2 - Creating a Basic Star Chart

Tutorial - Basic Star Chart

Let's begin our starplotting journey by creating a basic star chart that shows the entire sky at a specific time and place, like the chart above. Starplot calls these "Zenith" projections because the zenith is in the center of the chart.

Here's a look at the code to create the zenith chart above, which shows the sky as seen from Palomar Mountain in California on July 13, 2023 at 10pm PT:

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from datetime import datetime
from pytz import timezone
from starplot import MapPlot, Projection

tz = timezone("America/Los_Angeles")
dt = datetime(2023, 7, 13, 22, 0, tzinfo=tz)  # July 13, 2023 at 10pm PT

p = MapPlot(
    projection=Projection.ZENITH,
    lat=33.363484,
    lon=-116.836394,
    dt=dt,
    resolution=4000,
    scale=0.9,
)
p.constellations()
p.stars(mag=4.6)
p.horizon()

p.export("tutorial_02.png", transparent=True)

In the first few lines, we just import all the stuff we need. pytz is a required dependency of Starplot, so it should've been installed when you installed Starplot.

Next, we create a datetime for our plot, including the timezone. All datetime values in Starplot need to be timezone-aware. An exception will be raised if you try to pass a naive datetime.

On line 8, we create a MapPlot instance that specifies a few properties for the map:

  • projection: Method to use for transforming the curved shape of the three-dimensional sky to a flat two-dimensional map. In this example, we use a ZENITH projection, but Starplot supports many types of projections.
  • lat/lon: Observing location
  • dt: Observing date/time
  • resolution: Resolution (in pixels) of the widest dimension of the plot
  • scale: This controls the sizing of all text and markers. At scale 1.0 everything is optimized for a basic map of 1-3 constellations, so if you're plotting a larger area (or just want everything smaller), then it's a good idea to decrease the scale so the plot isn't too crowded.

When you create a plot instance, initially it'll be empty (i.e. it won't have any stars). In Starplot, you have to explicitly plot all objects. So, on line 16 we plot the constellations, which includes lines and labels. Then, we plot stars with a limiting magnitude of 4.6.

Finally, we export the plot to a PNG file.

In the next section, we'll learn how to add some styles and other objects to the plot...

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