Cartes Using du Ciel
Cartes du Ciel is free software available for download on the Internet and you may acquire for
your personal use the same version that we use in this lab by visiting the Cartes du Ciel website.
Installation is straightforward and takes only a few minutes. The documentation, as with much open
source software, is not as detailed as that provided with programs that you pay for, but weve found
Cartes du Ciel to be well-featured and relatively easy to use. We recommend Cartes du Ciel to anyone
whos looking for desktop-based planetarium software on a budget. We hope that your will find this
introduction to Cartes du Ciel to be a useful takeaway from todays lab.
In todays exercise you are using a combination of information obtained from the visibility data
chart in your lab manual, your planisphere and Cartes du Ciel to ascertain what planets are visible in the
sky tonight and the range of times that they are visible. Remember that the sky must be fairly dark to
see any of the planets because they reflect sunlight at a much lower magnitude that the Sun produces
it. You may follow the same set of steps to predict when and where planets will be visible for any
future date.
As mentioned in your lab manual, a planets brightness must be taken into account when
determining its visibility. Very bright planets, like Jupiter, are among the first objects visible as
twilight grows. Mars is not as bright and the sky must therefore be darker in order to see it. The
inferior planets (Mercury and Venus) are never far from the Sun in the sky (the superior planets are
sometimes close to the Sun as well) and need to be near maximum elongation to be visible very long
after sunset or before sunrise.
To use Cartes du Ciel for this
exercise open the program and click
Setup on the menu bar that runs
along the top of the screen, then
select Observatory from the pull
down menu. Make sure that the
latitude, longitude and Time zone are
all correct for eastern Idaho (shown
right). Once this has been done close
this box, select Setup once again, and
this time select the Date/time option
from pull the down menu. Uncheck the
Use system time box (if it is
checked) and then click the Tonight
button. This will create a chart of the
way that tonights sky will appear
shortly after sunset based on the
computers system time and date
(make sure that these are correct).
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Next make sure that the display menu (on the bar below the menu bar) has the same items
selected as shown in the screen shot below. The sky should have a color close to black if everything is
setup correctly and the system time and date are correct. Locate the increment and decrement
buttons near the center of the menu bar and make sure that the increment/decrement settings are 1
hour (as shown below). Decrement the chart 1 hour by clicking the decrement button and the sky color
should lighten. This indicates that the chart is set to display the sky at twilight. One more decrement
should lighten the sky to its lightest blue, indicating very early evening. The twilight time on Cartes du
Ciel (displayed as local sidereal time near the upper left of the chart) should correlate with the
predicted time of sunset you obtained using your Planisphere. Youll want to begin your search for
visible planets during this time.
Consider where planets would first appear in the night sky somewhere along the ecliptic. Use
the E, S and W buttons on the right side of the screen to toggle between these quadrants of the sky.
The ecliptic should be visible in all three of these quadrants. Are any planets visible anywhere along the
ecliptic at this time? If so are they close to the sun? Youll have to use the planet visibility chart along
with distance from the sun to estimate if planets are visible during twilight. Only the brightest planets
will be visible if they are close to the sun during twilight (or dawn).
Now use the increment button to scroll through the night hour by hour, examining the East,
South and West quadrants each time, observing any planets that appear along the ecliptic during the
night. Do this until dawn. Note that we are not interested in the north quadrant of the sky. Why is this
so?
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