Tuesday, May 19, 2015

Star trails over Milow, Germany

Blog reader

Polaris by JC Cabrejas is licensed under
a Creative Commons Attribution 4.0 International License.

Tuesday, May 12, 2015

LED color temperature

A new contact that works on lighting castles sent me the photo below. It compares the light provided by an incandescent lamp (left) to the "warmest" white LED that their group could find (right).

Image used with the permission of the
Prussian Palaces and Gardens Foundation Berlin-Brandenburg

The problem with the LEDs, from her perspective, is that the blue light component is too large, and the colors of the objects in the castles are not properly represented. LEDs can be adjusted to provide nearly any color that's desired, but their "luminous efficiency" is often worse than a very cold, blue-white LED. This is the main reason why so many LED street lights glare with such an ugly, cold light. But it doesn't have to be this way!

An overly narrow focus on the luminous efficiency of lamps misses the point about saving energy. For example, regardless of how high the luminous efficiency of the lamp in this photo is, it's not being used in an efficient and sustainable way:

Light on during the day by Christopher Kyba is licensed under
a Creative Commons Attribution 4.0 International License.
Some colleagues and I wrote an article about how a more common sense view of the "efficiency" of a lamp its energy use per year, not the efficiency with which it converts electricity into light causes a human visual response.

While making a decision about how to light a space, energy consumption is a very important consideration, but the people who will use the light should never be taken out of the equation! In Davis, California, the city decided to let citizens choose which lamps they liked after residents  had protested the installation 4,000 K LED streetlights. The public ended up choosing warmer 2,700 K lamps. In addition to being more liked (or at least more tolerated), warmer LED lamps also have a smaller impact on the night sky than the most efficient white LEDs.

When the Nobel prize was announced last year, I wrote:
"It's possible to imagine a future in which driverless cars run without headlamps ... 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."
For that to come to pass, the focus of sustainable lighting is going to have to shift beyond luminous efficiency, and keep the users of light in the center of focus.

Saturday, May 9, 2015

The night sky over Westhavelland, Germany

A few weeks ago I was in Sternenpark Westhavelland (International Dark-Sky Reserve Westhavelland) to try to measure the degree to which individual streetlights affect the night sky in a pristine area. The lamps are part of a biological and ecological field experiment of the Verlust der Nacht (Loss of the Night) project, funded by the German Ministry of Education and Research (BMBF).

Together with a colleague, we walked different distances from the lamps and then remotely the lights them off and on. In addition to measurements with a continuous logger, I took a few all-sky images. This one is from the middle of the field when the lights were off:

Verlust der Nacht field at night by Christopher Kyba is licensed
under a Creative Commons Attribution 4.0 International License.

You can download the full resolution version here. The sky is blue because it is lit by lunar twilight. The glow at the right (East) is a combination of the moon and the city of Berlin. The glow at top left (southeast) is the nearby town of Rathenow.

The next photo shows the view a few hundred meters from the field when the lights are turned on (the field is the bright glow at right):

Verlust der Nacht field lit at night by Christopher Kyba is licensed
under a Creative Commons Attribution 4.0 International License.

Finally, this animation shows how the whole environment near the field changes as the lights turn on:

Verlust der Nacht field turning on by Christopher Kyba is licensed
under a Creative Commons Attribution 4.0 International License.

I think the lighting up of the nearby tree and grass is the most dramatic - just think of what a complete difference this is for the insects and birds that live there! Here's a higher resolution version.

Tuesday, May 5, 2015

Sign up for our new monthly newsletter

We're starting a newsletter to remind project participants each month when the moon phase allows Loss of the Night app measurements to be taken. In the monthly mail, we'll also occasionally share news, such as announcements of new versions or project milestones that we've passed. You can sign up for the newsletter here, or just fill in the form below.

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Wednesday, April 22, 2015

The Loss of the Night app is two years old!

April 22 is the second anniversary of the Loss of the Night app! Since that time, tens of thousands of people have installed the app on their phone, and thousands of those people have used the app to make at least one observation of the night sky.

Here are some statistics from the first two years (for data up to April 18):

20,170 individual observations have been submitted from 9,825 unique devices from around the world (see map below). This number includes "demo mode" cases when people are just testing the app, and observations with clouds and sunlight or moonlight. Most devices have only ever observed once, but over 100 people have submitted ten or more observations.

App observations up to April 18. Black points are all observations,
red points are observations with no twilight, moonlight, or clouds
and at least 7 stars observed.

In the first few months, only about 10% of the submitted observations were suitable for analysis (no clouds, moonlight, twilight, and at least seven stars observed). This fraction has steadily increased over time, and is now close to 30% of the observations submitted. The number of good observations per month is also climbing, but slowly. The more participants we have, the quicker we'll be able to measure the average change in sky brightness worldwide, so tell your friends about the app!

Citizen scientists have searched for a total of 30,323 stars (under nighttime conditions). The star most commonly searched for so far is Capella (694 times), followed by Vega (593x) and Altair (554x). Since the new version was released, many of you are now submitting more than the minimum seven stars. We really appreciate it, because observing more stars leads to a more precise result.

