On the night of March 4th, all you'll need are your eyes to watch the Moon occult Aldebaran. Better yet, place yourself on the graze line.
It can't get much better than this: an occultation of the brightest star the Moon ever crosses, visible across most of the U.S. on a Saturday evening, with the Moon barely first-quarter (46% sunlit), and the star's dark-side disappearance visible without optical aid.
Moreover, along a narrow path skirting the U.S.-Canadian border, passing the Toronto area and then the U.S. Northeast, a spectacular grazing occultation will occur that, at least in the populous eastern part of the path, will be nearly as good as last July's well-observed Aldebaran graze in the southern plains.
The graze provides another opportunity to detect the angular size of a star other than the Sun. But this time, the Moon will be brighter with the graze events occurring closer to the northern cusp, so binoculars are recommended to see the gradual and partial occultation events that will reveal the star's angular size.
The occultation will also be visible at night throughout Mexico, most of Central America, the western Caribbean Sea, and Bermuda. The occultation will occur in daylight in Hawai'i (disappearance at 3:33 p.m. HST in Honolulu).
The southern-limit graze will occur on the Moon's sunlit limb 6° inside the southern cusp, as seen from a narrow path crossing Costa Rica, Panama, and Colombia. A telescope is needed to see or record the star's reappearance even at night, because this will occur on the Moon's sunlit edge.
Event times for selected cities are below. More precise times, and additional details including the altitudes of the Sun and the Moon, are listed for over 1,000 cities and towns on this predictions page.
Los Angeles, disappearance 7:08 p.m. PST, reappearance 8:27 p.m. PST; Seattle, d. 7:21 p.m., r. 7:50 p.m. PST; Denver, d. 8:33 p.m., r. 9:33 p.m. MST; Chicago, d. 9:57 p.m., r. 10:33 p.m. CST; Austin, d. 9:44 p.m., r. 10:52 p.m. CST; Atlanta, d. 10:56 p.m., r. 11:52 p.m. EST; Miami, d. 11:03 p.m., r. 12:02 a.m. EST; Pittsburgh, d. 11:03 p.m., r. 11:36 p.m. EST; Washington, DC, d. 11:04 p.m., r. 11:39 p.m. EST; New York, d. 11:10 p.m. EST, r. 11:31 p.m. EST; Miami, d. 11:03 p.m., r. 12:02 a.m.
The most interesting views will be from a strip of land only a few hundred yards wide along the occultation's northern limit. You can examine the precise graze path to street-level accuracy using the interactive Google Maps links in the special page the International Occultation Timing Association (IOTA) has set up for this event, also given at the end of the article.
Viewed from this narrow zone, the giant star should disappear and reappear multiple times as hills and valleys along the Moon's northern limb cover and expose it. Most of these events will appear non-instantaneous, even taking up to a full second, due to Aldebaran's large angular diameter: 20 milliarcseconds, or 40 meters at the Moon's distance.
We can now predict these narrow zones very accurately, thanks to the laser altimeters on recent lunar orbiting spacecraft. These mapped all of the Moon's topography to high accuracy. So now, you can choose your viewing location to within a few tens of meters in order to maximize the number of contact events you can see or record.
The angle of "central graze" changes along the path, causing the lunar profile to also change. South of Vancouver, where the graze happens only a mile north of the U.S. border, the star skims the sunlit limb. In eastern North Dakota most of the graze will be on the Moon's dark side edge although the high mountains just after central graze will likely be sunlit. As far east as Rhode Island, the Moon will be only 13° above the western horizon.
Occultation timings are not as compelling scientifically as they used to be. However, video recordings of grazes are so precise that small corrections to the spacecraft lunar-profile data, and to star positions, are still being found. The greatest value of lunar occultations is now in discovering and resolving very close double stars. But we know that Aldebaran has no close companion.
Information about IOTA expeditions to observe the graze will be posted on the graze web page noted below. Plans will change in response to weather updates.
Four hours before Aldebaran disappears behind the Moon's dark limb, the 5.0-magnitude Hyades star 75 Tauri will do the same for Atlantic States south of southern Pennsylvania.
Two hours before Aldebaran the Moon will occult some brighter Hyades stars, including 4.8-magnitude ZC 677 and the pair Theta1 and Theta2 Tauri, magnitudes 3.8 and 3.4, respectively. Detailed predictions for them are in the predictions link below.
• We at IOTA have set up a special webpage for the Aldebaran graze of March 4-5 (March 5th UT), with interactive Google Maps and much other information: occultations.org/aldebaran/2017march.
• Detailed predictions are available for more than 1,000 locations. Note that the page displays three long tables — for the disappearance, the reappearance, and the locations of cities — with less-than-obvious divisions between them.