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Museum ofApplied Arts Sciences
Observations

By The Museum of Applied Arts Sciences

June 8, 2011

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An ejected prominence on the Sun on 21 May 2011. Image and copyright Harry Roberts ©, all rights reserved plus the Solar Dynamics Observatory for last panel

Most solar filaments end their lives by ejecting into space, and when this happens at the solar limb, H-alpha users see an impressive event – often termed an “eruptive prominence”. Terrestrial observatories seldom record such events, as they do not monitor prominences continuously, though with luck the satellite may get an image.

Most filaments erupt while on the bright disc (rather than the limb) where they are harder to see. In most filters they abruptly vanish (termed “disparition brusque”) because the filament’s ejection velocity causes a Doppler blue shift that exceeds the filter’s pass bandwidth. For instance a 0.7Å filter will be ”blind” to a filament ejecting at approach velocity >35 km/sec – a “low velocity” where the sun is concerned. By contrast, an ejection at the limb is not Doppler shifted, as the ejecta has almost no approach velocity.

2011 May 21st was clear and hazy with very good “seeing”. Many solar features were visible on the disc; spots, filaments etc, and at the SE limb a large faint “hedgerow” prominence. Timings showed the feature stretched around the limb from 36ºS to 52ºS (~200Mm length) and was about 37Mm (37,000km) high. These latitudes were higher than those of current sunspots, and showed that the filament (prominence) was a so-called quiet region filament (QRF) formed by weaker (~10 gauss) solar surface fields – and was not associated with any current sunspots, where fields are ~ 2000 gauss.

After ten minutes logging other features the “hedgerow” was seen to be erupting. At its northern end, where earlier the height was 37Mm, bright material had risen to 50Mm (arrowed x in Fig), with a faint plume reaching to 90Mm (a-a in Fig). The plume was visibly in motion, and over the next three minutes rose to 110Mm – when trees ended viewing. These numbers give an ejection velocity for the faint plume of over 100km/sec.- fast for a QRF that typically eject at 20-30km/sec.

The filament may have ejected entirely (all 200Mm of it) had it been visible for the next half hour or so, but trees hid it. A web search showed the SDO satellite EUV 171 Å channel had logged the event – confirming my record, but not showing if the ejection was total or partial. The SDO image, when enhanced, faintly showed the taller plume, dark against bright corona (a-a in Fig). Signs of a spot group behind the limb were noted ~15º north of the prominence (the future AR11223 site, AR? in Fig). There appear to be no other records of the event.

This was not a major ejection – far from it; but it reminds us that filaments eject from the sun on an almost daily basis at current activity levels. Having done so, a QRF will quickly reform, and it’s not unusual for part of a filament to erupt while the rest ‘stays put’. Nevertheless, it was exciting to watch, and reminds us that the sun, in H-alpha, is always active.

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Happy Independence Day!

Riding a bike gives us independence from so many things. Bicycles are freedom machines that allow us to go where we want, when we want — and the only fuel they require is our own muscles.

Hope you get a chance to ride today — whether that’s to a street party, parade, BBQ, or whatever.

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➤ Read past entries .

I was taught to bike the old-fashioned way. My mother tossed me and a little red bike off the end of the pier by our house and I pedaled with all my might for land — and I was a competent bicyclist by the time a wave swept me onto the sandy shore. Or something like that.

Kids these days have it much easier with lots of nifty options that don’t involve the Pacific Ocean, avoid scraped elbows and knees, and aren’t uphill both ways. This week I’ll share what I’ve learned about balance bikes, tricycles and trailer bikes. [Read more…]

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