Objective – Describe how the use of telescopes helped us to better understand asteroids.
The work of astronomers Copernicus, Brahe, and Kepler was amazing. They did all their observations of the night sky using their eyes. The invention of the telescope allowed scientists to “extend their senses” for the first time. The telescope is one of the most important tools used by astronomers.
Who Invented the Telescope?
We don’t know who invented the telescope. One story is that two children were playing with lenses in the shop of Hans Lippershey, a Dutch reading-glasses maker. The children looked at a nearby weather vane through two lenses held together. It became larger and clearer. Lippershey put a tube in between the two lenses. This may have been one of the first telescopes. This early model only magnified an image by three or four times. A marble would have appeared three or four times larger than its actual size.
Lippershey tried to sell his telescope. In 1608, he applied for a patenton his telescope. This would protect his idea from being stolen by someone else. He was required to make three identical telescopes and to keep his method secret. Making more was not a problem. He had trouble keeping his secret. Jacob Metiusapplied for a patent on a device for "seeing faraway things as though nearby." His device was a tube with one convex lens (curved outward) and one concave lens that curved inward.
Government officials discussed the patent applications of both men. Neither man received a patent. The telescope design was easily copied. The patent request was refused. They did give Metius a small amount of money and paid Lippershey to make several telescopes. Hans Lippershey is given credit for inventing the telescope.
These looked more like “spyglasses” than our modern telescopes. Because they used lenses that refracted(or bent) light, they were called refractortelescopes.
Galileo Received Credit for the Refractor Telescope
In 1609, Galileo heard Lippershey was on his way to Venice. He planned to sell his invention that “that made distant objects seem near.” He needed money. He knew the Venetians were offering Lippershey a high price for his device. In 24 hours, Galileo had a telescope made. He sent word of “his invention” to a monk in a high office of the government. For this, Galileo received a raise in salary from 520 to 1000 florins per year.
We know three things about the invention of the telescope.
First, telescopes were not invented by scientists. They were invented by craftsman.
Second, Galileo did not invent the telescope.
Finally, telescopes changed astronomical observation. Scientists relied upon larger and better telescopes to continue their study of the heavens.
Galileo used a telescope with lenses that magnified objects about 20 times their size. With this telescope, he discovered the moons of Jupiter, the rings of Saturn, the changing apparent shape of Venus, sunspots, and solar rotation in less than ten years.During the same decade, at least ten other astronomers built their own telescopes using different combinations and types of lenses. Many of these were used to verify, support, and extend Galileo’s discoveries.
Early Refractor Telescopes Reached Their Limits
There were several problems with Galileo’s telescopes. They only allowed for a narrow field of view (what could be seen). The images produced through the lenses were blurry. Around 1630, a German astronomer, Johannes Kepler, proposed some solutions. To expand the area that could be visible through a telescope, Kepler suggested the concave eyepiece be replaced by a convex one. This design produced an upside-down image. It was corrected by the two-convex lens design. He discovered that by flattening the shape of the lens, the image quality could be improved. This solution caused a problem. With a flatter lens, the only way to increase the magnification power of the telescopes was to increase the length of these telescopes. By the middle of the 17th century, the length of telescopes became longer and longer. They were eventually were too large to control.
Isaac Newton Built a Reflector Telescope
Another problem was that the glass lenses caused light to separate into colors. You may have observed how a glass prism creates a rainbow effect. The early telescope lenses produced a ring of color around bright objects. This is called chromatic aberration. An English scientist, Sir Isaac Newton, solved this problem by using metal mirrors instead of glass lenses. This design solved the “color” problem. Better yet, it was six inches long. It could magnify objects 40 times.
Some of the best reflector telescopes were designed and built by William Herschel. He built a telescope that was used by Johann Schröter, the president of the “Celestial Police.” This group was formedto search for and discover the “missing planet.” Astronomers believed it would be found between the orbits of Mars and Jupiter.
Images continued to be blurry with the early reflector telescopes. Technology finally made it possible to grind the lenses and mirrors into different shapes. Newton’s design led to a new problem. The metal mirror became dull easily. It required frequent polishing. Even so, the introduction of the reflecting telescope inspired a new surge of astronomical discoveries. Scientific pursuits continued to inspire improvements to the telescope.
It was on a dark and starry night of New Year’s Day, 1801. Giuseppe Piazzi, an Italian monk, was at work in his observatory on Sicily. He was a member of the Celestial Police. This was a group of astronomers looking for a missing planet between Jupiterand Mars.
That night he was confirming and cataloging stars in Taurus. While checking other astronomers’ work, he saw a tiny point of light. He thought it was just a dim star no one had cataloged. He checked for it the next night, but it had moved! He watched it move on January 3 and 4. What he was observing was not a star! He wrote to Johan Bode and told him what he had found; Bode was certain he had found “the missing planet.”
While checking other astronomers’ work, he saw a tiny point of light. He thought it was just a dim star no one had cataloged. He checked for it the next night, but it had moved! He watched it move on January 3 and 4. What he was observing was not a star! He wrote to Johan Bode and told him what he had found; Bode was certain he had found “the missing planet.”
And the Plot Thickens . . .
Cloudy weather set in. Piazzi was so sick that he could not observe the skies on some January nights. By January 24, he realized what he had discovered. He wrote a friend: “I have announced the star as a comet. But the fact that the star is not accompanied by any nebulosity [clouds of dust and gas] and that its movement is very slow and rather uniform has caused me many times to seriously consider that perhaps it might be something better than a comet. I would be very careful, however, about making this conjecture [idea] public.”
He wrote to Bode the next day. He did not receive the letter until March 20. When the letter reached Bode, he studied his star maps. He convinced Piazzi that he had found the “missing planet.” Piazzi named the object Ceres. Piazzi’s friend, Baron von Zach announced the discovery in his Monthly Correspondence summer of 1801.
Piazzi tried to predict Ceres’ orbit. Astronomers need this information so they could try to find it. He observed Ceres for six weeks. He did not have enough information to determine Ceres’ orbit. After that, others searched for Ceres in vain. Several astronomers tried to work out Ceres’ orbit from his data. They each came up with different results. Ceres appeared to be lost. No one could verify Piazzi’s observations.
But Carl Friedrich Gauss, a young German mathematician, came to the rescue! In October 1801, he applied his new method of “determining the path of a celestial body” to Ceres’ orbit. With surprising speed and accuracy, Gauss used Piazzi’s observations to predict where the new “planet” should be found. Imagine Gauss’s excitement when Baron von Zach found Ceres on the night of December 7, just where Gauss said it would be!
Actually, von Zach found four stars at that location, but when the weather cleared again on December 18, one of the stars was gone. von Zach finally confirmed that he had recovered the missing object on January 1, 1802, exactly one yearafter Piazzi’s first sighting. Using Gauss’ results, Wilhelm Olbers, an amateur astronomer in Bremen, also found Ceres with his telescope.
Piazzi received a letter sent by the secretary of state on behalf of the king of Sicily commending him on the discovery of Ceres. Instead of giving Piazzi a medal, the king agreed to buy the Palermo Observatory a new telescope.
von Zach had two roles in this exciting event. He not only found the missing Ceres, but also, his publication, Monthly Correspondence, played a vital communication role in the recovery.
By 1809, Gauss had refined the mathematical procedure he used to determine Ceres’ orbit, and it became the standard procedure for orbital calculations.
The “missing planet” was found, lost, and found again. All’s well that ends well…except this was not the end! This was only the beginning! Many more asteroids had yet to be discovered. The NASA Dawn mission will travel to Ceres but first will study another asteroid named Vesta.
What Can You See With a Telescope?
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 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.
