Clear Sky Chart
Encyclopedia
Clear Sky Charts are web graphics which deliver weather forecasts designed specifically for astronomers
.
They forecast the cloud cover
, transparency and astronomical seeing
, parameters which are not forecast by civil or aviation forecasts. They forecast hourly data, but are limited to forecasting at most 48 hours into the future. Each individual chart provides data for only a 9 mile radius, and so are essentially point forecasts. There are clear sky chart forecasts for over 4000 locations, though the coverage area is limited to Canada, the USA and parts of Mexico and the Caribbean. Locations are typically cities, professional and public observatories, colleges and science center
s. However there are also clear sky charts for star parties
and backyard observatories.
s. The cirrus cloud modeling distinguishes Rahill's model from other cloud forecast models, as sufficient cirrus clouds to make a night unusable for astronomers is still called "clear" by civil weather forecasts.
In later years, Rahill added a forecast of astronomical transparency, which is a measure of how much starlight traverses the Earth's atmosphere when otherwise free of clouds. Rahill also added a forecast of astronomical seeing
which uses forecast data of turbulence
and temperature gradients in the atmosphere
to forecast its optical steadiness.
In 2001, Attilla Danko, computer programmer and amateur astronomer
, began to summarize Rahill's hundreds of forecast maps by displaying only one pixel, from each map, laid out in rows. The resulting meteogram
, called a clear sky chart, showed all of Rahill's forecast data, but for only one location. Danko writes "It shows at a glance when, in the next 48 hours, we might expect clear and dark skies for one specific observing site". Danko accepts requests from observatories and private individuals to create new CSCs for locations not currently covered. However, since CMC's GEM model only covers North America, CSCs are limited to North America.
However, there continue to be references to the old name on web sites not controlled by the domain cleardarksky.com.
Since the clear sky charts terms of use permit non-commercial web sites to display clear sky chart images, they are most commonly recognized by private and club astronomy websites in North America.
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
.
They forecast the cloud cover
Cloud cover
Cloud cover refers to the fraction of the sky obscured by clouds when observed from a particular location...
, transparency and astronomical seeing
Astronomical seeing
Astronomical seeing refers to the blurring and twinkling of astronomical objects such as stars caused by turbulent mixing in the Earth's atmosphere varying the optical refractive index...
, parameters which are not forecast by civil or aviation forecasts. They forecast hourly data, but are limited to forecasting at most 48 hours into the future. Each individual chart provides data for only a 9 mile radius, and so are essentially point forecasts. There are clear sky chart forecasts for over 4000 locations, though the coverage area is limited to Canada, the USA and parts of Mexico and the Caribbean. Locations are typically cities, professional and public observatories, colleges and science center
Science center
A science center or science centre is a science museum that emphasizes a hands-on approach, featuring interactive exhibits that encourage visitors to experiment and explore....
s. However there are also clear sky charts for star parties
Star party
A star party is a gathering of amateur astronomers for the purpose of observing the sky. Local star parties may be one night affairs, but larger events can last up to a week or longer and attract hundreds or even thousands of participants. Many regional star parties are now held annually and are an...
and backyard observatories.
History
In 2000, Allan Rahill, a meteorologist at the Canadian Meteorological Centre (CMC), created a forecast processing step that took data from CMC's Global Element Multi-scale (GEM) forecast model and created a new forecast of cloud cover. Rahill specially designed his cloud forecast to consider the formation of cirrus cloudCirrus cloud
Cirrus clouds are atmospheric clouds generally characterized by thin, wispy strands, giving them their name from the Latin word cirrus meaning a ringlet or curling lock of hair...
s. The cirrus cloud modeling distinguishes Rahill's model from other cloud forecast models, as sufficient cirrus clouds to make a night unusable for astronomers is still called "clear" by civil weather forecasts.
In later years, Rahill added a forecast of astronomical transparency, which is a measure of how much starlight traverses the Earth's atmosphere when otherwise free of clouds. Rahill also added a forecast of astronomical seeing
Astronomical seeing
Astronomical seeing refers to the blurring and twinkling of astronomical objects such as stars caused by turbulent mixing in the Earth's atmosphere varying the optical refractive index...
which uses forecast data of turbulence
Turbulence
In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...
and temperature gradients in the atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
to forecast its optical steadiness.
