MIT Infinite Corridor Astronomy - MIThenge

Originally prepared by Ken Olum. Maintained by Lenny Foner.

Recent and Upcoming MIThenge predictions

November 10, 2017:  4:19:36 pm  high pass
November 11, 2017:  4:20:51 pm  mid pass
November 12, 2017:  4:22:07 pm  low pass
November 13, 2017:  4:23:23 pm  probably too low to see
January 27, 2018:  4:52:15 pm  probably too low to see
January 28, 2018:  4:51:19 pm  low pass
January 29, 2018:  4:50:22 pm  mid pass
January 30, 2018:  4:29:22 pm  high pass
January 31, 2018:  4:48:21 pm  possibly too high to see
November 10, 2018:  4:19:17 pm  high pass
November 11, 2018:  4:20:33 pm  mid pass
November 12, 2018:  4:22:49 pm  low pass
November 13, 2018:  4:23:04 pm  probably too low to see

Note: These predictions are from high-resolution computations courtesy of Alan Eliasen.

Safety and MIThenge etiquette


The fact that the sun is at the horizon does not mean that it is safe to look at for more than a moment. Do not injure your eyes by staring at the sun. Use appropriate filters or glance only for a moment as you would at the sun up in the sky.
View from the Building 8 end.
Don't go up to the Mass. Ave. end of the corridor. You won't see anything special there, and you will prevent others from seeing.
Arrive early and don't block the corridor.
Especially given the apparent systematic tendency for our predictions to be 5-8 minutes late, it's best to arrive 15 minutes early. This helps make sure you're not trying to scramble for a spot and blocking somebody else's view. Above all, do not walk in the corridor in front of all the people trying to catch a glimpse of the sun.
Use the third floor.
The 3rd floor has the best view because it has an uninterrupted sweep of corridor, and because it is the highest usable floor. You can't see anything from the fourth floor because it doesn't go through.
Let others see.
Not very many people can get a good view of this phenomenon at once. Once you have seen, get out of the way and let others look.
Stand in the stairwell.
The place that has the largest unobstructed angle of view of the sky is the stairwell just below the third floor. Get your eye right by the edge of corridor floor. Great view? Now give someone else a chance.
Don't hurt your eyes
See the warning above.

Other MIThenge resources

2011 azimuth and extent update

Recent work by Ken Olum, Lenny Foner, Alan Eliasen, KJW and others have tried to measure a more accurate azimuth for the Infinite Corridor than the MIT property baseline. In November 2011, we used two video recordings from each side of the corridor to measure the total extent visible from the eastern end.

The resulting azimuth estimate is 245.81 degrees true, with uncertainty about +/- 0.03 degrees. The total horizontal extent viewable from the eastern stairwell runs from about 245.05 to 246.55 degrees true, taking advantage of the ability to move from one side of the corridor to another.

The vertical extent runs roughly to +0.8 degrees above the horizon, with low visibility below +0.4 degrees.

These video frames were used in the estimates:

11 Nov. 2011, 4:20:13 p.m., the right side of the sun (az. 246.03 degrees true) hits the center mullion of the Lobby 7 window, viewed from left edge of corridor.

11 Nov. 2011, 4:21:10 p.m., the sun's oval (centered at 245.94 degrees true, with width 0.28 degrees) can be estimated. From left edge of corridor.

12 Nov. 2011, 4:20:20 p.m., the sun's azimuth (245.56) hits the center mullion of the Lobby 7 window, viewed from right edge of corridor

What is MIThenge?

As viewed from a stationary point on the earth, the path of the sun through the sky is roughly a circle which moves north and south as the seasons go by. In mid-November and in late January every year, the circular path crosses the axis of MIT's Infinite Corridor, which runs a distance of 825 feet (251 meters) from the main entrance on Massachusetts Avenue through Buildings 7, 3, 10, 4 and 8. When this happens, the setting sun can be seen from the far end of the corridor. By analogy with Stonehenge, this phenomenon is sometimes called "MIThenge". (The same cannot be seen at sunrise because the other end of the Infinite Corridor is blocked by Building 18.)


Here are three photographs of this phenomenon, the first from approximately a third of the way down the corridor on the third floor, and the other two from the entire distance on the second floor. Click for full-size versions.

