diff --git a/src/celengine/astro.cpp b/src/celengine/astro.cpp
index 98f69a918..374ccce39 100644
--- a/src/celengine/astro.cpp
+++ b/src/celengine/astro.cpp
@@ -8,9 +8,9 @@
 // as published by the Free Software Foundation; either version 2
 // of the License, or (at your option) any later version.
 
-#include <config.h>
 #include <cstring>
 #include <cmath>
+#include <iostream>
 #include <iomanip>
 #include <cstdio>
 #include <utility>
@@ -19,33 +19,12 @@
 #include "univcoord.h"
 #include <celutil/gettext.h>
 #include <celmath/geomutil.h>
-#include <celmath/mathlib.h>
 
 
 using namespace Eigen;
 using namespace std;
 using namespace celmath;
 
-const double astro::speedOfLight = 299792.458; // km/s
-
-// epoch J2000: 12 UT on 1 Jan 2000
-const double astro::J2000 = 2451545.0;
-
-const double astro::G = 6.672e-11; // N m^2 / kg^2
-
-const double astro::SolarMass   = 1.989e30;
-const double astro::EarthMass   = 5.972e24;
-const double astro::LunarMass   = 7.346e22;
-const double astro::JupiterMass = 1.898e27;
-
-const double astro::SOLAR_IRRADIANCE  = 1367.6;        // Watts / m^2
-const double astro::SOLAR_POWER       = 3.8462e26;  // Watts
-
-// Angle between J2000 mean equator and the ecliptic plane.
-// 23 deg 26' 21".448 (Seidelmann, _Explanatory Supplement to the
-// Astronomical Almanac_ (1992), eqn 3.222-1.
-const double astro::J2000Obliquity = degToRad(23.4392911);
-
 static const Quaterniond ECLIPTIC_TO_EQUATORIAL_ROTATION = XRotation(-astro::J2000Obliquity);
 static const Matrix3d ECLIPTIC_TO_EQUATORIAL_MATRIX = ECLIPTIC_TO_EQUATORIAL_ROTATION.toRotationMatrix();
 
@@ -347,30 +326,21 @@ Vector3d astro::equatorialToGalactic(const Vector3d& v)
 
 
 
-astro::Date::Date()
+astro::Date::Date() : Date(0, 0, 0)
 {
-    year = 0;
-    month = 0;
-    day = 0;
-    hour = 0;
-    minute = 0;
-    seconds = 0.0;
-    wday = 0;
-    utc_offset = 0;
-    tzname = "UTC";
 }
 
-astro::Date::Date(int Y, int M, int D)
+astro::Date::Date(int Y, int M, int D) :
+    year(Y),
+    month(M),
+    day(D),
+    hour(0),
+    minute(0),
+    seconds(0.0),
+    wday(0),
+    utc_offset(0),
+    tzname("UTC")
 {
-    year = Y;
-    month = M;
-    day = D;
-    hour = 0;
-    minute = 0;
-    seconds = 0.0;
-    wday = 0;
-    utc_offset = 0;
-    tzname = "UTC";
 }
 
 astro::Date::Date(double jd)
diff --git a/src/celengine/astro.h b/src/celengine/astro.h
index f4660d26c..fc5ed6a65 100644
--- a/src/celengine/astro.h
+++ b/src/celengine/astro.h
@@ -11,11 +11,10 @@
 #ifndef _CELENGINE_ASTRO_H_
 #define _CELENGINE_ASTRO_H_
 
-#include <Eigen/Core>
 #include <Eigen/Geometry>
-#include <iostream>
+#include <iosfwd>
 #include <string>
-#include <cmath>
+#include <celmath/mathlib.h>
 
 #define SOLAR_ABSMAG   4.83f
 #define LN_MAG         1.085736
@@ -223,18 +222,22 @@ namespace astro
                  double& trueAnomaly, double& eccentricAnomaly);
     double meanEclipticObliquity(double jd);
 
-    extern const double J2000;
-    extern const double speedOfLight; // km/s
-    extern const double G; // gravitational constant
-    extern const double SolarMass;
-    extern const double EarthMass;
-    extern const double LunarMass;
-    extern const double JupiterMass;
+    // epoch J2000: 12 UT on 1 Jan 2000
+    constexpr const double J2000            = 2451545.0;
+    constexpr const double speedOfLight     = 299792.458; // km/s
+    constexpr const double G                = 6.672e-11; // N m^2 / kg^2; gravitational constant
+    constexpr const double SolarMass        = 1.989e30;
+    constexpr const double EarthMass        = 5.972e24;
+    constexpr const double LunarMass        = 7.346e22;
+    constexpr const double JupiterMass      = 1.898e27;
 
-    extern const double J2000Obliquity;
+    // Angle between J2000 mean equator and the ecliptic plane.
+    // 23 deg 26' 21".448 (Seidelmann, _Explanatory Supplement to the
+    // Astronomical Almanac_ (1992), eqn 3.222-1.
+    constexpr const double J2000Obliquity   = 23.4392911_deg;
 
-    extern const double SOLAR_IRRADIANCE;
-    extern const double SOLAR_POWER;  // in Watts
+    constexpr const double SOLAR_IRRADIANCE = 1367.6; // Watts / m^2
+    constexpr const double SOLAR_POWER      = 3.8462e26;  // in Watts
 }
 
 // Convert a date structure to a Julian date
diff --git a/src/celestia/url.cpp b/src/celestia/url.cpp
index cdf3945fe..409894668 100644
--- a/src/celestia/url.cpp
+++ b/src/celestia/url.cpp
@@ -30,7 +30,6 @@ using namespace Eigen;
 using namespace std;
 using namespace celmath;
 
-const unsigned int Url::CurrentVersion = 4;
 constexpr const uint64_t NewRenderFlags = Renderer::ShowDwarfPlanets |
                                           Renderer::ShowMoons        |
                                           Renderer::ShowMinorMoons   |
diff --git a/src/celestia/url.h b/src/celestia/url.h
index 526f752ec..9da33334f 100644
--- a/src/celestia/url.h
+++ b/src/celestia/url.h
@@ -72,7 +72,7 @@ public:
     std::string getName() const;
     bool goTo();
 
-    static const unsigned int CurrentVersion;
+    constexpr const static unsigned int CurrentVersion = 4;
 
     static std::string decodeString(const std::string& str);
     static std::string encodeString(const std::string& str);