IMAGING VARIABLE STARS (“PHOTOMETRY”), 21 FEB 2007

R Corona Borealis is my favourite variable star. After all, it’s easy to locate in the bright constellation of the Northern Crown, and it’s almost always about magnitude 6 – ie: at maximum brightness!

You estimate the brightness of variable stars by gauging them against nearby stars of known brightness. The AAVSO has charts for each variable, noting the most suitable comparison stars. Estimating brightness of stars is therefore part art, part science. It’s one of the more important contributions amateurs make to modern astronomy, well worth trying!

If you have a small telescope, an imaging camera and a V filter (a greenish colour) you can collect images of the variable stars and use the results to more accurately measure the changing brightness of variable stars. This is “photometry” and there is free software that will analyse the images to provide accurate readings. Telescopes and cameras are not just for taking “pretty pictures”.

Here’s an image of my favourite variable star, taken this morning with a V filter. R CrB is magnitude 5.9, or can’t you tell?

DON’T TRUST THAT CLEAR SKY CLOCK

It’s not Mr. Danko’s fault the CSC is misleading half the time… weather is hard to predict. Tuesday night the CSC predicted clear skies and good seeing from 8 pm on… alas, it didn’t work that way. I left a dinner engagement in time to be home at 8 pm… cloudy. Had to pass on observing with Steve K…. cloudy. The sky finally cleared at 2 a.m.

Transparency was excellent! I checked on a few variable stars with big binoculars… R Leonis stood out naked eye bright like a cherry in the sky. Saturn had passed the meridian and was out of reach for my 11″, but I set up a little GT80 refractor with the Rebel piggy-back to take some images of the sky. I tried a 135mm telephoto and then switched to imaging through the scope (using a barlow lens and diagonal). Clouds badgered my efforts. The seeing was poor but I managed a few images, and here is one of M-3, a globular near Arcturus:

Now, you may wonder why the centre of the image is so bright. That’s what happens when you obtain focus in a small telescope using a 1.25″ barlow lens in a 1.25″ diagonal! Lesson: use a 2″ setup on reflector so you can see the camera screen when shooting. That, and once achieving good focus, take a large number of shots for stacking purposes, to eliminate noise.

Up Before the Sun, 16 February

Scanning the very dark sky before twilight, Jupiter dominates the viw at magnitude -2, just 10 above the SE horizon. At the moment it sits between two ninth magnitude globular clusters, NGC 6235 and NGC 6287, moving closer to the latter with each passing day.

In a 6″ Maksutov with a zoom eyepiece (they’re very good) it is possible to make out a lot of detail even at the lower powers. The moons string out in a line with faint Callisto on the E side and Io, Europa and bright Ganymede in ascending distance from the planet on the W. The Great Red Spot is prominently separated from the SEB with a bright white boundary between them. GRS approaches the planet’s Central meridian and will be on it in less than an hour (5:30 a.m. in fact).

Here’s the scene:

Jupiter with the 4 moons strung out in a line

BREEZING THROUGH THE SKIES, 10 February 07

With all the complaints of bad seeing lately, I was pleasantly surprised with the skies over Hamilton Saturday night, 10 February. It was a night of good transparency with long periods of great seeing after 11 pm.

As you’d know if you attended the Feb monthly meeting, Saturn’s about to eclipse the moon Iapetus in a few days. The 10th magnitude moon is half black, half white. Its orbit is inclined 7 degrees to the ring plane, so while we can still see the rings, at the moment Iapetus transits Saturn (or is eclipsed) as it orbits with a 90 day period.

I had a 5″ apo refractor set up before 7 pm and invited members to come over after preparing for a cold (-13C) and windy (20 km/hr) observing night. Jackie took up the challenge. She brought the smallest digital camera I have ever seen, a recent purchase.

Saturn was up in the East before 8 pm and I was delighted to see Iapetus just 51″ N of Titan (easy to find). It was Jackie’s first time seeing Iapetus and she said she couldn’t tell which half was black and which was white. There were a number of other moons in sight: Rhea was on the E side of the planet and when we took some 15s exposures with the Digital Rebel, Enceladus, Tethys and Dione were also visible. Jackie preferred the 3.5mm Nagler to a 4mm Radian (“I like the spacious view”) but I think the best views were in a 10mm SpearsWALER recently purchased from Khanscope. After 10 pm the seeing improved and for the first time this year I was able to see the Airy disk of various stars.

