DISTANCES IN SPACEor

“Are we there yet?”

Miles

Feet

Inches

Kilometers

Meters

Centimeters

Diameter of Earth using common units of length

7,926

41,849,280

502,191,360

It’s important to use the correct scale for the distance you are measuring

12,736

12,756,000

1,275,600,000

These scales can still be used for relatively close objects, like the moon, but at 240,000 miles (384,000 kilometers) you can see how large the numbers are already getting.

The Hubble Deep Field (HDF) is an image of a small region in the constellation Ursa Major, constructed from a series of observations by the Hubble Space Telescope. They pointed Hubble at a fairly empty region of space, one where very few stars are seen. The image was assembled from 342 separate exposures taken with the Space Telescope's Wide Field and Planetary Camera 2 over ten consecutive days between December 18 and December 28, 1995.

The field is so small that only a few foreground stars in the Milky Way lie within it; thus, almost all of the 3,000 objects in the image are galaxies, some of which are among the youngest, and most distant, known.

It’s very hard for us to understand just how large the Universe is. Scientists tell us that the largest number our minds can really comprehend, or grasp, is about a hundred thousand (100,000). Because astronomers study objects over such

extremely large distances, they commonly use units of length that are much bigger

than the ones we usually use. Two common units of distance used in

astronomy are the astronomical unit (AU) and the light-year.

Astronomical Unit

The astronomical unit (AU) is the average distance from the Earth to the Sun, measured to be about 1.5 x 108 km (150,000,000 km) or 93,000,000 miles. It is a convenient unit to use when discussing distances within our solar system.

Saturn has an average distance of 9.5 AU’s from the sun. How many kilometers is this? How many meters?

150,000,000 km

X 9.5

X 1,000

1,425,000,000 km

1,425,000,000,000 m

Pluto is about 6x109 km from the sun. How many astronomical units (AU) is this?

150,000,000 km

6,000,000,000 km = 40 AU

Speed of Light

Nothing in the Universe moves as fast as light. In one second a beam of light will travel 186,282 miles or 300,000 km. At that speed a ray of sunlight takes 8 minutes to reach Earth.

Light can travel forever without getting weaker, so the speed of light remains constant in the Universe

Speed of Light

300,000 km/sec or 186,000 mi/sec.

The average distance to the moon is 382,500 km. How many seconds does it take for the sun’s light reflected by the moon to reach us?

382,500 km

300,000 km/sec= 1.275 sec

Light-year

Most stars are very far from Earth so it takes their light thousands or even millions of years to reach our planet. When we study the light coming from that star it is like peaking into the past.

The light-year is defined as the distance that light travels in a year. It is equal to a distance of approximately 9,500,000,000,000 km. For instance, Alpha Centauri, the closest star to the Earth after the sun, is 4.3 light-years from us.

How long does it take light from this star to reach us?

4.3 years

The star Betelgeuse,…

not Beetlejuice,…

…meaning “armpit of the giant”, is 310 light-years from Earth. How many hours does light from this star take to reach Earth?

310 yr X 365 day X

year

24 hr =

day

2,715,600 hours

How many AU’s are in a light-year?

9,500,000,000,000 km =

63,333.33 AU’s

150,000,000 km

Parsec A parsec is an abbreviation for parallax second. (We will study parallax Friday) Scientists use parsecs when even light years are too small to conveniently express distances. A parsec is 3.26 light-years, or well over nineteen trillion miles (19,000,000,000,000).

How many AU’s are in a parsec?

19,000,000,000,000 miles =

204,301 AU’s

93,000,000 miles

SUPER SCIENCE GEEK MOMENTWhat’s wrong with this clip from Star Wars?

AKAa conversation

with Mr. D