In 2001, Attilla Danko, computer programmer and amateur astronomer
Amateur astronomy
Amateur astronomy, also called backyard astronomy and stargazing, is a hobby whose participants enjoy watching the night sky , and the plethora of objects found in it, mainly with portable telescopes and binoculars...
, began to summarize Rahill's hundreds of forecast maps by displaying only one pixel, from each map, laid out in rows. The resulting meteogram
Meteogram
A meteogram is a time cross-section that produces and uses data for a specific weather station on the ground. It can display past weather conditions up to the current time or forecast conditions from the current time out into the future...
, called a clear sky chart, showed all of Rahill's forecast data, but for only one location. Danko writes "It shows at a glance when, in the next 48 hours, we might expect clear and dark skies for one specific observing site". Danko accepts requests from observatories and private individuals to create new CSCs for locations not currently covered. However, since CMC's GEM model only covers North America, CSCs are limited to North America.
Name change
On February 29, 2008 Danko changed the name of the CSCs to "clear sky charts" to avoid any possibility of legal action on the part of Skyclock company of Michigan who owns a USA registered trademark on the name "SKYCLOCK". Danko's attorney opined that he was not infringing Skyclock Company's trademark, but also advised that changing the name was the "least painful" and least "expensive" solution.However, there continue to be references to the old name on web sites not controlled by the domain cleardarksky.com.
Recognition
Rahill and Danko have received awards from meteorological and astronomical organizations:- In 2010, the Astronomical Society of the PacificAstronomical Society of the PacificThe Astronomical Society of the Pacific is a scientific and educational organization, founded in San Francisco on February 7, 1889. Its name derives from its origins on the Pacific Coast, but today it has members all over the country and the world...
awarded their Amateur Achievement Award to Allan Rahill on behalf of the Clear Sky Chart team composed of Allan Rahill and Attilla Danko. - In 2009, Asteroid discoverer Andrew LoweAndrew LoweAndrew Lowe is a Canadian geophysicist and amateur astronomer. He has discovered a number of asteroids.With the discovery of the asteroid 2010 AX2 on January 7, 2010, he became one of only six individual observers worldwide with discoveries spanning five or more consecutive decades...
named asteroids 161693 Attilladanko (2006 HL46) and 171153 Allanrahill (2005 GL81) in recognition of Danko's and Rahill's forecasts. - In 2004, the Canadian Meteorological and Oceanographic Society (CMOS) granted a citation to Rahill and Danko for a "vivid example of meteorology in support of astronomy".
- In 2005, the Royal Astronomical Society of CanadaRoyal Astronomical Society of CanadaThe Royal Astronomical Society of Canada is a national, non-profit, charitable organization devoted to the advancement of astronomy and related sciences. At present, there are 29 local branches of the Society, called centres, located in towns and cities across the country from St. John's,...
awarded Danko the Ken Chilton Prize in recognition of the "Clear Sky Clock". - In 2003, the Astronomical LeagueAstronomical LeagueThe Astronomical League is an umbrella organization of amateur astronomy societies. Currently their membership consists of over 240 organizations across the United States, along with a number of Members-at-Large, Patrons, and Supporting members....
awarded Danko the Omega Centauri Award for making observing more efficient though the clear sky clock.
Since the clear sky charts terms of use permit non-commercial web sites to display clear sky chart images, they are most commonly recognized by private and club astronomy websites in North America.
External links
- Clear Sky Chart Official website
- Clear Sky Alarm Clock free email notification service
- Weather forecast for astronomy from Environment Canada
- The Canadian Meteorological Centre
- The Clear Sky Clock widget for MacOS (10.4 or greater)
- ClearSkyClock Windows Vista Sidebar Gadget
- SkyCharts iPhone/iPod Touch Web App
- myCSC iPhone/iPad/iPod Touch App