Archive for March 2, 2017

03/02/2017 – Ephemeris – Saturday night’s occultation of the bright star Aldebaran

March 2, 2017 Comments off

Note:  this program is for a very specific location in the northern lower peninsula of Michigan.  The occultation of Aldebaran is visible from most of the United States except Alaska and Central America.  For predictions for your locations you can use a planetarium type program like Stellarium, Cartes du Ciel (Sky Charts), which can be downloaded free from the right column on this blog page, or the commercial planetarium program of your choice.  Make sure the program is zoomed in so the Moon is actual size, and set for your location, and play around with the time.

Occultation map

Path of the occultation of Aldebaran for March 4-5, 2017. Note where the top edge of the path goes. Right through northern Michigan.

On to the program:

Ephemeris for Thursday, March 2nd.  The Sun will rise at 7:17.  It’ll be up for 11 hours and 14 minutes, setting at 6:32.  The Moon, 3 days before first quarter, will set at 11:26 this evening.

Saturday night just after 11 p.m. the upper right edge of the Moon will just cover the bright star Aldebaran,  the angry red eye of Taurus the bull.  That is for some of us.  For those of us south of a line from Leland to just south of Mancelona and off across the state the Moon will occult or hide the star.  For those north of that line Aldebaran will just miss the Moon.  Start looking at 11 p.m. or so.  The center of the occultation as it I called is about 11:13 p.m.  The farther south of that line you are the longer the occultation will last.  At 11 p.m. the star will be just off the upper right edge of the Moon.

Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.


Occultation Graze

The north limit of the occultation zone as it passes through the Grand Traverse Region. Locations north of the green line will not see an occultation, Locations south of that line will see the occultation. Map credit Google Earth.

The file to load for this occultation map overlay is:

Occultation of Aldebaran

The point of the mid occultation from the NMC Observatory. Note that in reality Aldebaran would be completely covered by the Moon. This is the Moon and Aldebaran as they would be seen in the west at that time. Created using Cartes du Ciel (Sky Charts).

The occultation of Aldebaran as seen from three sample locations

The occultation of Aldebaran as seen from three sample locations in the IPR listening area. Credit IOTA’s Occult4 program.  The Moon is shown in equatorial orientation.

Here’s the legend for the labels:

# H M S (Mag)

#: 1 First contact, Aldebaran disappears

2 Middle of the occultation

3 Last contact, Aldebaran reappears

H: hour UT, 4 = 11 p.m. EST

M: Minute

S: Second

Mag:  Magnitude of the star, 0.9 (First magnitude star)

An article I wrote about this occultation in the March 2017 issue of  the Grand Traverse Astronomical Society newsletter The Stellar Sentinel:

The Grazing Occultation of Aldebaran, March 4th

Late Saturday night March 4th the Moon will pass in front of, or not the bright star Aldebaran.  The “or not” depends on where you are.

The event is called an occultation.  The word comes from occult, which, despite its baggage, simply means hidden.  When one celestial body moves in front of another and completely covers it an occultation occurs.  In actuality a total solar eclipse is an occultation.  However a lunar eclipse is still an eclipse as we see it, but an occultation as the Sun sees it.

Above there’s a map of the Leelanau and Old Mission peninsulas and a bit of the Lower Peninsula of Michigan with a line drawn across it from north of Leland to just south of Mancelona.  That is the calculated northern limit of the occultation.  Observers within a mile of so of that line could see Aldebaran winking in and out as it’s light encounters mountains and passes through valleys at the northern limb of the Moon.

Even though we’ve landed humans on the Moon and have mapping satellites orbiting it, there is still a need to add more data to the accumulated knowledge we have of the surface and position of the Moon. Observers in a coordinated effort can be set up perpendicular to the graze line and using coordinated time signals produce a map of the edge of the Moon.

Graze results

Plot of the results of a grazing occultation of Delta Cancri on May 9-10, 1981. Each horizontal line is one observer’s timings. From “An Introduction to Grazing Occultations” at