Image: The asteroid Eros
This picture of Eros, the first of an asteroid taken from an orbiting spacecraft, is a mosaic of four images obtained by the NEAR Shoemaker spacecraft in 2000 on Valentine's Day, immediately after the probe went into orbit.
updated 2/3/2012 8:06:32 PM ET 2012-02-04T01:06:32

In 1931, the close approach of the asteroid Eros allowed professional astronomers to calculate its distance and make that era's most accurate measurement of the solar system. As the asteroid passes near Earth this week, amateur astronomers and students from around the world have been re-creating the historical experience.

Today's technology allows for much more precise methods of measuring the distance to planets and other orbiting bodies. It can make it easy to forget how challenging astronomy was long ago.

"Hundreds of years ago, scientists were sent out on long expeditions around the world in order to observe a rare astronomical event," Michael Richmond of the Rochester Institute of Technology told

"They had lots of adventures — it was sort of a romantic thing. They go off into the wilderness and set up an observatory in the middle of nowhere, and then they have to fight their way back," he said.

One important event was the close approach of the asteroid Eros in 1931. Astronomers in Germany, Algiers, Johannesburg, Tokyo and California captured photographs of the asteroid against the background of stars. [Closeup Photos of Asteroid Eros]

"It really was a worldwide effort," Richmond said.

By comparing images taken at the same time but from different locations, they could use trigonometry to determine exactly how far away the asteroid passed. From this, they could calculate the distance to other planets, taking the best measurement of the bodies orbiting the sun.

"It was a small milestone in solar system astronomy," Richmond said.

This time around, Richmond provided technical assistance to Steven van Roode, a physics teacher and amateur astronomer in the Netherlands who set up a website to chronicle Eros' close approach. Visitors from around the world can upload their images as Earth passes between the asteroid and the sun this week, and use them to recalculate just how far away Eros travels.

Richmond calls van Roode's project "an opportunity for students and amateur astronomers to re-create what was, 80 years ago, an important step in solar system research."

Telescopes instead of muskets
In 2004, Venus passed between Earth and the sun for the first time in 122 years. These rare transits occur in pairs, and the second one will take place in June. As with Eros, these events can allow astronomers to calculate the size of the solar system.

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"One of the people who was most interested in encouraging students to do this project ... was Steven van Roode," Richmond said. "He noticed that, in addition to this transit of Venus occurring in 2012, there was another rare astronomical event that was … going to occur this year" — the opposition of Eros.

Discovered in 1898, Eros is one of the larger near-Earth asteroids, measuring 20 miles wide. It was visited by NASA's Near Earth Asteroid Rendezvous mission, also known as the NEAR Shoemaker mission, in 2000.

On Jan. 31, Eros made its closest approach to Earth, passing only 16.6 million miles (26.7 million kilometers) from the planet.

Richmond was quick to point out that the asteroid posed no threat to the planet.  "It's not in any way dangerous," he said.

Stargazers should turn their eyes to the constellations of Leo, Sextans and Hydra to glimpse this rare visitor. If you don't have a telescope, a pair of binoculars should make it clear. The asteroid will travel a little farther than the diameter of the moon, so a patient observer will see it move over several hours.

The asteroid is at its brightest between Jan. 25 to Feb. 13, and is due to become dimmer starting on Valentine's Day.

Because the asteroid is so far away, the window of opportunity is very broad. Van Roode's website has been collecting and comparing data between Jan. 28 and Feb. 3, when Eros makes its nearest pass. However, Richmond says that you could still use the tools to calculate distances as late as the middle of February, assuming you had a partner taking pictures at the same time.

Using van Roode's website, visitors can use online software to determine a precise distance to the asteroid.

Although modern radar provides more-accurate data, Richmond stresses that the point of the project is that students and astronomers can measure the size of the solar system for themselves.

"It's like people who re-create Civil War battles," he said. "They're not teaching historians about the battle, but they're having a lot of fun, and they're learning something ... for their own sake."

And there's something to be said about sharing a connection for the skywatcher pioneers of yesteryear, Richmond added.

"We're historical re-enactors of astronomy."

Visit Eros and the Solar Parallax Project to participate in this historical re-creation and help measure the size of the solar system for yourself.

