# Tag Info

29

The short answer is: BECAUSE THE ICE IS BLUE. Now we have to explain why it seems perfectly transparent on ice cubes and industrial ice blocks. It has to do with the fact that most transparent materials are not perfectly transparent, and instead absorb (and/or scatter) part of the light that hits them. And when the transparency is better for one specific ...

13

As noted in the comments, this answer applies to things like sun-bathing and solar panels, but it does not apply so much to a specific point-receptor like an eyeball. If all objects in question are pointing directly at the sun, then the angle of incidence is equal for all of them and this answer does not apply. For an optic facing its target, the amount of ...

11

As you suggest, longer the path, larger the proportion of scattered radiation. Since the shorter wavelengths are more strongly affected by the Rayleigh scattering, sunlight appears more red when the sun is low. Lower solar elevation angle will also result in longer path through the ozone layer, and hence stronger absorption at the UV-B wavelength range. ...

9

There are many references about this on the web, such as Wikipedia and the NOAA site. At sunrise and sunset the angle the Sun's light makes with the Earth at those locations is low compared with angle the light makes at midday. Because of the low angle, the light has to travel through more of the atmosphere before it reaches the Earth's surface and the eyes ...

6

The reason why fog bows lack colour, compared to rainbows, is due to the size of the drops of water. Fog is composed of very small drops of water - less than 0.05 mm diameter. Because of this the wavelength of light is critical, with diffraction smearing out colours that the larger drops of water in a rainbow would make.

6

It can be measured in units of energy per surface area, for example, kWh/m2. The official SI name would be radiant exposure but I haven't seen that phrase used in a climate or weather context. For example, here is a map by NREL of average radiation per day in the US for July: (Source: National Renewable Energy Laboratory) And here is a map for Sweden for ...

4

It appears from your picture that there is some mist above the lake surface. The phenomenon will be due to the same mechanism that causes conventional rainbows. The angles between the sun, the mist/cloud, and the observer will be identical but you will only see this with the sun low in the sky since the mist is near the water. That will also make the rainbow ...

4

Civil twilight: the sun is between 0 and 6 degrees below the horizon Nautical twilight: the sun is between 6 and 12 degrees below the horizon Astronomical twilight: the sun is between 12 and 18 degrees below the horizon I believe if the sun is lower than 18 degrees below the horizon, all sun rays can no longer reach your location. Hence it is completely ...

4

chlorophyll is green because that was the part of the spectrum that was left when plants evolved. The bulk of the spectrum was already being harvested by other photosynthetic life. there is actually a wide variety of photosynthetic pigments chlorophyll is just one of many. You may want to check out the purple earth hypothesis. Sauce

3

To ask why chlorophyll is green is a bit like asking why haemoglobin is red. That is just the colour of them, in the case of haemoglobin due to the iron content and in the case of chlorophyll probably due to the magnesium atom at the centre of every chlorophyll molecule. As you very likely know, the function of chlorophyll is to carry out photosynthesis, ...

3

From an human eye perspective. Civil twilight=you will be able to read a newspaper. Nautical twilight=you will be able to see the contours of mountains and the brightest stars will be visible. Astronomical twilight=you will no longer be able to see the contours of mountains and the atmosphere will have a very dark color,lots of stars are visible. Night=...

3

In addition to radiant exposure, for certain locations, some meteorological services record hours of sunlight for periods during each day when the solar radiance equals or exceeds ${120\ \rm{W/m^2}}$. The weather observations for Sydney airport, for June 2015 can be seen here. Column 7 lists the sunlight hours for each day listed. In terms of measuring data ...

3

I get a blank entry for May 03. The Sun didn't set on Bovinia, New York on May 03 when time is expressed as Universal Time. Sunsets from May 04 to August 16 occur before sunrise. (Also note that August 16 has two sunsets.) The solution is simple: Fill in the time zone. Ignoring daylight savings time, time in Bovinia New York is offset by 5 hours from UTC. ...

3

In this case I'd say it's a combination of Rayleigh scattering, Mie scattering and the angle of the sun. Rayleigh scattering is related to the chemical composition of the atmosphere and occurs when the particles causing the scattering are smaller in size than the wavelengths of radiation in contact with them (this is why the sky appears blue most of the ...

3

Some time ago I posted this answer about how rainbows are formed, and the Wikipedia link Trond Hansen posted mentions droplet size relative to the wavelength of light. For a rainbow to form, the droplet size has to be large enough, relative to the color with the longest wavelength of visible light, for it to be refracted before reflecting off the backside ...

3

One direction to look in might be the various GIS systems that exist to forecast the amount of light that will reach photovoltaic (solar panel) installations. I don't know about the US, but I would be very surprised if there isn't one - try googling for "PV GIS" or similar. Now, that will give you insolation (illuminance) in W/m2. It may be further broken ...

2

One significant biological event that requires a specific "type" of moonlight is the reproduction of corals in Great Barrier Reef, in Australia. 'One week each year in spring, after a full moon, millions of corals release eggs and sperm in what Bill Leggat, a co-author of the new study, called "a slow symphony."' 'An ancient light-sensitive gene has been ...

2

Not being an expert in the subject, I agree with your hypothesis. But, I think that what you are measuring with the difference in the readings is the anisotropy of the illumination. In very cloudy skies, the amount of light from all directions in the sky is the same (that's why you can't tell where is the Sun). In a extreme case, like the condition refereed ...

2

At the coast the horizon facing the ocean is unobstructed, so a larger part of the sky is visible than inland, where trees, buildings, etc., block the view of the horizon. Also, the horizon sky is brighter than the overhead sky. At or near the horizon the sky appears lighter blue than at the zenith, or even whitish. Looking vertically at the zenith is ...

2

Yes, definitely. In general, REE minerals tend to be fluorescent. In our lab we deal a lot with REE and we have a UV lamp just for fun, to see the colours. Other minerals that are commonly associated with REE deposits are also fluorescent, with the best example being calcite, fluorite, and apatite. The fluorescent properties of REE-bearing solid state ...

2

I think the answer to your question have to be no. Lots of minerals are fluorescent in UV light,You can take a look here https://geology.com/articles/fluorescent-minerals/ So as you can see in the linked summary of fluorescent minerals it can be hard to tell what you have found unless you know what to look for. A better way to find Rare Earth Elements ...

2

Twilight occurs when the sun is just slightly below the horizon. You cannot see the sun but light will still be available due to atmospheric processes. The different stages of twilight depend on the angle of the sun to the horizon leading to different degrees of darkness. Down all day just means that the sun will never pass the horizon. But twilight may ...

1

Another online database to try is this one, which lists minerals for various colors

1

This type of information is made available through the USGS Spectroscopy Lab. There is a researchable database of their current spectral library with the appropriate information for each mineral signature (formula, sample_id, type and more). Here is an example of the signature for Hematite: Further, there is an up to date publication accompanying the ...

1

Sorry to be un-arty but you should be able to measure scattered light intensity at the coast versus inland. My guess is that it is brighter at the coast which also probably also means it gets lighter in the morning and light lasts longer into the evening. Land in the place I live is covered in green and is quite absorbent of light, i.e. dark. It's pretty, ...

1

As an addition to the already mentioned effect of the atmosphere for lower solar elevations. As you seem to care about minute differences too. You might want to consider Doppler effect. The Earth-Sun distance during aphelion and perihelion differs by 5,000,000 km. Therefore, the mean radial velocity of Earth with respect to the Sun is 1,141 km/h or 317 m/s. ...

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