RAMADAN MOON WATCH JANUARY 9: THE BRIGHTEST STAR
CAN IMPROVE YOUR CHANCES OF SPOTTING THE BEAUTIFUL CRESCENT
From: Abrams Planetarium, Michigan State University
By a wonderful coincidence, Sirius, the brightest star in the night sky,
can lead the way for North Americans to make the first naked-eye
sightings of a very special crescent Moon low in west-southwest at dusk
on Thursday, January 9.
This month's first visible evening crescent Moon is special, because it
marks the beginning of Ramadan, the holy month of fasting for a
quarter of the world's population who follow the Islamic faith.
Don't be confused by the bright object near the Moon low in east-
southeast at dawn on Tuesday, January 7. Tuesday's crescent is an old
Moon, at the end of a lunar month. And the bright object near the moon
that morning isn't a star. It's Venus.
Moon and Sirius on January 9 will not appear close together at all.
Instead, they'll follow one another through a small patch of sky, low in
west-southwest: First Sirius during predawn darkness, and then the
Moon at dusk, over 13 hours later.
Sirius is easy to spot at this time of year. Following Orion across the
sky, and directly in line with the Hunter's belt, the brilliant, twinkling
blue-white star rises in ESE just after nightfall, reaches its high point in
the south before the middle of the night, and sinks into the WSW in the
cold darkness before dawn.
The Moon on January 9 will be more difficult to spot. A very thin
delicate crescent, it follows the Sun across the sky that day and is lost in
the glare of the bright daylight sky near the Sun. Only after sunset,
when the Moon hangs low above the WSW horizon briefly, can the
beautiful hairline crescent be spotted in deepening twilight.
Here are directions for using the star Sirius to help you spot the Moon:
Observers in the eastern U.S. who are willing to make an observation of
Sirius at the right time on some morning prior to the evening of Jan. 9
can use that star as an excellent predictor of where the Moon will be that
evening. For example, an observer in East Lansing, Michigan on Jan. 9
at 4:32 a.m. EST will find Sirius at exactly the same place in the sky as
the illuminated lower edge of the Moon later that day at 5:48 p.m. (25
minutes after sunset). Below are similar predictions for several cities
across the eastern U.S. and eastern Canada. The data may be especially
useful to crescent-watchers in the northeastern U.S. and nearby Canada,
where the visibility of the crescent will be more difficult. Knowing
exactly where to look for the crescent greatly improves an observer's
chances of seeing it in borderline cases.
Of course it is too much to expect a clear sky both in the morning and in
the evening on Jan. 9 in the northeastern U.S. We'd be fortunate just to
get a clear evening on Jan. 9. If a clear morning comes along sometime
between now and then, just add 3 min 56 sec for each day before Jan. 9
to get the time to observe Sirius. For example, if Sirius is seen on Jan.
6, then you would look 11 min 48 sec later than the time given for Jan.
9, which would be 4:43:48 a.m. EST on Jan. 6. A sighting of Sirius
made at that time in East Lansing would accurately preview the Moon's
position (lower limb) for Jan. 9 at 5:48 p.m. (25 minutes after sunset).
As it happens, the position of the Moon 25 minutes after sunset can be
very accurately predicted with a prior observation of Sirius from these
cities:
January 9 January 9
Predawn 25 min after sunset Altitude difference
CITY Look for Sirius Look for Moon (Moon minus star)
Philadelphia 4:04.4 a.m. EST 5:19 p.m. 0 arcmin
Detroit 4:27.2 a.m. EST 5:43 p.m. 0 arcmin
E Lansing MI 4:32.0 a.m. EST 5:48 p.m. 0 arcmin
Minneapolis 3:58.5 a.m. CST 5:16 p.m. 0 arcmin
From locations north of the line connecting these cities, the Moon will
appear lower than the star's position previewed at the same azimuth;
from locations south of that line, the Moon will appear higher than the
previewed position of Sirius. For example:
January 9 January 9
Predawn 25 min after sunset Altitude difference
CITY Look for Sirius Look for Moon (Moon minus star)
Washington DC 4:14.2 a.m. EST 5:29 p.m. + 3 arcmin
Boston 3:41.0 a.m. EST 4:55 p.m. - 6 arcmin
Halifax 4:05.0 a.m. AST 5:18 p.m. -15 arcmin
Toronto 4:09.6 a.m. EST 5:25 p.m. - 5 arcmin
Montreal 3:40.5 a.m. EST 4:55 p.m. -11 arcmin
Miami 4:59.0 a.m. EST 6:12 p.m. +48 arcmin
New Orleans 4:27.7 a.m. CST 5:43 p.m. +39 arcmin
New York 3:57.5 a.m. EST 5:12 p.m. - 3 arcmin
Pittsburgh 4:21.7 a.m. EST 5:37 p.m. + 3 arcmin
Atlanta 4:56.8 a.m. EST 6:12 p.m. +22 arcmin
Chicago 3:46.5 a.m. CST 5:03 p.m. + 3 arcmin
Kansas City 4:21.7 a.m. CST 5:39 p.m. +14 arcmin
Austin TX 4:56.6 a.m. CST 6:13 p.m. +43 arcmin
This means, from Washington DC, if you go out to observe Sirius on
Jan. 9 at 4:14:12 a.m. EST (or on Jan. 8 at 4:18:08 a.m., etc.) and note
position of the star, and return to the same place on the evening of
January 9, the lower limb of the crescent will appear in the same
azimuth (above the same point of the horizon), but just 3 arcminutes
(about one-tenth of a lunar diameter) higher.
