• 4.3-meter Lowell Discovery Telescope

  • 4.3-meter Lowell Discovery Telescope

  • 4.3-meter Lowell Discovery Telescope


Happy Jack, Arizona

Elevation: 7740 feet


The LDT is the 5th largest optical telescope in the continental United States and one of the most versatile in the world.

Experience the LDT

Discovery Circle Members receive daytime tours of the Lowell Discovery Telescope.

The Swiss Army Knife of Telescopes

The 4.3-meter Lowell Discovery Telescope (LDT) is Lowell Observatory’s flagship research instrument. Its revolutionary instrument cube, which allows for the simultaneous attachment of 5 instruments, makes it one of the most versatile telescopes in the world, inspiring former Lowell Observatory Director Bob Millis to call it the Swiss Army Knife of Telescopes.

Lowell Observatory solely owns and operates the telescope, and has formed scientific partnerships that grant access to scientists from Boston University, the University of Maryland, the University of Toledo, Yale University, and Northern Arizona University. The observatory also maintains a media access and marketing partnership with Discovery, Inc., which funded $10 million of the $53 million cost of the LDT’s construction.

Research with the Lowell Discovery Telescope

Areas of Research

Lowell astronomers and our partners use the LDT for a variety of research, ranging from nearby asteroids to far-distant galaxies.

Asteroids, comets, planets, Kuiper belt objects, double stars, planets around stars other than the Sun, massive stars, dwarf galaxies, colliding galaxies, and more are all fair game.

The LDT's Research Instruments

Imaging with the Largest CCD Possible

The Large Monolithic Imager (LMI) is the LDT’s workhorse camera, and contains the largest CCD that can be made using current manufacturing techniques—a massive 36 megapixel CCD with a field of view of 12.5 x 12.5 arc minutes (the Moon is 30 arc minutes across) when used with the LDT. This is an incredibly wide field of view for this size of telescope.

The philosophy behind the LMI is to enable imaging of a significant field of view in one exposure. Smaller CCDs have to be assembled in a mosaic to cover a large field of view, which reduces observing efficiency and creates complications in data reduction. The LMI avoids these problems and gives the LDT a highly effective and efficient imaging camera.

Searching for Earth-sized Planets

Astronomers at Yale University, in collaboration with Lowell Observatory, have embarked on a search that will answer one of the oldest questions in astronomy: Are there planets similar to Earth orbiting other stars?

The LDT gathers light from stars and feeds it into the Extreme Precision Spectrometer (EXPRES). A spectrometer splits light into different colors, similar to how shining light through a prism produces a rainbow. Astronomers then analyze the light to search for the signatures of a planet. In this case, a change in the motion of the star along our line of sight –the radial velocity– would indicate the presence of a planet.

During the daytime, EXPRES is used by the Lowell Observatory Solar Telescope (LOST) to study the motion of the Sun. This study attempts to detect the planet Venus by measuring its gravitational tug on the Sun, which is the same way EXPRES is being used to hunt for exoplanets around distant stars.

Exploring Gamma Ray Bursts

The Rapid infrared IMAger Spectrometer (RIMAS) was designed for Target of Opportunity (ToO) observations that require urgent data gathering, such as Gamma Ray bursts that last for only a short time. RIMAS combines imaging and spectroscopic capabilities in one compact setup and is mounted onto one of the large ports of the LDT instrument cube.

RIMAS images objects in the infrared part of the spectrum, just as LMI does in the optical, though with a smaller field of view. The spectroscopic capabilities include both a very low resolution mode as well as a higher resolution mode, complementing the capabilities of NIHTS and allowing researchers to conduct a diverse set of projects using it, including the chemical signature of Gamma Ray bursts.

Studying the Kuiper Belt

The Near-Infrared High-Throughput Spectrograph (NIHTS, pronounced “nights”) is a low-resolution near-infrared prism spectrograph that is able to conduct spectroscopy at the same time that LMI is imaging the object. This low-resolution spectrograph was funded by NASA’s Planetary Astronomy and Planetary Major Equipment programs. Former Lowell astronomer Henry Roe was the Principal Investigator for NIHTS, one of the LDT’s “first light” instruments.

