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Hubble Focus: Gravitational Lenses ― Nature’s Giant Telescopes

Hubble Focus: Gravitational Lenses e-book cover. Black background that holds a gravitational lens and several galaxies dotted throughout the image. NASA Meatball logo in the upper right. An illustration of the Hubble Space Telescope is in the upper left with the opening of the telescope acting as the "o" in Focus. The bottom of the image has the words, " Gravitational Lenses Nature's Giant Telescopes."
This e-book is part of a series called Hubble Focus, which presents some of Hubble's recent cosmic discoveries. Its cover, shown here, shows an alignment of a trio of galaxies that creates a gravitational lensing effect called an Einstein Ring. The light of the most distant galaxy is warped into a ring around the foreground galaxies.
NASA Goddard Space Flight Center

What if you could build a telescope as big as a galaxy, or even bigger? Luckily, we don’t have to imagine, because the universe has already done that for us. “Gravitational Lenses: Nature’s Giant Telescopes” explores some of Hubble’s discoveries involving the cosmic lensing effect created when light is bent, distorted and magnified by massive objects in space. This NASA Hubble Space Telescope downloadable e-book is the seventh edition of the Hubble Focus series.

Massive cluster of galaxies with a gravitational lensing distortion effect.
Massive galaxy cluster Abell S1063 magnifies and distorts the light of distant galaxes beyond the cluster, which appears as streaks or arcs.
NASA, ESA, and J. Lotz (STScI)

Hubble is a powerful telescope, but everyone can use a boost. Einstein theorized that space and time are warped and curved by immense mass, a theory verified by the way light behaves as it travels past massive objects like galaxy clusters. The light from distant background objects is bent, magnified and even replicated as it travels through the cluster. This enhancement allows Hubble to see objects that would be too far away for it to glimpse otherwise, even though their images are distorted by this natural lensing phenomenon.

A dark star field with several small galaxies features a yellowish galaxy in the center. Surrounding this galaxy is a blue nearly circular horseshoe shaped object. Please see the explanation for more detailed information.
The “Blue Horseshoe” is an Einstein Ring created when the light of the foreground galaxy, seen as a reddish sphere in the center of the ring, magnifies and bends the light of a distant background galaxy. The galaxies have to be perfectly aligned for such a ring to form.
ESA/Hubble & NASA

Hubble in particular, thanks to its sensitivity and resolution, has been able to observe lensed objects that would be undetectable to ground-based telescopes over the past three decades. Hubble has used gravitational lensing to measure dark matter in galaxy clusters and galaxies, observe otherwise invisible exoplanets, and view some of the earliest galaxies seen in the universe.

This e-book is compatible with most electronic devices. If you have problems with the EPUB version, we suggest trying the more widely accessible PDF version.

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Hubble Focus: Gravitational Lenses e-book cover. Black background that holds a gravitational lens and several galaxies dotted throughout the image. NASA Meatball logo in the upper right. An illustration of the Hubble Space Telescope is in the upper left with the opening of the telescope acting as the "O" in Focus. The bottom of the image has the words, "Gravitational Lenses Nature's Giant Telescopes."

PDF format

Aug 3, 2026

PDF (17.87 MB)

Hubble Focus: Gravitational Lenses e-book cover. Black background that holds a gravitational lens and several galaxies dotted throughout the image. NASA Meatball logo in the upper right. An illustration of the Hubble Space Telescope is in the upper left with the opening of the telescope acting as the "O" in Focus. The bottom of the image has the words, "Gravitational Lenses Nature's Giant Telescopes."

EPUB format

Aug 3, 2026

(65.87 MB)

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