Last night's lunar eclipse, viewed from space

Each night, an instrument called VIIRS DNB takes visible band images of the entire Earth. When the moon is up, it's really easy to see the patterns of the clouds, and when the moon is set you can basically only see the artificial light from cities. But what happens when you have a lunar eclipse? This:

2014/10/08 lunar eclipse viewed by VIIRS DNB by Christopher Kyba & NOAA
is licensed under a Creative Commons Attribution 4.0 International License.
Based on a work at http://ngdc.noaa.gov/eog/viirs/download_ut_mos.html.
Image and Data processing by NOAA's National Geophysical Data Center.

As the Earth's shadow darkened the face of the moon, there was progressively less light for DNB to be able to see land, clouds, and sea. As a result, with each pass of the satellite the image gets darker. The satellite takes about an hour and a half to go around the Earth, so the effect lasts over 2-3 passes. Since we don't have a geostationary satellite capable of imaging the Earth in moonlight, it's not yet possible to produce an video, like this one of a solar eclipse.

For the next several days, you can access the full (giant) resolution image from NOAA. You can get an in-between resolution image from my personal webpage.

If you'd like to see images of hurricanes imaged by VIIRS DNB with moonlight, follow @DanLindsey77 on twitter:

Super Typhoon #Vongfong from #VIIRS Day Night Band - 1703 UTC today Oct. 7. ~All reflected light is from the moon! pic.twitter.com/cu8ACmwiUE
— Dan Lindsey (@DanLindsey77) October 7, 2014

Note for new visitors: This blog is about the Loss of the Night citizen science app, which lets regular people measure how bright the sky is by looking at stars. The goal of the app is to track how the brightness of the sky changes as LED lighting is implemented worldwide. The app is free, and can be downloaded for Android phones. An iPhone version is in development and will come out soon.

The promise and the peril of LED lighting

Wonderful news for Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura, who won the physics Nobel Prize today "for the invention of efficient blue light-emitting diodes which has enabled bright and energy-saving white light sources"!

When used for outdoor lighting, white LEDs (which are built out of blue LEDs) have two incredibly useful properties. First, they can be directed more carefully than the older gas discharge tube lamps, and that means that with good design it's possible to put light on a walkway and the surrounding areas without shining lights up into the sky, into people's bedroom windows, and without glaring down the street. Second, they can be turned on and off and dimmed instantaneously. This means that dusk-till-dawn lighting can become a thing of the past, and in the future city lighting will hopefully be delivered on-demand, rather than left burning on every street all night long.

 It's possible to imagine a future in which driverless cars run without headlamps (the car itself can be dimly lit to make it visible), pedestrian and cyclist lights provide more uniform lighting at greatly reduced light levels, and the sky above even large cities once again glitters with thousands of stars.

But unfortunately, this future won't come about simply thanks to the genius of the physicists honored today. It will take the combined efforts of hundreds of thousands of other lighting innovators: engineers, designers, city planners, and perhaps most importantly, lawmakers. The problem is that without careful design and planning, high efficiency LEDs can end up looking like this during the night:

Exposure set to match street level

Exposure set to image the screen

At the corner of one of the busiest pedestrian crossings in Berlin (Kurfürstendamm and Joachimstraße), drivers turning right through a crosswalk are blinded by an LED screen that's left running at daytime appropriate levels during the night!

Due to the remarkable compactness of LEDs, the glowing area of the lamps themselves are far brighter than many older style lamps. This, combined with their greater component of blue light can make them far more glaring, a problem that disturbs both drivers and pedestrians alike on many poorly lit LED streets.

Interesting architectural lighting can be accomplished using highly efficient 1 Watt LEDs. But if it's poorly designed, it blind visitors to the city coming out of a train station into an unfamiliar surrounding, such as this problematic area just outside of the Alexanderplatz station in Berlin:

Exposure adjusted to street levels

Exposure auto-set by camera

In the coming decade, LED lighting is going to entirely change the way we light both indoor and outdoor spaces, and for that we should most certainly thank today's prizewinners. But will we actually save energy - or just waste extra light? And will we have a more pleasant living environment? The answers to these questions will depend mainly on their implementation.

Note for new visitors: This blog is about the Loss of the Night citizen science app, which lets regular people measure how bright the sky is by looking at stars. The goal of the app is to track how the brightness of the sky changes as LED lighting is implemented worldwide. The app is free, and can be downloaded for Android phones. An iPhone version is in development and will come out soon.

Announcing the "International Nights of Skyglow Observation" in 2015

In many areas of the world, the Milky Way is no longer visible, due to waste light emitted from cities. This "skyglow" represents a great deal of lost energy, and is in a large part due to poorly designed or incorrectly installed light fixtures. For the last century, skyglow has increased dramatically year after year, but with the development of new lighting technologies and laws regulating light emission, it seems possible that skyglow could actually be reduced in the future - without turning all the lights off. Because skyglow may be having important effects on ecology, scientists want to track how it is changing. One of the best ways to do this is through citizen science.

While it is possible to take citizen science data about skyglow all year round, such data is easiest for scientists to analyze if it is taken in a burst around the same time each year.  Therefore, two "International Nights of Skyglow Observation" are being established as a part of the International Year of Light. Citizen scientists from around the world will measure how bright the night sky is, and report their data either through the web (GLOBE at Night) or via their smartphone with the Loss of the Night (Android/iOS) or Dark Sky Meter (iOS) apps.

In addition, we expect that in several cities, "Flashmob for Science" events will be organized, where tens or hundreds of people come together to make observations at the exact same time and place. This will help us understand how measurements vary with different observers (and different phones).

