Mercury will pass across the face of the sun Monday (May 9) in its first such "transit" since 2006.
The Mercury transit — which begins Monday at 7:12 a.m. EDT (1112 GMT) and ends at 2:42 p.m. EDT (1842 GMT) — is accessible to amateur astronomers, as long as they have the right equipment to view the event safely. (Warning: Never look directly at the sun without protection; serious and permanent eye damage can result.)
Here's a brief rundown of the ways you can safely watch the transit, either first-hand or live online. [The Mercury Transit of May 9: How to See It and What to Expect]
Projecting the image
Mercury is so small that projecting the image using a simple pinhole camera, as many observers do to view solar eclipses, will not produce good results; it's likely you won't be able to see anything at all. Instead, you can project the image using refractors or small Newtonian telescopes. (Schmidt-Cassegrain and Maksutov designs can't be used for this, because of the risk of damage.)
Put a low-power eyepiece into your telescope — one that you don't mind losing if the sun's heat cracks it. Do not look through the eyepiece or the finderscope. Instead, align the telescope using its shadow on the ground. The more closely aligned the scope is to the sun, the darker and more circular its shadow will appear, according to the British Astronomical Association (BAA).
Take a piece of white paper and hold it about 1 foot (30 centimeters) away from the eyepiece to see the image. You may need to wiggle the telescope a bit to get a good view.
Binoculars or telescopes
You can also outfit your binoculars or telescope with solar filters to view the transit. The type of solar filter depends on your equipment, so check with the manufacturer to see what's approved.
Alternatively, you can make your own filters using a sheet of Mylar or Baader Astro Solar Film. Just be sure that the homemade filter is securely over the front end of your binoculars or telescope, with no cracks.
"It is essential that the filter fixes very securely to your telescope, that it is undamaged, and that it is designed for safe use with your telescope," the BAA officials wrote in a press release. "Only buy from reputable suppliers you trust, and thoroughly inspect your filters for damage every time you use them."
Filters designed for eyepieces should never be used because they are "of suspect quality" and often crack when exposed to the sun's heat, the BAA added.
Many museums or amateur astronomy organizations are holding special public events for the Mercury transit. So if you don't have your own gear, check the nearest science museum or astronomy club to see if they are going to set something up somewhere in your community.
A selection of European events, for example, is available here: http://www.cosmos.esa.int/web/bepicolombo-mercurytransit/locations.
Another option is to watch the transit from wherever you happen to be that day, which is especially handy if you are stuck at work or school. NASA will post nearly real-time images from its Solar Dynamics Observatory at http://www.nasa.gov/transit.
The space agency will also have a live program on NASA TV and Facebook Monday between 10:30 a.m. and 11:30 a.m. EDT (1430 and 1530 GMT). The show will include experts from the fields of heliophysics, astrophysics and planetary science. You can chime in with questions on Facebook or on Twitter using the hashtag #AskNASA.
The European Space Agency will also have a livestream at http://www.cosmos.esa.int/web/cesar/streaming.
Europlanet, which describes itself as Europe's community for planetary science, asks viewers to follow live updates using the hashtag #mercurytransit. If you take any selfies from your Mercury observing events, use the hashtag #MercuryTransitSelfie.
Editor's note: Visit Space.com on Monday to see live webcast views of the rare Mercury transit from Earth and space, and for complete coverage of the celestial event. If you SAFELY capture a photo of the transit of Mercury and would like to share it with Space.com and our news partners for a story or gallery, you can send images and comments in to managing editor Tariq Malik at email@example.com.
This story was updated on May 9 to correct the time of the start of the Mercury transit at 7:12 a.m. EDT.