SN 2011fe is the brightest supernova as seen from Earth in nearly 20 years. It's a rare event that astronomers around the world are excited about -- it's not only a beautiful spectacle, it may also teach us new things about supernovae and the universe that we live in. Here you'll find information on what SN 2011fe is, why astronomers around the world are watching it, and most importantly, how you can make your own observations and help create a scientific record of this supernova!
Supernovae are caused by the sudden death and destruction of a star. There are several different kinds of supernovae, each of which comes from a different type of star. The two main progenitors of supernovae are the explosion of a stellar remnant called a white dwarf, and the collapse and explosion of a massive star many times the mass of our own Sun. White dwarfs can form supernovae when, as members of binary star systems, they accrete enough mass from the other star in the system that they reach a critical mass of about 1.4 times the mass of the Sun. When a white dwarf reaches this mass limit -- called the Chandrasekhar Limit -- it can no longer support itself against gravity and it collapses. The result of this collapse is the sudden thermonuclear burning of the interior of the white dwarf, which then explodes. This explosion is what we see as the supernova. The explosion releases as much energy over the course of a few months as all the other stars in a galaxy combined. This is what makes supernovae so bright and easy to see across large distances.
Supernova 2011fe was discovered on August 24, 2011  by the Palomar Transient Factory, a research program run by astronomers at CalTech. Their telescopes caught the explosion very soon after it occurred while they were making routine observations of the galaxy Messier 101 near the Big Dipper (the constellation Ursa Major). Within a few hours of the explosion, the supernova brightened from invisibility to become one of the brightest objects within M101, and has since become even brighter still. It's now nearly a thousand times brighter than when it was first spotted by PTF, and is visible in medium sized back yard telescopes, outshining all of the rest of M101 combined!
An analysis of the light from SN 2011fe shows that it is the type of supernova that originates from a white dwarf, known as a "Type-Ia Supernova". Type-Ia supernovae are very important for cosmology because they can be used to measure distances to the galaxies where they occur. All Type-Ia supernovae give off the same amount of light at their peak brightness, and by measuring the amount of light that we detect, we can measure how far away they must be. We already know the distance to M101 pretty well, but SN 2011fe will allow us to calibrate the relationship between peak brightness and distance better than ever, and will also allow us to study the evolution of this supernova in greater detail than we normally can.
Observations of SN 2011fe made by AAVSO observers since August 24, 2011. This graph, known as a light curve, shows the change in brightness of the supernova over time. Different colors of points indicate observations made with cameras using different colored filters. Observations in black are visual estimates made by eye. Over 1000 observations of the supernova have been submitted to the AAVSO so far.
Astronomers from around the world -- including AAVSO observers -- have been following SN 2011fe since it was announced to the world. Amateur astronomers have thus far created a comprehensive record of the outburst -- a "light curve" -- and observations are continuing. The supernova will likely be bright enough to see with backyard telescopes for the rest of 2011.
The supernova is located near the end of the handle of the Big Dipper (the tail of Ursa Major). M101 is directly above the midpoint between the last two stars of the handle, Mizar and Alkaid, forming triangle with those two stars. It is currently shining at 10th magnitude, which will be visible in very large binoculars or a telescope with an aperture of 6 inches (15 centimeters) or more.
These finder charts will help you locate M101 and the supernova within it, and will also provide you with "comparison stars" -- stars of known brightness -- that will help you estimate how bright the supernova currently is. The galaxy itself will be faint except for its bright central regions, but the supernova and comparison stars should be visible in suitable equipment.
How do you estimate the brightness of a variable star with your eyes? It's easy! Visit our Observers  page to learn more about how to make a visual estimate of SN 2011fe and thousands of other variable stars in the sky! We have tutorials, charts and observing manuals, and instructions on how to become an official AAVSO observer and submit observations!
If you have a CCD camera for your telescope, you can make observations too! Check out our resources for CCD observers to learn more about how to extract photometric data from your images.
For deep sky photographers: did you image M101 any time between August 23 and August 25, 2011? If so, you may have caught the supernova early on without knowing it! Please check your images against our star charts to see if the supernova is visible. If so, please measure its brightness and submit your observations! Every observation counts!
2012 January 04: AAVSO observers continue to submit both visual and CCD observations of the supernova, and the resulting light curve traces the behavior very clearly. It has been over four months since the supernova was first detected (August 24, 2001), and the supernova has declined to magnitude 14 in all bands. Observers have reached the 7,000-observation mark as well! The supernova may be bright enough to observe with backyard telescopes for several more months, and we strongly encourage its continued observation in 2012 for as long as you can see it!
2011 November 28: SN 2011fe remains well within reach of moderate-sized backyard telescopes, and observers continue to obtain multicolor photometry and visual estimates. The object is difficult for evening observers of the Northern Hemisphere now, being low in the north in the evening sky. Observing is much easier in the pre-dawn hours, and we encourage observations of the supernova by early morning observers! To date, over 6850 observations have been submitted to the AAVSO.
2011 November 7: The supernova has faded substantially in the two months since its maximum back in September, but it remains bright enough to be seen in larger backyard telescopes. The B-band (blue) light curve faded rapidly but is now fading more slowly than the longer-wavelength light. This is due in part to the change in what's powering the supernova light; the shallower decline during this stage is due to energy from the decay of the radioactive isotope 56Cobalt. To date, 161 observers have made over 6,700 observations of SN 2011fe and submitted them to the AAVSO!
2011 October 21: We're nearly two months past the start of the supernova, and over a month since maximum light, but SN 2011fe is still around 12th magnitude. The past few weeks brought the secondary maximum in R and I bands, and now the broadband light is clearly declining, about half a magnitude in the past 10 days. As of this moment, observers just like you have submitted a combined 6411 observations of this supernova, exceeding the total number of observations submitted for supernova 1987A. It's important to remember that most of the observers of 1987A were visual observers, while most of the data coming in for this supernova are instrumental -- taken with CCD and other digital cameras. Supernova 1987A was incredibly well-observed by the visual observer community. Will SN 2011fe be as well covered throughout its lifetime? Keep observing and it will be!
2011 October 4: We are nearly a month after maximum light, and we clearly see a secondary maximum taking shape in the redder R and I bands of the light curve. SN 2011fe appears to be behaving like a typical Type-Ia supernova. Please continue following this bright supernova for as long as you can -- the more data we have, the better we'll be able to track all of the changes that the supernova will undergo while it fades.
We also note that the 2011 Nobel Prize in Physics was awarded to Saul Perlmutter, Adam Reiss, and Brian Schmidt  for their collective work on high-redshift Type-Ia supernovae and the discovery of dark energy and cosmic acceleration. The AAVSO extends its congratulations to Drs. Perlmutter, Reiss, and Schmidt on their achievement!
2011 September 27: SN 2011fe is obviously declining in brightness, but is still brighter than magnitude 11.0. The AAVSO has received over 3200 observations from 138 observers so far and is now the second-best observed supernova in the AAVSO's history! Only SN 1987A was observed more, having 5869 total observations. Unlike SN 1987A most of our observations of SN 2011fe come from observers with CCD cameras: we've received 423 visual estimates, and 2842 instrumental measurements.
2011 September 10: SN 2011fe was within a few days of maximum at this time, reaching a visual magnitude of about 10.0. As of noon UT on September 10, the AAVSO had received over 1200 observations of the supernova!