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Several people have asked how the "zooming into planets" effect in my Sky this Week videos are produced. Like most things, they are done with a combination of tools, in this case Adobe's Photoshop Elements and Premiere Elements.

The black background surrounding the image of the planet is removed by using the Photoshop "magic wand" tool to select and then cut. Then the remaing jagggies close to the planet are removed with the eraser tool. For planets which show as crescents a black ellipse is placed in a layer beneath the planet layer so that the stars won't shine through in the wrong place. The file is then saved in PSD format (Premiere can read lots of video, image, and audio formats). Fortunately this only needs to be done once for each planet as they can be re-used.

The star chart is created with Cartes du Ciel and copied into the paste buffer. Then I use Photoshop and create a new file from the paste buffer. It is then resized to be 1280 pixels wide to match resolution of HD 720P video format -- this is not absolutely necessary but seems to look better. A new layer is added and the constellation boundaries and figures are traced with the pencil tool in that layer, setting the line width to 5 pixels -- otherwise they won't show up very well in the videos. The star chart file is then saved in PSD format.

In Photoshop Premier the star chart PSD file is imported and placed into a lower video layer. By default when images are imported by the Premier tool they are duplicated 150 times to span 5 sec (30 fps). However, that time span can be easily adjusted by stretching the image across the time line -- Premiere handles adding additional frames or removes them automatically so this is trivial to do.

The Planet image is then imported into Premier and placed above the star chart layer. Its time span is adjusted as necessary, in this case about 2 sec. The scale (ie zoom factor), position, rotation angle, transparency, brightness, contrast, and many other attributes of any video layer may be set at various points on a time line. The Premiere tool interpolates the settings for each frame as it renders the video. As shown below, the "saturn-transparent.psd" layer is selected and its settings are shown in the upper right. The points I have set on the time line are the diamond-shaped markers. The points may be set interactively by scrolling the time line to the desired point and then changing the setting of the particular attribute. The image at the left is updated to reflect the setting so its pretty easy to do. For the planet zooms, the attributes of interest of course are "Position" and "Scale".

Lots of other special effects can be easily done. For example, I used multiple star chart layers in the current video: one with only stars and another with constellation figures. That way the constellation figure and boundaries lines appear to fade into the scene.