An examination of the table shows that the "waiting time" between the
observation of Sirius on the morning of January 9 until the observation
of the Moon at the same azimuth 25 minutes after sunset that same
evening is close to 13-1/4 hours for all the cities listed, ranging from 13
hr 13.0 min in Miami and Halifax, Nova Scotia, to 13 hr 17.5 min in
Minneapolis.
An observer wanting to know in advance exactly where to look for the
Ramadan crescent on Jan. 9 can therefore follow these steps:
1. Determine, in advance, the sunset time for January 9 (to the nearest
minute will suffice).
2. Add 25 minutes. This "Moonwatch time" will be a good time to spot
the lunar crescent, which will then be about 5 degrees above the WSW
horizon for eastern U.S. (The Moon may well be first spotted sooner
than 25 min after sunset, especially from southern and western parts of
the region covered by the table.)
3. Subtract the "waiting time" interval from the Moonwatch time
obtained in step 2. From central upper New York and central
Pennsylvania to the Florida panhandle it's 13 hours 15 minutes. From
Boston it's a minute less, and from Miami and Halifax, 2 minutes less,
or 13 hours 13 minutes. From Wisconsin through Missouri and central
Texas, it's 13 hours 17 minutes. Subtract this "waiting time" interval
from the "Moonwatch time" obtained in step 2 to determine the "Sirius
watch" time for the morning of January 9.
4. Since the sky can not be counted on to be clear on the morning of
Jan. 9, it would be prudent to take advantage of the first clear morning
to mark the location of Sirius. The star will occupy the same position
in the sky about 4 minutes earlier for each day before Jan. 9. For
example, from East Lansing, Michigan, it has been determined that
Sirius reaches the desired position on Jan. 9 at 4:32 a.m. So Sirius will
reach the same position on Jan. 8 around 4:36 a.m., and on Jan. 7 at
4:40 a.m., and so on, adding 4 minutes (more precisely, 3 min 56 sec)
for each day earlier.
5. On a clear morning for which you have calculated the time of the
"Sirius watch" to preview the Moon's position, set your watch
accurately, so you can make a record of your observations that will
come in handy on Jan. 9. Allow yourself enough time to find a good
vantage point to view Sirius from at least 10 minutes before until 10
minutes after the nominal time of the "Sirius watch." Take good notes as
you watch the star setting, being sure to note over what object (e.g.,
distant tree, smokestack, or rooftop) Sirius is located during each
passing minute. Make special note of the star's position at the moment
of the calculated "Sirius watch". The star will then be in the same
azimuth (above the same object if you stand in the same place on Jan. 9)
as the Moon will be 25 min after sunset on Jan. 9. Making drawings of
what you see may be very helpful. Later you can add to the drawing the
corresponding times when the Moon will appear in the same azimuth, a
little above or below the Moon's positions, or nearly coinciding with
them, as the case may be.
6. Once you are sure where the Moon will be, invite your friends or
your students to come to your moonwatch site around sunset on Jan. 9,
and enjoy the view as the beautiful crescent becomes visible!
Planetariums and astronomy clubs may wish to host a Ramadan Moon
watch. We have checked the location of Sirius from the top of a parking
ramp behind our planetarium and are planning to announce a public
moonwatch for early that evening, sky conditions permitting.
We are interested in observations of the lunar crescent from eastern
U.S. and eastern Canada, the Bamahas, Bermuda, the Caribbean, and
northern South America on Jan. 9. Optically aided sightings are also
possible from west Africa and offshore islands. Note your location
(longitude, latitude if possible), time you first spotted crescent,
instrument used, sky conditions, description of what you saw, and
other items you noted. Timed naked-eye observations of the crescent on
Jan. 9 made by an individual before he/she saw the Moon with optical
aid (telescope or binoculars) are of special interest.
Best wishes for a clear evening on January 9th!
Robert C. Victor
victor@pilot.msu.edu
Abrams Planetarium
Michigan State University
East Lansing, MI 48824
USA