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Crab Nebula
The Crab Nebula in Taurus is the 6-light-year-wide remnant of a supernova explosion seen in 1054 AD. We know it resulted from the violent death of a massive star, because the star's collapsed core remains visible as a pulsar — a rapidly rotating, highly magnetic neutron star — in the nebula's heart. This composite image was assembled from 24 exposures by the Hubble Space Telescope’s Wide Field and Planetary Camera 2.
NASA, ESA, J. Hester and A. Loll (Arizona State University)
In collaboration with key organizations of amateur and professional astronomers, Sky & Telescope established the free AstroAlert e-mail news service to alert telescope users when significant celestial transients occur (or are predicted to occur) for which scientists are requesting CCD images or other observations from advanced amateur astronomers. A typical AstroAlert will tell you what to look for, where and when to look, what kinds of observations are needed, and how and to whom to report your results.

The Next Nearby Supernova

AstroAlert grew out of a partnership between Sky & Telescope, the SuperNova Early Warning System (SNEWS), and the Hubble Space Telescope project. Our goal is to be prepared to spring into action the next time a massive star in our galaxy dies in a core-collapse supernova — something that hasn't happened in at least 400 years but that could occur again at any moment. Detailed studies of the first nearby supernova since the invention of the telescope will advance our understanding of stellar evolution enormously.

When a massive star's core implodes at the end of its life, it spews countless subatomic particles called neutrinos in all directions before blasting its outer layers into space in a brilliant flash. Some of these neutrinos will reach Earth before the supernova becomes visible at any wavelength. But neutrino detectors are able to tell only roughly which direction the particles are coming from. So when a pulse of neutrinos arrives from a galactic supernova, we may know its location only to the nearest few degrees. This isn't precise enough to target Hubble and other professional telescopes, whose fields of view are measured in arcminutes.

This is where AstroAlert comes in. Immediately upon recognizing a supernova neutrino pulse, the SNEWS collaboration will post an AstroAlert telling amateur astronomers approximately where to look for a brightening "star" that wasn't there before. Thanks to their use of small telescopes with wide fields of view, amateurs will likely be the first to spot the supernova and report its position. Sky & Telescope will serve as a clearinghouse for these early observations and will convey the results to our SNEWS and Hubble partners so they can point their more powerful telescopes to the supernova as quickly as possible.

Nobody knows how much time will elapse between a supernova neutrino burst and the first visible light from the explosion. It could be minutes, hours, or days, depending on the nature of the dying star's outer layers and the amount of obscuring dust beween the supernova and Earth. Researchers are especially keen to see the light turn on, because the details of how this occurs can tell us much about the physics of the explosion. So time is of the essence, and very early CCD images and other observations from amateurs could be of prime importance.

AstroAlert Upgrade

When we unveiled AstroAlert in 1999, it featured 11 separate mailing lists, one for nearby supernovae and the rest for other types of transient sky events, such as lunar and asteroidal occultations, solar storms, gamma-ray bursts, and unusual planetary activity. As of mid-February 2007, the old e-mail server underlying the original AstroAlert system was decommissioned. AstroAlert has now been moved to the same server that our website resides on and will use the same mailing-list software that we use for S&T's Weekly Bulletin and Monthly Blog Report. This means you now have the option of receiving AstroAlerts in HTML, including finder charts where appropriate; if you'd rather receive them in plain text without illustrations, you can do that instead. The new system will also enable us to archive AstroAlerts on our website for future reference.

How to Sign Up

If you're an advanced amateur or professional astronomer and wish to subscribe to AstroAlert, go to our e-newsletters page. (If you're just a casual stargazer, you'll probably be happier with our free Weekly Bulletin instead.) If you haven't already registered with, you'll be asked to do so before you can sign up for AstroAlert or any of S&T's other e-mail bulletins. Registration is a quick and easy process during which we ask for little more than your name and e-mail address. You can sign up for AstroAlert right on the registration form.

Once you register and sign up, you'll be sent an e-mail to confirm your free AstroAlert subscription. This is a security measure to ensure that nobody but you can add your e-mail address to our list. The e-mail will come from, the same address from which all AstroAlerts themselves will originate. If your e-mail system requires you to approve senders' addresses, please add to your "white list." If you don't see an e-mail from AstroAlert in your "in" box within a few minutes of signing up on our website, check your spam filter — it's probably in there. You must reply to the confirmation e-mail to activate your subscription, at which point you'll get a thank-you e-mail.

For more information about catching the next galactic supernova, see the articles linked below. Good luck, and clear skies!

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