Wednesday, August 14, 2024
Ian's Astrophotography challenge, imaging Corona Borealis to catch the Blaze Star
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| Sky chart facing north on Saturday, August 17 as seen from Adelaide at 19:11 ACST (90 minutes
after sunset, click to embiggen). The location of T CrB is shown with a circle. Similar views will be seen 90 minutes after Sunset elsewhere in Australia. | Sky chart facing north on Saturday, August 17 as seen from Adelaide at 19:11 ACST (90 minutes
after sunset, click to embiggen). Constellation names and lines are shown for clarity. |
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| My image of Corona Borealis taken on 10 August with my Samsung S24 in astrophography mode at 5x zoom. Stars down to magnitude 7.5 are visible. The approximate location of T CrB is shown with a star above Ɛ CrB. | AAVSO chart of Corona Borealis showing the magnitude of surrounding stars. The decimal points have been omitted eg 22 is 2.2, 89 is 8.9 |
If you look to the North at astronomical twilight (90 minutes after sunset), you will see a prominent bright orange star, Arcturus (see top chart), if you look downwards and to the right you will see a dainty circlet of stars. Corona Borealis, the northern crown.
While pretty in its own right, it houses a most unusual star, T Coronae borealis (T CrB), also known as the blaze star. T CrB is a recurrent nova, a binary system where gas from a red giant star accretes on a white dwarf companion. Eventually the gas builds up to a density where a nuclear explosion occurs and this is seen as a nova.
A recurrent nova is one where there is a (semi) regular patter of repeated outbursts. T CrB seems to erupt every 80 years, with the last in 1946. Recent patterns of brightening and dimming look like the pre outburst phase of the 1946 eruption, and it is predicted that T CrB may go nova between now and the end of September this year.
When that happens, T CrB will rapidly rise to from its current magnitude 10 (well below eye or binocular visibility) around magnitude 2 about the same brightness as Alphecca, 𝛂 Coronae Borealis (see bottom left-hand panel), the brightest star in the constellation. It will only remain above unaided eye visibility for a week or so.
T CrB is located on the right-hand side to the circlet, just above Ɛ CrB (see bottom left-hand panel) where the line of stars turn down, there are no other bright stars in the region, so when it erupts it will be easily visible.
The challenge:
Take an image of Corona Borealis every clear night during Ausgust-September awaiting the eruption. You will need a stack of ~ 10 images at high ISO of around 1 second duration, then stacked in appropriate software to pick up the faint stars. It would be best if you zoomed in so that Corona Borealis occupies most of the camera field (with a bit of space on the right-hand side so you don’t miss out on T CrB. That way hopefully you will catch not only the eruption, but the fade as well, doing a bit of backyard astrophysics.
Be patient, after a few night astrophotography you will become familiar with the stars and will easily see when T CrB erupts.
You can also follow the T CRB Nova watch on Space weather (in the the righthand panel). Currently magnitude 19.
Labels: astrophotography, citizen science, nova, T CrB
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