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Distances in Space

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How Far Away are Stars & Other Celestial Bodies? Use Stellarium to observe the sky and discuss what observations you might be able to use to determine which objects are closest to Earth. Do size and brightness always lead to accurate conclusions about the distances between Earth and objects out in space?

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Distances in Space Objects in space are so far apart that it doesn’t make sense to use units of measurement like kilometers. Instead, we use astonomical units (AU’s) or light years to describe these huge distances.

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Astronomical Unit used for measuring “local distances” … those INSIDE our solar system 1 AU = average distance from the center of Earth to center of the Sun (149 599 000 km) Science In Action p. 379

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Light Year = ~10 trillion km used for measuring distances outside our solar system IT DOES NOT MEASURE TIME – it is the distance light can travel in a year light travels about 300,000 kilometers per second. there are 60 seconds in a minute, 60 minutes in an hour, 24 hours in a day, and about 365.25 days in a year. if we multiply all those numbers together, we come up with approximately 10 trillion kilometers as the distance light can travel in one year.

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Views of the Past because it takes time for light from an object to travel to Earth what we see is images from the past – light from the Moon is 1.3 seconds old – light from the Sun is ~8 minutes old – light from Pluto is 5 hours old – light from a star in the centre of our galaxy is 25 000 years old – using the Hubble Space Telescope we can see images that have taken 12 billion years to reach Earth (…the Earth is about 4.6 billion years old!)

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Parallax How do we know the distance to various stars and planets? – In 1672, Giovanni Cassini used parallax to determine the distance from Earth to the Sun What is parallax? – Hold a finger up about three to five inches in front of your nose, focus on a distant object, and then alternately open and close each eye. – What happens?

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With parallax… if you look at the same star from two different location on Earth at the same time, nearby stars will appear to shift in position relative to other, more distant stars. Closer Star Distant Star A Distant Star B baseline

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OR you can look at the same star from the same place on Earth… but at 2 different times of the year Science In Action p.450

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Triangulation How can parallax be used to measure distances in space? It involves triangulation which involves the mathematics of triangles, angles and trigonometry

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1 st - we need to use our knowledge of parallax… take a measurement of an object in space from 2 points on Earth (or from the same point at 2 different times) that gives us 2 angles for our triangle

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2 nd - we need to measure the base of our triangle 3 rd – we need to understand trigonometry …sometime after grade 9!

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Let’s try it out… Instead of using trigonometry… we will create a scale diagram to figure out the distance to an object!

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