Moon Hides Hyades, Occults Aldebaran Friday

After a late-night ramble through the Hyades cluster, the waning gibbous Moon will cover up the bright star Aldebaran for observers across North America Friday morning. 


Los Angeles astrophotographer Michael Stecker captured this scene moments before the April 10, 1997, occultation of Aldebaran by the waxing crescent Moon.

After getting eclipsed by Earth's shadow last week, it's the Moon's turn to do the covering. Late Thursday night, October 1, it will inch across the Hyades star cluster, occulting several moderately bright members. The farther north you live, the more stars the Moon will blank out.

And that's just the warm-up act. Nine hours later, on Friday morning the 2nd, the Moon exits the cluster in grand style by occulting the +0.9 magnitude star Aldebaran. Skywatchers in the far western U.S., western Canada, and Alaska will see the occultation in morning twilight, while the rest of us can catch it after sunrise. A stellar way to start a morning!

Don't let the daytime sky scare you away. Although Aldebaran won't be visible with the unaided eye from eastern regions, a small telescope should show it right alongside the bright lunar limb. The only requirement: a deep blue, haze-free sky. Fortunately, the Sun will still be relatively low in the east and far from the Moon at the time of occultation, so glare won't be an issue.

Footprint of disappearance

The viewing zone for Friday morning's occultation of Aldebaran by the Moon. A white outline shows where the occultation is visible at night, blue for twilight and dotted red for daylight. Alaskans will see it in a dark sky; observers in the coastal states and coastal provinces in morning twilight.
Occult 4.0

If you've never seen a star in full daylight, the Aldebaran occultation presents a unique opportunity. Find the Moon, point your telescope at it, and use the charts below to get oriented. You just might catch a glimmering orange point of light minutes before it disappears in an instant behind the Moon's bright western limb.

I once saw Sirius through a telescope around 9 a.m., so I'm really looking forward to testing my observing chops on Aldebaran. Daylight star-searching is a bit of a sport, like young Moon spotting or finding a planet just after solar conjunction. The challenge stretches and deepens our observing abilities and offers a new perspective on familiar objects.

So let's do this thing.

Near miss

Facing east at 12:10 a.m. October 2, 2015 from Minneapolis, Minnesota, the Moon is on the verge of occulting Gamma Tauri. During its slow crawl toward Aldebaran overnight, a variety of fainter Hyades stars will be covered. All occultations during the event occur at the Moon's bright limb; stars will reappear at the trailing dark limb. In this case, Gamma pops back into view about 12:18 a.m.

From about Minneapolis (latitude 45°) north, Gamma Tauri, the 3.6-magnitude star at the junction of two halves of the Hyades "V", will snap out of view behind the bright lunar limb shortly after midnight CDT (1:00 a.m. EDT, 11:00 p.m. MDT, and 10:00 p.m. PDT).

Blink of an eye - gone!

Edmonton, Alberta residents can watch Theta-1 disappear behind the Moon around 3:15 a.m. MDT Friday morning.
Source: Stellarium

About 4 hours later, Canadian observers living north of latitude 53° north can watch the Moon cover the attractive little pair of stars θ1-θ2 Tauri (magnitudes +3.8 and +3.4). Edmonton, Alberta has a great view of Theta-1's disappearance around 3:15 a.m. MDT; to see them both occulted, you'll need to head up to the Yellowknife in the Northwest Territories at 62° north. Bring a coat. Friday's high temperature will just graze the freezing mark.

The BIG event occurs around 8:45-9:00 a.m. CDT (10:00 a.m. EDT, 8:00 a.m. MDT and 6:45 a.m. for the Far West) Friday morning. The Moon's altitude varies widely across the occultation zone, from 18° for Boston to 60° for Los Angeles, which is located just a hair inside the zone's southern border.

South of L.A., roughly along the U.S.-Mexico border, observers will see a wonderful grazing occultation, where Aldebaran will pop in and out of view as it flirts with mountain peaks along the Moon's southern limb. Watching a bright star or planet graze the Moon's edge always gives me a visceral sensation seeing the night sky from the surface of another world.

A widely-viewable occultation

Four selected views from four different cities showing Aldebaran just a couple minutes being occulted. Bob King / Stellarium

I've selected several cities to show where along the lunar limb to look for Aldebaran as the Moon approaches it Friday morning. For a list of cities where the star's disappearance and reappearance occurs in deep twilight or night, check out this International Occultation Timing Association (IOTA) page. Times listed there are in Universal Time, or UT. Remember to subtract 4 hours for EDT, 5 for CDT, 6 for MDT, 7 for PDT and 8 for AKDT.

Here's a brief list of times for several major cities. Depending on Aldebaran's path, the occultation could last from just a few minutes to over an hour. The farther south you live, the more the Moon shifts north against the starry backdrop due to parallax; the opposite happens if you travel north.

* New York — Disappears at 10:01 a.m. EDT (Friday) with the Moon 20° high in the western sky
* Miami — Disappears at 10:32 a.m. EDT, Moon 16° high / Reappears at 10:56 a.m. EDT
* Chicago — Disappears at 8:53 a.m. CDT, Moon 31° high / Reappears at 9:55 a.m. CDT, Moon 20° high
* Denver — Disappears at 7:40 a.m. MDT, Moon 47° high / Reappears at 8:44 a.m. MDT, Moon 35° high
* Tucson — Disappears at 7:00 a.m. MST, Moon 50° high / Reappears at 7:24 a.m. MST, Moon 45° high
* Seattle — Disappears at 6:04 a.m. PDT, Moon 56° high / Reappears at 7:19 PDT, Moon 48° high

Meet our occultees

At 153 light-years distance, the Hyades is the nearest star cluster to the Solar System. Despite appearances, Aldebaran isn't a true member but a foreground star 65 light-years away.
Bob King

If you get skunked by weather, there's almost no end to these stellar blackouts. We're on a roll.The October 2nd occultation is one of a series of 49 occultations of Aldebaran by the moon that began in January this year and concludes on September 3, 2018. Some will be visible from one location and not another. The next, on October 29th, happens over Europe. North American observers will see the November 26th event before dawn at full Moon.

We'd love to hear from you on your results during the upcoming event. Please drop by and post a comment. Thanks!

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2 thoughts on “Moon Hides Hyades, Occults Aldebaran Friday


    What’s the problem in mentioning the UT of an astronomical event along with (A,B,C,D, …)DT’s! The globe extends beyond the North America and why do you think that there are no readers of S&T there?

    1. Bob KingBob King Post author

      The only reason I didn’t mention the UT of this event is that it’s visible primarily over the U.S. and Canada. Instead I gave conversions for each relative time zone including Alaska. If it were widely visible elsewhere I would have included UT. However, your point is still well taken, and I’ll include it in future articles. Thanks!

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