January 2001. Photograph by Matt Yourst November 1999. Photograph by Joseph Kaye
If you have more photographs of the sun through the length of the Infinite Corridor, please send them to Alan Eliasen (; they may aid in more-precisely determining the corridor's azimuth. If your photographs are precisely dated and timed, even better: this helps our understanding of the corridor's azimuth and the light-bending effects of the atmosphere needed to correctly predict when MIThenge will occur. Please see the section on Ideal Observations on Alan's site for how to get timing and positioning data we can use.
February 2, 1998. Photograph by Paul Schechter, courtesy Rainer Weiss

What you'll see

As the sun becomes better and better aligned with the corridor the amount of floor that is illuminated goes up and up. Since the floor is very reflective this means that the reflected sun can be seen far down the corridor as the event approaches. The orange light reflected onto the ceiling is often striking. This phenomenon is visible for a week or two around the actual sunset days.

At some point, some portion of the sun's disc will be visible from the far end of the corridor. Which part of the disc will be seen first depends on whether the sun is crossing above or below the corridor. If the altitude in the table above is high, the sun will cross the upper right edge of the corridor as seen from the lower left. If the altitude is low, the sun will cross from the center left of the corridor and set below the hill.

The disc of the sun is close to the area of sky visible from the end of the corridor. Therefore if your timing is right and you get a good vantage point you will see almost nothing of the sky except for the interior of the sun's disc.

Observing this event depends strongly on atmospheric conditions. The best is a very red sunset. This decreases the total light intensity and makes it possible to see the corridor and the sun at the same time. If the sky is brilliantly transparent right down to the horizon then the setting sun will be too bright to look at. When you use a filter to save your eyes (see below) you won't be able to see much of the corridor.

The period of time during which the sun can be seen from the corridor end is quite short -- no more than two minutes, and only as long as that under ideal conditions.

Moon illusion and other unrelated effects

Ken Olum has found that the Infinite Corridor produces the "moon illusion", in which the setting sun looks gigantic in the sky, even though it is no larger at the horizon than it is at the zenith. On an unrelated point, note that the size of the moon does indeed vary by approximately 12 percent between perigee and apogee. For more information, see John Walker's "Inconstant Moon" page, which includes the following (again unrelated to MIT or the Infinite Corridor) to-scale diagram (650 km/pixel) of the Earth-Moon system:

An anomalous photograph that led to azimuthal soul-searching: Until several years ago, the only available azimuth for the Infinite Corridor was the surveyed baseline of MIT's property along the Charles River baseline, of 245.47391075 degrees true. (Note that at this precision, an error of 1 in the last decimal place corresponds to a crosswise error of 438 angstroms over the length of the infinite corridor, or to shooting a bullet from the earth at the center of the sun and missing the center by 29 yards.) Ken Olum, Alan Eliasen, Lenny Foner, and KJW worked to improve this figure. We now believe the viewing centerline is roughly 245.81 degrees true, about 20 arcminutes from the property line. One early hint that the surveyed azimuth was wrong comes from the 1998 photo above. On the day Professor Schechter took the photograph (2/2/98), the sun's altitude was 1'58'' (almost 2 degrees) when it was at the right azimuth (4:44:48, with the photograph marked as "4:45"), with very little dependence (+/- five arcminutes) on temperature and barometric pressure. By our predictions (with the Infinite Corridor approximately 9 feet by 13 feet by 825 feet), this should not even have been visible.

Here is a graph showing the path of the center of the sun and its lower edge the day the picture was shot, using the same methodology used to predict MIThenge events. As you can see, the Sun disc comes nowhere near a level Infinite Corridor. The azimuth appears to be correct and confirmed by the "4:45" notation from the photograph, but the elevation seems to be way off. (Note: the plot says, "Time extent: 4:40 to ..." but the bottom of the Sun disc does not actually start to show up on the plot until 4:42:57.) If indeed the Infinite Corridor is tilted up as much as would be necessary to see this predicted sun, that would mean the floor in building 7 is higher (in ellipsoid height) than the ceiling in building 8. This seems hard to believe.

You can help improve the predictions by taking sightings during the event. Especially valuable are photographs from the length of the corridor with a precise timestamp, particularly if they show only half of the doorway on the far side of the corridor filled with the sun. If the entire doorway is filled with the sun, that's okay too, but then we don't know what part of the sun you ended up photographing (middle, side, etc.) You should make sure not to damage your camera. If your photographs are precisely dated and timed, even better: this helps our understanding of the corridor's azimuth and the light-bending effects of the atmosphere needed to correctly predict when MIThenge will occur. Please see the section on Ideal Observations on Alan's site for how to get timing and positioning data we can use, and send photos to him at

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