Asteroid Number / Year of Discovery / Asteroid Name / Brightest Magnitude Through 2016 / Asteroid Number / Year of Discovery / Asteroid Name / Brightest Magnitude Through 20161 / 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.
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 ground-based telescopes are about magnitude 30.
Name ______
1. Why were the work of astronomers Copernicus, Brahe, and Kepler remarkable?
a. They were the first to use a telescope.
b. All their observations were made using their eyes.
c. They took photographs through a telescope.
d. They worked together to answer astronomical questions.
2. The telescope is considered one of the most important instruments in the Scientific Revolution of the 17th century.
a. Trueb. False
3. While nobody knows who invented the telescope, who is usually considered to have been a possible inventor?
a. Tycho Brahec. Hans Lippershey
b. Galileod. Baron von Steuben
4. Who is given credit for inventing the refractor telescope?
a. Tycho Brahec. Hans Lippershey
b. Galileod. Baron von Steuben
5. There are three things certain about the invention of the telescope. Which statement below is not one of the three?
a. First telescopes were invented by craftsman.
b. Galileo did not invent the telescope.
c. Telescopes change astronomical observations.
d. Telescopes were not widely accepted until the 18th century.
6. Which was not a discovery made by Galileo?
a. The Moons of Jupiter.c. The division in Saturn’s rings.
b. Channing shape of Venus.d. Sunspots and solar rotation.
7. What were problems with Galileo’s telescopes?
a. Allowed for a narrow field of view (what could be seen).
b. Were not portable.
c. Images were blurry.
d. Both a and b.
e. Both a and c.
f. Both b and c
8. Why did refractor telescopes become too large to control?
a. They weighed too much.c. They were too tall.
b. They became longer and longer.d. The lenses were too large.
9. What did Sir Isaac Newton use instead of lenses in his reflecting telescope?
a. Prismsc. Lights
b. Glass mirrors.d. Metal mirrors
10. Who built some of the best reflector telescopes?
a. Sir Isaac Newtonc. Johann Schröter
b. William Herscheld. George Gamov
11. Who was the astronomer who was working in his observatory on New Year’s Day, 1801?
a. Johann Bodec. Giuseppe Piazzi
b. Herman Olbersd. Baron von Zach
12. The Celestial Police was a group of astronomers looking for a(n) ______between Mars and Jupiter.
a. asteroidc. meteoroid
b. cometd. missing planet
13. During an observation session, Giuseppe Piazzi noticed a tiny point of light. He looked for it the next night and he couldn’t see it. What had happened?
a. The “star” had moved.c. He hadn’t really seen a “star.”
b. The “star” had blown up.
14. Piazzi seriously considered the “star” something other than a comet.
a. Trueb. False
15. Who convinced Piazzi he had found the missing planet?
a. Johann Bodec. Giuseppe Piazzi
b. Herman Olbersd. Baron von Zach
16. Who announced the discovery of the missing planet in his Monthly Correspondence?
a. Johann Bodec. Giuseppe Piazzi
b. Herman Olbersd. Baron von Zach
17. Piazzi had enough information to determine Ceres’s orbit.
a. Trueb. False
18. Who was able to determine the orbit of Ceres?
a. Carl Friedrich Gaussc. Edwin Hubble
b. Sir William Herscheld. Baron von Zach
19. How long after Piazzi discovered Ceres was it recovered?
a. 3 monthsc. 9 months
b. 6 monthsd. 12 months (1 year)
20. Baron von Zach had two roles in this event. What were they? (There are two answers to this question.)
a. He found the missing Ceres.
b. His publication, Monthly Correspondence, play a vital communication
role in the recovery.
c. He financed Piazzi’s work.
d. He was very encouraging.
What Can You See With a Telescope?
21. How many years passed between the discovery of the first four asteroids and the fifth asteroid?
a. 10c. 30
b. 20d. 40
22. 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.
23. When see through a telescope, the four largest asteroids looked very much like…
a. comets.c. planets.
b. moons.d. stars.