Hubble’s 25th Anniversary

We’re celebrating the Hubble Space Telescope today—glancing at images, singing songs, and generally toasting the quarter-century-old space telescope. Join us!

To begin with, even as we gawk at the awesome 25th anniversary image, we always have our favorites, so joining the New York Times roster of astronomers describing their favorite Hubble images, we’ll kick things off with a personal perspective on a particular picture. And then, of course, we all know that Hubble won’t last forever, so we take a look at what’s next for space-based astronomy.

Hubble Ultra-Deep Field

Of all the powerful, compelling, beautiful imagery that the Hubble Space Telescope has sent down to Earth over the past two decades, there is a single image that I have to call out as my favorite. It is an answer to an odd question, startlingly huge and deep, breathtakingly gorgeous, and it is the image that really compelled me to go into astronomy. The Hubble Ultra Deep Field (HUDF) is my favorite Hubble image.

At first blush, the picture seems odd. Very different than the nebulae and galaxies that are the focus of other images, this one seemingly lacks a subject. The inky black of the background is spotted and speckled with points of many colors. It would be tempting to call it a starfield, but the points are too large, too wide. These are not stars, but whole galaxies.

The HUDF is the successor to the Hubble Deep Field (HDF) taken in 1995. After an optics upgrade in December 1993, the newly refurbished telescope peered into a seemingly “empty” patch of sky near Ursa Major’s “Big Dipper” and took over three hundred exposures before layering them together to get an early “deep view” of the Universe. Within a tiny patch of the sky, the HDF revealed thousands of galaxies.

Inspired by HDF and other deep surveys, the HUDF was taken a few years later. Astronomers selected a patch of sky that appeared free of nearby stars, dust, and debris. This ideal dark patch was located south of Orion in the southern sky’s Fornax constellation. From September 24, 2003, through January 16, 2004, Hubble peered into a tiny patch of darkness, one-tenth the diameter of the full moon, and found unparalleled beauty.

Within this single image, we can see galaxies evolving. The most distant parts contain light that was emitted almost 13 billion years ago, when the Universe was only 800 million years old. We can see the galaxies age and change over time, since the objects closer to us in space are also closer to our present time. The ten thousand galaxies contained therein are made of uncountable stars and inestimable worlds. As a high school student looking at this image, a profound realization came to me about the scale of the Universe. With all the Universe out there, how can we consign ourselves to only one planet, in only one star system, in only one galaxy?

As huge and deep as this image is, it also calls to mind what is perhaps an even more startling revelation: with so many galaxies in such a small window, what does the rest of the sky contain? The answer is quite simple, more of the same In every direction, with very little variation there is another HUDF waiting to be captured.

Confronted by the awe-inspiring scale of the Universe, it seems too big to comprehend or to care about, but remember—Hubble has shown us just how beautiful our Universe is! If no one is looking, all of that beauty would go unnoticed. So, on this historic anniversary I invite you to do your part, look at a Hubble image, attend a lecture, or even find a nice, dark, clear patch of sky and do some observing for yourself. –Josh Roberts

After Hubble: The James Webb Space Telescope

When it was launched in 1990, the Hubble Space Telescope was given an estimated lifespan of 15 years. Thanks to several servicing missions by space shuttle crews, it has surpassed that by far, and scientists are anticipating that it may remain operational through 2020. With the space shuttles now retired and no further visits by astronauts possible, gravity and atmospheric drag will eventually cause it to fall out of orbit and come crashing to Earth. NASA’s current plan is to wait until the day Hubble’s usefulness has ended, then robotically attach a rocket booster to steer it in a controlled re-entry to a remote part of the ocean.

No direct successor to Hubble is planned that will operate in the same visible, near-infrared, and ultraviolet regions of the electromagnetic spectrum, the broad continuum of mostly-invisible energy of which visible light is a tiny part. In fact, adaptive optics that correct for atmospheric distortion have reduced the advantage that Hubble, which operates above most of the atmosphere, has over ground-based telescopes. This, combined with the larger diameter of some planned telescopes, such as the Thirty Meter Telescope in Hawaii and the 24.5-meter Giant Magellan Telescope in Chile, will give Earth-bound telescopes capabilities that surpass Hubble’s 2.4-meter mirror.

However, a new instrument, the James Webb Space Telescope (or JWST, formerly known as the Next Generation Space Telescope), is now in preparation as a replacement for both Hubble and the infrared Spitzer Space Telescope. JWST features a 6.5-meter segmented mirror and will operate in the long-wavelength visible to mid-infrared regions of the spectrum, allowing astronomers to study the most distant objects in the Universe. The visible light from those objects, such as quasars and the youngest galaxies, is Doppler-shifted to the infrared region, which ground-based telescopes have difficulty detecting.

Scheduled for launch in 2018, JWST will be placed at the L2 libration point, about a million miles farther from the Sun than Earth, but gravitationally locked to Earth so that it orbits at the same speed. This is also where the European Space Agency placed several of its other major space observatories—Herschel, Gaia, and the now-deactivated Planck. Unlike the low-orbiting Hubble, Webb it won’t have to contend with having its view blocked by Earth or tolerate the thermal stress of passing from Earth’s shadow into direct sunlight and back every 49 minutes.

Perpetually pointing away from the Sun, JWST must operate at a very low temperature and so will be protected by a large, multi-layered sunshield. Both the 18-segment primary mirror and the sunshield will be folded up for launch, then will automatically unfold in space—a tricky proposal, since the telescope will be too far out for any kind of servicing or repair in case something goes awry.

But if all goes well, JWST is expected to give astronomers an unprecedented view of the early cosmos, helping them better understand the birth of stars, planets, and galaxies, the nature of planetary atmospheres, and the origins of life. –Bing Quock

Image: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team