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Interactive: Below the belt

Photos: Month in Space: January 2014

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  1. Southern stargazing

    Stars, galaxies and nebulas dot the skies over the European Southern Observatory's La Silla Paranal Observatory in Chile, in a picture released on Jan. 7. This image also shows three of the four movable units that feed light into the Very Large Telescope Interferometer, the world's most advanced optical instrument. Combining to form one larger telescope, they are greater than the sum of their parts: They reveal details that would otherwise be visible only through a telescope as large as the distance between them. (Y. Beletsky / ESO) Back to slideshow navigation
  2. A balloon's view

    Cameras captured the Grandville High School RoboDawgs' balloon floating through Earth's upper atmosphere during its ascent on Dec. 28, 2013. The Grandville RoboDawgs’ first winter balloon launch reached an estimated altitude of 130,000 feet, or about 25 miles, according to coaches Mike Evele and Doug Hepfer. It skyrocketed past the team’s previous 100,000-feet record set in June. The RoboDawgs started with just one robotics team in 1998, but they've grown to support more than 30 teams at public schools in Grandville, Mich. (Kyle Moroney / AP) Back to slideshow navigation
  3. Spacemen at work

    Russian cosmonauts Oleg Kotov, right, and Sergey Ryazanskiy perform maintenance on the International Space Station on Jan. 27. During the six-hour, eight-minute spacewalk, Kotov and Ryazanskiy completed the installation of a pair of high-fidelity cameras that experienced connectivity issues during a Dec. 27 spacewalk. The cosmonauts also retrieved scientific gear outside the station's Russian segment. (NASA) Back to slideshow navigation
  4. Special delivery

    The International Space Station's Canadian-built robotic arm moves toward Orbital Sciences Corp.'s Cygnus autonomous cargo craft as it approaches the station for a Jan. 12 delivery. The mountains below are the southwestern Alps. (NASA) Back to slideshow navigation
  5. Accidental art

    A piece of art? A time-lapse photo? A flickering light show? At first glance, this image looks nothing like the images we're used to seeing from the Hubble Space Telescope. But it's a genuine Hubble frame that was released on Jan. 27. Hubble's team suspects that the telescope's Fine Guidance System locked onto a bad guide star, potentially a double star or binary. This caused an error in the tracking system, resulting in a remarkable picture of brightly colored stellar streaks. The prominent red streaks are from stars in the globular cluster NGC 288. (NASA / ESA) Back to slideshow navigation
  6. Supersonic test flight

    A camera looking back over Virgin Galactic's SpaceShipTwo's fuselage shows the rocket burn with a Mojave Desert vista in the background during a test flight of the rocket plane on Jan. 10. Cameras were mounted on the exterior of SpaceShipTwo as well as its carrier airplane, WhiteKnightTwo, to monitor the rocket engine's performance. The test was aimed at setting the stage for honest-to-goodness flights into outer space later this year, and eventual commercial space tours.

    More about SpaceShipTwo on PhotoBlog (Virgin Galactic) Back to slideshow navigation
  7. Red lagoon

    The VLT Survey Telescope at the European Southern Observatory's Paranal Observatory in Chile captured this richly detailed new image of the Lagoon Nebula, released on Jan. 22. This giant cloud of gas and dust is creating intensely bright young stars, and is home to young stellar clusters. This image is a tiny part of just one of 11 public surveys of the sky now in progress using ESO telescopes. (ESO/VPHAS team) Back to slideshow navigation
  8. Fire on the mountain

    This image provided by NASA shows a satellite view of smoke from the Colby Fire, taken by the Multi-angle Imaging SpectroRadiometer aboard NASA's Terra spacecraft as it passed over Southern California on Jan. 16. The fire burned more than 1,863 acres and forced the evacuation of 3,700 people. (NASA via AP) Back to slideshow navigation
  9. Where stars are born

    An image captured by NASA's Spitzer Space Telescope shows the Orion Nebula, an immense stellar nursery some 1,500 light-years away. This false-color infrared view, released on Jan. 15, spans about 40 light-years across the region. The brightest portion of the nebula is centered on Orion's young, massive, hot stars, known as the Trapezium Cluster. But Spitzer also can detect stars still in the process of formation, seen here in red hues. (NASA / JPL-Caltech) Back to slideshow navigation
  10. Cygnus takes flight

    Orbital Sciences Corp.'s Antares rocket rises from NASA's Wallops Flight Facility on Wallops Island, Va, on Jan. 9. The rocket sent Orbital's Cygnus cargo capsule on its first official resupply mission to the International Space Station. (Chris Perry / NASA) Back to slideshow navigation
  11. A long, long time ago...

    This long-exposure picture from the Hubble Space Telescope, released Jan. 8, is the deepest image ever made of any cluster of galaxies. The cluster known as Abell 2744 appears in the foreground. It contains several hundred galaxies as they looked 3.5 billion years ago. Abell 2744 acts as a gravitational lens to warp space, brightening and magnifying images of nearly 3,000 distant background galaxies. The more distant galaxies appear as they did more than 12 billion years ago, not long after the Big Bang. (NASA / NASA via AFP - Getty Images) Back to slideshow navigation
  12. Frosty halo

    Sun dogs are bright spots that appear in the sky around the sun when light is refracted through ice crystals in the atmosphere. These sun dogs appeared on Jan. 5 amid brutally cold temperatures along Highway 83, north of Bismarck, N.D. The temperature was about 22 degrees below zero Fahrenheit, with a 50-below-zero wind chill.

    Slideshow: The Year in Space (Brian Peterson / The Bismarck Tribune via AP) Back to slideshow navigation
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