function asseenfrom(observer, name, pos, rot, travelduration, waitduration)
	travelduration = travelduration or 10 -- 5 for testing, 10 for a longer wait.
	waitduration = waitduration or 7 -- 3 for testing, 7 for a longer wait.
	pos = pos or celestia:find(name):getposition()
	rot = rot or observer:getorientation()

	--observer:goto(celestia:find(name), travelduration)

	parameters = { }
	parameters.duration = travelduration
	parameters.from = observer:getposition()
	parameters.to = pos
	parameters.initialOrientaion = observer:getorientation()
	parameters.finalOrientation = rot
	if name == "Regulus" then
		parameters.startInterpolation = 0
	end
	observer:goto(parameters)

	elapsedwait(0.75 * travelduration)
	-- A travelduration coefficient of 0.325 is good when the travelduration is 5.
	-- A travelduration coefficient of 0.3 is good when the travelduration is 10.
	-- A travelduration coefficient of 0.25 is good when the travelduration is 30.
	celestia:flash("       As seen from " .. name, waitduration +
			(0.0001*travelduration^2 - 0.0065*travelduration + 0.355)
			* travelduration)
	elapsedwait(0.5 * waitduration)
	--celestia:setrenderflags{constellations = true}
	-- celestia:showconstellations()
	elapsedwait(0.5 * waitduration)
	--celestia:setrenderflags{constellations = false}
end

function elapsedwait(duration)
	starttime = celestia:gettime()
	endtime = starttime + duration / 24 / 60 / 60
	while celestia:gettime() <= endtime do
		wait(0)
	end
end

-- Set time to 3:43 AM CDT on July 21.
celestia:settime(celestia:utctotdb(2011, 7, 21, 8, 43, 0))

-- Select Megrez instead to improve 3D perspective.
celestia:select(celestia:find("Megrez"))
-- TODO: Follow nothing.
celestia:unmarkall()

-- celestia:settextcolor(177/256, 177/256, 254/256)

celestia:setoverlayelements{Time = false, Velocity = false, Selection = false, Frame = false}

-- celestia:hideconstellations()
celestia:setconstellationcolor(0.125, 0.125, 0)
celestia:setconstellationcolor(0.4, 0.4, 0, {"Ursa Major"})
-- celestia:showconstellations{"Ursa Major"}

-- Mark Castor and Pollux so they can be seen from Aldebaran.
for i, star in ipairs({"Castor", "Pollux"}) do
	celestia:find(star):mark("purple", "filledsquare", 7, 0.75)
end

-- Brighten the stars of the Big Dipper.
celestia:setrenderflags{markers = true}
for i, star in ipairs({"Alkaid", "Alcor", "Alioth", "Megrez", "Phecda", "Merak", "Dubhe"}) do
	celestia:find(star):mark("yellow", "disk", 5, 0.75)
end

celestia:setrenderflags{constellations = true}

observer = celestia:getobserver()
--observer:setframe(celestia:newframe("universal"))
observer:track(nil)

-- Always remain looking at the Big Dipper.
-- The view from Duluth is not horizontal if Phecda is tracked here.
--observer:track(celestia:find("Phecda"))

-- asseenfrom(observer, "Sol/Earth")
earth = celestia:find("Sol/Earth")
observer:synchronous(earth)
observer:gotolonglat(earth, math.rad(-92.098194), math.rad(46.786939), earth:radius() * 2, 0)
-- Without this wait, the observer does not go to the above latitude and longitude.
wait(0)
observer:gotosurface(earth, 10)
elapsedwait(10)
celestia:flash("       As seen from Duluth", 7)
elapsedwait(7)

-- Always remain looking at the Big Dipper.
-- The view from Duluth is horizontal if Phecda is tracked here.
--observer:track(celestia:find("Phecda"))

observer:setframe(celestia:newframe("universal"))

pos = celestia:newposition("AABYAOsR1HqI6On7/////w", "ADR5CoLr0KU30gk", "AIAxSsPh8NHO4p/9/////w")
rot = celestia:newrotation(0.295384, -0.547602, -0.541268, 0.565605)
asseenfrom(observer, "Regulus", pos, rot)

pos = celestia:newposition("AADCg6Exgq6QJjb//////w", "AOD6ihjzfklXAjw", "AACC0l7zNzHUcCn+/////w")
rot = celestia:newrotation(0.570359, -0.285928, -0.663429, 0.390894)
asseenfrom(observer, "Pollux", pos, rot)

pos = celestia:newposition("AIBS5t+BTqpGoPf+/////w", "AEArtxa0sO/8EIg", "AMAJlmIZuiVRBTP9/////w")
rot = celestia:newrotation(0.486686, -0.324719, -0.737474, 0.33738)
asseenfrom(observer, "Castor", pos, rot)

pos = celestia:newposition("AAAAAAAAED5Ru10B", "AAAAAAAAihO6HZ///////w", "AAAAAAAAIOLHA0r8/////w")
rot = celestia:newrotation(0.537383, -0.234457, -0.784567, 0.201753)
asseenfrom(observer, "Aldebaran", pos, rot)

pos = celestia:newposition("2LCYvQYZAIMH", "P30XajnICQ", "IHj45WqmHi0O")
rot = celestia:newrotation(0.760644, -0.285348, -0.500984, 0.29835)
asseenfrom(observer, "Sol/Earth", pos, rot)