Gamma Leonis turned out to be an precious view. The two components were separated by a blackness that highlighted their golden colours. I tried to get Jackie to play the “guess the magnitude game”, but she was already across the sky, looking elsewhere in her 50mm binoculars. I think our Club 2007 observing project should be a double star booklet, double stars are such fun to see.

Jackie took some shots with her tiny digital camera, too. Then we put the ToUcam on the scope to capture some AVI files for stacking – they turned out ok despite the sometimes shakey seeing. Things got more difficult when we tried magnifying the imaging using 2x and 4x powermates. The ToUcam was now brushing patio stones and I had the darndest time getting a good focus without scraping my knuckles.

Meanwhile, our attention had turned to 5.9 magnitude U Orionis high overhead, like a small red LED at the tip of Orion’s err… club. Jackie looked at the Trapesium awhile; the nebula was extensive in 15 x 70 binoculars but only three dancing stars could be distinguished.

It was cold. Every hour we’d come in to warm up, then go back at it. As Saturn climbed to the meridian, the refractor’s eyepiece got lower and lower until my butt was on the patio stones and it was a cramped observing position to say the least. The TAL eq mount worked flawlessly; being Russian, it seemed to like the cold.

By 1 a.m. we had pictures galore, a couple of movies, frozen digits and a lot of wires all over the patio. All the equipment was brought inside to thaw (“here’s a counterweight… watch your fingers don’t freeze to it”). Then with Arcturus rising high in the East it was time to see R CrB, my favourite variable star (“almost always at maximum”) in binoculars. End of show.

Winter nights can be glorious for observing.

This week’s podcast on the Universe Today web site deals with a favourite topic of mine; variable stars. Fraser Cain and Dr. Pamela Gay spend a half hour exploring different types of variables and offer some insight as to why some stars can change brightness so dramatically.

The podcast is at this web link: http://www.universetoday.com/2007/02/05/podcast-variable-stars/

Transcripts and show notes can be found at this url: http://feeds.feedburner.com/astronomycast

Enjoy

A Spotty Sun, 6 February 2007

Is it trite to say “It’s c-c-cold out there”, after the -20ish temperatures during the past week?

Here is what the sun looked like at 8:30 this morning through a 5″ refractor using an Orion glass “can’t-poke-a-hole-in-me” solar filter. The image has been reduced to 450 pixel wide JPG (shh… it’s an “interior picture”):

Last Saturday (January 20, 2007), I decided to go to my brother’s place near Freelton, ON, to take a stab at imaging the sky with my Canon EOS Digital Rebel 300D digital SLR camera on my Super Polaris equatorial mount (I got a half decent shot of Orion, which I may post later)… and BRRRR!!, it was cold! -15 deg C.

Just before I left, I saw the moon and Venus setting over Mapleview Mall, from my condo complex parking lot, and I thought I try taking a few fixed-tripod images of them. Little did I know at the time that I would (barely) get Delta Capricorni right beside the moon, just ten or eleven minutes from being occulted by the moon! (Although Tim H. beat me to the punch!)

Binbrook Report for Saturday Jan 20, 2007 – by Tim Harpur

Observer’s Notes: COLD

Actually, I lasted about 3 hours before deciding to pack it in (just as Jackie showed up) – no wind, but cold and crisp (painfull on the fingers when touching anything metal) – excellent seeing though – at least until 8:30pm when we left.

I snapped off a few shots of the moon and Venus – and just happened to catch the lunar occultation of Deneb Algiedi.

I also took a few shots of M31 (Andromeda), M32, and M110.

Just starting into astrophotography, but getting a little discouraged by photos that are always washed out? Don’t be, the following is a typical long exposure image shot without the use of a filter.

This is the same image after having the colour space remapped (a process that literally takes less than a minute on a typical computer with the right software).

The only thing left to do to create the final picture is to stack a series of these images in software such as Registax and maybe do some final adjustments of the colour space.

So it was a little cool – but almost no wind – and properly dressed – not bad at all and well worth it. Jackie and Ben braved the cold also. Crisp and clear – for the most part – we did have some clouds roll in for about 15 minutes – then they vanished – in all we got about 2 hours of very clear skies before the clouds came back for good.

I took a little extra care on polar aligning and also, thanks to Mike, had new batteries for my illuminated guiding eyepiece. I spent most of the time imaging (6 minute exposures) the Flaming Nebula in Orion – then, before packing up, took a couple of shots of Orion’s sword again.