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Photograph a New Star

Astronomers predict a new naked-eye star will emerge in the night sky in 2024. While the star may be newly visible to you and me, the fresh point of light is actually a recurrent nova, having been recorded in 1866 at magnitude=2 and in 1946 at magnitude=3. If you photograph that part of the sky now with a cell phone camera, when the nova appears again you'll be one of the few people ahead of the news curve with your own before-and-after photos of this celestial phenomenon.

While astronomer Jim Kaler anticipated (2011) its reappearing in 2026 after another 80-year cycle (it's been sighted in 1217, 1787, 1866, and 1946), a recently observed "pre-eruption dip" suggests we'll instead have a summer 2024 interloper in the night sky. Fraser Cain explains what's happening in the opening story of this Space Bites.

The Reappearance

The ancient star, named T Coronae Borealis (T CrB ), is actually a closely bound pair of stars, with the gravity of one massive white dwarf ripping off the outer layers of its less-dense yet larger companion star, a red giant star (M3). Eventually a critical mass accretes around the white dwarf and it emits a mighty outburst. T CrB suddenly becomes 1,500 times brighter, rising from unseen (magnitude=10) to about as bright as the north star Polaris (magnitude=2). Within a few days or weeks the apparition retreats from its brief effulgence back into the darkness.

For me the beauty of T CrB isn't so much the visibility of the exploding star itself but the predictive nature of science. Jim Kaler and others have been telling us it's coming; let's watch and see. I recommend you find the constellation Corona Borealis, then take some long-duration (e.g., 3 seconds) pictures with a cell phone camera. Grab a shot every night you step outside--find the northern crown, open camera, take 3-second exposure, done. Look for change.

When T CrB blows, continue taking photos of the same area. Revel in seeing a rare nova naked-eye, and celebrate with your before-and-after images that reveal the nova's trajectory.

In Practice

On June 15, 2024, despite moonlight and wispy clouds, I took some twilight photos of the southwestern sky. As the weeks pass, the target gradually moves westward at the same given hour. It's amazing how well a newer phone captures stars with a 3-second exposure. Hold still!

Bluish sky with faint stars and clouds.
Three-second exposure with cell phone camera (iPhone 13) at twilight reveals stars.

From the curved handle of the Big Dipper, "follow the arc to Arcturus," the bright yellowish star in the constellation Boötes. The connected dots look like a kite with a short tail, or an ice cream cone with a large scoop on top. Next to Boötes is Corona Borealis, the northern crown. Its prominent star Alphecca is also known as Gemma, the gem star in the crown. Keeping with the summer theme, you could consider Corona Borealis a cup into which you could put a smaller scoop of ice cream.

Stars with arrow and constellation outlines.
From the Big Dipper handle, "follow the arc to Arcturus," which anchors Boötes. Left, to its east, is Corona Borealis, the northern crown.

Faint outlines of constellations Boötes and Corona Borealis drawn in red.

Zoom in on the crown. Sure enough, even in twilight the camera picks up seven main stars.

Star chart paired with cell phone photo shows where to find T Coronae Borealis (T CrB). Chart courtesy of Fraser Cain.

When you hear in the news that a dynamic star has appeared in the night sky, go back out and re-image Corona Borealis. Did you capture the explosive nova? You are citizen paparazzi chasing an ephemeral new starlet, T Core Bee.

Here's a zoomed star chart to help confirm.

Star chart shows location of T Coronae Borealis (T CrB). Chart courtesy of Fraser Cain.

The Stars

Jim Kaler further describes (2011) the dynamics of T Coronae Borealis (T CrB), and hints at an extreme case of nearby nova candidate Epsilon Coronae Borealis accreting mass that exceeds a tipping point:

...The "recurrent nova" T Coronae one of only eight known. Normally of tenth magnitude, T CrB consists of a class M3 giant in a 227-day orbit with a massive white dwarf. Tidally distorted by its companion (and thus variable as it presents different-sized cross-sections with different temperatures to us), the giant feeds matter onto the white dwarf (at a rate close to a million times that of the solar wind). When the layer of fresh hydrogen is sufficiently great, the heat of compression causes the layer to blow up like a hydrogen bomb. Normal novae are made of lower mass white dwarfs that feed off low mass ordinary dwarfs, and after the new layer is thick enough, should pop off every few tens or hundreds of thousands of years. But T's white dwarf is so massive that the intervals between explosions are short. In 1866 the star hit magnitude 2, and in 1946 mag 3, taking but a few days to drop back to invisibility. Are we due for another blowup around 2026? Nobody really knows, but keep your eye on Epsilon [note: Epsilon Coronae Borealis is a nearby nova candidate]. The event could be far grander. The accreted matter could push the white dwarf over the fabled 1.4 solar mass limit, beyond which the WHOLE STAR would collapse and blow up in a grand (Type Ia) supernova that -- even at a distance of 2500 light years -- could become as bright as a crescent Moon!

To go deeper into T Corona Borealis, see AAVSO presentation by Dr. Brad Schaefer originally broadcast 2023 September 9:


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