Friday, March 8, 2019

Stargazing opportunity from a hotel balcony

Today my colleague Andrej Mohar sent me some information about a new boutique hotel that has opened in

Vila Planinka Hotel by Andrej Mohar is licensed under
a Creative Commons Attribution 4.0 International License.

And here is a map of light emissions in the area where it is located, you can see that it is nestled in a "dark island":

Light emissions near Jezersko, from the Radiance Light Trends webapp

According to Andrej, the surrounding mountains block out light pollution towards the horizon, so the view is stunning.

If you look at the hotel website, you'll see that one of their photos shows a telescope in the room. I'm not sure if that is included generally or not, but it shows that the hotel is sees a view of the stars as one of the attractions of their location.

I have stayed in a number of hotels where the balcony had a light on all night, or the facade is floodlit, and I find it really unpleasant. It's great to see that some hotels are realizing that there is value in letting guests enjoy the dark!

Tuesday, March 5, 2019

Looking for stars with the Loss of the Night app

I have a new photo showing someone looking for stars with a phone:

This work by Christopher Kyba is licensed under a
Creative Commons Attribution-NonCommercial 4.0 International License.

Tuesday, February 26, 2019

Can we get 2000 Globe at Night cloud-free observations this March?

I am currently preparing an analysis of the Globe at Night sky brightness data taken from 2006 up until today. It's really important that we do this, because the world is switching to LED lighting, and visual observations are the only way to really know if the sky is getting brighter or darker. The work is going well, but there is a problem - a problem I need your help with.

When Globe at Night started, it was a campaign that only took place in one month out of the year: March. Over time, Globe at Night expanded to allow people to do observations at any time during the year. This was intended to make it easier for people to take part. For example, if a teacher wanted to have his students make Globe at Night observations, it might make more sense to do it at another time during the semester. And some places frequently have cloudy weather, so an amateur astronomer might be disappointed if she can't make an observation one year.

However, I believe that the change to a full-year campaign had an unintended side effect of reducing the excitement and urgency of making observations. When observations can be made at any time, there is less urgency, less social media buzz, and it is therefore in some sense harder to motivate people to take part. Perhaps as a result, the total number of Globe at Night observations has been slowly dropping over the years. The bigger problem from my point of view, however, is that the number of observations taken in March has dropped even faster:

Annual number of Globe at Night observations. Observations in March are shown with a dashed line.
For the purposes of this plot, multiple observations from a single location in a single month are counted only once, and only cloud-free data is included.

This is a problem for me, because the reviewers of my paper might rightly ask whether it's fair to compare annual data taken during 2011-2019 to the March-only data from 2006-2010. Furthermore, can we really make strong conclusions about trends when there were thousands of March Globe at Night observations in the past, but only a few hundred in recent years?

For that reason, I'm asking amateur astronomers, light pollution activists, and citizen science promoters to help me promote Globe at Night this March. If we work together to activate our networks, can we get March participation back up to the levels it had when Globe at Night first started? Please help by sharing a link to the Globe at Night webapp in social media, posting on message boards where the members would be interested in making observations, and of course making one or more observations yourself! The webapp is available in 28 different languages, so if English is not the first language of your community, be sure to share the relevant app.

The most important days to target this year will be the weekends of March 1-3 and March 29-31. It would therefore be most helpful to spread the word within your networks on March 1 and March 29. Observations are possible throughout the periods February 26-March 7, and March 27-April 5.

I hope that together, we can get a big bump in the data in March, 2019! Thank you for your help in spreading the word!

Friday, October 5, 2018

What prevents us from seeing the stars?

Last night I was in Brussels, Belgium, and as the sky was clear I had the chance to look for stars at an open area just outside of the Brussels Central Station. When I first looked up, it seemed as if there weren't any stars at all, and I think this is the impression that most people would have. But when you look at the dark sky for a bit longer, and screen out some of the glaring light using your hands, it turns out you can see quite a few stars!

Here is my observation:

The limiting magnitude was around 3.5, which means that a few constellations (including Cassiopeia and the Big Dipper) were visible. But I think if I had asked passersby how many stars they thought they could see, their initial guess would be either zero or perhaps "one or two". The problem is not only that the sky is bright, but especially that glaring lights and illuminated buildings make it hard to look at the sky with dark adapted eyes. Here is a street view several blocks away from the station:
"Street view in Brussels" by Christopher Kyba is licensed
under a Creative Commons Attribution 4.0 International License.

