diff --git a/.travis.yml b/.travis.yml
index 113c902..827456c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -54,7 +54,6 @@ env:
     matrix:
         # Make sure that egg_info works without dependencies
         - PYTHON_VERSION=2.7 SETUP_CMD='egg_info'
-        - PYTHON_VERSION=3.3 SETUP_CMD='egg_info'
         - PYTHON_VERSION=3.4 SETUP_CMD='egg_info'
         - PYTHON_VERSION=3.5 SETUP_CMD='egg_info'
         - PYTHON_VERSION=3.6 SETUP_CMD='egg_info'
@@ -98,7 +97,7 @@ matrix:
         - os: linux
           env: PYTHON_VERSION=2.7 NUMPY_VERSION=1.7
         - os: linux
-          env: PYTHON_VERSION=3.3 NUMPY_VERSION=1.8
+          env: PYTHON_VERSION=3.4 NUMPY_VERSION=1.8
         - os: linux
           env: PYTHON_VERSION=3.4 NUMPY_VERSION=1.9
         - os: linux
diff --git a/CHANGES.rst b/CHANGES.rst
index 74d7967..0631a0e 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -1,6 +1,8 @@
 0.10 (unreleased)
 -----------------
-- No changes yet.
+- Handle non-backwards compatible changes to astropy.constants in astropy 2.0.
+- Handle deprecated longitude, latitude attributes for astropy >= 2.0.
+- Remove tests against python 3.3 (3.4-3.6 are still tested).
 
 0.9 (2017-05-11)
 ----------------
diff --git a/specsim/observation.py b/specsim/observation.py
index b17733b..def1268 100644
--- a/specsim/observation.py
+++ b/specsim/observation.py
@@ -222,8 +222,13 @@ def initialize(config):
         nominal_start = exposure_start
         point_radec = pointing.transform_to('icrs')
         hour_angle = astropy.coordinates.Angle(adjust_ha)
+        try:
+            lon = location.lon
+        except AttributeError:
+            # Required for astropy < 2.0
+            lon = location.longitude
         exposure_start = specsim.transform.adjust_time_to_hour_angle(
-            nominal_start, point_radec.ra, hour_angle, location.longitude)
+            nominal_start, point_radec.ra, hour_angle, lon)
         # Put the requested HA at the middle of the exposure.
         exposure_start -= 0.5 * constants['exposure_time']
 
diff --git a/specsim/transform.py b/specsim/transform.py
index fe926cf..6c537a6 100644
--- a/specsim/transform.py
+++ b/specsim/transform.py
@@ -310,7 +310,12 @@ def create_observing_model(where, when, wavelength, temperature=15*u.deg_C,
     # See https://en.wikipedia.org/wiki/Vertical_pressure_variation
     if pressure is None:
         h = where.height
-        p0 = astropy.constants.atmosphere
+        # The atmosphere constant in astropy < 2.0 was renamed to atm in 2.0.
+        try:
+            p0 = astropy.constants.atm
+        except AttributeError:
+            # Fallback for astropy < 2.0.
+            p0 = astropy.constants.atmosphere
         g0 = astropy.constants.g0
         R = astropy.constants.R
         air_molar_mass = 0.0289644 * u.kg / u.mol
@@ -336,7 +341,7 @@ def sky_to_altaz(sky_coords, observing_model):
     two steps.  First, define the atmosphere through which the sky is being
     observed with a call to :func:`create_observing_model`.  Next, call this
     function. For example, to locate Polaris from Kitt Peak, observing at
-    a wavelength of 5400 Angstroms:
+    a wavelength of 5400 Angstroms (we expect altitude ~ longitude ~ 32 deg):
 
     >>> where = observatories['KPNO']
     >>> when = astropy.time.Time('2001-01-01T00:00:00')
@@ -346,8 +351,6 @@ def sky_to_altaz(sky_coords, observing_model):
     >>> print('alt = %.3f deg, az = %.3f deg' %
     ... (altaz.alt.to(u.deg).value, altaz.az.to(u.deg).value))
     alt = 32.465 deg, az = 0.667 deg
-    >>> print('lat = %.3f deg' % where.latitude.to(u.deg).value)
-    lat = 31.963 deg
 
     The output shape is determined by the usual `numpy broadcasting rules
     <http://docs.scipy.org/doc/numpy/user/basics.broadcasting.html>`__ applied