light

All posts tagged light

All photos Brocken Inaglory CC-BY-SA, except as noted

All photos Brocken Inaglory CC-BY-SA, except as noted

Cloud of the Day – Glory

Glory is an optical phenomenon which has become much more commonly observed since the rise of widespread flight.

Fogbow_glory_spectre_bridge_Brocken-Inaglory-CC-BY-SA

Glory is seen in clouds or mist when the Sun (or rarely the Moon) is directly behind the observer.

AndiW - Public Domain

AndiW – Public Domain

The observer must be higher than the clouds or mist because, since the Sun (or Moon) is above the horizon, the glory must be below the opposite horizon.

Glory_spectre_fogbow-Brocken-Inaglory-CC-BY-SA

Glory is most commonly observed from a high vantage point, like a mountain, a bridge, a tall building or an aircraft.

Brocken Inaglory - Public Domain

Brocken Inaglory – Public Domain

In some cases the glory will surround the shadow of the aircraft.

Reeftraveler - CC-BY-SA

Reeftraveler – CC-BY-SA

When the glory surrounds the dramatically large shadow of the observer, when standing on a mountain top, say, it is called a Brocken spectre, named for a German mountain renowned for the effect.

Spectre_of_the_Brocken_Brocken-Inaglory-CC-BY-SA

No one has yet devised a generally accepted theory for the formation of glories. The rings are all centered on the observer’s eyes, so they’re obviously dependent on the observer’s position. And they’re obviously optical, resulting from one or more of the reflection, refraction, interference, and tunneling of light. It’s not nailed down yet, though.

Solar_Glory_with_helicopter_shadow_around_Mauna_Loa-Brocken-Inaglory-CC-BY-SA

Tap the photos for large originals.

rjb

All photos in this post by Jim Bowering CC-BY-SA

All photos in this post by Jim Bowering CC-BY-SA

It’s wildfire season here, and this year is particularly bad. We’ve had evacuations in my town, but it’s even worse south of the border in the United States. Unfortunately, we’ve had a south wind for the last few days, so all the smoke is coming up here. The above photo shows the view from my dining room window, and that’s what I see these days while having dinner. If you look closely you can almost see the other side of the valley, which I estimate to be about a kilometer away.

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This shot is the same time. It shows up the distant hills a little better. To the eye, the Sun was actually a deep ruby red, but my camera couldn’t capture it.

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This is the next day. I tried a different setting on the camera and it got a little closer, but still no ruby. You can see that the visibility has improved and you can make out the hills easily.

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Almost got it, but I obviously need a better camera and more talent. I was able to stare directly at the Sun with no discomfort.

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Yesterday morning I gave it a try with the “Sunrise” setting. Not bad, but I assure you the sky was not that color.-) Look closely again and you will see a hint of the east side of the valley. And the smoke was thin enough overhead to show that contrail.

smoke-morning-2

Looking east again this morning, with the “Sunset” setting. The sky is closer to its actual color, but the Sun is still too yellow. The visibility is improving, with the eastern hills making a better showing. Also the aircraft fighting the fires are allowed to fly again, having been grounded by low visibility.

smoke-morning-3

Looking east on my morning walk. I made sure to walk slowly, to keep the inhalation of “particulates” to a minimum. It’s good to get out, though. I’ve been staying in with all the doors and windows sealed, and definitely not doing any strenuous work in the yard. I used to fight these fires, with the heat on my skin and the smoke in my lungs, but that was back when I was young and invincible.-)

Looking forward to a nice rainy day,

rjb

PS, WordPress seems to be randomly failing to display images lately. I can see no reason why one of these should be treated differently from the others. Oh well. Waiting and hoping for an update to fix it.

rjb

PPS, I think I fixed the non-displaying images. I disabled “Photon,” which uploads the images to a WordPress server and serves them from there.

rjb

Credit - Brocken Inaglory - CC-BY-SA - Click for larger

Credit – Brocken Inaglory – CC-BY-SA – Click for larger

Cloud of the Day – Pillar

The pillar is an optical phenomenon where a light source, the Sun or the Moon or a streetlight, eg, is accompanied by a vertical column of light. Depending on the position of the light relative to the viewer, the pillar can be above or below the source, or both. Pillars are related to halos, being caused by light interacting with ice crystals, but can appear alone.

Credit S Moeller - Public Domain - Click for larger

Credit S Moeller – Public Domain – Click for larger

Credit Ikonet.com

Credit Ikonet.com

While halos are produced by the refraction of light through ice crystals, pillars form when the light reflects off of them. Because the ice crystals are all in different orientations as they sift through the air, the light source is reflected to you from different altitudes, elongating the reflection. Usually the type of ice crystal involved is the flat, hexagonal plate.

Credit - Hannes Grobe - CC-BY-SA - Click for larger

Credit – Hannes Grobe – CC-BY-SA – Click for larger

The pillar is not associated with any type of weather, only with the presence of ice crystals between the viewer and the light source.

rjb

Corona diagram

Corona diagram

All images, except where noted, credit Wiebke Salzmann CC-BY-SA. Click images for larger versions.

Cloud of the Day – Corona

Here is a meteorological phenomenon that is often misnamed “halo.” A corona is similar to a halo in that they both form rings around the Sun and Moon. The Sun’s corona (the one formed in Earth’s atmosphere, not the one around the actual Sun) is hard to see because the Sun is so bright. A corona is a more subtle effect and needs the more muted light of the Moon to really show itself.

Corona-bright-Wiebke-Salzmann-cc-by-saWhile haloes result from the light being refracted by ice crystals high in the atmosphere, coronae are caused by the diffraction of light scattered by particles – water droplets, ice crystals, dust motes, etc – in the lower atmosphere. A corona can also form on a foggy window pane. Haloes have fixed dimensions, calculable from the known refractive index of ice. Coronae come in various sizes due to the variability in the size of the light-scattering particles. Smaller droplets make larger coronae. In addition to the light scattered from the surface of the particle, small contributions to the corona are made by light that reflects directly off the droplet, or passes through it.

Corona around street lamps through an aspirated window pane.

Corona around street lamp through an aspirated window pane.

Artificial corona around LED lamps of different colors, created with lycopodium spores. As can be seen the diffraction rings of red light have a greater radius than those of blue light.

Artificial corona around LED lamps of different colors, created with lycopodium spores. As can be seen the diffraction rings of red light have a greater radius than those of blue light.

Image credit - Florian Marquardt - CC-BY-SA

Interference patterns – Florian Marquardt – CC-BY-SA

A classic corona consists of a bright aureole in the center, with one or more colorful rings around it. For the sharpest coronae, the droplets must be all close to the same size, so the interference pattern in the light can be well defined. It is constructive and destructive interference among the scattered light waves, where they add to make bright regions and subtract to make dark regions, that make the alternating rings of bright and dark.

rjb