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Supernova Surprise: How to Spot a Fallen Star

Attendees of a Royal Astronomical Society meeting in Wales this week are likely abuzz over a study presented yesterday that says there really was a bright star that appeared the day King Charles II was born in May 1630.

Dubbed the royal star, this legendary celestial guest was described as a star shining so bright that it was visible during the day with the naked eye.

“Never [had] any Starre appeared before at the birth of any (the Highest humane Hero) except our Saviour,” English writer Edward Matthew penned in a 1661 pamphlet.

Although most historians thought such stories were royal propaganda, new evidence suggests the “star” may have been a supernova called Cassiopeia A.

(Related: “‘Light Echo’ Helps Solve Supernova Mystery.”)

CassA was once a massive star that ended its life in a violent explosion. According to the new calculations, since light from the blast would have taken about 10,000 years to reach Earth, the supernova would have appeared right around Charles’s 17th-century birth.

Whether the royal story is true or not, it is possible for people on Earth to witness the light from emerging supernovae.

One of the most famous examples is SN 1572, also known as Tycho’s Remnant. The object is named for Danish astronomer Tycho Brahe, who was among many people to record seeing a new star rivaling Venus in brightness that suddenly appeared in the constellation Cassiopeia in 1572.

Not all supernovae will be close enough or powerful enough to be seen from Earth with the naked eye. But sometimes you can glimpse a new “star” in popular astronomical objects that are visible with backyard telescopes.

For instance …

Supernovae Happen: The 2005 Whirlpool “Star”

by Robert J. Vanderbei

The Whirlpool Galaxy, aka M51, is not far—3.5 degrees—from the end of the handle in the Big Dipper. It is a popular target for observers from April through July, when the Dipper is high in the night sky.

M51 is especially interesting because it is actually a pair of interacting galaxies. They are flying past each other (on a time scale of hundreds of millions of years) and their mutual gravitational attraction creates some interesting distortions.

In May 2005 I took a picture of the Whirlpool Galaxy. About month later, a star in the Whirlpool exploded into a supernova.

The explosion was first noticed by amateur astronomer Wolfgang Kloehr on an image he took of the galaxy on June 28, 2005, using an eight-inch reflector telescope.

Even though the galaxy is 31 million light-years away (and therefore the explosion actually took place 31 million years ago), the supernova was bright enough to be seen using fairly modest telescopes here on Earth.

When I heard about this relatively rare cosmic event, I waited with great anticipation for the next clear night. On July 10, 2005, I got my opportunity, and I took a second picture of the galaxy.

I used exactly the same equipment as before so that I could easily do a side-by-side comparison of the two pictures.

Shown here is the first picture of the Whirlpool I took in May (top) and the followup shot I made in July. Click to see full size.

Note that the July 10 picture is identical to the earlier picture—except for a new bright spot just off to the right, a bit from the core of the galaxy. This is supernova SN 2005cs.

At its brightest, the supernova appeared to us as bright as a magnitude 14 star.

When I took my second picture, we were nearing the end of the season for observing M51—the Whirlpool was low in the northwest at sunset. Over the following weeks it became harder to see/photograph because it was very low in the west after sunset.

By the time the Whirlpool moved back into prime position several months later, the supernova had faded from view. I was very lucky to get a picture of it.

The last time a supernova was observed in our home galaxy, the Milky Way, was in 1604.

(Related: “Supernova Blast Seen in ‘Exploding’ Galaxy.”)

On average, supernovae in the Milky Way should occur once every 50 years or so. We might have missed a few if they happened on the other side of the Milky Way but, regardless, we are long overdue for a supernova event in our sector of the galaxy.

Hopefully, the next one will occur sometime soon.

Robert VanderbeiRobert J. Vanderbei is chair of the Operations Research and Financial Engineering department at Princeton University and co-author of the National Geographic book Sizing Up the Universe. Vanderbei has been an astrophotographer since 1999, and he regularly posts new images on his astro gallery website.


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