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Telescope mountings. Altazimuth lets the telescope pivot up & down (in altitude) & swing from side to side (in azimuth). You have to keep adjusting it to keep an object in view as the Earth turns. The equatorial mount “pan” axis is parallel to the Earth's rotation axis. So you can keep an object in view by turning this axis as the Earth turns, maybe with a motor drive. (Credit: moreheadplanetarium.org) Mona Evans, “Choosing and Using a Telescope”…

Linné crater on the Moon. Relief map made using the Lunar Reconnaissance Orbiter Camera (LROC) as a stereo camera. Linné (2.2 km diameter) is a very young and beautifully preserved impact crater. The colors represent elevations; cool colors are lowest and hot colors are highest [NASA/GSFC/Arizona State University]. Mona Evans, “The Moon – Earth's Daughter” http://www.bellaonline.com/articles/art32833.asp

from CBC News

Telstar satellite's legacy, 50 years on

Telstar 1. Launched on July 10, 1962, it was the first active communications satellite and transmitted the first live television pictures across the Atlantic. (credit: Alcatel Lucent/Associated Press) Mona Evans, "Telstar - Herald of the Modern Age" http://www.bellaonline.com/articles

Measuring parallax. (Image: Christine Guy Schnittka, Murphy & Bell)) To measure the distance of a star, astronomers use the same method as surveyors on Earth - triangulation. Stars show a slight change in position when viewed from two widely separated locations, usually opposite sides of the Earth’s orbit. This change in position is known as a parallax. The amount of parallax tells us the distance. Mona Evans, "Distances in Space" http://www.bellaonline.com/articles/art29665.asp

With parallax technique, astronomers observe object at opposite ends of Earth’s orbit around the Sun to precisely measure its distance. CREDIT: Alexandra Angelich, NRAO/AUI/NSF.

Eratosthenes and the Circumference of the Earth. (Credit: Rogue Robot PRO) This short film tells how, 2500 years ago, mathematician & geographer, Eratosthenes, worked out with great accuracy, the circumference of the Earth. The film was shortlisted for the 2014 Guardian Witness Science Film Award & came second place in the Scan Velocity 2014 film competition. Mona Evans, "Columbus and the Flat Earth Myth" http://www.bellaonline.com/articles/art301140.asp