileo in 1609 and 1610.

Mercury is at superior conjunction on March 6. About a week later, the planet emerges from behind the sun and we can once again observe it.

We see Mercury’s phases change quickly as it races around the sun. We’ll see a quarter-Mercury by the end of March.

By April 20 it reaches inferior conjunction. The unlit side is directly between the Earth and the sun, and Mercury is lost in the sun’s glare. A few days later a slender crescent re-appears.

Brilliant Venus is also racing toward its own inferior conjunction on March 25. As March progresses, watch its crescent get thinner and thinner, as the planet’s size appears larger and larger because it is getting closer to Earth.

Venus will dive deeply in altitude, getting closer to the horizon as it catches up to the sun’s position in our sky.

Finally, look for Jupiter to rise in the east over Mount Baker. It will be visible all month from late evening until dawn.

Catch up on solar system missions and all of NASA’s missions at nasa.gov.

The RASCals of Cattle Point meet at Fairfield Community Centre Mondays at 7:30 p.m. Learn more at facebook.com/groups/VictoriaRASCals/

Dark Skies to all friends of Cattle Point Star Park.

Written by Bill Smith and the RASCals of Cattle Point, volunteers at Cattle Point DARK SKY Urban Star Park, from the transcript of What’s Up in March 2017 by NASA announcer and astronomer Jane Houston Jones with specific permission for localization to Cattle Point and the Oak Bay News. Subscribe to her weekly blog at solarsystem.nasa.gov/news/category/10things