A Workhorse Spectrograph

The DeVeny Optical Spectrograph is the former Kitt Peak White Spectrograph, now on permanent loan to Lowell Observatory. After being used on the 1.8-meter Perkins Telescope at Anderson Mesa–formerly owned by Lowell, but now owned and operated by Boston University–it was upgraded and mounted onto the LDT in February 2015. The DeVeny Spectrograph is a moderate resolution optical spectrograph, working between 3200 Å and 1 µm.

High-Resolution Speckle Imaging

The Quad-camera, Wave-front-sensing, Six-wavelength-channel Speckle Interferometer (QWSSI) is expected to be the default speckle camera for the LDT. Speckle interferometry involves taking large numbers of short exposures to capture the few images that are undistorted by our moving atmosphere. This method yields unusually clear final images of a celestial object targeted by the LDT.

Tell Me More!

Before astronomers could explore the heavens with the LDT, engineers had to first build it, test it, and get it into prime working condition.

The LDT employs what is called a Ritchey-Chrétien optical design. Light enters the telescope through the dome slit and is reflected off the 4.3-meter primary mirror, which is figured into a concave hyperbola with a precision of 50 to 75 nanometers. (For comparison, a human hair is about 80,000 – 100,000 nanometers thick.) The light then reflects off the 1.4-meter secondary mirror, which is a convex hyperbola. It returns through a hole in the center of the primary mirror and arrives at the focal plane, where the light is sent to the selected instrument.

The primary mirror of the LDT measures 4.3 meters (14 feet) across and only 10 centimeters (4 inches) thick and weighs 6700 pounds. It must be removed every 5 years to receive a new coating of aluminum. Besides this, it must be cleaned monthly so that the surface is maximized for collecting light from space. 

The lens is mounted to a massive telescope frame lined with electrical wires and tubes for feeding super-chilled liquids to the instruments so they operate properly. The telescope is operated by a network of computers and anchored into the ground, with the entire assembly housed by a 7-story dome.

All this technology needs constant care, and Lowell maintains a team of engineers that daily monitor operations and make repairs as needed, so the telescope stays in optimal working condition.

It’s a long way from early engineering drawings to photons reflecting off the mirror and hitting the detector. Lowell broke ground for the new telescope on July 11, 2005. Half a dozen years later, in September 2011, astronomers recorded the first image from just the primary mirror, using a small test camera mounted where the secondary mirror would eventually go. This “zeroth light” test produced a seemingly plain image of a star, not in very good focus and distinctly not round. It’s not great by the standards of a fully-commissioned telescope, but it was a very encouraging result for a completely untested, point-and-shoot first try.

“First light” is a telescope’s debut: the dome shutter and mirror cover are open, the detector is ready to go, and all systems are up and running. It reveals an initial demonstration of the quality of the telescope’s optics and overall system performance, so it is one of the most significant milestones for a facility like LDT.

First light for the Lowell Discovery Telescope occurred on April 3, 2012, just a few months after the secondary mirror was installed (January 2012).

A milestone like first light deserves a proper party, and on July 21, 2012, some 730 guests joined Lowell staff at Flagstaff’s High Country Conference Center to celebrate the completion of a ten-year journey. The featured speaker for the evening was Neil Armstrong. Nearly a half century since visiting Flagstaff for astronaut geology training, Armstrong gave an inspiring keynote address, tying together his own voyages of discovery with the ones LDT was now poised to make. 

The first light image taken on April 3, 2012, was of  barred spiral galaxy M109.

The LDT project got underway in 2003, when Discovery founder and former CEO John Hendricks proposed what would become a $10 million gift to Lowell Observatory from what was then called Discovery Communications (now Discovery, Inc.), with a further $6 million coming from his foundation. This gift proved crucial to funding the $53 million project, and in return Discovery received naming rights to the telescope.

When the initial agreement between Lowell and Discovery ended in 2017, leaders from the two organizations developed a new agreement that included changing the name of the telescope for clarity. As Lowell Director Jeff Hall explains, “The name Lowell Discovery Telescope makes clear that Lowell Observatory is its owner and operator, while the word Discovery takes on a fun double meaning. It recognizes the generous support gift from Discovery that enabled us to build the telescope and emphasizes the observatory’s tradition and mission of astronomical discovery.”

LDT Tours

Become a member of the Friends of Lowell Observatory at the Discovery Circle ($5,000) level and you and your guests will receive an exclusive, behind-the-scenes tour of the LDT.