# Tag Info

Accepted

### Why does glacier ice look blue?

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 ...
• 17.3k

### Is spectrum of sunlight the same in the summer as in the winter?

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 ...
• 391
Accepted

### Why does the intensity of sunlight depend on your latitude?

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 ...
• 341
Accepted

### What causes the colors seen during a sunset / sunrise?

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 ...
• 23k
Accepted

### How can daily brightness be quantified or measured?

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 ...
• 11.4k
Accepted

### What actually happens to reduce the perceived color in a 'white rainbow" or "fog-bow"?

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 ...
• 23k

### Why does the camera do this and what does the sky really look like around 87,000 ft altitude?

The footage turns blue because the camera adjusts its settings to the darker part. It probably raised the ISO and/or the exposure time to capture more light. This results in a brighter picture. This ...
• 370

### Does this optical phenomenon have a name?

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/...
• 4,359

### How can daily brightness be quantified or measured?

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 ${120\ \rm{W/m^2}}$. ...
• 23k
Accepted

### Why does chlorophyll only come in green?

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 ...
• 6,679

### Why does chlorophyll only come in green?

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 ...
• 4,507

### What does it mean when polar nights have twilight?

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 ...

### Light at the coast - is it different?

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 ...
• 750

### Why was the sky SO yellow?

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 ...
• 324
Accepted

### At what point are water droplets too small to make a rainbow?

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 ...
• 2,157

### Where can I find weather data on ambient outside illumination?

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 ...
• 5,870
Accepted

### US Naval Observatory Sunrise/Sunset Data: Blank Sunrise/Sunset Times?

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 ...
• 22.4k

### Is spectrum of sunlight the same in the summer as in the winter?

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 ...
• 17.3k

### Is moonlight a significant condition for making life possible on earth?

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, ...
• 23k

### Calculating a cloud cover index based on comparison of horizontal and tilted irradiance from pyranometers

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 ...
• 17.3k

### Where may I find spreadsheet data on the spectral density of daylight at various times throughout the day from morning to evening?

You probably can take the data outputs of this awesome tool to your problem. It is the Photovoltaic Geographical Information System , designed to calculate solar energy input to photovoltaic ...
• 121

### What does it mean when polar nights have twilight?

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. ...
• 1,840

### What does it mean when polar nights have twilight?

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 ...
• 994
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### What are the risks of developing geoengineering?

We don't know, and that's why we have to develop it. that's the thing about undeveloped sciences we don't know what many of the risks are, Its a case of knowing what we don't know. Which is one big ...
• 6,679
Accepted

### Can I just walk around Greenland with a UV light and find rare Earth minerals on the ground?

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 ...
• 22.8k

### Can I just walk around Greenland with a UV light and find rare Earth minerals on the ground?

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 ...
• 1,840
1 vote

### Database of color wavelengths of minerals

Another online database to try is this one, which lists minerals for various colors
• 23k
1 vote
Accepted

### Database of color wavelengths of minerals

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 ...
• 2,623
1 vote

### Light at the coast - is it different?

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 ...

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