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Moon hides bright Aldebaran tonight

The moon was to the west of Aldebaran yesterday, on January 18.

The moon was to the west of Aldebaran yesterday, on January 18.

Occultation map above via IOTA (International Occultation Timing Organization). All places within the solid white lines can see the occultation of Aldebaran sometime during the nighttime hours on January 19-20, 2016.

Tonight – January 19, 2016 – the waxing gibbous moon passes in front of – or occults – Aldebaran, an ex-pole star and the brightest star in the constellation Taurus the Bull. Will you see Aldebaran near the moon tonight? Not if you’re looking for it when the occultation is in progress. At that time, Aldebaran will be behind the moon for about an hour. For an idea of Aldebaran’s whereabouts, check the chart at right, which is yesterday’s chart (January 18, 2016).

What do you want to see here? You want to see the exact moment when Aldebaran disappears behind the moon. The time of that special moment is a bit different for all of us in the occultation path. The good news is that Aldebaran will disappear behind the moon’s dark side and reappear on its illuminated side. So the disappearance will be easier to spot than the reappearance.

A telescope will show it best, but also try watching in binoculars, if you have them. Although the moon’s glare will be bright, you might also be able to glimpse something of this event with the unaided eye.

Here is something very important. Many of the times listed on the link below are in Universal Time (UT). To convert Universal Time (UT) to your local time:

Atlantic Standard Time = UT – 4 hours
Eastern Standard Time = UT – 5 hours
Central Standard Time = UT – 6 hours
Mountain Standard Time = UT – 7 hours
Pacific Standard Time = UT – 8 hours.

Click here for occultation times for your location in Universal Time (UT). Or scroll down to the chart below for the local times of the occultation for 30 North American cities.

We also give the occultation times for four U.S. cities in local time, below:

New York, NY Eastern Standard Time (EST)
Occultation begins: 9:31 p.m. EST
Occultation ends: 10:43 p.m. EST

Kansas City, MO Central Standard Time (CST)
Occultation begins: 7:47 p.m. CST
Occultation ends: 9:03 p.m. CST

Denver, CO Mountain Standard Time (MST)
Occultation begins: 6:29 p.m. MST
Occultation ends: 7:46 p.m. MST

Los Angeles, CA Pacific Standard Time (PST)
Occultation begins: 5:03 p.m. PST
Occultation ends: 6:14 p.m. PST

Find out more: Occultation of Aldebaran on January 19-20

View larger | Occultation of Aldebaran on Tuesday, January 19, 2016. Chart by Curt Renz, shared by Stephen Aman at EarthSky Facebook..

View larger | Occultation of Aldebaran on Tuesday, January 19, 2016. Chart by Curt Renz, shared by Stephen Aman at EarthSky Facebook..

Aldebaran, the ex-pole star

Although Aldebaran now reigns as a star of the Zodiac, did you know that Aldebaran is a former pole star?

It’s true, and it’s a fascinating story.

Many people know that Polaris is the present-day North Star, but few know that Aldebaran reigned as the North Star some 450,000 years ago.

What’s more, Aldebaran appeared several times brighter in the sky then than it does now. Plus – 450,000 years ago – Aldebaran shone very close to the very bright star Capella on the sky’s dome. In that distant past, these two brilliant stars served as a double pole star in the astronomical year -447,890 (447,891 BCE).

At this point, we should probably insert a note about astronomical dating. In ancient times, there was no zero year, so the year AD 1 followed the year 1 BC. However, present-day astronomical calculating is made simpler by equating the astronomical year 0 with the year 1 BC. Thus, the astronomical year -1 corresponds to 2 BC and the astronomical year -2 corresponds to 3 BC. And so on . . .

But back to Aldebaran and Capella as dual pole stars. The identity of the pole star shifts over time, due to the 26,000-year cycle of precession. To read more about that, click into this article about Thuban, another former pole star.

Still, how can it be, you might wonder, that the stars Aldebaran and Capella were once so near each other on the sky’s dome? They’re not especially close together now. Aren’t the stars essentially fixed relative to one another? The answer is that, yes, on the scale of human lifespans, the stars are essentially fixed. But the stars are actually moving through space, in orbit around the center of the galaxy. In our solar system, galaxy and universe … everything is always moving. So the sky looked different hundreds of thousands of years ago than it does today.

Here’s another kind of motion you might pay attention to tonight. It’s the spin of the Earth you’re standing on, which causes the moon and Aldebaran to shift westward throughout the night. And yet another motion … the moon is also going eastward relative to the fixed stars (which we now know aren’t really fixed), because of the moon’s orbit around Earth.

In other words, tonight and for the next several days, if you look carefully over a period of hours (or from one night to the next), you can watch the moon traveling eastward in front of the constellation Taurus.

Aldebaran is a noted star of the Zodiac – the band of stars in front of which the sun, moon and planets make their rounds.

But Aldebaran wasn’t always a star of the Zodiac. Some 450,000 years ago, Aldebaran and Capella teamed up together to serve as Earth’s double north pole star!*

*Source: Page 363 of Mathematical Astronomy Morsels V by Jean Meeus

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This illustration shows the view from Seen from present-day Arizona in 447,000 B.C., when Aldebaran and Capella served as double pole stars.  Illustration via Carina Software and Instruments

This illustration shows the view from Seen from present-day Arizona in 447,000 B.C., when Aldebaran and Capella served as double pole stars. Illustration via Carina Software and Instruments

Bottom line: The moon occults – or covers – the bright star Aldebaran on January 19, 2016. We give occultation times for four major U.S. cities and links to timings elsewhere. Plus we tell the story of Aldebaran as the pole star some 450,000 years ago, when it had the company of a fellow bright pole star, Capella.

Click here for occultation times for your location in Universal Time (UT).

Bruce McClure

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