Olav Kolbu

NASA makes a new Image Of The Day available every day in their gallery, 
complete with a fairly detailed description of what you see. This plugin 
grabs a thumbnail of the current image along with an extract of the 
accompanying description, and makes it available as a WordPress sidebar 
widget. Clicking on the thumbnail will take you to the NASA Gallery where 
you can view the full sized image and read the rest of the text. No 
local storage is used, the image and text is fetched on every view.
A friendly user let me know that the Image Of The Day is also 
available as an RSS feed. That greatly simplified this plugin and 
should make it impervious to cosmetic changes at NASA. In 
addition to this, the image width is now customizable. The height 
is calculated per image so that it stays proportional when scaled 
(down) to width.
<a href="https://downloads.wordpress.org/plugin/nasa-image-of-the-day.zip" rel="nofollow ugc">Download now!</a>
<a href="http://www.kolbu.com/2008/03/28/nasa-image-of-the-day-plugin/" rel="nofollow ugc">Support</a>

NASA Image Of The Day

Adds a sidebar widget to display the current image from the NASA Image Of The Day Gallery. Now using RSS.

rhewlif

Provides a simple sidebar widget to display NASA’s Earth Observatory Image of the Day and/or the RSS feed. Numerous options are available to display the content the way you want, including control on the image width and description.
The widget can also output just the RSS feed, providing links to previous images for up to the last 10 days (maximum available in feed).
Thumbnail images are cached to the plugin folder daily if needed, and the RSS feed is updated hourly.

Earth Observatory IOTD Widget

Provides a widget to display the NASA Earth Observatory's Image of the Day and/or the RSS feed on your sidebar.

NASA Image Of The Day vs Earth Observatory IOTD Widget