Tropical year

A tropical year (also known as a solar year), for general purposes, is the time that the Sun takes to return to the same position in the cycle of seasons, as seen from Earth; for example, the time from vernal equinox to vernal equinox, or from summer solstice to summer solstice. Because of the precession of the equinoxes, the seasonal cycle does not remain exactly synchronized with the position of the Earth in its orbit around the Sun. As a consequence, the tropical year is about 20 minutes shorter than the time it takes Earth to complete one full orbit around the Sun as measured with respect to the fixed stars (the sidereal year).

Since antiquity, astronomers have progressively refined the definition of the tropical year. The Astronomical Almanac Online Glossary 2015 states:

An equivalent, more descriptive, definition is "The natural basis for computing passing tropical years is the mean longitude of the Sun reckoned from the precessionally moving equinox (the dynamical equinox or equinox of date). Whenever the longitude reaches a multiple of 360 degrees the mean Sun crosses the vernal equinox and a new tropical year begins". (Borkowski 1991, p. 122)

Solar

Solar may refer to:

Astronomy

Other uses

Goddard Space Flight Center

The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory established on May 1, 1959 as NASA's first space flight center. GSFC employs approximately 10,000 civil servants and contractors, and is located approximately 6.5 miles (10.5 km) northeast of Washington, D.C. in Greenbelt, Maryland, USA. GSFC, one of ten major NASA field centers, is named in recognition of Dr. Robert H. Goddard (1882–1945), the pioneer of modern rocket propulsion in the United States.

GSFC is the largest combined organization of scientists and engineers in the United States dedicated to increasing knowledge of the Earth, the Solar System, and the Universe via observations from space. GSFC is a major U.S. laboratory for developing and operating unmanned scientific spacecraft. GSFC conducts scientific investigation, development and operation of space systems, and development of related technologies. Goddard scientists can develop and support a mission, and Goddard engineers and technicians can design and build the spacecraft for that mission. Goddard scientist John C. Mather shared the 2006 Nobel Prize in Physics for his work on COBE.

Spaceflight

Spaceflight (also written space flight) is ballistic flight into or through outer space. Spaceflight can occur with spacecraft with or without humans on board. Examples of human spaceflight include the U.S. Apollo Moon landing and Space Shuttle programs and the Russian Soyuz program, as well as the ongoing International Space Station. Examples of unmanned spaceflight include space probes that leave Earth orbit, as well as satellites in orbit around Earth, such as communications satellites. These operate either by telerobotic control or are fully autonomous.

Spaceflight is used in space exploration, and also in commercial activities like space tourism and satellite telecommunications. Additional non-commercial uses of spaceflight include space observatories, reconnaissance satellites and other Earth observation satellites.

A spaceflight typically begins with a rocket launch, which provides the initial thrust to overcome the force of gravity and propels the spacecraft from the surface of the Earth. Once in space, the motion of a spacecraft—both when unpropelled and when under propulsion—is covered by the area of study called astrodynamics. Some spacecraft remain in space indefinitely, some disintegrate during atmospheric reentry, and others reach a planetary or lunar surface for landing or impact.

Solar Dynamics Observatory

The Solar Dynamics Observatory (SDO) is a NASA mission which has been observing the Sun since 2010. Launched on February 11, 2010, the observatory is part of the Living With a Star (LWS) program. The goal of the LWS program is to develop the scientific understanding necessary to effectively address those aspects of the connected Sun–Earth system directly affecting life and society. The goal of the SDO is to understand the influence of the Sun on the Earth and near-Earth space by studying the solar atmosphere on small scales of space and time and in many wavelengths simultaneously. SDO has been investigating how the Sun's magnetic field is generated and structured, how this stored magnetic energy is converted and released into the heliosphere and geospace in the form of solar wind, energetic particles, and variations in the solar irradiance.

General

The SDO spacecraft was developed at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and launched on February 11, 2010, from Cape Canaveral Air Force Station. The primary mission is scheduled to last five years and three months, with expendables expected to last for ten years. Some consider SDO to be a follow-on mission to the Solar and Heliospheric Observatory (SOHO).