photo:comets
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| photo:comets [2026/04/16 11:48] – [photographing comets:] gary1 | photo:comets [2026/04/16 11:50] (current) – [photographing comets:] gary1 | ||
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| ===comets near the sun=== | ===comets near the sun=== | ||
| - | *astronomic twilight is usually defined when the sun is 18deg below the horizon (ie. 60-90min before sunrise or after sunset depending upon latitude and month of the year) in which case by that time the sky is considered dark enough for all stars to become visible at a dark sky site | + | *astronomic twilight is usually defined |
| *assuming you would want a comet to be a further 5 deg at least above the horizon to reduce atmospheric haze, this means **long exposure or high ISO images of comets require the comet to be at least 23-30deg from the sun vertically** | *assuming you would want a comet to be a further 5 deg at least above the horizon to reduce atmospheric haze, this means **long exposure or high ISO images of comets require the comet to be at least 23-30deg from the sun vertically** | ||
| *when the comet is closer than this, twilight will interfere and reduce contrast between the sky and the comet as well as lighten the sky enough that only short exposures at relatively low ISOs are only possible - this means the comet would need to be at least magnitude 1 in brightness to be visible in such twilight and the tail may be lost in the sky | *when the comet is closer than this, twilight will interfere and reduce contrast between the sky and the comet as well as lighten the sky enough that only short exposures at relatively low ISOs are only possible - this means the comet would need to be at least magnitude 1 in brightness to be visible in such twilight and the tail may be lost in the sky | ||
photo/comets.txt · Last modified: 2026/04/16 11:50 by gary1