Download What Can You See With a Telescope

Objective – Describe the history of asteroid discovery and how technology was used to learn about the asteroids.
The first four asteroids—Ceres, Pallas, Juno, and Vesta— were discovered between 1801 and 1807.
No asteroids were found until 1845—almost forty years later—even though groups of amateur
and professional astronomers designed special sky-mapping projects to search for them.
A Lull in Asteroid Discovery
Why were no new asteroids found during
this period? Most were too small and dim
to be easily observed through the early
19th-century telescopes. Even the largest
telescopes were not big enough to find
asteroids that were much smaller and/or
dimmer than the first four asteroids that
had already been found. Even when the
four largest asteroids were seen through
those telescopes, they appeared only as
points of reflected Sunlight. They looked
very much like the stars around them, except that they moved.
Size a Factor in Asteroid Discovery
Ceres, the largest asteroid (now smallest dwarf planet), is about 600 miles in diameter.
Pallas is about 350 miles in diameter. Vesta is about 340 miles in diameter. Juno is the
smallest. It is about 145 miles in diameter.
William Herschel attempted to measure the
size of Ceres and Pallas by looking at the
asteroids through a telescope with one eye
and comparing them to a small disk of a
known size at a given distance. Herschel’s
estimated diameters of 160 miles for Ceres
and 140 miles for Pallas were smaller than
their actual diameter.
Most of the asteroids discovered
between 1845 and 1890 ranged in size
between 50 and 80 miles in diameter. Hygeia, found in 1849, is an exception, with a
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Objective – Describe the history of asteroid discovery and how technology was used to learn about the asteroids.
diameter of about 250 miles. It is dimmer than any of the first four discovered. Only about 30
asteroids with diameters greater than 120 miles have been found. It is estimated that there are
250 asteroids larger than 62 miles in diameter and perhaps 1,000,000 with diameters greater
than one-half a mile.
Asteroid Brightness—Another Factor to Consider
The size of the majority of asteroids is quite small, but that is not the whole story. An asteroid’s
brightness varies according to its orbital position and its distance from Earth. It also
depends on what is on its surface. Another factor is the shape of the asteroid. An asteroid with an
irregular shape will have a changing brightness that depends on which part of the surface
or face of the object is facing Earth and is lit by the Sun.
The table on the next page shows the brightest magnitude for the first ten asteroids, the higher the
magnitude, the dimmer the asteroid appears to an observer on Earth.
Sometimes, when I see my granddaughters make small discoveries of their own, I wish I
were a child.
Dr. Seuss
Asteroid
Year of
Number Discovery
Asteroid Magnitude Asteroid
Name
at
Year of
Number Discovery
Asteroid Magnitude
Name
Discovery
at
Discovery
1
1801
Ceres
6.6
6
1847
Hebe
7.7
2
1802
Pallas
7.0
7
1847
Iris
6.8
3
1804
Juno
7.6
8
1847
Flora
8.5
4
1807
Vesta
5.4
9
1848
Metis
8.4
5
1845
Astraea
8.7
10
1849
Hygeia
9.1
 Ceres is about twice the size of Vesta.
 Vesta, which is 219,480,000 miles from the Sun, orbits slightly closer to the Earth than does
Ceres, which is 257,610,000 miles from the Sun.
 Vesta reflects four times more light than Ceres.
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Objective – Describe the history of asteroid discovery and how technology was used to learn about the asteroids.
The Sun’s magnitude is -27, the Moon -12, Venus -4. The brightest stars are –1. An object of
approximately the 6th magnitude, like 3 Juno, is barely visible to a person with good eyesight on a
clear, Moonless night. With a good set of binoculars, one can see objects down to the 10th
magnitude. With an 8-inch reflecting telescope, an observer can manage to see objects of
14th magnitude on very dark nights. The faintest objects detectable with the largest groundbased telescopes are about magnitude 30.
Worksheet
1. How many years passed between the discovery of the first four asteroids and the fifth asteroid?
a. 10
b. 20
c. 30
d. 40
2. Why were no new asteroids found during this period?
a. The asteroids were too far away.
b. The asteroids were too dim.
c. The asteroids were too small to be seen.
d. The asteroids were too small and dim to be observed through early 19th century
telescopes.
3. When see through a telescope, the four largest asteroids looked very much like…
a. comets.
b. moons.
c. planets.
d. stars.
4. The difference between an asteroid and a star is the asteroid moves.
a. True
b. False
Match the asteroid with its diameter.
______5. Ceres
A. 145 miles
______6. Juno
B. 340 miles
______7. Pallas
C. 350 miles
______8. Vesta
D. 600 miles
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Objective – Describe the history of asteroid discovery and how technology was used to learn about the asteroids.
9. Most asteroids discovered between 1845 and 1890 ranged in size between 50 and 80 miles except
this one.
a. Flora
b. Hebe
c. Hygeia
d. Iris
10. It is estimated there are how many asteroids with a diameter greater than one-half a mile?
a. 30
b. 250
c. 1,000,000
11. An asteroid’s brightness does not vary according to its distance from Earth.
a. True
b. False
12. An asteroid with an irregular shape will have a changing brightness that depends on which part
of the surface or face of the object is facing Earth and is lit by the Sun.
a. True
b. False
13. The higher the magnitude, the brighter the asteroid appears to an observer on Earth.
a. True
b. False
Match the telescope/binocular to the faintest magnitude it can be used to see.
_____14. 8” mirror
A. 10th magnitude
_____15. Binoculars
B. 16th magnitude
_____16. Largest telescopes
C. 30th magnitude
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Objective – Describe the history of asteroid discovery and how technology was used to learn about the asteroids.
What Can You See With a Telescope? – Key
1. How many years passed between the discovery of the first four asteroids and the fifth asteroid?
d. 40
2. Why were no new asteroids found during this period?
d. The asteroids were too small and dim to be observed through early 19th century
telescopes.
3. When see through a telescope, the four largest asteroids looked very much like…
d. stars.
4. The difference between an asteroid and a star is the asteroid moves.
a. True
D 5. Ceres
A 6. Juno
B 7. Pallas
C 8. Vesta
9. Most asteroids discovered between 1845 and 1890 ranged in size between 50 and 80 miles except
this one.
c. Hygeia
10. It is estimated there are how many asteroids with a diameter greater than one-half a mile?
c. 1,000,000
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Objective – Describe the history of asteroid discovery and how technology was used to learn about the asteroids.
11. An asteroid’s brightness does not vary according to its distance from Earth.
b. False
12. An asteroid with an irregular shape will have a changing brightness that depends on which part
of the surface or face of the object is facing Earth and is lit by the Sun.
a. True
13. The higher the magnitude, the brighter the asteroid appears to an observer on Earth.
b. False
B 14. 8” mirror
A 15. Binoculars
C 16. Largest telescopes
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Objective – Describe the history of asteroid discovery and how technology was used to learn about the asteroids.
What Can You See With a Telescope? – Scoring
Guide
15-16 – 4
14 – 3.5
13 – 3
12 – 2.5
10-11 – 2
9 – 1.5
8-7 – 1
1-6 – .5
0–0
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