Content Benchmark E.8.B.5
Students know the Sun is many thousands of times closer to Earth than any other star, and
billions of times closer than the far end of the Milky Way Galaxy. W/L
“Space is big - really big - you just won't believe how vastly, hugely mind-bogglingly big it is.
You may think it's a long way down the road to the chemist, but that's just peanuts to space.”
(Douglas Adams from The Hitchhiker’s Guide to the Galaxy).
The Milky Way Galaxy (Figure 1) is home to at least 200 billion stars. Some estimates suggest
that number could be closer to 400 billion stars (http://seds.org/MESSIER/more/mw.html).
Figure 1. Milky Way Galaxy
(From http://map.gsfc.nasa.gov/media/ContentMedia/dirbe123_2p6dec.jpg)
Out of all those billions, the star closest to Earth is Sol, the lone star of our own solar system.
Sol, more commonly referred to as “the Sun” is centrally located within the solar system. With
such proximity, the Sun is far brighter than any other star twinkling in the sky (Figure 2).
Figure 2. Solar System
(From http://www.solarviews.com/raw/misc/solarsystem.jpg)
The Sun is located an average distance of 149.6 million kilometers (93 million miles) from Earth
(http://www.windows.ucar.edu/tour/link=/sun/statistics.html). Distances in millions of
kilometers or millions of miles are comprehendible to most people, but to make the numbers less
cumbersome, we typically measure distances within the solar system in astronomical units (AU).
One AU is equivalent to the average distance from Earth to the Sun. When dealing with
interstellar and intergalactic distances, even the AU is too limiting. Instead, distances are
measured with respect to the distance light can travel in a defined time. Figure 3 depicts how
many light minutes the Sun is from the terrestrial planets and how many light hours the Sun is
from the Jovian planets.
Figure 3. Distances from the Sun to the Planets.
(From http://www.solarviews.com/eng/solarsys.htm)
Light minutes and light hours work within our solar system, but light years is a unit preferable
when referring to distances between stars and galaxies. The speed of light is 299,792.458 km/sec
and a year equals 365.25 days (or 31,557,600 seconds). Multiplying the speed of light by the
number of seconds in a year (299,792.458 km/sec * 31,557,600 sec) lets us compute that light
would travel 9.46 x 1012 km in a year (thus, this value equals the distance known as a light year).
To determine, for comparative purposes, how many light years the Sun is from Earth, divide the
distance between the two (149,600,000 km) by 9.46 x 1012 km per light year. This calculation
shows the Sun is 1.58 x 10-5 light years (or approximately 8 light minutes) from Earth.
When viewing the night sky with our unaided, naked eye, we generally observe stars (other than
our Sun) as close as around 4 light years and as far away as a few hundred light years. A few
stars are large enough and bright enough that we detect them with our naked eye to distances as
far as 2000 light years (http://www.uwgb.edu/dutchs/CosmosNotes/distance.htm).
Figure 4 is a chart of some of the nearest stars to Earth. After the Sun, Proxima Centauri is
closest to Earth at 4.2 light years. Dividing this value by the distance between Earth and Sun
(4.2 light years / 1.58 x 10-5 light years) reveals Proxima Centauri to be 265,823 times as far
from Earth as is the Sun. So…the nearest star after the Sun is more than one-quarter of a million
times further away. Progressing to the next stars out, the difference in distances increases even
more. For example, Wolf 359 (of Star Trek - The Next Generation fame) is 7.6 light years from
Earth, and therefore 481,013 times further from Earth than the Sun (7.6 light years / 1.58 x 10-5
light years).
The most distant stars we can see with the naked eye, at around 2000 light years, are
126,582,280 times further from Earth than our Sun (2000 light years / 1.58 x 10-5 light years).
To put things into perspective, the distance to those stars are just 0.02 of the diameter of the
Milky Way Galaxy. Our stellar neighbors, even the closest ones, are so far away as to render us
unable to readily drop by and borrow a cup of star dust.
Figure 4. Twenty-two Nearest Stars to Earth
(From http://www.essex1.com/people/speer/stars.html)
The Milky Way is a barred-spiral galaxy. Figure 5 displays the Sun’s location within the Orion
Arm of the Milky Way Galaxy. From this diagram, it is apparent that the Sun is over halfway
from the center of the galaxy towards the perimeter of the galactic disk.
Figure 5. The Sun within the Orion Arm of the Milky Way Galaxy
(From http://www.atlasoftheuniverse.com/milkyway.html)
Figure 6 more specifically depicts the distances involved regarding the Sun’s location in the
Milky Way. From one edge of the galactic disk to the other is between 95,000 – 100,000 light
years. The Sun is approximately 28,000 light years from the center of the Milky Way Galaxy.
