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.

Saturn’s moon Epimetheus from the Cassini spacecraft.
Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA
and APOD.

On the bus in Denali National Park a few years ago, I found myself sitting next a couple from the East Bay. If you’ve ever been on the Denali bus, you know that it’s a long ride and it was just a matter of time before we struck up a conversation. As often happens, we wound up talking about work and then about astronomy research. Both of them were very interested in the field but were unsure of where to find good information on the web. At the time, I hadn’t really thought about that and wasn’t much help.

Now that I’m writing for QUEST, I am much better suited to answer them. I spend a lot of time surfing the web for images and links to websites to provide the full details for readers who want to follow up on my posts. Over the course of a year or so, I’ve discovered quite a few resources and have settled on a few favorites. Of course, being a Berkeley and Cornell grad, I have a few biases…

First of all, it is common for a university astronomy department to organize a public outreach campaign. I won’t bother with the obvious disclaimers and instead will just say that two of my favorites are “Ask an Astronomer” at Cornell University and the Berkeley Center for Cosmological Physics.

These two sites are quite different. As the name implies, the Cornell site encourages questions and suggestions from readers. The content of the site is therefore governed by the public, covering a wide variety of topics in fairly brief, straightforward language. The Berkeley site is much more structured. They cover the history of cosmology and outline the history of our universe with all the appropriate links (scroll down to see the links). This provides a very detailed and organized explanation of a specific field of astronomy.

In addition to universities, there are quite a few NASA missions that maintain excellent public relations. Almost everyone knows the Hubble Space Telescope and Mars Rovers. Both sites are updated almost daily with galleries, discoveries, and recent news. NASA also has several other large missions at other wavelengths that are probably not as well known. Three examples are the Chandra X-ray observatory, the WMAP mission, and the Spitzer infrared observatory. Like the Hubble and Rover sites, these space-based observatories perform ground-breaking science and do an excellent job explaining their discoveries to the public.

Besides QUEST, there are also quite a few other excellent blogs out there. Each site has a different approach and finds its own balance between astronomy coverage, opinion, and discussion of general science. One of the most popular is the Bad Astro site–we even have a link on the right hand side of the QUEST blog web page. You can also check out About.com’s top ten space and astronomy blogs.

Of course, one obvious place to learn about astronomy is from journalists. Two websites that do a very good job of covering the field are Space.com and New Scientist (some content requires subscription).

Finally, if you enjoy beautiful images of the sky, a great place to look is the “Astronomy Picture of the Day.” This is where I got my image for today. If you look tomorrow you’re guaranteed to find something just as exciting!

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: 37.8768, longitude: -122.251

Star or Comet?Yesterday was a very long day at work. I was stuck in meetings with our collaborators for over 6 hours! To make it worse, we spent the entire time discussing a single topic. I even wrote my last paper on it. What could possibly be so captivating, you ask?

Remember the solar wind I wrote about a few weeks ago? This stream of protons does more than create comet tails and aurora, it also destroys all of those fancy electronics we work so hard to put into orbit.

The protons streaming from the sun carry a lot of energy, and they leave a lot of this energy behind as they pass through satellites and astronauts that don’t have the Earth’s atmosphere to protect them. The energy released wrecks havoc on the system, throwing electrons and atoms around like a game of ping-pong. This is one form of radiation damage.

Definitely a comet!
This radiation damage is harmless over short periods of time, much like an occasional X-ray at the dentist. However the solar wind becomes a problem for something like the Hubble Space Telescope or our proposed satellite SNAP which are exposed for many years.

To understand how a telescope degrades from exposure to radiation, let me give an extremely quick explanation of how we gather astronomical images. A telescope is very similar to a camera you buy in the store. The large mirror is equivalent to the lens on your camera. The part that suffers the most radiation damage is the Charge Coupled Device, also known as a CCD.

The CCD is essentially the same as the 8-megapixel chip in your digital camera. This serves as an electronic version of film, recording the image through the photoelectric effect rather than through a chemical reaction. If you can still remember how photography was in the days of film, I’m sure you can appreciate the relief of going digital. Astronomers realized this early on and were pioneers in the use of CCDs.

The photons from the subject of the photograph collide with electrons in the silicon of a CCD, knocking them free from their parent atom. The free electrons are then collected in a well near the site of the collision. Once the exposure is complete, charge is moved one well (or pixel) at a time toward a transistor which then reports the number of electrons found. This process is usually described through the analogy of a bucket brigade passing buckets of water from a reservoir to a fire.

When the CCD is brand new, the bucket brigade performs almost perfectly. If I want to observe a star, the image comes out crystal clear. However, after enough time in space and in the solar wind, the CCD begins to show its wear. The bucket brigade gets sloppy at work and has to contend with an increasingly difficult obstacle course, spilling a little bit of water (or electrons) during each transfer. That same star now leaves a trail of charge behind and begins to look more like a comet.

Now, if I am observing a star, I want my image to look like a star, not like a comet. Is that really too much to ask? Unfortunately, the CCD will inevitably deteriorate in space and astronomers have to find ways to predict and correct for this deterioration. This is what we spent yesterday discussing. We passed around some pretty good ideas but still have a bit of work to do before we can prove a new method for correcting the images. I just hope we it figured out before our satellite launches in 2015!

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: 37.8768, longitude: -122.251