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Issachar Conference Group

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Jacob Taylor
Jacob Taylor

Transit [TOP]


Commuter Services Transit provides information on regional transit options including MARC commuter rail, MTA commuter bus, Metrobus and Metrorail & other commute alternatives. Transit is a member of Commuter Connections, a program of the Washington Metropolitan Council of Governments. This computerized carpool and vanpool matching service is offered free to Frederick area commuters.




transit


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Employer OutreachFree service to local employers to assist in commute strategies for their employees, assistance setting up telework programs, parking strategies, pre-tax transit benefits, and more.


Customer Feedback Transit Services of Frederick County welcomes your feedback at any time. If you have feedback on bus stops or bus shelters that are broken or in need of attention, please use FCG FixIT. As always, you are welcome to call TransIT at 301-600-2065 or reach us by e-mail at transit@frederickcountymd.gov.


The Transit Village Initiative is an excellent model for Smart Growth because it encourages growth in areas where infrastructure and public transit already exist. Municipalities must meet the Transit Village Criteria and complete a Transit Village Application in order to be designated a Transit Village.


In addition to community revitalization, the Transit Village Initiative seeks to reduce traffic congestion and improve air quality by increasing transit ridership. Studies have shown that adding residential housing options within walking distance of a transit facility; typically a one-half mile radius, increases transit ridership more than any other type of development. Therefore, one of the goals of the Transit Village Initiative is to bring more housing, businesses and people into the neighborhoods around transit stations.


We connect people to places by providing a high-quality, safe, reliable, clean, and efficient mass transit system that meets the travel needs of the County's growing population and we provide vital transportation infrastructure systems and services.


The General Transit Feed Specification (GTFS), also known as GTFS static or static transit to differentiate it from the GTFS realtime extension, defines a common format for public transportation schedules and associated geographic information. GTFS "feeds" let public transit agencies publish their transit data and developers write applications that consume that data in an interoperable way.


A GTFS feed is composed of a series of text files collected in a ZIP file. Each file models a particular aspect of transit information: stops, routes, trips, and other schedule data. The details of each file are defined in the GTFS reference.


An example feed can be found in the GTFS examples. A transit agency can produce a GTFS feed to share their public transit information with developers, who write tools that consume GTFS feeds to incorporate public transit information into their applications. GTFS can be used to power trip planners, time table publishers, and a variety of applications, too diverse to list here, that use public transit information in some way.


If you're at a public agency that oversees public transportation for your city, you can use the GTFS specification to provide schedules and geographic information to Google Maps and other Google applications that show transit information.


Planets may give themselves away when they pass in front of a starand dim some of its light. The passage of a planet between a star andEarth is called a "transit." If such a dimming is detected at regularintervals and lasts a fixed, repeated length of time, then it is verylikely that another, dimmer object is orbiting the star. Some of thesetransiting objects might be small, dim stars (in which case the pair iscalled an eclipsing binary), but most of them are planets.


How much a star dims during a transit directly relates to the relative sizes of the star and the planet. A small planet transiting a large star will create only a slight dimming, while a large planet transiting a small star will have a more noticeable effect. The size of the host star can be known with considerable accuracy from its spectrum, and photometry therefore gives astronomers a good estimate of the orbiting planet's diameter, but not its mass. This makes photometry an excellent complement to the radial-velocity method, which allows an estimate (a lower limit) of a planet's mass, but provides no information on the planet's diameter. Using both methods, combining mass and diameter, scientists can calculate the planet's density. Density, in turn, can suggest whether a planet is rocky, gassy, or in between.


Transits provide scientists with estimates of planet diameters, a physical property not otherwise measurable. Because transiting exoplanets orbit in orbital planes that are necessarily edge-on to Earth-based observers, using both the transit method and the radial-velocity method to observe the same planet can provide the planet's mass and therefore its density and likely composition. Transits can provide scientists with a great deal of infFirst and foremost the "dip" in a star's luminosity during transit is directly propotionate to the size of the planet. Since the star's size is known known with a high degree of accuracy, the planet's size can be deduced from the degree to which it dims during transit.


