diff --git a/shell.nix b/shell.nix
deleted file mode 100644
index 012a7a3..0000000
--- a/shell.nix
+++ /dev/null
@@ -1,4 +0,0 @@
-{ pkgs ? import <nixpkgs> {} }:
-pkgs.mkShell {
-  buildInputs = with pkgs; [ espeak ];
-}
diff --git a/sun_hours/shell.nix b/sun_hours/shell.nix
new file mode 100644
index 0000000..66451b3
--- /dev/null
+++ b/sun_hours/shell.nix
@@ -0,0 +1,9 @@
+{ pkgs ? import <nixpkgs> {} }:
+pkgs.mkShell {
+  buildInputs = [
+    pkgs.python3Packages.astral
+    pkgs.python3Packages.matplotlib
+    pkgs.python3Packages.click
+    pkgs.python3Packages.timezonefinder
+  ];
+}
diff --git a/sun_hours/sun_hours.py b/sun_hours/sun_hours.py
new file mode 100644
index 0000000..814eb79
--- /dev/null
+++ b/sun_hours/sun_hours.py
@@ -0,0 +1,71 @@
+import astral
+import astral.sun
+import click
+import datetime
+import matplotlib.dates
+import matplotlib.pyplot
+import operator
+import sys
+import timezonefinder
+
+
+def days_between(start: datetime.datetime, end: datetime.datetime):
+    delta = end - start
+    for offset in range(delta.days):
+        yield start + datetime.timedelta(days=offset)
+
+
+tf = timezonefinder.TimezoneFinder()
+
+
+def sun_for(day: datetime.datetime, *, latitude: float, longitude: float):
+    observer = astral.Observer(latitude, longitude)
+    return astral.sun.sun(
+        observer, date=day, tzinfo=tf.timezone_at(lat=latitude, lng=longitude)
+    )
+
+
+def time_to_float(time: datetime.datetime) -> float:
+    return time.hour + (time.minute / 60)
+
+
+@click.command()
+@click.option(
+    "--start",
+    default=datetime.datetime.today(),
+    type=click.DateTime(),
+    help="Start date",
+)
+@click.option(
+    "--end",
+    default=datetime.datetime.today() + datetime.timedelta(days=365),
+    type=click.DateTime(),
+    help="End date",
+)
+@click.option("--latitude", type=float, default=52.52, help="Observer latitude")
+@click.option("--longitude", type=float, default=13.4, help="Observer longitude")
+def main(start, end, latitude, longitude):
+    print("Using", tf.timezone_at(lat=latitude, lng=longitude), file=sys.stderr)
+
+    days = list(days_between(start, end))
+    sun_info = [sun_for(day, latitude=latitude, longitude=longitude) for day in days]
+
+    sunrises = [time_to_float(sun["sunrise"]) for sun in sun_info]
+    sunsets = [time_to_float(sun["sunset"]) for sun in sun_info]
+    sun_hours = [set - rise for set, rise in zip(sunsets, sunrises)]
+
+    matplotlib.pyplot.gca().xaxis.set_major_formatter(
+        matplotlib.dates.DateFormatter("%d.%m.")
+    )
+    matplotlib.pyplot.gca().xaxis.set_major_locator(
+        matplotlib.dates.DayLocator(interval=30)
+    )
+    matplotlib.pyplot.plot(days, sunrises)
+    matplotlib.pyplot.plot(days, sunsets)
+    matplotlib.pyplot.plot(days, sun_hours)
+    matplotlib.pyplot.gcf().autofmt_xdate()
+    matplotlib.pyplot.savefig(sys.stdout, format="svg")
+
+
+if __name__ == "__main__":
+    main()