If you have to look up directly into a streetlight, you're not going to be able to seem much more than the streetlight... Contrast that contemporary view with van Gogh's impression of a night scene in Arles.

Van Gogh's scene is notable in how there are no glaring lamps at all, and for the relative darkness of the building facades. The scene provides an inspiration of what I think we should aim for in urban lighting: warm feeling light, no glare, no street light directly shining on windows, good uniformity in the pedestrian areas, and above it all, bright stars shining visibly in the night sky.

If you look up again at my observation, you will see that for a number of stars I had to report that I wasn't sure if I could see them or not. These stars were mainly in the constellation Draco, which is quite extended, and therefore hard to orient towards when the sky is bright. I hope that in a future version of the app, we will be able to further optimize which stars the app asks you to examine. I recently requested funding from the EU for a big project, in which the Loss of the Night app plays a small part. If the proposal is successful, I would be able to produce a new version of the app sometime in 2019 or 2020. Please cross your fingers for me!

Monday, August 20, 2018

Timelapse video of conversion of lamps from HPS to LED in Innsbruck

Christoph Malin sent me this video quite a while ago, and I have been meaning to post it to the blog for ages. Check out his time lapse showing the same streets in Innsbruck, Austria lit with HPS and LED lights.

Christoph is a photographer and cinematographer. You can follow him on twitter.

Wednesday, August 15, 2018

Luojia-1, a new night imaging cubesat

This week I had a visit from Xi Li, a professor at Wuhan University in China. Among many other things, we discussed the Luojia-1 cubesat which was designed by Wuhan University and launched several months ago. The satellite is already providing exciting imagery from a number of locations around the world. For example, compare the image of Berlin from the DNB monthly composite (left) to the Luojia-1 image (right) below.

Two images of Berlin at different resolutions. Tegel airport is at top left,
Schoenefeld/Berlin Brandenburg International airport is at bottom right.

Luojia-1 takes images at a resolution of about 130 meters, a major improvement over the ~750 meter resolution of the DNB. The higher resolution makes it possible to see smaller features, such as the major road network of cities or individual bright large buildings. The downside of high resolution is that Luojia-1 can only take images of smaller areas, rather than imaging the entire world the way DNB does each night.

In the coming years, Luojia-1will create a map of light emissions for the entire country of China. It will also acquire images of a number of cities worldwide, and will be tasked to take images of some areas for humanitarian regions, such as to provide information about infrastructure damage in war zones or overview of areas experiencing wildfires.

The data acquired by Luojia-1 is made freely available a short time after it has been transmitted to Earth. The data is not yet radiometrically calibrated, but it is already georeferenced. (Note: in some of the photos from June, I noticed some relatively large errors in the georeferencing.In images from July, the error is typically only a few pixels).

The team from Wuhan University has already produced a web portal to allow everyone to discover and download the data.When you go to the site, a login screen will appear with the public login information already filled in. Click up at the top right to change the interface to English and log in.

From the next page, you can use a tool to draw a polygon to select your region of interest and check whether imagery is available. Keep in mind that the satellite has only been acquiring data for a few months, and because it is a cubesat the total bandwidth available for downloading data is limited.

I am looking forward to seeing the interesting results that come out of this new data source (as well as the data from another upcoming cubesat from the Adler Planetarium in Chicago)! If you have questions about the data or would like to request imagery for a specific location, contact Xi Li.

Thursday, June 7, 2018

Perspective of a facade from above

One of the systematic issues that nighttime imagery has to deal with is the fact the orientation of lights and their position relative to buildings and other objects affects whether they can be seen from above. Take for example, these two images of the area near Berlin's Zoologischer Garten station.

This work by Alejandro Sanchez de Miguel, Christopher Kyba, and Freie Universit├Ąt Berlin
is licensed under a Creative Commons Attribution 4.0 International License.

When our aircraft was north of the area, it was able to see north facing facades that were illuminated. These illuminated facades are invisible, however, when viewed from the South. This means that when satellites take images of the Earth at night, the "answer" for how bright a city is depends to some extent on where the satellite was when it took the image.

Update (August 5, 2019)

My student Jacqueline Coesfeld wrote a paper that uses these images, and considers how this effect (and others) result in variations in how much light is seen by satellites from night to night: