Mount Wilson Observatory facts for kids
| Location | Mount Wilson, California, US | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Quick facts for kids
|
|||||||||||
The Mount Wilson Observatory (MWO) is a famous place for studying stars in Los Angeles County, California, United States. It sits on Mount Wilson, a mountain about 1,740 meters (5,710 feet) high. This mountain is in the San Gabriel Mountains, not far from Pasadena and Los Angeles.
This observatory is home to two very important telescopes. One is the 2.5-meter (100-inch) Hooker telescope. It was the biggest telescope in the world from 1917 to 1949. The other is the 1.5-meter (60-inch) 60-inch telescope. When it was finished in 1908, it was the largest working telescope anywhere. The observatory also has solar telescopes and the CHARA array. This array uses six smaller telescopes together. It started working fully in 2004.
Mount Wilson is a great spot for astronomy because the air is very steady. This is due to a special weather pattern called an inversion layer. This layer traps warm air and smog below the mountain. This steady air is perfect for a special way of observing called interferometry. Even though light pollution from Los Angeles makes it harder to see faint objects far away, the observatory is still very active. The CHARA array, for example, continues to do important research on stars.
The idea for an observatory on Mount Wilson began in the 1880s. George Ellery Hale was the person who really made it happen. He had already built the world's largest telescope at the Yerkes Observatory. The Carnegie Institution of Washington started funding the Mount Wilson Solar Observatory in 1904. They leased the land from the Mount Wilson Hotel. One rule of the lease was that the public had to be allowed to visit.
Contents
Solar Telescopes: Studying the Sun
Mount Wilson Observatory has three solar telescopes. These are special telescopes designed to look at the Sun. Today, only one of them, the 60-foot Solar Tower, is still used for solar research.
Snow Solar Telescope
The Snow Solar Telescope was the first telescope set up at Mount Wilson. It was the first solar telescope that stayed in one place. Before this, solar telescopes were often moved around to chase solar eclipses. Helen Snow of Chicago gave this telescope to Yerkes Observatory. George Ellery Hale brought it to Mount Wilson to use it for serious science.
This telescope has a 60-foot (18-meter) focal length and a 24-inch (61-cm) main mirror. It worked with a tool called a spectrograph. This allowed scientists to study sunspots and how the Sun spins. They also took daily pictures of the Sun in different types of light. Later, it was used to study bright stars. Today, college students often use the Snow telescope. They learn about solar physics and how to analyze light. It was also used for the public to watch Mercury cross the Sun in 2016.
60-foot Solar Tower
The 60-foot (18-meter) Solar Tower was built soon after the Snow telescope. It was finished in 1908. This telescope was built vertically, like a tower. This design helped it get much clearer images and light readings than the Snow telescope. Being higher off the ground meant the optics avoided heat distortion from the Sun warming the ground.
On June 25, 1908, Hale used this tower to see Zeeman splitting in sunspot light. This was the first time anyone showed that magnetic fields exist somewhere other than Earth. Later, scientists found that sunspots in new solar cycles had reversed magnetic poles. In the 1960s, Robert Leighton used this tower to discover that the Sun vibrates every five minutes. This led to a new field of study called helioseismology. The University of Southern California now operates the 60-foot Tower.
150-foot Solar Tower
The 150-foot (46-meter) Solar Tower is even taller. It has a special "tower-in-a-tower" design. The inner tower holds the optics, while an outer tower surrounds it. This protects the optics from wind. Two mirrors send sunlight to a 12-inch (30-cm) lens. This lens focuses the light down to the ground floor. It was finished in 1910.
Scientists used this tower to study how the Sun rotates and the magnetic fields of sunspots. They also made daily sunspot drawings. This solar telescope was the largest in the world for 50 years. It was surpassed in 1962 by a telescope in Arizona. In 1985, UCLA took over running the solar tower.
60-inch Telescope: A Giant Leap
The 60-inch (1.5-meter) telescope began with a gift. George Ellery Hale received the 60-inch mirror blank from his father in 1896. This glass disk was 19 cm (7.5 inches) thick and weighed 860 kg (1,900 pounds). Hale got funding from the Carnegie Institution in 1904 to build the observatory. Grinding the mirror took two years, starting in 1905.
The telescope's parts were built in San Francisco. They barely survived the 1906 earthquake. Getting the heavy pieces up Mount Wilson was a huge challenge. The telescope saw its "first light" on December 8, 1908. At that time, it was the largest working telescope in the world.
The 60-inch telescope is a reflector telescope. It can be set up in different ways to collect light. It became one of the most successful telescopes ever. Its design and ability to gather light helped scientists make big discoveries. They used it for spectroscopic analysis (studying light), measuring parallax (distances to stars), taking pictures of nebulas, and measuring star brightness. Even after the 100-inch Hooker telescope was built, the 60-inch remained very important for decades.
In 1992, the 60-inch telescope got an early adaptive optics system. This system helped correct distortions caused by Earth's atmosphere. It made the telescope's images much clearer.
Today, the 60-inch telescope is used for public outreach. It is the second largest telescope in the world dedicated to the general public. Groups can book the telescope for an evening to look at the Moon, planets, and deep-sky objects.
100-inch Hooker Telescope: Changing Our View of the Universe
The 100-inch (2.5-meter) Hooker telescope at Mount Wilson Observatory was finished in 1917. It was the biggest telescope in the world until 1949. This telescope is famous for its role in 20th-century observational astronomy.
Edwin Hubble used it to make two huge discoveries that changed how we see the Universe. In 1922–1923, Hubble used the Hooker telescope to prove that the Universe goes far beyond our own Milky Way galaxy. He showed that some nebulae were actually millions of light-years away. Then, he showed that the Universe is expanding.
| Year | Description |
|---|---|
| 1923 | Edwin Hubble proves the Andromeda nebula is a galaxy outside the Milky Way. |
| 1929 | Hubble and Milton Humason confirm the Universe is expanding and measure its speed. |
| 1930s | Fritz Zwicky finds evidence for dark matter. |
| 1938 | Seth Nickolson discovers two new moons of Jupiter, called Lysithea and Carme. |
| 1940s | Walter Baade's observations lead to understanding different stellar populations. He also finds two types of Cepheid variable stars, which doubles the known size of the Universe. |
Building the Hooker Telescope
After the 60-inch telescope was well underway, Hale immediately wanted to build an even bigger one. John D. Hooker gave $45,000 to buy and grind the mirror. Andrew Carnegie provided money for the rest of the telescope and its dome. The mirror blank was cast in France in 1908. The Hooker telescope was finally finished and saw "first light" on November 2, 1917. Like the 60-inch telescope, it uses mercury to help support its huge 100-ton weight.
In 1919, the Hooker telescope got a special attachment. It was a 6-meter (20-foot) astronomical interferometer designed by Albert A. Michelson. Michelson used this equipment to measure the exact size of stars, like Betelgeuse. This was the first time the size of a star had ever been measured. Henry Norris Russell also used observations from the Hooker to create his system for classifying stars.
In 1935, the mirror's silver coating was replaced with aluminum. This new coating reflected 50% more light and lasted longer.
Edwin Hubble made many key discoveries using the Hooker telescope. In 1923, he found the first Cepheid variable star in the Andromeda nebula. This discovery helped him figure out the distance to Andromeda. He showed it was a separate galaxy outside our Milky Way. Hubble, with help from Milton L. Humason, then observed how fast many galaxies were moving away from us. In 1929, they published a paper showing that the Universe is expanding.
The Hooker telescope was the largest in the world for 30 years. Its reign ended when the 5-meter (200-inch) Hale Telescope was completed in 1949. This new telescope was at Palomar Observatory, about 144 km (90 miles) south.
By the 1980s, astronomers started focusing on very distant objects. This needed darker skies than what Los Angeles could offer due to growing light pollution. In 1989, the Carnegie Institution gave the observatory to the non-profit Mount Wilson Institute. The 2.5-meter telescope was stopped for a while. But it was restarted in 1992. In 1995, it got a visible light adaptive optics system.
As its use for scientific research slowed down again, a decision was made to use it for public viewing. A system of mirrors and lenses was developed to allow people to look through it from the bottom of the telescope. This conversion was finished in 2014. The 2.5-meter telescope then became the world's largest telescope used by the public. Regular public viewing began in 2015. The telescope can see details as small as 0.05 arcsecond.
Interferometry: Seeing Finer Details
Astronomical interferometry has a long history at Mount Wilson. At least seven interferometers have been used here. This is because the very steady air over Mount Wilson is perfect for this technique. Interferometry uses multiple viewing points to combine light. This helps telescopes see much finer details, like the actual size of stars.
20-foot Stellar Interferometer
The first of these was the 20-foot Stellar Interferometer. In 1919, the 100-inch Hooker telescope got this special attachment. It was developed by Albert A. Michelson and Francis G. Pease. It used the Hooker telescope as a stable base to stay pointed at stars. By December 1920, Michelson and Pease used it to measure the exact size of a star, the red giant Betelgeuse. This was the first time a star's angular size had ever been measured. In the next year, they measured six more red giants.
50-foot Stellar Interferometer
To do more work, Pease, Michelson, and George E. Hale designed a 50-foot interferometer. It was installed at Mount Wilson in 1929. It successfully measured Betelgeuse's diameter. However, it could not measure many other stars that the 20-foot interferometer had not already measured.
Optical interferometry reached its limits with the technology of that time. It took about 30 years for new tools like faster computers, electronic detectors, and lasers to make bigger interferometers possible again.
Infrared Spatial Interferometer
The Infrared Spatial Interferometer (ISI) is run by the University of California, Berkeley. It uses three 1.65-meter telescopes that work in infrared light. These telescopes can be moved. At Mount Wilson, they can be placed up to 70 meters (230 feet) apart. This allows them to act like one huge telescope with that diameter. The signals are changed into radio frequencies and then combined electronically. The longest distance, 70 meters, gives a very clear view of 0.003 arcseconds. In 2003, ISI made the first "closure phase" measurements in infrared light.
CHARA Array
The Center for High Angular Resolution Astronomy (CHARA) is built and run by Georgia State University. It is an interferometer made of six 1-meter telescopes. They are arranged along three lines, up to 330 meters (1,080 feet) apart. The light beams travel through vacuum pipes. They are then delayed and combined using mirrors. This needs a building 100 meters (330 feet) long with movable mirrors. This keeps the light in sync as Earth rotates.
CHARA began scientific work in 2002 and regular operations in early 2004. In infrared light, it can see details as small as 0.0005 arcseconds. All six telescopes are used for observations. By late 2005, they were regularly getting images. In 2007, the array captured the first image of the surface of a main sequence star other than our Sun.
Other Telescopes
In 1966, a 61-cm (24-inch) telescope with an infrared detector was used by Eric Becklin. He used it to find the center of the Milky Way galaxy for the first time.
In 1968, Gerry Neugebauer and Robert B. Leighton used a 157-cm (62-inch) reflecting dish they built. They used it to make the first large map of the sky in near-infrared light. This telescope, called the Caltech Infrared Telescope, is now on display at the Udvar-Hazy Center. This is part of the Smithsonian Air and Space Museum.
Events and Public Access
- The Mount Wilson Observatory has a special exhibition at the Museum of Jurassic Technology. It shows unusual letters and theories sent to the observatory between 1915 and 1935.
- The observatory faced danger during the August 2009 California wildfires and the Bobcat Fire in September 2020. Firefighters worked hard to protect it.
- The English poet Alfred Noyes was there for the "first light" of the Hooker telescope on November 2, 1917. He wrote about this night in his poem Watchers of the Sky. He said he was the first to see one of Jupiter's moons through the telescope that night.
Sunday Afternoon Concerts in the Dome
On one Sunday each month during the warmer parts of the year, Mount Wilson Observatory hosts concerts. These are chamber music or jazz concerts held inside the dome of the 100-inch telescope. The idea for concerts started in 2017. A board member, Dan Kohne, and a cellist, Cécilia Tsan, found that the dome had amazing acoustics. They said it was like famous concert halls around the world.
These concerts help support the observatory. Since the observatory can't do much deep-space research anymore due to light pollution, it doesn't get much scientific funding. The concerts and public viewing nights help pay for keeping this historic landmark open and maintained.
In Popular Culture
The observatory was the main setting for "Nothing Behind the Door." This was the first episode of the radio series Quiet, Please, which aired in 1947.
It was also a filming location for a space-themed episode of Check It Out! with Dr. Steve Brule.
See also
In Spanish: Observatorio del Monte Wilson para niños
