Using a Planisphere
| Basic Celestial Phenomena | Constellations
can I get a planisphere?
- Any planisphere will do, but some kind of planisphere or star
wheel is required for getting to know the night sky. These handy
maps of the night sky work every night every season of the year,
and fit in a purse or the small pocket of a backpack.
- Get a laminated model for durability.
- Ten inch planispheres are easier to use but less
convenient to carry than the 5.5 inch models.
- Choose a planisphere that is set for your latitude. 25-35
degrees (Texas and southern Oklahoma). 35-45 degree
planispheres are more suitable for Missouri, Kansas or Colorado
- Order a planisphere for your latitude at Sky and Telescope's
Practice using the planisphere (one of the three main astronomical
tools for planetarium and skywatch labs at OBU --the other two are
the star-clock and the
protractor quadrant). This page contains the lesson plan for a
planetarium lab. In fact, it may not make much sense until after you
have attended the first planetarium lab in which we will do what is
indicated here. Yet many students may get more out of the planetarium
lab by previewing or reviewing this page.
- Set the planetarium sky so that Scorpius and Sagittarius are
visible due south. With a little foresight, this can be done
during the last diurnal rotation of Cowboy Astronomer.
- Using the planetarium star projector, introduce the
- Fish-hook to Polynesians.
- What is it known as in the western tradition? A scorpion,
creeping low along the horizon, its stinger the tip of the
- Antares, as red as its
mythological rival Mars, is the
heart of the Scorpion.
- Its claws were chopped off by the Romans to make the tiny
or Balance. Not only are they equally bright (dim, but equally
so); in the days of the Roman empire, the sun was in Scorpius
on the day of equinox, when the hours of daylight and nighttime
were equally balanced.
- Using the star projector, introduce the constellation
- Archer. Chiron the Centaur.
- Star clusters rise like steam from the teapot.
- General instructions.
- Examine your planisphere, front and back. Note that
constellations are labelled in ALL CAPS with a
large font; bright stars or asterisms are
labelled in lower case with a smaller font.
- Find the north, south, east and west horizons on the
planisphere. First find north (designated by an arrow), then
the other cardinal directions ("never eat slimy worms").
- Position yourself so that you face south.
Star charts are usually designed for facing due south,
optimized for about half-way up from the horizon.
- Read road maps looking down, but read star charts
looking up. Hold the planisphere above your head so
that the north arrow points north.
- Find Sagittarius and Scorpius on the planisphere, turning
the inside dial as needed. Note that the planisphere is a guide
to the sky, not a replica of the sky's actual appearance.
Expect distortion in the arrangement of stars and
constellations that are close to the horizon. Check with your
neighbor to see if your results agree.
- Practice aligning planispheres.
- With the planetarium starfield on, and using your red
flashlight as needed, turn the planisphere dial so that the
position of Sagittarius and Scorpius are aligned on the
planisphere's south horizon corresponding to their position on
the dome. Check with your neighbor to see if your results
- Without changing the relative position of the two dials,
find the current date and read the corresponding standard
- From April to October add 1 hour to obtain Daylight Savings
- Compare with your neighbor to see if your times agree.
- Predict the appearance of the sky at a specified time.
- With the room lights on, set your planisphere to show
tonight's sky at 10:00 pm our time (DST if necessary). Remember
that DST is one hour later than the standard time the
- Note carefully the positions of Sagittarius and
- With room lights off and the planetarium stars on, the star
projector will simulate the passing of the evening hours. Call
"HALT!" as soon as the sky reaches the position you expect to
find at 10:00. Don't be shy; try to be the first one.
- Go outside tonight, listen to the perfect silence of the
stars, and practice aligning your planisphere with the night
- Look for any visible planets.
- The distortion of the star patterns on the planisphere for
constellations near the horizon, such as Scorpius and
Sagittarius, is not the only complication. Sometimes there are
extra bright stars in the real sky not shown on the
planisphere! What might these extra bright stars be, that
wander from constellation to constellation across the sky?
- (Display the ecliptic and celestial equator.) The celestial
equator, shown as a solid line, is a projection of the earth's
equator out into space. The stars lying on the celestial
equator would pass directly overhead an observer located on the
earth's equator. The ecliptic, shown as a dotted line, is the
path travelled by the sun throughout a year. By the end of the
fall semester, the sun will enter Scorpius and then
Sagittarius. At that time these constellations will lie in the
daytime sky, invisible unless there is a solar eclipse.
- The planets generally follow the path of the sun, never
straying too far above or below the ecliptic. Constellations
that include the ecliptic are called zodiac constellations, and
often contain planets. If you see a bright star in a zodiac
constellation that doesn't belong, you've found a planet!
- Note some bright stars that give a general indication of
the path of the ecliptic around the sky. For this part of the
sky, you can use lambda-Sagittarii, the top of the teapot, or
Antares, the heart of the Scorpion.
Next: Using the Starclock