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Laser Pointer, Green - Green laser pointers are used to point out celestial objects such as constellations. Green lasers work because our eyes are especially attuned to green light at night (while having almost no red sensitivity), because they tend to be more powerful than red lasers, and because green light scatters better off of dust in the atmosphere, making a green beam much more visible than a red one would be.

Latitude - Latitude is a measure of a location's distance from Earth's equator. The equator has a latitude of 0°, the north pole is at 90° North latitude, and the south pole at 90° South latitude. Tucson, for example, has a latitude of 32° North, meaning it is located 32° north of the equator. This is important information to know for using an equatorially mounted telescope because the polar axis must be set to the correct latitude to allow automatic tracking of the night sky.

LED - Light Emitting Diode. Red LEDs are often used in flashlights to preserve observers' night vision while stargazing. LEDs are also used in reflex finders. LEDs have a vastly longer lifespan than regular light bulbs and consume less power.

Lens Shade - A lens shade is simply an extension of a telescope tube that extends beyond the objective lens to block glare from light sources. Most commonly a lens shade is used to block glare from the sun in a spotting scope or camera lens, but they also work to block stray light when stargazing. A lens shade can also function as a dew shield to prevent moisture from forming on a lens. The terms lens shade and dew shield are often used interchangeably.

Light Pollution - This is extraneous light which brightens the sky and hinders the observing of celestial objects. Mostly, light pollution is city light, but technically there is such a thing as natural light pollution (including auroras and zodiacal light) that prevent even the most remote observing sights from having pure black skies.

Light Pollution Filter - Many street lights emit light at specific frequencies rather than at every wavelength in the visible spectrum. This allows light pollution filters to be made that in turn block those particular frequencies of light while transmitting the rest of the spectrum. This darkens the sky and allows fainter detail to be seen.

Light-Year - A light-year is a measure of distance. Astronomical distances are so great that measuring things in miles becomes absurd. A light-year is simply the distance traveled by light in one year. Light moves at 186,000 miles per second, so in one year it would go about 6 trillion miles. The nearest star to the sun, for example, is 4.3 light-years away, or 25.8 trillion miles. Star clusters and nebulae are on the order of 10 to 100 light-years in size. Galaxies are tens or hundreds of thousands of light-years across. The distances between galaxies are measured in millions of light-years. Equivalently, the distance to an object in light-years tells you how long it takes light to reach Earth from that object. The Andromeda galaxy is 2.8 million light-years away, so the light we see from that galaxy required 2.8 million years to reach us. This means the farther away we look, the farther back in time we see.

Low-Dispersion Glass - Glass refracts light of different wavelengths by different amounts, which results in the familiar prism effect of light being dispersed into a rainbow of colors. Low-dispersion glass reduces how much the different wavelengths of light are dispersed, allowing for better chromatic aberration correction in refractors, camera lenses, and binoculars. Glass that has exceptionally low dispersion characteristics is called extra-low dispersion glass, or ED glass. Other similar terms include SD (super-low dispersion) and UD (ultra-low dispersion) glasses.