The dates for 2015 are March 14 and September 12.

This could be you next year in March and September next year!

 If you want to hold a Flashmob for Science in your city, please read our guidelines for holding the event, and then get in touch with me.

To make the event a success, we need as many people to know about it as possible!  Please pass the dates and this link on to anyone you think might be interested (e.g. teachers, amateur astronomers, or jorunalists).

(Click here to see all posts on this blog related to the International Nights of Skyglow Observation)

Update October 17: DaNel Hogan points out that if you want to truly get into the spirit of Pi-day, then you should make your observation at 9:26 pm (i.e. 3/14/15 9:26)!

Star trails in Australia

One of the original testers* of the Loss of the Night app recently created this cool photo of star trails far from city lights in the Outback of Australia:

South Celestial Pole Star Trail by Andrew Cool is licensed
under a Creative Commons Attribution 4.0 International License.

Andrew says that there was a great amount of green airglow visible on the night he made the photos. The image was originally published by the Planetary Society.


*I was very grateful for Andrew's help in testing the app in the Southern Hemisphere. It turned out that the first version we gave him to test asked him to look for the stars that were currently up in the sky... over Germany! So Andrew was left staring at his boots instead of up into the sky.

Moon free observing period has started

The 9th period of GLOBE at Night's 2014 campaign begins tonight, and that means that Loss of the Night app observations are possible again as well. The current observation period lasts until September 24 (and several days later for our app, if you're willing to stay up until the moon sets).

Can you see colors and read text under (full) moonlight? Yes!

If you look around the web for the answer to this question, you'll find a lot of conflicting information. A number of seemingly authoritative sources declare flat out that colors cannot be seen under moonlight, because the eye's cone cells are not active. The same sites also often mention that normal sized printed text cannot be read in moonlight, because the central fovea is packed with cones that won't be active. Both of these claims are false.

Since this is something that's really easy to test, there's no reason for this misconception to persist. All you have to do is wait for a night with a full moon, find a place outside that doesn't have any direct lamp light (e.g. a park), take something colorful with you (e.g. a children's book), and see if you can recognize the colors or not.

I did it last night, with Mr. Forgetful:

I found out the answer right away: I was able to distinguish the red hat and blue body not as different shades, but as "red" and "blue". I did have more trouble on some other pages. For example, on the page below I was pretty sure that the "grass" wasn't green, but I had no idea what color it was. When I went back inside I found out it was not actually grass, but brown dirt:

I also had no trouble at all reading the text, which is probably about 14 point font. I tried reading a text with a smaller font, and while I had a bit more difficulty, it was certainly still possible.

But please don't take my word on this! This is a science experiment that can be performed by anyone without vision impairment, so the next time there's a full moon, go out and try it yourself!


You might ask why any of this matters. It turns out that this actually came up one time in court! A witness claimed to have seen a red car under moonlight, and experts called to testify disputed the fact that such a feat was even possible. The case motivated some Australian researchers to do a controlled test. It turns out that certain colors are easier than others (red is the easiest), and the color of larger objects is easier to discern than smaller objects.

But there's another reason why it's important. The confusion online demonstrates the extent to which vision at night is poorly understood. It's almost certainly the case that lighting levels in our cities could be dramatically reduced without meaningful effects on visual performance. Doing so would save money, energy, might help people sleep better, and would bring many stars back to our urban skies. But how low can we go and still be able to see well on city streets? The world spends something close to 100 billion dollars per year on outdoor area lighting, so spending a few million to get the right answer could result in a massive payback in reduced electricity bills.

The harvest moon and lunar elevation

Tonight is the full moon, and since it's the moon closest to the autumnal equinox, it's the "Harvest Moon". I found a number of explanations of why it's called the harvest moon online (e.g. this one by Bob King), and everyone mentions the fact that for several days, the moon rises near the sunset time. The moon therefore allows people to bring in crops by moonlight, hence "harvest" moon. I'm not a historian, but I have a very strong suspicion that this is only a part of the story.

autumnal equinoxa

autumnal equinox

autumnal equinox

autumnal equinox

autumnal equinox

Moonrise over Nationalpark Müritz by Alejandro Sanchez de Miguel is licensed
under a Creative Commons Attribution 3.0 Unported License.

If you think back to a memory of walking through the country on an extremely bright moonlit night, the odds are very good that you'll be thinking of a snow-covered winter landscape. Snow of course makes the landscape much brighter, but full moons are also brighter in winter because the full moon rises much higher in winter than it does in summer. (A useful way to remember this is that the full moon always does the opposite of the sun: in summer it's low in the sky, and in the winter it's high).

But it's a bit more complicated in the spring and fall. At those times, the highest elevation moons are during either the first quarter (spring), or the third quarter (fall). Now here's where I think the "harvest" moon comes in. In the days shortly before the full moon in autumn, the moon sets shortly after midnight, and the landscape isn't particularly brightly illuminated because the moon doesn't rise very high in the sky (both of which are not so useful if you want to work all night). In contrast, the moon soars high in the sky in the days immediately after the full moon in autumn.

This year in Berlin, the moon on September 6 (3 days before the full moon) reaches only 24° above the horizon. On September 12 it's 47° above, and that makes the landscape about 78% brighter (if I accounted properly for the light absorbed and scattered by the atmosphere, it would increase that number even further).

I'd love to hear from a historian whether I'm right about the nighttime harvest taking place on the days after the full moon rather than before. If you anyone knows, or can find information about this from a reliable source on the Internet, please make a post in the comments.