STScI

NASA and the Space Telescope Science Institute are offering free e-books about space telescopes.

Free books from NASA, the Hubble Space Telescope's science team and the European Space Agency bring Earth and the heavens to life — as long as you have an iPad, and the patience to wait for a longish download.

Even if you have a regular old computer, you can still download the books about Hubble and its successor, the James Webb Space Telescope, as PDF files. But you'll miss out on all the interactive features.

Those two books were unveiled today by the Baltimore-based Space Telescope Science Institute, which takes care of the science programming for the two NASA-funded telescopes. They're joining the ESA's first iBook, "Earth From Space: The Living Beauty," on my iPad bookshelf.

The Hubble book guides you through scores of pictures from the world's most famous space telescope, organized into categories ranging from cosmology to planetary science. There's also a chapter on the telescope itself, with a 3-D model and a diagram you can tap on to learn about all the components. (Our Flash interactive about Hubble takes a similar approach.) When you tally up all the interactives, videos and picture galleries, the content adds up to a lot more than the 84 pages on the screen.

NASA / STScI

The iBooks are crammed with cosmic images.

The 74-page e-book about the Webb telescope uses a similar approach to explain the science behind the $8.8 billion observatory, which is currently scheduled for launch in 2018. There aren't any pictures from the Webb, of course, but the book's interactives, videos and photo galleries explain how the telescope will observe the cosmic frontiers in infrared wavelengths.

"These new e-books from NASA will allow people to discover Hubble and Webb in a whole new way — both the science and the technology behind building them," Amber Straughn, an astrophysicist on the Webb telescope project at NASA's Goddard Space Flight Center, said in today's news release. "They collect all of the amazing resources about these two observatories in an excellent product that I think people will really enjoy."

While the NASA iBooks look outward, ESA's iBook looks back toward Earth, incorporating stunning images from Europe's Earth-observing satellites. The 104 pages cover our planet from the core to the cryosphere, from the oceans to the wilderness. You can set color-coded virtual globes spinning with a brush of your fingertip.

ESA

"Earth From Space" is the European Space Agency's first iBook.

"By turning the virtual pages of this iBook you will discover how some of the latest technology has changed the way we see Earth," Volker Liebig, director of ESA's Earth observation programs, said in the space agency's publication announcement. "So, it was time to bring these ‘scientific voyages’ to you in a dynamic way. I believe that electronic media hold a huge potential, just like satellite technology. They help you to discover the scientific world of spaceflight."

While the Hubble and Webb e-books are downloadable via Apple's iBookstore, you download "Earth From Space" directly from ESA's website and follow the instructions. You'll need to be patient: Each book packs in hundreds of megabytes' worth of data, so the download can take as long as 20 minutes over a home broadband connection. There were times when I wondered whether it'd ever finish. But if you're a fan of space imagery, these books are well worth the wait — especially when you consider that they're free.

More space imagery:

• 2012: The Year in Space
• Space slideshow gallery
• App lets you take the planet's pulse
• 2012 Cosmic Log Space Advent Calendar

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.