DISTANCES IN SPACE
or
“Are we there yet?”
Diameter of Earth using common units of length
Miles
7,926
Feet 41,849,280
Inches 502,191,360
12,736 Kilometers
12,756,000
Meters
1,275,600,000 Centimeters
It’s important to use the correct scale for the distance you are measuring
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
1,425,000,000 km
X 1,000
1,425,000,000,000 m
Pluto is about 6x109 km
from the sun. How many
astronomical units (AU) is
this?
6,000,000,000 km
150,000,000 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,…
…meaning “armpit of the giant”, is 310 lightyears from Earth. How many hours does light
from this star take to reach Earth?
310 yr X
365 day X
year
24 hr =
day
not Beetlejuice,…
2,715,600 hours
How many AU’s are in a light-year?
9,500,000,000,000 km
150,000,000 km
=
63,333.33 AU’s
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
93,000,000 miles
=
204,301 AU’s
SUPER SCIENCE GEEK MOMENT
What’s wrong with this
clip from Star Wars?
AKA
a conversation
with Mr. D