User:Anotherdoon/GaN devel

GLOBE at Night is an international citizen science initiative designed to crowdsource light pollution measurements. The next opportunity to take part is March 13-22, 2012. It is an offshoot of the GLOBE Program.

Goals

An example of how light pollution reduces the visibility of the constellation Orion

The GLOBE at Night project has two main goals. The first is to be an awareness raising campaign, generating public and media interest in the issue of light pollution. The project encourages members of the public to go outside on dark moonless nights and report how many stars are observable. The project specifically encourages students, teachers, and families to become involved, and has produced activity packets targeted to these groups in 13 languages. The program also distributes teaching kits designed to demonstrate how fully shielded lights can improve visibility by reducing glare .

The second goal of the project is to provide the assembled data to researchers and the public. The project provides a mapping interface that displays the data overlaid on Google maps.

Methods

At least an hour after sunset, citizen scientists are asked to go outside and let their eyes adjust to the ambient light level. They then observe a specific constellation depending on their location (Northern or Southern Hemisphere) and the time of year. By comparing the stars they see with star charts showing stellar visibility under different light pollution conditions, they effectively measure light pollution. For dedicated amateur astronomers, it is also possible to submit readings taken using a Sky Quality Meter. Data are then submitted via a web interface, using a computer or a smartphone (to allow automatic determination of location).

With this technique, observers are effectively reporting the naked eye limiting magnitude (NELM) in the range of 1-7. Humans are able to observe stars below 7th magnitude, although this may require blocking out other sources of light. In the case of clear, unpolluted skies, measurement of NELM should be strongly correlated with the level of light pollution, but other factors can reduce NELM, including:

• atmospheric water content (especially clouds)
• atmospheric aerosols (e.g. dust or air pollution)
• visual acuity of the observer
• wind (causes stars to twinkle, and renders dim stars invisible)
• aurora (e.g. Northern lights)
• airglow, gegenschein, and Zodiacal light
• age of the observer
• scattered moonlight (this is not a factor for GLOBE at Night measurements, since the observation dates are set around the time of the new moon.)
• twilight (GLOBE at Night measurements are requested to be taken at least an hour after sunset to avoid this)
• Presence of the Milky Way

Reasons for concern about light pollution

Artificial lights attract many insects, a fact that some spiders are able to take advantage of, as on this lighted bridge over the Loire River, France. These changes in behavior can then affect food webs and cause further knock-on effects.

Main article: Light pollution

Main article: Ecological light pollution

There are several reasons the GLOBE at Night project wants to raise awareness about light pollution. The introduction of artificial light into formerly dark ecosystems is one of the most drastic changes that human beings have made to the natural environment. Exposure to light can prove fatal for some organisms (e.g. moths that fly into a burning flame), can interrupt a life cycle phase for others (e.g. glowworms are unable to attract mates), and can reduce the possibilities for finding food (because of increased risk of predation). Light at night can also interfere with the chronobiology of many animals, including human beings (through suppression of melatonin secretion).

There are also cultural and economic reasons for concern about excessive light at night. Skyglow prevents large fractions of the Earth's population from viewing the Milky Way, which our ancestors would have been very familiar with, and which drove the development much of ancient science, mythology, and religion. In the USA, the cost of generating wasted light is estimated to be 7 billion US dollars per year, and the production of the electricity for this wasted light also results in the release of chemical pollution and greenhouse gasses.

Conversion of GLOBE at Night measurements into other units

GLOBE at Night observations work by identifying the dimmest stars that are visible given the surrounding conditions. In addition to light pollution, many other factors can affect stellar visibility, as discussed above. Nevertheless, assuming normal visible acuity and clear skies, it is possible to approximately convert GLOBE at Night naked eye limiting maximum estimates into other units:

NELM	Visible stars	mcd/m^2	mag/arcsec^2
1	10	160	14.6
2	30	60	15.6
3	80	20	16.6
4	250	8	17.8
5	800	3	19.0
6	2,500	0.8	20.4
7	7,000	0.2	22.0

History

Locations of GLOBE at Night observations from 2009-2011.

The GLOBE at Night project was originally launched as a NASA program, and measurements were only made in the United States. The project quickly expanded internationally, and was part of the outreach effort of the International Year of Astronomy in 2009. The size of the project (in terms of number of observations) expanded dramatically in that year.

The number of observations for each year are reported on the GLOBE at Night webpage:

• 2006 - 3,990 total observations
• 2007 - 8,490 total observations
• 2008 - 6,838 total observations
• 2009 - 15,300 total observations
• 2010 - 17,805 total observations
• 2011 - 14,249 total observations
• 2012 - 5,661 total observations (as of March 12)

Use of data in academic studies

In addition to raising awareness of light pollution, the GLOBE at Night program provides the collected data to amateur and academic researchers for use in scientific studies. It has been used, for example, in a study of how lighting is related to the foraging habits of bats.

See also

• Bortle Dark-Sky Scale
• Earth Hour
• Ecological light pollution
• History of street lighting in the United States
• International Dark Sky Association
• Light pollution
• GLOBE Program

External links

• GLOBE at Night home page
• GLOBE Program home page
• International Dark-Sky Association
• Conversion of NELM into other units