Caveman Astrophotography

Adventures in el-cheapo astrophotography - please navigate back to Chapter 1 using the page links at the bottom of this page for the start of the journey...

After a couple of months of no new novae reported, and just when you thought it was safe to venture out into the Milky Way again, two possible novae were announced in quick succession in early September. A nova (plural novae) occurs when a white dwarf star which has been accreting material from a larger companion star explosively sheds its outer layers. We typically see this from Earth as a star brightening relatively quickly in a position where no star was known before, and dimming off again over time.

Both of the possible novae were well situated for southern observers, one in Centaurus and one in Scorpius. With a decent break after a couple of months of cloudy weather, I dusted off the gear and set-up to 'shoot' them. Limited pretty much by my crap gear to shooting at 55mm with the Canon 400D, the objects proved easy to locate, not packed in a dense cluster of similar magnitude stars like sometimes happens. First I went for the Centaurus one...

Quite close to the Pointers to the Southern Cross. This shot was hand-guided using slow-motion controls on an EQ1 mount, with a Celestron NexImage in a home-built 80mm achro refractor to provide the guidestar. Very ricketty, and as I've said before it pretty much limits you to widefields. But quite adequate for this sort of stuff. Clouds did come in on this first evening, and I only got a single shot.

Next was Scorpius, taken when the clouds broke later in the night...

This time, I got three subs and stacked them in Deep Sky Stacker.

On subsequent nights, I saw the Scorpius object rise to about mag 8, plateau for a couple of nights, then gradually dim off. And I saw the Centaurus object gradually dimming off from just brighter than mag 9 to around 9.6.

Taking advice from Terry B on the forum, I extracted the green channel from each night's shots to estimate brightness, and submitted my observations to AAVSO (American Association of Variable Star Observers). Obs from all over the world are used to create 'light curves' for analysis of the stars.

What I did should not be confused with photometry, which uses CCD cameras to accurately measure magnitudes. DSLRs use a different chip, and have inherent limitations because of 'anti-blooming' gates universally installed (among a number of things!). But the green channel I used most closely approximates the 'V' filter used in photometry, and has the peak quantum efficiency (whatever that means, LOL!!).

The Scorpius one has since been confirmed as a 'classical' nova - Nova Scorpii 2008 - while news of the Centaurus one is yet to be announced...

And speaking of stars blowing up, there are supernovae too! These are catastrophic star detonations, triggered in a variety of ways. While we're still waiting for the next Milky Way one, they go off regularly in dim & distant galaxies. You might think that these distant events are in the realm of big scopes & flash CCD cameras etc, but you might also be wrong! Sometimes when they're bright enough, all you need is an entry level DSLR and a zoom lens....

OK, OK, it's a terrible shot, LOL! It was taken by me a couple of months back, hand-guiding using 200mm zoom on the Canon 400D. Zoom is way too much for the guiding, but hey, it shows at least!!

This supernova is designated 2008bk, a Type II supernova, and the brightest one so far reported in 2008. It is located in the outer regions of NGC7793, a mag 10 spiral galaxy in the Sculptor group. I just find it fascinating - what impact must this have had on the surrounding areas of NGC7793, when to us it looks for all the world like a faint MW star, and the other stars of 7793 are but a billionth part of a tiny grey fog.

That light has been travelling for 13 million years across the Universe in an ever expanding sphere, stretching thinner & thinner - and yet a camera on a wobbly mount can still capture photons from the event!!