The Hubble Space Telescope being serviced by Space Shuttle
Atlantis astronauts in May 2009. Credit: NASAFour hundred years ago, Galileo built his telescope and became the first on record to point the new device (invented the previous year) at objects in the sky. Today (in fact, even as I write!) what has become a symbol for the current state of evolution of the telescope—the Hubble Space Telescope–is being repaired and upgraded by the crew of the Space Shuttle Atlantis…for the last time.

Galileo's telescope had a magnification of only about 27x, allowing him to see that Venus has phases like the Moon, Jupiter has four large moons of its own, Saturn does not appear as a simple disk but has unusual "projections" to either side, and the Milky Way contains far more stars than is apparent to the naked eye. And though these are features that can be seen through the least powerful home telescopes today, Galileo's observations changed the way we look at the universe.

Hubble has done the same thing, but on a modern scale of magnitude. Not a large telescope by the standards of ground-based behemoths like Keck in Hawaii (Hubble's primary mirror is 2.4 meters in diameter), Hubble's "edge" is it's location in space, orbiting the Earth over 300 miles high, outside of our atmosphere. Particularly in its earlier days before ground based telescopes were using adaptive optics techniques to compensate for atmospheric distortion, Hubble's vision on the universe was unparalleled in its clarity.

Here's is a recap of a few of the many big discoveries Hubble has made possible:

Dark Energy: By accurately measuring the distance and velocity of distant supernovae, over a large range of distances, Hubble has refined out knowledge of the rate of expansion of the universe–leading to the discovery that the expansion of the universe is actually accelerating, contrary to what was expected. Scientists suggest the existence of a mysterious "dark energy" throughout the universe that exerts an antigravitational repulsive pressure on the cosmos.

Age of the Universe: Since Edwin Hubble (for whom the Space Telescope was named) discovered that the universe is expanding, astronomers have been trying to determine how long ago the expansion began–how long ago the "starting gun" of the Big Bang was fired, and thus the beginning of the universe. Through precise observations with the Hubble, astronomers in recent years have been able to peg it between 12 and 14 billion years. (Most recently, observations made with the WMAP mission have honed that down to 13.7 billion years, give or take 0.13 billion.)

Supermassive Blackholes: Hubble found the clues that point to the existence of "supermassive" blackholes at the heart of maybe most–or every–galaxy. The Milky Way's own central blackhole has a mass equivalent to four million Suns.

Stellar Dust Disks: Before the first extrasolar planets were actually detected, Hubble observations revealed that flat disks of dust encircling young and developing star systems–aka "protoplanetary disks"–is commonplace. This has given us a glimpse at what our own solar system may have looked like before the planets formed.

It has been seven years since the last Hubble servicing mission, with another servicing scheduled a few years ago cancelled in the wake of the Columbia disaster. Several failing systems will be repaired or replaced this time, and other instruments are receiving upgrades that will make Hubble more powerful than ever in its declining years.

This mission to service the Hubble will be the last. Since NASA is retiring the Space Shuttle fleet after 2010, we will no longer have a space vehicle large enough to carry upgrade and replacement equipment to and from the Hubble. After that, the next new big space-based descendent of Galileo's spyglass will be the James Webb. Stay tuned…

Last night we completed our observations for the Supernova Legacy Survey. This was a five year program to study supernovae using a 4-meter telescope in Hawaii in combination with several of the largest optical telescopes in the world.

The project was headed by a group at a university in Toronto and a group at a university in Paris. Canada and France sponsor the 4-meter telescope that is used to discover and observe the supernovae from the point of explosion to the final days when the supernova fades from view. We call this the imaging part of the program. This data constrains the apparent brightness and life cycle of the supernova, and eventually the absolute distance to the supernova.

Our contribution to the project was primarily through our affiliation with Keck Observatory. We were typically awarded four nights a year to observe recently discovered supernovae spectroscopically. The data is used to determine the redshift and the kind of supernova explosion.

The supernovae are used to study the rate of expansion of the universe. It was this type of experiment that was first used to discover that the universe is actually dominated by dark energy.

No one really suspected the presence of dark energy for almost the entirety of the 20^th century. Now, we not only know it exists but are actually trying to understand it in the same way we understand gravity, protons, and electrons. That is where projects like the Supernova Legacy Survey come in. With projects like this, we work to collect enormous samples of well-studied supernovae that can improve our understanding of dark energy.

We use a certain type of supernova as yardsticks to measure distances in the universe. We then model the affects of dark energy on the expansion history of the universe by comparing distances and rates of expansion. This comparison is typically represented in a Hubble Diagram.

The Supernova Legacy Survey has been very successful in its attempts thus far. On the right, I show the Hubble Diagram from the first year of data. This is less than 20% of the full sample. The dotted line outlines the expectations of the 1990's cosmology crowd. The solid line shows the prediction from the more sophisticated cosmologists of the 21^st century. As you can see, the original expectations were pretty far off the mark – the supernovae just don't lie on top of the dotted line.

Now that this program is finishing up, we should be seeing similar figures that are teeming with supernovae. Future programs should do an even better job of making these measurements. Someday we may actually understand this dark energy thing, it may turn out to be something else completely new and unexpected!

Kyle S. Dawson is engaged in post-doctorate studies of distant supernovae and development of a proposed space-based telescope at Lawrence Berkeley National Laboratory.

The Forest

Venus Landing. Credit:
Soviet Planetary Exploration ProgramIt's time to get back to some of the reader’s questions. Over the last couple of months I've focused on the easy ones like "how big is the universe?". Now, people are asking the tough ones, like that from Mike:

"There’s been a recent debate in our local papers regarding Venus' high planetary temperature being related to the dearth of carbon dioxide on the planet. Apparently Venus is much, much hotter than Mercury, even though Venus is twice as far from the sun. Could you explain a bit about our system’s planets and how they differ compositionally? What is it about the Earth's composition of elements that makes it just right for 99% of the life on the planet? I say 99% because it seems 1% of the life is strange enough to exist in all sorts of harsh conditions."

When it comes to the landscape of our own neighborhood, it gets a little more complicated for me. I have a tendency to look right past the solar system in my research of the distant Universe. I'm sure there's an explanation for this in the cliché of missing the forest for the trees. I just do it in reverse.

The Trees

Hubble Deep Field. Credit:
R. Williams, The HDF Team (STScI), NASATruth is, the trees are quite intriguing in their own right. I think people are more impressed with the observations of our solar system because the proximity lends to very detailed images and observations. Compare an image of the surface of Venus to one of the deepest images from Hubble Space Telescope. The image of Venus fits within our sense of scale that we established in our time here on Earth. You can even see familiar rocks and the feet of the Soviet robot. The Hubble Deep Field… needs a bit of explanation.

For the rest of the year, I am going to pull back from the farthest reaches of the universe and focus on Venus and the other planets. It will give me a chance to learn a little about what the Solar System actually looks like. It will also give me a chance to explore some of the most breath-taking images that NASA has created. I'm just going to have to do a little research to get it right.

Kyle S. Dawson is engaged in post-doctorate studies of distant supernovae and development of a proposed space-based telescope at Lawrence Berkeley National Laboratory.

latitude: 37.6797, longitude: -121.698