If the transiting planet has an atmosphere, some of the light from the star passes through the planet's atmosphere on its way to Earth. Some wavelengths of that starlight are preferentially blocked by gases in the atmosphere. By studying the spectrum of a star both during a transit and outside a transit, astronomers can find telltale dips in the spectrum of starlight that are diagnostic of the presence of atmospheric gases. Water vapor is one molecule that can be observed using transit spectroscopy.


In addition to "primary" transits, which occur when a planet passes in front of its star, scientists are also interested in "secondary" transits, which occur when a planet completely disappears behind the star as seen from Earth. By deducting the star's light spectrum when the planet is hidden from the spectrum when it is visible, scientists can arrive at the planet's spectrum (that is, its color). The color of the light emitted by a planet is a clue to its temperature and can also hint at the composition of its atmosphere.


The main difficulty with the transit-photometry method is that in order for the photometric effect to be measured, a transit must occur. Not all planets orbiting other stars transit their stars as seen from Earth; a distant planet must pass directly between its star and Earth. Unfortunately, for most extrasolar planets this simply never happens. In order for a transit to occur the orbital plane must be almost exactly edge-on to the observer, and this is true only of a small minority of distant planets. The rest will never be detected with photometry.


Another problem is that a planet's transit lasts only a tiny fraction of its total orbital period. A planet might take months or years to complete its orbit, but the transit would probably last only hours or days. As a result, even when astronomers observe a star with a transiting planet, they are extremely unlikely to observe a transit in progress. The problem is further compounded because in order to establish the presence of a planet, astronomers need to observe not only one, but many transits occurring at regular intervals. Therefore, the transit photometry method is heavily biased toward the discovery of short-period planets (ones that orbit quite close to their stars). Many such short-period planets are in the habitable zones of their host stars because the host stars are very dim, so it is possible to discover habitable planets orbiting other stars with the transit photometry method.


The transit photometry method tends to produce false positives, because the smallest stars can have diameters that are similar to those of giant planets. Therefore, objects that transit stars are considered only candidate planets until further measurements confirm that their diameters and/or masses are small enough for them to be considered planets.


In order to have a good chance of observing transiting planets at the moment of transit, searches must continuously cover vast stretches of sky containing many stars for long periods of time. Transit-photometry searches are conducted by automated telescopes that stare at stars for as long as possible (hours at a time for ground-based telescopes and months for space-based telescopes).


Kepler and CoRoT were succeeded by the Transiting Exoplanet Survey Satellite (TESS), which has been surveying for new planets since 2018, and the Characterising Exoplanet Satellite (CHEOPS), which launched in December 2019 to perform follow-up observations of transiting exoplanets to measure atmospheric composition.


Many ground-based observatories survey the skies for transiting exoplanets, including the 2 telescopes of TRAPPIST, the 7 telescopes of HATNet, the 2 telescopes of the MEarth project, and the forthcoming 4-telescope SPECULOOS survey.


While the discovery of a new planet with photometry requires the most advanced professional equipment (or an inordinate amount of luck), observing the transit of a known planet is much easier. This is because if one knows where to look and when, the effect of the transit itself can be quite substantial and easily detectable even with a relatively small telescope. In May 2001, for example, thousands of amateur astronomers around the world turned their telescopes towards a nearby red dwarf known as Gliese 876. This star was known to be orbited by two planets, both of which were discovered using the radial-velocity method. Since the star is small, and the planets orbiting it are large, the transit of the larger of the two dimmed the star substantially. This made it possible for amateurs the world over to observe the telltale signs of the presence of an extrasolar planet. The Exoplanet Section of the American Association of Variable Star Observers (AAVSO) coordinates amateur-astronomer participation in exoplanet transit observations. 041b061a72


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