The mean time to observe a star is 34 seconds, but the most frequently occurring time needed to make a decision is 11-15 seconds. Your data help us understand which are the "best" stars for us to ask you to look for. I hope that we will do one last update to the app's "star selection algorithm" in the next year or two, so the more stars you observe, the more you'll improve the app.

In addition to the naked eye observations which are the main purpose of the app, citizen scientists have also used the app to submitt 239 observations taken with Sky Quality Meters under nighttime conditions. Of these, 188 of which were taken with with no cloud cover.

Thank you to everyone who has taken part in this project to measure how Earth's night sky is changing. It wouldn't be possible without you! The next moon-free observing period starts around May 7. If you don't yet have the app, here are the links for downloading it for Android and iOS.

Tuesday, April 21, 2015

Minor bug report

Users at high latitudes (like Germany) may have noticed today that the app crashed after it acquired a GPS signal. The bug was caused by an expectation that the "next good time" to observe should be within 30 days, but during the summer at high latitudes the twilight extends past the time we thought people would be interested in observing.

The bug has been fixed, and in the next few hours the update should be available in the Play and App stores. We didn't notice the bug in testing, because our testing took place after the midsummer twilight was over last year.

Observers in Germany that are willing to stay up past midnight are able to observe from about May 7-18. If you live at a lower latitude, the bug probably didn't affect your phone.

Monday, March 30, 2015

Future upgrades to the app

How can we improve the app?

A bit more than a year ago I asked for your help in how we could improve the app. I updated the list as suggestions came in through comments, email, and in-person discussion, and with the release last fall a lot of the improvements made it into the app.

Now that the new version has been out for a few months, I want to start a new list for a future third - and ideally final - release. We have no source of funds at the moment, but I think it's valuable to keep track of what needs changing/fixing. If you have more suggestions, please let me know in the comments.

Things to change/improve in a future version of the app

Star search

  • Further improve star selection based on app data (preferentially use easier stars)
  • Make more use of "pointing stars"
  • Allow search to start with Venus or Jupiter
  • Allow the user to change the sensor settings (speed and/or damping) to make the display more comfortable
  • When screen is frozen, allow navigation by sliding finger 
  • Allow the user to adjust the number of stars displayed on the screen to match a given skyglow level? (a bit dangerous, as this could potentially cause biased observations)
  • Shaking the phone unlocks the locked circle (goes back to arrow) 
  • Try to work out that the user is standing on a balcony, and don't suggest stars in that direction 


  • Figure out what causes the occasional crash on startup
  • Better way to deal with very bright locations
  • Strategies for classifying areas with NELM>5
  • Interface to allow advanced users to submit what their estimate of the limiting magnitude is
  • New "constellation mode". Highlights a single constellation, and the user has to click on a star to declare it visible (turns from dot to star) and click a second time to declare it invisible (turns from star to empty circle or x), click third time for "just at visible limit"
    •  Or extend this mode to cover several hundred stars over the whole sky, and the observer can just pick which ones she wants to label?
  • Arrange "my measurements" by date
  • Manual way to calibrate the compass to remove azimuth error 
    • Add a compass-free option in "settings" menu for places with weird magnetic fields
  • Investigate behavior of auto brightness on Android (does it turn to full on app startup?)


  • Have the database in the background: users can log in see their observations - where they were taken, how they relate to those of others, see the observations of others, tools to examine how it is changing over time, see the accuracy of the data they gathered themselves
  • Graphical web display of your like I have shown on the blog in the past
  • Option to share your observation via facebook and twitter
  • Badges - you've observed 7 stars, you've repeated an observation at the same location ~1 year later, you've done 10 observations, 5 times in a single city, 5 locations, etc...
  • Guide users to locations that we particularly need measurements (e.g. repeat measurements from previous years).
  • Incentivize good data: Have a friendly competition where the best quality and quantity is rewarded (with a visit to the closest telescope and a personal lecture from an astronomer). Reward observations in particularly important locations

Extra features

  • A "talking" tutorial that tells you how to find the stars, asks you to turn in different directions, etc.
  • Video tutorial
  • Find a way to calibrate the compass within the app (on Android, iOS already has this)
  • Port to WindowsPhone and Blackberry
  • Allow observing below 45 degrees and making maps of the stellar visibility on the full sky dome
  • Check the clock using GPS and warn the user if their phone's clock is off by more than 2 minutes (and then exit app). Prevents records having a false time
  • Allow option of displaying user's location on a map to make sure it is correct
  • Check whether the phone has a compass, and don't allow install if there is no compass
  • Ability to export your observations (e.g. to an email)


  • Change behavior of star search with "averted vision" decision (technical)  
  • Start looking for GPS location on app start up, verify again before star search
    • Especially for SQM report, GPS should run in the background while typing value
  • Reduce the size/thickness of the circle during the star search on Android
  • Better messaging in "Not dark enough" menu during high latitude summer

Now it's your turn. What other changes should we make to the app?