Mercury will stroll in front of the sun on Monday, and you can watch it

Venus transits the sun in 2012 as seen through the special sun research lenses of NASA'S Solar Dynamics Observatory Satellite. On Monday the observatory will capture Mercury cruise across the sun

There will be a little black spot on the sun Monday.

It’s the rare transit of Mercury — the fastest and closest planet to the sun — slowly crossing our radiant, life-giving star over several hours on May 9, offering humanity a chance to enjoy a natural show.

Barring cloudiness all day, you can have breakfast, lunch and an afternoon tea with the lithe little planet. The eastern United States gets to view the full 7.5-hour transit, starting at 7:12 a.m. Eastern time.

Mercury will reach its transit midpoint at 10:57 a.m., and it all ends around 2:40 p.m., according to retired NASA astronomer Fred Espenak, who runs the EclipseWise.com website.

Even the Midwest and the Western states can enjoy the transit for hours, as the cosmic performance either starts soon after sunrise or it will have been underway by sunrise in those time zones.

Take caution: Do not look directly into the sun through a bare telescope, or bare binoculars, or with your naked eye — and that includes sunglasses. If you do, you will go blind. View the transit only through proper solar-safe filters on optical instruments. Although this website is for solar eclipses, the safety principles for transits ring true.

Transits back in the day

The transits by Mercury and Venus yield key physical, scientific detail that helps us understand our place in the solar system and the universe. We get to learn the size of other planets and our sun’s distance from Earth and find out how long it takes for other planets to orbit the sun. Humanity saw its first Mercury transit in 1631, a mere two decades after the invention of the telescope.

Espenak, on his EclipseWise website, explains that famed astronomer Edmund Halley realized that transits yield measurements for the Sun’s distance and provide us a scale for the solar system. Expeditions in 1761 and 1769 to observe Venus transits produced the “first good value for the Sun’s distance,” Espenak said.

The time between Venus transit pairs is more than a century, but there are 13 Mercury transits for each century. So far this millennium, we’ve enjoyed Mercury transits in 2003 and 2006. Beyond 2016, the next one will be Nov. 11, 2019 — Veterans Day.

Much like eclipses belong to a “saros,” or family, planetary transits belong to a long series. Monday’s transit belongs to Series 7, which means that the Mercury transits on May 9, 1970, May 8, 1924, and May 6, 1878, are all in the same family. The next Series 7 Mercury transit will be May 10, 2062, and the series ends on May 13, 2154.

Where to watch

Online

• Slooh.com: If you’re stuck at work, pinned in a meeting or frowning from cloudiness, the sun always shines at slooh.com. Live coverage — using telescopes from all over the world — begins at 7 a.m., with astronomers Paul Cox and Bob Berman calling the play-by-play and offering color. Featured guests include: 10 a.m. — Bart Thomas, teacher, Naples High School, Florida. Thomas’s school will be projecting the transit throughout the day, and he will speak on inspiring youth about space. 11 a.m. – Lisa Kaltenegger, Cornell professor of astronomy and director of Cornell’s Carl Sagan Institute. She will discuss how using events similar to transits can teach us about exoplanets (planets beyond our solar system). Noon — Angela Fritz, deputy weather editor of The Washington Post’s Capital Weather Gang, will explain Mercury in retrograde and what it means.
• NASA: Launched in 2010, NASA’s Solar Dynamics Observatory (SDO) satellite will observe a Mercury transit for the first time. From about 6:30 a.m. Eastern time, the SDO will follow the planetary black dot across the sun for about nine hours. NASA is providing a near-live feed here. The images will be delayed a few minutes, as the website provides self-updating movies. The movies will include a visible channel and channels for the extreme ultraviolet wavelengths. Pick your perfect wavelength. Additionally, NASA will stream a live program on NASA TV and the space agency’s Facebook pagefrom 10:30 to 11:30 a.m. Jim Green, NASA’s planetary science director, Lika Guhathakurta, the agency’s heliophysics program scientist, and Nicky Fox, project scientist at the Johns Hopkins University Applied Physics Laboratory, will discuss the science behind the transit. Viewers can ask questions via Facebook and Twitter using #AskNASA.

Viewing parties in the Washigton area

• Air and Space Museum: Transit viewing with properly filtered telescopes at the Phoebe Waterman Haas Public Observatory on the museum’s eastern side, 7 a.m. to 3 p.m. Lectures: Geologist Jim Zimbelman on “The Transit of Mercury: What’s the Big Deal About a Planet in Front of a Star?” at 11 a.m. Space historian David DeVorkin on “Explaining the Mystery of Mercury’s Motion,” at 1 p.m. For both talks, meet at the museum’s Great Seal, at the building’s Mall entrance.
• Montgomery College: Safe telescopes will be set up in the parking lot adjacent to the Montgomery College planetarium from 7:15 a.m. to 2:15 p.m. If cloudy, participants are invited into the planetarium at 7611 Fenton St., Takoma Park.
• David M. Brown Planetarium, Arlington: Friends of the Planetarium volunteers will guide you with Sunspotter telescopes from 10 a.m. to 2 p.m. Parking is at a premium during school hours; paid parking is nearby. The planetarium is near the Ballston, Virginia Square and Clarendon Metro stations, at 1426 N. Quincy St., adjacent to Washington-Lee High School.
• University of Maryland: Telescopes, binoculars and other safe ways to observe will be at the Computer & Space Science Building (Building 224) front patio on the College Park campus, from 9:45 a.m. to 2:45 p.m., weather permitting.