Showing posts from January, 2021

What's this bolt do? Saving your scope from disaster.

Most high-end mounts attach to the telescope using a dovetail clamp. The telescope itself has a dovetail bar on it, which has a trapezium cross-section. This normally bolts to tube rings, which encircle the tube so they don't crimp it in any one spot, but some light tubes bolt directly to the dovetail. All you have to do is open the clamp on the mount, slide the telescope in so the clamp goes over the dovetail, and wind the clamp shut. Simple. The main advantage of having a clamp is that it keeps your scope parallel with the RA axis on the mount. It also doesn't scratch your dovetail bar. But are there disadvantages? I certainly never thought so. However, last time I was up at the dark sky site I was talking with far better astronomer than I, past ASV president, and general all-round good guy Russell Cockman. Russell was looking at my rig and brought up the subject of dovetail clamps. He asked me if I was scared of using one. This is my previous scope sitting on its mount

Finding exomoons

Moons are, we think, very common. After all, every single planet that humans have lived on has had at least one moon. Most of the planets in our solar system have at least one moon, and some large planets have lots. By extension, why shouldn't we expect that exoplanets would also have moons? But how do we find them? There are a few methods. I'll try to explain the "transit" method for exomoon detection here, although there are others. Scientists record the amount of light coming from a star. A dip in the luminosity may indicate the transit of an exoplanet. By extension, higher-resolution measurements may be able to detect the transit of an exoplanet with a moon, but it would depend on the arrangement of star, planet and moon to be just right. Have a look at the sequence in the graphic above, and my scribbled light trace over time. In the first panel, the planet and moon are approaching transit. Here the luminosity would still be 100% of normal.

Reading a photo - manual astrometry

I was talking about wide-field images with a customer last year. Mal showed me a photo he'd taken while back "up north". He'd used a now-elderly Canon M3 mirrorless with a Samyang 2.8mm fisheye. Mal told me that when he took this photo, he was in an area so dark that he hadn't noticed he was underneath a powerline until he previewed the photos on the back of the camera. You can see the lines go through the Small Magellanic Cloud. We both agreed that we enjoyed working in the dark. The bluish colour on the horizon is a car on a main road. That power pole provides a subject for the centre foreground. Without it, these photos get boring - just fields of stars. The shot was less than 30 seconds at f/2.8. He'd set the ISO very high. The camera has a clever noise reduction system, which takes three "light frames" and one "dark". Noise measured in the dark frame is subtracted from the lights, which are then stacked, further reducing

Two days on the Razorback

The Victorian Alpine country is beautiful, and is recovering from the gigantic fire of 2013, and smaller fires of the last few years. Below the treeline, the fire-ravaged Snowgums are beginning to sprout again, with white, weathered branches standing over round bushes of juvenile growth. Above the treeline, flowers were everywhere - Dandelions waving in the breeze, but also natives - a range of everlastings and the fascinating trigger plants, which breed by whacking bees on their backs with their pollen-laden hammers. Between Diamantina Hut on Mount Hotham and Federation Hut at the base of Mount Feathertop runs a high crooked ridge called the Razorback. Below and to the east, the Diamantina River flows into the Kiewa River. Below and to the west, a maze of creeks arrange themselves into the upper reaches of the Ovens river. In some parts, the ridge is literally two metres across. The track perches precariously on top reminding hikers to stay alert for wind gusts. In sheltered areas,

Planning your observation night using Right Ascension data, or, how to be a top-class geek

A random walk through the sky When I first started in astronomy ( back at school ), our astro club's observation nights were unplanned affairs. We'd turn up, maybe have a quick squiz at Norton's Star Atlas to see what's up, and then grab a scope. We'd wander randomly from one target to another, exploring the sky on our own. With a plan, you don't miss a target Inevitably though, the day afterwards, someone would start talking about the Lagoon Nebula or some other cool target. When we'd find out where it was so we could see it, we'd find it was just setting in the evening and we'd have to wait six months to see it. (Geek bullying - find some really cool object in the sky, then wait to tell your victim about it until it's too close to the Sun to observe. How very Niles Crane .) Observation nights always go better when you can plan your targets. And it's not just visual observers, either. Astrophotographers want to expose the target for as