What does a telescope’s main lens or mirror chiefly do?
Andrew Dunn / Wikimedia Commons / CC BY-SA 2.0
Gathering power goes with area, so doubling the width of the opening collects four times the light, and that is what decides how faint an object can be seen at all.
Which Italian scientist used a telescope from 1609 to observe the Moon’s surface and four moons of Jupiter?
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His instruments magnified only about twenty or thirty times, but that was enough to show that the Moon had relief and that another planet had satellites of its own.
A telescope that gathers light with a curved mirror is called what?
Andrew Dunn / Wikimedia Commons / CC BY-SA 2.0
A mirror can be supported across its whole back, where a lens can only be held at its rim, which is why every very large telescope uses one.
Which English scientist built the first working reflecting telescope, in 1668?
Andrew Dunn / Wikimedia Commons / CC BY-SA 2.0
His tube was only about 15 centimetres long with a metal mirror barely two and a half centimetres across, and a flat secondary threw the image out to the side.
Which large steerable dish at Jodrell Bank in Cheshire is used for radio astronomy?
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The 76-metre bowl was completed in 1957, and parts of its mounting were salvaged from the gun turrets of scrapped battleships to keep the cost down.
Which Hawaiian mountain carries a cluster of large observatories above the cloud layer?
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The summit stands above 4,200 metres, where the air is thin, dry and unusually steady, though building there has long been contested by Native Hawaiian groups.
What is an observatory dome for?
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It rotates so the slit follows the instrument, and good designs also vent air through the building so the temperature inside tracks the night air.
Which German-born astronomer, working in England, discovered Uranus in 1781 with a telescope he had built himself?
Andrew Dunn / Wikimedia Commons / CC BY-SA 2.0
He was a working musician who ground his own mirrors, and he first took the object for a comet before its slow, almost circular motion gave it away.
What problem does light pollution create for an observatory?
Andrew Dunn / Wikimedia Commons / CC BY-SA 2.0
A faint object has to be picked out against the glow, so the brighter the background the longer the exposure needed, and some targets stop being reachable at all.
Which country hosts the Roque de los Muchachos Observatory, on the island of La Palma?
Andrew Dunn / Wikimedia Commons / CC BY-SA 2.0
The site sits at about 2,400 metres on the rim of a caldera, and regional law has limited lighting and air traffic around it since the 1980s.
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