User`s guide

196 Starry Night User’s Guide
stars have shifted in the sky, due to the
precession of Earth, and the astronomical
constellation boundaries no longer match
the astrological constellation boundaries.
Starry Night shows the astronomical
constellation boundaries. With Starry
Night, you can set the time back to about
600 BC (when the astrological boundaries
were set), and you will find that the dates
when the sun was in each constellation
back then match the astrological dates.
How do I find my birth sign?
Adjust the date and time to your birthdate
in the toolbar. If you were born during the
day, choose View->Hide Daylight to turn
off daylight so that you can see the stars as
they appeared at the moment of your birth.
Turn on the Zodiac constellations by
choosing the Zodiac stick figures from the
Constellation Options dialog box in the
Constellations layer of the Options pane
and label the Zodiac constellations by
checking the Labels option in the
Constellations layer. The constellation
which the Sun is located in is your
astronomical birth sign. This may not
agree with your astrological sign, for the
reasons given in the previous question.
Solar System Bodies
How do I see the phases of the Moon?
Open the Find pane and double-click on
the Moon’s name. If you get a message
saying that the moon is beneath the
horizon, click the Best Time button. Zoom
in on the Moon if you want a closer look.
Now change the time step in the toolbar to
a discrete value of 1 day. Use the Single
Step Forward button in the time mode
controls to watch the Moon's phase change
day-by-day. You may have to hide the
horizon by choosing View->Hide
Horizon to keep the Moon in view. This
option is available in Starry Night Pro and
Pro Plus.
How accurate are the positions of the
planets and moons in Starry Night?
The position of the eight major planets
should be accurate to within 5 arcseconds
for times within 3000 years of the present.
The theory used to predict Pluto’s position
is less accurate: between the years 1885
and 2099, its position is accurate to within
1 arcsecond, but the accuracy will decline
significantly outside these dates. The
position of our moon should be accurate to
within 10 arcseconds for several thousand
years in either direction. The theories used
to predict the positions of other moons are
simpler and therefore potentially less
accurate.
Why can't I find Halley's Comet at the
Battle of Hastings?
Unfortunately, predicting comet positions
on past trips around the sun is one area of
astronomy where simulation programs like
Starry Night are not very effective. As a
comet goes around sun, its orbit is altered
by the gravitational influence of the sun
and planets in ways that can't be predicted
by Starry Night. The gas and dust released
by the comet as it gets closer to the Sun
also causes the orbit of the comet you are
interested in to change. For example, the
orbital period of Halley's comet has varied
from 76 years to 79 years over the last
thousand years. The bottom line is that the
orbital elements for a comet in Starry