This places the Sun a bit less than 22,000 light years to its nearest edge of the galactic disk, and
around 78,000 light years to its furthest edge of the galactic disk.
Using the aforementioned distances, the closest edge of the galaxy is 1,392,405,100 times further
from Earth than is the Sun (22,000 light years / 1.58 x 10-5 light years), the center of the galaxy is
1,772,151,900 times further from Earth than is the Sun (28,000 light years / 1.58 x 10-5 light
years), and the furthest edge of the galaxy is 4,936,708,900 times further from Earth than is the
Sun (78,000 light years / 1.58 x 10-5 light years).
Figure 6. The Sun’s location within the Milky Way Galaxy
(From http://boojum.as.arizona.edu/~jill/NS102_2006/Lectures/MilkyWay/milkyway.html)
Content Benchmark E.8.B.5
Students know the Sun is many thousands of times closer to Earth than any other star, and
billions of times closer than the far end of the Milky Way Galaxy. W/L
Common misconceptions associated with this benchmark
1. Students mistakenly believe the Sun is not a star because it doesn’t shine at night.
Since early childhood, students have learned the bright object in the daytime sky is called the
Sun and that the small, twinkling dots of light in the nighttime sky are called stars. They are
not taught that the Sun is a star till later in their education, and even then, their own
observations conflict with the information that our Sun is simply a star (albeit a star at the
center of a solar system) because they do not look and act the same. Students must also be
taught that when they are experiencing nighttime, the Sun (our star) is visible and shining for
persons in the daylight on the opposite side of the world.
For information discussing the Sun as a star, refer to http://www.nineplanets.org/sol.html
This misconception as well as numerous others can be found at the following site,
(http://amazingspace.stsci.edu/resources/myths/solar_system.php.p=Teaching+tools%40%2Ceds%2Ctools%
2C%3EMyths+vs.+realities%40%2Ceds%2Ctools%2Ctype%2Cmyths.php%3EOverview%3
A+Solar+system+myths%40%2Ceds%2Coverviews%2Cmyths%2Csolar_system.php&a=%
2Ced
2. Students have a misconception that nighttime visible stars are located within our solar
system.
Such a notion has been considered since the times of the ancient Greeks. Aristotle proposed
a geocentric model of the solar system with Earth at the center. Crystalline spheres
surrounded Earth. Each of those spheres contained the celestial bodies, with the Moon in the
first sphere surrounding Earth, followed by spheres containing Mercury, Venus, the Sun,
Mars, Jupiter and Saturn. The last sphere containing celestial objects held the stars (Figure
7). It simply appears that the stars are close and are therefore members of our solar system.
The planets even resemble the stars, leading to further presumption of association. It is
difficult to discern the actual depth of field of the starry sky by merely looking at it; distances
to the stars required the development of mathematical strategies involving parallax, and a
knowledge of the diameter of Earth’s orbit about the Sun.
For additional views on early beliefs that the stars are part of our solar system, review the
information found at http://www.pas.rochester.edu/~blackman/ast104/aristotle8.html
and at http://astronomy.nmsu.edu/nicole/teaching/ASTR110/lectures/lecture11/slide01.html.
This misconception as well as others can be viewed at the following site,
(http://www.huntel.net/rsweetland/science/misconceptions/space.html)
Figure 7. The Celestial Spheres of Aristotle
(From http://www.pas.rochester.edu/~blackman/ast104/aristotle8.html)
3. Students incorrectly believe the closest stars are nearer to Earth than is the Sun.
This mistaken belief stems both from visual misperception (the stars appear to be about as
close to Earth as is the Moon and students know the Moon is closer than the Sun) as well as a
vague understanding of the relationship between the various measurement units utilized in
astronomy. When students find themselves reading values recorded as millions of
kilometers, Astronomical Units (A.U.), and light years, they often have no basis of
comparison. In such circumstances, it may be natural to assume that the smaller number
represents a closer distance and the larger number represents a further distance. For example,
when comparing distances of 4 light years, 10 A.U. and 150 million kilometers, students
believe these are already arranged in order of closest to furthest distance based on the
numerical value of each.
The Astronomical Conversion Calculator will help students understand the relationships
between the various units used in astronomical measurement. This site is found at
http://www.sciencelab.com/data/conversion_calculators/astronomical-conversion.shtml
This misconception was pulled from an extensive list of astronomy misconceptions and can
be viewed at the following site.
http://www.physics.umaine.edu/ncomins/stars.htm#distance
4. Students may incorrectly belief that all the stars in the sky are the same distance from
Earth.
