The phenomenon is called "Manhattanhenge," a play on Stonehenge. At the English site, the rising sun on the summer solstice lines up with some of the vertical stones of the monument. In New York, Manhattanhenge occurs twice a year with the full sun and twice a year with the half-sun (when half the sun appears below the horizon at the time of sunset), typically in May and July. In 2014, the half-sun Manhattanhenge occurs today (May 29) and July 12. The full-sun Manhattanhenge occurs tomorrow (May 30) and July 11.

Sunset occurs at 8:18 p.m. ET today, and skywatchers are advised to head out about 30 minutes prior to that time to watch the sun descend between the walls of the city's steel-and-glass canyons. Astronomer Neil deGrasse Tyson, who coined the term Manhattanhenge, recommends heading as far east in Manhattan as you can, while still keeping New Jersey visible down the avenues. Wide cross streets like 14th, 23rd, 34th, 42nd and 57th provide good viewing. And, Tyson notes in a blog post on the Hayden Planetarium website, 34th and 42nd streets have the Empire State Building and the Chrysler Building, respectively, providing a cherry on top of the solar view. [Gallery: See Photos of Manhattanhenge Sunsets]

Why does Manhattanhenge happen but a few times a year? As Tyson explains, the point of the sunset wanders across the horizon over the course of the year, due to the tilt of Earth's axis. On the spring equinox and the autumn equinox, it sets at due west. The rest of the time, sunset is slightly off of due west.

Manhattan's orderly grid pattern is not lined up with the compass, either — it's rotated 30 degrees east from true north, Tyson writes. Thus, Manhattanhenge doesn't occur on the equinoxes, because the cross streets don't run exactly east-west.

The skyscrapers that make up the New York City skyline do their part to make the event beautiful, rather than just an annoyance to drivers traveling toward the sunset. Clouds may cover some Manhattanhenge views tonight, according to AccuWeather, but there should be clear intervals for viewing, too.

To snap the best sunset photographs, the New York Institute of Photography (NYIP) recommends using bracketed shots, meaning multiple shots of the same scene using different exposures. Sunsets can be tricky to shoot, because a camera's light meter will take note of the brightness of the sky and underexpose the image. Bracketing shots enables the photographer to play with the exposure to find the best look.

If your camera isn't manual, you can still do a quick-and-dirty version of bracketing by pointing your camera at the sunset and taking a shot, then pointing it at the sky, locking in the exposure (usually by pushing the shutter-release button halfway down) and then recentering the image on the setting sun. Do the same thing again, but focus on the ground first this time.

The longer the lens, the larger the sun will appear in the sky, but the NYIP recommends using a tripod with a long lens to prevent the camera from shaking and blurring your beautiful sunset shot. Warning: The rule about not looking directly at the sun counts double when peering through a long camera lens, so protect your eyes by not looking directly at the sun while it's still bright yellow.

Editor's Note: If you have an amazing Manhattanhenge or general science photo you'd like to share for a possible story or image gallery, please contact managing editor Jeanna Bryner at LSphotos@livescience.com.

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