SpaceRef - Interactive - Astronomy Resources

'xTime' - A Time Conversion Utility for Rossi X-ray Timing Explorer Mission (RXTE) - "This utility is intended to aid the user in converting time as it is used throughout the RXTE mission between relevant and/or useful time systems and formats."

Earth and Moon Viewer - "You can view either a map of the Earth showing the day and night regions at this moment, or view the Earth from the Sun, the Moon, the night side of the Earth, above any location on the planet specified by latitude, longitude and altitude, from a satellite in Earth orbit, or above various cities around the globe. Images can be generated based on a full-colour image of the Earth by day and night, a topographical map of the Earth, up-to-date weather satellite imagery, or a composite image of cloud cover superimposed on a map of the Earth, or a colour composite which shows clouds, land and sea temperatures, and ice." Hosted by Fourmilab, Switzerland

Local Apparent Sidereal Time Calculator, US Naval Observatory - This page at the US Naval Observatory allows you to compute local sidereal time. Sidereal time is the hour angle of the vernal equinox, the ascending node of the ecliptic on the celestial equator. The daily motion of this point provides a measure of the rotation of the Earth with respect to the stars, rather than the Sun. Astronomers use local sidereal time because it corresponds to the coordinate right ascension of a celestial body that is presently on the local meridian.

SkyView - "SkyView is a Virtual Observatory on the Net. Astronomers can generate images of any portion of the sky at wavelengths in all regimes from radio to gamma-ray. Users tell SkyView the position, scale and orientation desired, and SkyView gives users an image made to their specification. The user need not worry about transforming between equinoxes or coordinate systesm, mosaicking submaps, rotating the image, .... SkyView handles these geometric issues and lets the user get started on astronomy." NASA GSFC.