When students look at the night sky, it appears as though all the stars are painted upon some
celestial tapestry. There are obvious differences in brightness of the stars, but to the casual
viewer, the stars appear to be near each other and all the same distance from Earth. By the
same reasoning, students believe the stars in the various constellation are all in the same
plane.
For further discussion on this topic, visit the following site
http://www.space.com/spacewatch/070124_ns_far_constellations.html
The above stated misconception came from a list of misconceptions found at
http://www.newyorkscienceteacher.com/sci/miscon/common-miscon/astr.php
5. Students have the misconception that there are millions of stars in close proximity to
Earth
As students star watch, they observe more stars in the night sky than they can count. They
already have the misconception that all the stars are located the same distance from the Earth,
and the stars seem tantalizingly close. It follows for them that these millions of stars they see
must all be quite close to Earth. In reality, there are just 40 stars located within 16 light years
of Earth. Our solar system is located in a sparsely populated region of the Milky Way
Galaxy. Stars are more densely-packed and closer together nearer the center of the galaxy.
More information on proximity of stars to Earth can be found at
http://hyperphysics.phy-astr.gsu.edu/Hbase/starlog/strclos.html#c0
The above stated misconception came from the following list of misconceptions,
http://www.physics.umaine.edu/ncomins/stars.htm#distance
Content Benchmark E.8.B.5
Students know the Sun is many thousands of times closer to Earth than any other star, and
billions of times closer than the far end of the Milky Way Galaxy. W/L
Sample Test Questions
Questions and Answers to follow on separate document
Content Benchmark E.8.B.5
Students know the Sun is many thousands of times closer to Earth than any other star, and
billions of times closer than the far end of the Milky Way Galaxy. W/L
Answers to Sample Test Questions
Questions and Answers to follow on separate document
Content Benchmark E.8.B.5
Students know the Sun is many thousands of times closer to Earth than any other star, and
billions of times closer than the far end of the Milky Way Galaxy. W/L
Intervention Strategies and Resources
The following is a list of intervention strategies and resources that will facilitate student
understanding of this benchmark.
1. The Milky Way Galaxy
This comprehensive website covers many details of the Milky Way Galaxy. It provides
numerical relationships, describes and provides links for terms. The site also discusses the
structure of the Milky Way Galaxy and has links to many photos and graphics.
To access this site, go to http://seds.org/MESSIER/more/mw.html
2. An Atlas of the Universe
Graphic views of the universe as seen outward from the Earth and Sun are provided through this
site. The URL takes you to a main page with links to nine other pages. Respectively, graphic,
clickable images and information are provided for: 1) 12.5 light years from the Sun, 2) 250 light
years from the Sun, 3) 5000 light years from the Sun, 4) 50,000 light years from the Sun, 5)
500,000 light years from the Sun, 6) 5 million light years from the Sun, 7) 100 million light years
from the Sun, 8) 1 billion light years from the Sun, and 9) 14 billion light years from the Sun.
To access this site, go to http://www.atlasoftheuniverse.com/
3. Parallax and Distances to the Sun and Stars
The information at these sites helps to explain how scientists are able to determine the distance to
stars and galaxies. The Parallax site includes a graphic which shows how the measurement is
made, while the Distances to the Sun and Stars site includes a historical perspective along with
information on current technology used in determining stellar distances.
To access the site that explains parallax, go to
http://hyperphysics.phy-astr.gsu.edu/Hbase/astro/para.html#c1
To access the site on the Distance of the Sun and Stars, go to
http://www.uwgb.edu/dutchs/CosmosNotes/distance.htm
4. The 3-D Sky
This site provide the user with a VRML 3-D model of the Sun (in yellow) surrounded by the 375
brightest stars within 600 light years of the Sun. As the model is rotated, it helps give a feel for
the Sun’s position with regards to its neighbors. Links are provided for VRML 3-D models of
Stars and of Galaxies
To access this site, go to http://www.honeylocust.com/Stars/
5. Mysteries of Deep Space
Many space-related activities are available at this site. The two activities which are particularly
useful for this benchmark would be Time Travel to the Edge of the Universe and Back! and
Demonstrating the Distances of Stars. Both of these activities involve working toward an
understanding of the vast distances between stars.
To access this site, go to http://www.pbs.org/deepspace/classroom/
6. The Cosmic Distance Scale
This site is similar to a “powers of ten” presentation. The user is able to zoom in or zoom out of
the universe, first starting with Earth. At each zoom, it is possible to click on an information link
which provides further detail.
To access this site, go to http://heasarc.gsfc.nasa.gov/docs/cosmic/
To access an activity on cosmic scale, visit
http://www.dlese.org/library/catalog_DLESE-000-000-006-009.htm