Polaris Star Clock
Courtesy of the OBU Planetarium
Designed by Ben Randell, Science Education major, class of '98
- Print and cut out the outer dial, which indicates dates of the
Click here to view a printable Outer
- Print and cut out the inner dial, which displays a
chart. Be sure to cut out its little notch also (in order to
reveal the time of night written on the outer dial).
Click here to view a printable Inner
- Fasten the two dials together at their centers. The center of
the outer dial is clearly marked, but note that the center of the
inner dial (where the grid lines converge) does not exactly
coincide with the location of Polaris, the North Star. Polaris is
displaced about a degree away from the center.
Possible fasteners include a staple, a piece of thread, a paper
brad or rivet, or a thumbtack; any arrangement that allows the
dials to rotate freely around their centers without tearing.
- If you use a staple or piece of thread, secure each end by
taping it down on the front and back sides.
- If you use a thumbtack, an eraser (e.g., a small
cylindrical one removed from a pencil) makes a good fastener on
the back side.
- A larger laminated card stock, laser-printed version of the
dials is available from the Planetarium for $1. Or laminate the
printed versions yourself for increased durability and
performance, which will cost about 30¢ in the Media Center
(located in the lower floor of the Mabee Learning Center).
- Try out your star clock! You may need to cut the notch in your
small circle slightly deeper if the a.m./p.m. indicators under the
clock face hours do not appear within the notch at every point
around the circle.
Telling Time with the Star
- Go outdoors at night with a red flashlight and face north.
Find Polaris (the North Star) in Ursa Minor (the Little Bear); the
Big Dipper (in Ursa Major, the Big Bear), and Cassiopeia, which
are illustrated on the inner dial.
- Find the Date: Locate today's date on the outer dial and hold
it at the top with your thumb.
- Position the Clock:
- Hold the star clock up at arms length, keeping today's date
at the top.
- Close one eye, and gaze above the star clock directly at
- Tilt the clock face so that it is perpendicular to your
line of sight; that is, it should be tilted and not vertical.
- Keeping your gaze steady, raise the star clock until your
line of sight to Polaris would line up with, or pass through,
the center of star clock. Of course, the center of the star
clock is not transparent, so getting a consistent result may
take a little practice!
(Hint: Point the index finger of the hand not holding the star
clock horizontally toward Polaris. Then when you raise the star
clock up vertically you can use your index finger to show you
when to stop.)
- Align the Star Chart: Without moving the orientation of the
outer dial or the clock as a whole, rotate the inner dial until
the star chart on its face corresponds with the location of the
stars in the sky. Look especially for the location of the Big
Dipper and Cassiopeia, but any of the constellations identified on
the star clock will work.
- Read Time: Read the approximate Central Standard time off the
scale on the outer dial revealed by the notched area of the inner
- The star clock is accurate to within a quarter of an hour.
- The star clock is calibrated for the Central time zone. If
you use it in California or Florida, you'll have to convert to
your own time zone.
- The star clock displays Standard time. Add one hour for
Daylight Savings Time, if needed, between April and
- Can't get it to work? Come to the
Friday night shows of the
OBU Planetarium. Weather permitting, a telescope is set up outside
for viewing after each show. The students at the telescopes will
be more than happy to assist you in using your star clock.
- Optional: The star clock is a convenient way to convert
Sidereal Time to local time.
Previous: Using the
Welcome to the Basic Celestial Phenomena web site
provided by the OBU Planetarium.
The logo of the OBU Planetarium is not based on a
To provide explanations of basic observational astronomy to
students, teachers, families, and visitors to the planetarium these
pages have been written by the Planetarium Director, Kerry Magruder;
the Unified Studies Natural Science Coordinator Mike Keas; and the
students who work in the planetarium. These web pages may be printed,
copied, and distributed for educational use by any non-profit
educational group so long as they are not edited or altered in any
way, nor distributed for profit, nor repackaged or incorporated into
any other medium or product, and so long as full credit is given to
the OBU Planetarium.
This Basic Celestial Phenomena page and many others from the same
web site may be accessed from the OBU Planetarium home page: