diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7f133eb6..a8268f33 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,8 +1,142 @@
-# See elsewhere for changelog
+# pypa:pywwt 0.10.0 (2020-10-21)
 
-This project’s release notes are curated from the Git history of its main
-branch. You can find them by looking at [the version of this file on the
-`release` branch][branch] or the [GitHub release history][gh-releases].
+- Fix build for traitlets >= 5.0 and in fact start requiring it.
+- Update minimum Python version to 3.7, as required by traitlets 5.
+- Require version 1.0 of the NPM package, so that we extrapolate clock
+  information from data provided by the JavaScript layer. This dramatically
+  reduces the level of traffic between the JS and Python layers.
+- Adopt Cranko for release automation, and revamp the continuous integration
+  infrastructure to implement such automation.
 
-[branch]: https://github.com/WorldWideTelescope/pywwt/blob/release/CHANGELOG.md
-[gh-releases]: https://github.com/WorldWideTelescope/pywwt/releases
+
+# pywwt 0.9.0 (2020-08-29)
+
+- pywwt now obtains the WWT WebGL SDK code from web.wwtassets.org, rather than
+  a private copy hosted on the pywwt GitHub Pages instance.
+- Live notebook links now point to mybinder.org rather than the old private WWT
+  instance of BinderHub, because HTTPS support is now working!
+- Fix Jupyter server plumbing when operating in the JupyterHub single-user
+  environment.
+
+
+# pywwt 0.8.0 (2020-04-03)
+
+- Improve performance when changing size parameters for tabular layers. In these
+  cases, the performance is e.g. more than 1000x better for a 50,000 row
+  dataset. [#224]
+- Improve performance when changing colormap parameters for tabular
+  layers, for a subset of colormaps. In these cases, the performance
+  is e.g. more than 1000x better for a 50,000 row dataset. [#223]
+- Added a `cmap` parameter on image layers to control the colormap. [#244]
+- Incorporate time series behavior for data layers; add method that
+  returns current time in the viewer. [#187]
+- Drop support for Python 2.7 and now require at least Python 3.6. [#259]
+- Fix compatibility with Jupyter 2.0. [#260]
+
+
+# pywwt 0.7.0 (2019-09-20)
+
+- You can now save your WWT views as interactive figures to be used in journal
+  articles! (Actually, they're just standalone web pages, so they can be used
+  anywhere you've got a web server.) This feature is new so it will still have
+  some rough edges — keep your eyes open for improvements. And the docs haven't
+  been written yet :-( [#215, #227]
+- Relatedly, there is new first-draft support for interactive controls for
+  image layers through the `image.controls` meta-property. This will also
+  evolve over the next few releases. [#217]
+- Initial support for data layers with Cartesian (XYZ) rather than spherical
+  (lat, lon, alt) coordinates. [#190]
+- Fix compatibility with the JupyterLab 1.0.x series. [#216, #219, #221]
+- Expose all available imagery layers. [#220]
+- Validate coordinate frame names used with tabular data layers. [#195]
+- Fix the widget `reset` method . [#212]
+- Various improvements to CI infrastructure, docs, landing pages, etc. [#218,
+  #225, #228, #229, #230]
+
+
+# pywwt 0.6.1 (2019-06-10)
+
+- Fixed issues when calling `reset()`. [#212]
+- Fixed resizing issues in Jupyter Lab. [#216]
+- Fixed server URL when using Jupyter Lab. [#219]
+
+
+# pywwt 0.6.0 (2019-05-29)
+
+- Implement support for color-coding and scaling points in layers according
+  to table attributes. [#183]
+- Removed `load_fits_data` and added `layers.add_image_layer` instead,
+  which provides control over the image stretch, and renamed
+  `layers.add_data_layer` to `layers.add_table_layer`. [#188, #201]
+- Added support for drag and drop events in Qt widget. [#202]
+- Added support for `get_center` for the Jupyter widget, and add a new
+  `get_fov` method to get the current field of view. [#206]
+- Fixed compatibility with notebook>=5.7.6 which requires mime
+  types for served files to be correct. [#192, #208]
+- Fixed display of table layers on Windows. [#207]
+
+
+# pywwt 0.5.3 (2019-01-16)
+
+- Exposed option to turn off large-scale SDSS data in 3D mode, improving
+  performance. [#176]
+- Make sure default altitude type is set correctly. [#176]
+
+
+# pywwt 0.5.2 (2019-01-08)
+
+- Added instructions for using Jupyter Lab. [#170]
+- Fixed `set_view('Mars')`. [#171]
+- Fixed issue with layers not appearing under certain circumstances. [#173]
+
+
+# pywwt 0.5.1 (2019-01-04)
+
+- Fixed a bug that caused layers to not immediately update when updating
+  data. [#167]
+- Fixed a bug that caused some columns to be pre-assigned to e.g. size_att
+  based on column name. [#167]
+
+
+# pywwt 0.5.0 (2019-01-04)
+
+- Fixed issues with zooming using trackpad/scroll wheel. [#166]
+- Added support for customizing the layer marker type (`marker_type`), the
+  option to specify whether the marker size is absolute or relative to the
+  screen (`marker_scale`), and the option to show points on the far side of
+  an object (`far_side_visible`). [#165]
+- Fixed a bug that caused issues with the distance/altitude of points when not
+  centered on the Earth. [#165]
+
+
+# pywwt 0.4.1 (2018-12-23)
+
+- Work around an issue with getting base URLs on e.g. mybinder.
+- Improvements to documentation. [#160, #164]
+
+
+# pywwt 0.4.0 (2018-12-20)
+
+- Added keyboard shortcuts for movement in-viewer. [#81]
+- Disable crosshairs by default. [#157]
+- Added `pause_time` and `play_time` for controlling time and make it
+  possible to control the rate of passage of time. [#146, #152]
+- Added support for displaying fields of view for common telescope. [#102]
+- Added `minor_orbits` and `stars` attributes to control the visibility
+  of minor orbits and stars in solar system mode. [#145]
+- Added support for showing tables of data using layers. [#122, #136, #139, #140, #143, #147, #150]
+- Added `load_fits_data` method for Qt and Jupyter clients. [#78]
+- Added support for non-sky modes (e.g. solar system mode). [#74, #83, #95, #98]
+- Added GUI controls for imagery layers using the `layer_controls` attribute. [#64]
+- Added support for exploring available imagery layers. [#71]
+- Added support for showing circle collections with annotations. [#54]
+- Switch to use OpenGL API. [#73]
+- Fixed compatibility with Jupyter Lab. [#63, #65]
+- Fixed compatibility with older versions of Qt. [#133]
+- Fixed compatibility with unicode strings for colors on Python 2. [#105]
+- Improved documentation. [#60, #70, #84, #101, #109]
+
+
+# pywwt 0.3.0 (2017-12-20)
+
+- Initial version with changelog
diff --git a/ci/azure-build-and-test.yml b/ci/azure-build-and-test.yml
index 2fdd526a..7d01c971 100644
--- a/ci/azure-build-and-test.yml
+++ b/ci/azure-build-and-test.yml
@@ -56,7 +56,7 @@ jobs:
         set -euo pipefail
         source activate-conda.sh
         set -x
-        \conda create -y -n build setuptools matplotlib pip pyopengl pyqt python="$PYTHON_SERIES" qtpy
+        \conda create -y -n build setuptools matplotlib pip pyopengl 'pyqt>=5.12' python="$PYTHON_SERIES" qtpy
         conda activate build
         pip install $BASH_WORKSPACE/sdist/*.tar.gz
       displayName: Install from sdist
@@ -134,7 +134,7 @@ jobs:
       set -euo pipefail
       source activate-conda.sh
       set -x
-      \conda create -y -n build setuptools matplotlib pip pyopengl pyqt python=3.8 qtpy
+      \conda create -y -n build setuptools matplotlib pip pyopengl 'pyqt>=5.12' python=3.8 qtpy
       conda activate build
       pip install $BASH_WORKSPACE/sdist/*.tar.gz
     displayName: Install from sdist
@@ -178,7 +178,7 @@ jobs:
       set -euo pipefail
       source activate-conda.sh
       set -x
-      \conda create -y -n build setuptools matplotlib pip pyopengl pyqt python=3.8 qtpy
+      \conda create -y -n build setuptools matplotlib pip pyopengl 'pyqt>=5.12' python=3.8 qtpy
       conda activate build
       pip install $BASH_WORKSPACE/sdist/*.tar.gz
     displayName: Install from sdist
diff --git a/ci/azure-deployment.yml b/ci/azure-deployment.yml
index 686ebdbc..609c29aa 100644
--- a/ci/azure-deployment.yml
+++ b/ci/azure-deployment.yml
@@ -76,7 +76,7 @@ jobs:
 
         # If we ever become a monorepo, we'll need to figure out how to make sure
         # that we only upload the proper packages.
-        if cranko show if-released --exit-code pywwt ; then
+        if cranko show if-released --exit-code pypa:pywwt ; then
           twine upload $BASH_WORKSPACE/sdist/*.tar.gz
         fi
       displayName: Publish PyPI releases
diff --git a/docs/installation.rst b/docs/installation.rst
index 95cc4d78..c7071902 100644
--- a/docs/installation.rst
+++ b/docs/installation.rst
@@ -109,7 +109,7 @@ If you want to use the Jupyter widget, you will also need to run::
 
 And if you additionally want to use the widget in JupyterLab, run::
 
-    jupyter labextension install .
+    jupyter labextension install frontend
     jupyter labextension list  # check that the output shows pywwt as enabled and OK
 
 Besides ``pywwt``, the ``@jupyter-widgets/jupyterlab-manager`` and
diff --git a/frontend/CHANGELOG.md b/frontend/CHANGELOG.md
index 4f7a0f8a..18bbc578 100644
--- a/frontend/CHANGELOG.md
+++ b/frontend/CHANGELOG.md
@@ -1,3 +1,10 @@
+# npm:pywwt 1.0.0 (2020-10-21)
+
+- Address #258 by transmitting WWT clock information using a reference point and
+  a rate, rather than constantly transmitting the current time. Dramatically
+  reduces JS <=> Python traffic.
+- Tidy up the JavaScript files.
+
 # npm:pywwt 0.9.1 (2020-10-18)
 
 - First release with version number decoupled from the pywwt Python package.
diff --git a/frontend/lib/embed.js b/frontend/lib/embed.js
deleted file mode 100644
index a1429a78..00000000
--- a/frontend/lib/embed.js
+++ /dev/null
@@ -1,9 +0,0 @@
-// Entry point for the unpkg bundle containing custom model definitions.
-//
-// It differs from the notebook bundle in that it does not need to define a
-// dynamic baseURL for the static assets and may load some css that would
-// already be loaded by the notebook otherwise.
-
-// Export widget models and views, and the npm package version number.
-module.exports = require('./wwt.js');
-module.exports['version'] = require('../package.json').version;
diff --git a/frontend/lib/extension.js b/frontend/lib/extension.js
deleted file mode 100644
index 5735a62e..00000000
--- a/frontend/lib/extension.js
+++ /dev/null
@@ -1,19 +0,0 @@
-// This file contains the javascript that is run when the notebook is loaded.
-// It contains some requirejs configuration and the `load_ipython_extension`
-// which is required for any notebook extension.
-
-// Configure requirejs
-if (window.require) {
-    window.require.config({
-        map: {
-            "*" : {
-                "pywwt": "nbextensions/pywwt/index",
-            }
-        }
-    });
-}
-
-// Export the required load_ipython_extension
-module.exports = {
-    load_ipython_extension: function() {}
-};
diff --git a/frontend/lib/index.js b/frontend/lib/index.js
index 298db72e..3b693e06 100644
--- a/frontend/lib/index.js
+++ b/frontend/lib/index.js
@@ -1,7 +1,2 @@
-// Entry point for the notebook bundle containing custom model definitions.
-//
-// Setup notebook base URL
-
-// Export widget models and views, and the npm package version number.
 module.exports = require('./wwt.js');
 module.exports['version'] = require('../package.json').version;
diff --git a/frontend/lib/plugin.js b/frontend/lib/jupyterlab.js
similarity index 72%
rename from frontend/lib/plugin.js
rename to frontend/lib/jupyterlab.js
index 585167cf..6c3115d1 100644
--- a/frontend/lib/plugin.js
+++ b/frontend/lib/jupyterlab.js
@@ -1,3 +1,6 @@
+// This file implements the JupyterLab extension, as linked up through this
+// module's `package.json` file (`jupyerlab.extension` keyword).
+
 var wwt = require('./index');
 
 var base = require('@jupyter-widgets/base');
diff --git a/frontend/lib/version.js b/frontend/lib/version.js
deleted file mode 100644
index d29068f7..00000000
--- a/frontend/lib/version.js
+++ /dev/null
@@ -1 +0,0 @@
-export const version = require('../package.json').version;
diff --git a/frontend/lib/wwt.js b/frontend/lib/wwt.js
index e1fca17c..2da73dc9 100644
--- a/frontend/lib/wwt.js
+++ b/frontend/lib/wwt.js
@@ -1,7 +1,7 @@
 var widgets = require('@jupyter-widgets/base');
 var _ = require("underscore");
 
-var version = require('./version').version;
+var version = require('./index').version;
 
 var WWTModel = widgets.DOMWidgetModel.extend({
     defaults: _.extend(widgets.DOMWidgetModel.prototype.defaults(), {
@@ -24,7 +24,7 @@ var WWTModel = widgets.DOMWidgetModel.extend({
 
 var WWTView = widgets.DOMWidgetView.extend({
 
-    initialize : function() {
+    initialize: function() {
 
         // We use an iframe to show WorldWideTelescope, because it does not
         // otherwise support having multiple instances running on the same
@@ -42,11 +42,14 @@ var WWTView = widgets.DOMWidgetView.extend({
 
         WWTView.__super__.initialize.apply(this, arguments);
 
+        // Monitor the view data so that we can transmit updates. We handle the
+        // clock specially so as not to be sending updates continually.
+        this.lastClockUpdate = 0;
         var self = this;
-        setInterval(function () { self.update_view_data(); }, 100);
+        setInterval(function () { self.update_view_data(); }, 150);
     },
 
-    _try_init_wwt_window : function() {
+    _try_init_wwt_window: function() {
         iframe = this.el.getElementsByTagName('iframe')[0];
         if (iframe != null) {
             this.wwt_window = iframe.contentWindow;
@@ -80,17 +83,17 @@ var WWTView = widgets.DOMWidgetView.extend({
     },
 
     processLuminoMessage: function(msg) {
-      // We listen for lumino resize events so that when Jupyter Lab is
-      // used, we adjust the canvas size to the tab/panel in Jupyter Lab.
-      // See relayout for more details.
-      WWTView.__super__.processLuminoMessage.apply(this, arguments);
-      switch (msg.type) {
-      case 'resize':
-      case 'after-show':
-          this.relayout();
-          break;
-      }
-  },
+        // We listen for lumino resize events so that when Jupyter Lab is
+        // used, we adjust the canvas size to the tab/panel in Jupyter Lab.
+        // See relayout for more details.
+        WWTView.__super__.processLuminoMessage.apply(this, arguments);
+        switch (msg.type) {
+        case 'resize':
+        case 'after-show':
+            this.relayout();
+            break;
+        }
+    },
 
     relayout: function() {
         // Only do resizing if we are not in the notebook context but in a
@@ -145,42 +148,52 @@ var WWTView = widgets.DOMWidgetView.extend({
     },
 
     handle_custom_message: function(msg) {
+        if (this.wwt_window == null && !this._try_init_wwt_window()) {
+            return;
+        }
 
-      if (this.wwt_window == null && !this._try_init_wwt_window()) {
-        return;
-      }
-
-      if (msg['url'] != null && msg['url'].slice(4) == '/wwt') {
-        msg['url'] = this.wwt_base_url + msg['url'];
-      }
-
-      // If the user has created a view for our widget and then hidden it, our
-      // iframe gets removed and all sorts of things stop working (e.g.,
-      // Chrome will refuse to send XMLHttpRequests anymore, and Firefox won't
-      // set timeouts). If we let exceptions from these operations bubble up,
-      // they break the code that applies widget events to *all* views, which
-      // then breaks the JupyterLab use case of (1) setting up a WWT widget,
-      // (2) creating a view of it in a separate tab, and then (3) hiding the
-      // view in the original notebook, because the second view will never
-      // receive any messages. We should handle things better when widgets get
-      // hidden, but in the meantime, try to keep things limping along by
-      // swallowing exceptions here. Note that this approach will mean that
-      // the two views will get out of sync regarding, e.g., image layers that
-      // have been loaded.
-
-      try {
-        this.wwt_window.wwt_apply_json_message(this.wwt_window.wwt, msg);
-
-        if (msg['event'] === 'center_on_coordinates') {
-          this.update_view_data();
+        if (msg['url'] != null && msg['url'].slice(4) == '/wwt') {
+            msg['url'] = this.wwt_base_url + msg['url'];
+        }
+
+        // If the user has created a view for our widget and then hidden it, our
+        // iframe gets removed and all sorts of things stop working (e.g.,
+        // Chrome will refuse to send XMLHttpRequests anymore, and Firefox won't
+        // set timeouts). If we let exceptions from these operations bubble up,
+        // they break the code that applies widget events to *all* views, which
+        // then breaks the JupyterLab use case of (1) setting up a WWT widget,
+        // (2) creating a view of it in a separate tab, and then (3) hiding the
+        // view in the original notebook, because the second view will never
+        // receive any messages. We should handle things better when widgets get
+        // hidden, but in the meantime, try to keep things limping along by
+        // swallowing exceptions here. Note that this approach will mean that
+        // the two views will get out of sync regarding, e.g., image layers that
+        // have been loaded.
+
+        try {
+            this.wwt_window.wwt_apply_json_message(this.wwt_window.wwt, msg);
+
+            switch(msg['event']) {
+                case 'load_tour':
+                case 'resume_tour':
+                case 'pause_tour':
+                case 'resume_time':
+                case 'pause_time':
+                case 'set_datetime':
+                    this.lastClockUpdate = 0;
+                    break;
+            }
+        } catch (e) {
+            console.log('failed to process custom_message for a pyWWT Jupyter widget view:');
+            console.log(msg);
+            (console.error || console.log).call(console, e.stack || e);
         }
-      } catch (e) {
-        console.log('failed to process custom_message for a pyWWT Jupyter widget view:');
-        console.log(msg);
-        (console.error || console.log).call(console, e.stack || e);
-      }
     },
 
+    // This function is called very frequently, so we make sure to not send
+    // updates unless something has changed. Ideally we'd be triggered on
+    // updates rather than polling, but we're not well set up to do that right
+    // now.
     update_view_data: function () {
         if ((this.wwt_window == null && !this._try_init_wwt_window()) || !this.wwt_window.wwt) {
             return;
@@ -189,35 +202,58 @@ var WWTView = widgets.DOMWidgetView.extend({
         var needUpdate = false;
 
         if (this.model.get('_ra') != this.wwt_window.wwt.getRA()) {
-          this.model.set({ '_ra': this.wwt_window.wwt.getRA() });
-          needUpdate = true;
+            this.model.set({ '_ra': this.wwt_window.wwt.getRA() });
+            needUpdate = true;
         }
 
         if (this.model.get('_dec') != this.wwt_window.wwt.getDec()) {
-          this.model.set({ '_dec': this.wwt_window.wwt.getDec() });
-          needUpdate = true;
+            this.model.set({ '_dec': this.wwt_window.wwt.getDec() });
+            needUpdate = true;
         }
 
         if (this.model.get('_fov') != this.wwt_window.wwt.get_fov()) {
-          this.model.set({ '_fov': this.wwt_window.wwt.get_fov() });
-          needUpdate = true;
+            this.model.set({ '_fov': this.wwt_window.wwt.get_fov() });
+            needUpdate = true;
         }
 
-        var stc = this.wwt_window.wwtlib.SpaceTimeController;
-        if (this.model.get('_datetime') != stc.get_now().toISOString()) {
-          this.model.set({ '_datetime': stc.get_now().toISOString() });
-          needUpdate = true;
+        // By default, the clock is always ticking. We throttle updates by having
+        // the listener extrapolate the clock itself given reference times and the
+        // "time rate".
+        //
+        // For compatibility reasons, the engine's time must be exposed using a
+        // trait named `_datetime`. If any of the time-related parameters are
+        // changed discontinuously, set lastClockUpdate to 0 to force an update.
+        var nowUnixMs = Date.now();
+        var updateTimeParams = (nowUnixMs - this.lastClockUpdate) > 60000;
+
+        if (updateTimeParams) {
+            var stc = this.wwt_window.wwtlib.SpaceTimeController;
+            var rate = stc.get_timeRate();
+
+            if (!stc.get_syncToClock()) {
+                // When time is paused by setting syncToClock to false, the WWT
+                // "rate" remains unchanged, but as far as the Python layer is
+                // concerned, the rate should be 0.
+                rate = 0.0;
+            }
+
+            this.model.set({
+                '_datetime': stc.get_now().toISOString(),
+                '_systemDatetime': (new Date()).toISOString(),
+                '_timeRate': rate
+            });
+
+            this.lastClockUpdate = nowUnixMs;
+            needUpdate = true;
         }
 
         if (needUpdate) {
-          this.touch();
+            this.touch();
         }
     }
-
 });
 
-
 module.exports = {
-    WWTModel : WWTModel,
-    WWTView : WWTView
+    WWTModel: WWTModel,
+    WWTView: WWTView
 };
diff --git a/frontend/package.json b/frontend/package.json
index 82a95ea5..f4b90071 100644
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -4,7 +4,8 @@
     "url": "https://github.com/WorldWideTelescope/pywwt/issues"
   },
   "dependencies": {
-    "@jupyter-widgets/base": "^2  || ^3"
+    "@jupyter-widgets/base": "^2  || ^3",
+    "underscore": "^1"
   },
   "description": "AAS WorldWide Telescope from Python",
   "devDependencies": {
@@ -18,7 +19,7 @@
   ],
   "homepage": "https://github.com/WorldWideTelescope/pywwt",
   "jupyterlab": {
-    "extension": "lib/plugin"
+    "extension": "lib/jupyterlab"
   },
   "keywords": [
     "jupyter",
@@ -38,5 +39,5 @@
     "clean": "shx rm -rf dist",
     "pywwt-export": "npm run build && npm pack && node pywwt-export.js"
   },
-  "version": "0.9.1"
+  "version": "1.0.0"
 }
diff --git a/pyproject.toml b/pyproject.toml
index e2bb03df..43ca2518 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -9,4 +9,4 @@ annotated_files = [
 ]
 
 [tool.cranko.internal_dep_versions]
-"npm:pywwt" = "manual:^0.9.0"
+"npm:pywwt" = "thiscommit:29e64671926d2fce87bbcad78d54980a"
diff --git a/pywwt/_version.py b/pywwt/_version.py
index 79f4d964..e1570132 100644
--- a/pywwt/_version.py
+++ b/pywwt/_version.py
@@ -1,4 +1,4 @@
-version_info = (0, 9, 0, 'final', 0)  # cranko project-version tuple
+version_info = (0, 10, 0, 'final', 0)  # cranko project-version tuple
 
 _specifier_ = {'alpha': '.a', 'beta': '.b', 'candidate': '.rc', 'final': '', 'dev': '.dev'}
 
diff --git a/pywwt/jupyter.py b/pywwt/jupyter.py
index 9f495740..9093a5df 100644
--- a/pywwt/jupyter.py
+++ b/pywwt/jupyter.py
@@ -3,6 +3,7 @@
 # because we instead use JSON messages to transmit any changes between the
 # Python and Javascript parts so that we can re-use this for the Qt client.
 
+from astropy.time import Time
 import ipywidgets as widgets
 from traitlets import Unicode, Float, default, link, directional_link
 
@@ -14,7 +15,7 @@
 
 __all__ = ['WWTJupyterWidget']
 
-_npm_version = '^0.9.0'  # cranko internal-req npm:pywwt
+_npm_version = '^1.0.0'  # cranko internal-req npm:pywwt
 VIEW_MODULE_VERSION = _npm_version
 MODEL_MODULE_VERSION = _npm_version
 
@@ -34,12 +35,17 @@ class WWTJupyterWidget(widgets.DOMWidget, BaseWWTWidget):
     _view_module_version = Unicode(VIEW_MODULE_VERSION).tag(sync=True)
     _model_module_version = Unicode(MODEL_MODULE_VERSION).tag(sync=True)
 
+    # wwt=None tag needed to avoid linkage to 'wwt.settings.set_' type traits
+    # (see _on_trait_change() in core.py)
     _ra = Float(0.0).tag(sync=True, wwt=None)
     _dec = Float(0.0).tag(sync=True, wwt=None)
     _fov = Float(60.0).tag(sync=True, wwt=None)
+    # this is the WWT engine's clock at last check-in:
     _datetime = Unicode('2017-03-09T12:30:00').tag(sync=True, wwt=None)
-    # wwt=None tag needed to avoid linkage to 'wwt.settings.set_' type traits
-    # (see _on_trait_change() in core.py)
+    # this is system clock at last check-in:
+    _systemDatetime = Unicode('2017-03-09T12:30:00').tag(sync=True, wwt=None)
+    # this is the rate at which the WWT engine clock proceeds relative to the system clock:
+    _timeRate = Float(1.0).tag(sync=True, wwt=None)
 
     def __init__(self):
         widgets.DOMWidget.__init__(self)
@@ -67,7 +73,10 @@ def _get_view_data(self, field):
         elif field == 'fov':
             return self._fov
         elif field == 'datetime':
-            return self._datetime
+            engine_time = Time(self._datetime, format='isot')
+            system_time = Time(self._systemDatetime, format='isot')
+            engine_delta = self._timeRate * (Time.now() - system_time)
+            return engine_time + engine_delta
         else:
             raise ValueError("'field' should be one of: 'ra', 'dec', "
                              "'fov', or 'datetime'")
diff --git a/pywwt/nbextension/static/extension.js b/pywwt/nbextension/static/extension.js
index 903980a3..81a568e8 100644
--- a/pywwt/nbextension/static/extension.js
+++ b/pywwt/nbextension/static/extension.js
@@ -1,3 +1,10 @@
++// This file contains the Javascript that implements the Jupyter notebook
++// extension, as linked up in `pywwt/nbextension/__init__.py` with the `require`
++// keyword.
++//
++// It contains some requirejs configuration and the `load_ipython_extension`
++// which is required for any notebook extension.
+
 define(function() {
     "use strict";
 
@@ -8,6 +15,7 @@ define(function() {
             },
         }
     });
+
     // Export the required load_ipython_extention
     return {
         load_ipython_extension : function() {}
diff --git a/pywwt/nbextension/static/wwt_json_api.js b/pywwt/nbextension/static/wwt_json_api.js
index eb8e91fb..e65adade 100644
--- a/pywwt/nbextension/static/wwt_json_api.js
+++ b/pywwt/nbextension/static/wwt_json_api.js
@@ -129,7 +129,6 @@ function wwt_apply_json_message(wwt, msg) {
       break;
 
     case 'annotation_set':
-
       var name = msg['setting'];
       // TODO: nice error message if annotation doesn't exist
       annotation = wwt.annotations[msg['id']];
@@ -137,7 +136,6 @@ function wwt_apply_json_message(wwt, msg) {
       break;
 
     case 'remove_annotation':
-
       var name = msg["setting"];
       // TODO: nice error message if annotation doesn't exist
       shape = wwt.annotations[msg['id']];
@@ -145,7 +143,6 @@ function wwt_apply_json_message(wwt, msg) {
       break;
 
     case 'circle_set_center':
-
       var name = msg["setting"];
       // TODO: nice error message if annotation doesn't exist
       circle = wwt.annotations[msg['id']];
@@ -153,7 +150,6 @@ function wwt_apply_json_message(wwt, msg) {
       break;
 
     case 'polygon_add_point':
-
       var name = msg["setting"];
       // same TODO as above
       polygon = wwt.annotations[msg['id']];
@@ -161,7 +157,6 @@ function wwt_apply_json_message(wwt, msg) {
       break;
 
     case 'line_add_point':
-
       var name = msg["setting"];
       // same TODO as above
       line = wwt.annotations[msg['id']];
@@ -169,9 +164,7 @@ function wwt_apply_json_message(wwt, msg) {
       break;
 
     case 'set_datetime':
-
       var date = new Date(msg['isot']);
-
       stc = wwtlib.SpaceTimeController;
       stc.set_timeRate(1);
       stc.set_now(date);
@@ -190,16 +183,13 @@ function wwt_apply_json_message(wwt, msg) {
       break;
 
     case 'image_layer_create':
-
       layer = wwt.loadFits(msg['url']);
       layer._stretch_version = 0;
       layer._cmap_version = 0;
-
       wwt.layers[msg['id']] = layer;
       break;
 
     case 'image_layer_stretch':
-
       var layer = wwt.layers[msg['id']];
 
       if (layer.get_imageSet() == null) {
@@ -228,42 +218,33 @@ function wwt_apply_json_message(wwt, msg) {
       }
       break;
 
-      case 'image_layer_cmap':
-
-        // See image_layer_stretch for why we need to do what we do below
-
-        var layer = wwt.layers[msg['id']];
-
-        if (layer.get_imageSet() == null) {
-          setTimeout(function(){ wwt_apply_json_message(wwt, msg); }, 200);
-        } else {
-          if (msg['version'] > layer._cmap_version) {
-            layer.set_colorMapperName(msg['cmap']);
-            layer._cmap_version = msg['version'];
-          }
+    case 'image_layer_cmap':
+      // See image_layer_stretch for why we need to do what we do below
+      var layer = wwt.layers[msg['id']];
 
+      if (layer.get_imageSet() == null) {
+        setTimeout(function(){ wwt_apply_json_message(wwt, msg); }, 200);
+      } else {
+        if (msg['version'] > layer._cmap_version) {
+          layer.set_colorMapperName(msg['cmap']);
+          layer._cmap_version = msg['version'];
         }
-        break;
+      }
+      break;
 
     case 'image_layer_set':
-
       var layer = wwt.layers[msg['id']];
       var name = msg['setting'];
-
       layer["set_" + name](msg['value']);
-
       break;
 
     case 'image_layer_remove':
-
       // TODO: could combine with table_layer_remove
-
       var layer = wwt.layers[msg['id']];
       wwtlib.LayerManager.deleteLayerByID(layer.id, true, true);
       break;
 
     case 'table_layer_create':
-
       // Decode table from base64
       csv = atob(msg['table'])
 
@@ -306,7 +287,6 @@ function wwt_apply_json_message(wwt, msg) {
       break;
 
     case 'table_layer_update':
-
       var layer = wwt.layers[msg['id']];
 
       // Decode table from base64
@@ -319,7 +299,6 @@ function wwt_apply_json_message(wwt, msg) {
       break;
 
     case 'table_layer_set':
-
       var layer = wwt.layers[msg['id']];
       var name = msg['setting'];
 
@@ -351,13 +330,10 @@ function wwt_apply_json_message(wwt, msg) {
       break;
 
     case 'table_layer_remove':
-
       var layer = wwt.layers[msg['id']];
       wwtlib.LayerManager.deleteLayerByID(layer.id, true, true);
       break;
-
   }
-
 }
 
 // We need to do this so that wwt_apply_json_message is available as a global