It’s bad luck if a cat crosses our path, but what about the solar system’s smallest member? Mercury, the tiniest planet in our celestial neighborhood, is passing between the Earth and the sun today. The rare trip occurs just 13 times per century and offers an opportunity for scientists to study Mercury’s thin, comet tail-shaped atmosphere.
The crossing started at 7:15 a.m. ET and will continue for nearly seven hours. Everyone in the U.S. will have a chance to see the event at sunrise, whereas sunset will provide the best views for Africa, the Middle East and Europe west of the UK. The entire transit will be visible from Brazil and most of South America. Sorry, Australia, Japan and most of Indonesia — the spectacle won’t be visible from your longitudes.
If you want to view the Mercury crossing, then you’ll need a special telescope or a digital screen. Staring straight at the Sun can damage your eyes, so NASA recommends using a telescope with a safe solar filter. Don’t own one? You could always contact a local astronomy club to see if it is hosting a viewing party. (Mercury is too small to witness with the naked eye.) The other option is watching a livestream via NASA’s Solar Dynamics Observatory.
Watch NASA’s livestream of Mercury’s transit across the Sun
Scientists at the Solar Dynamics Observatory plan to use today’s event to examine Mercury’s ultrathin atmosphere. Mercury’s air absorbs and emits different colors as sunlight strikes it. For instance, sodium in Mercury’s atmosphere will appear yellow-orange to Earthlings at the National Solar Observatory in Sunspot, New Mexico, where NASA scientists will be studying today’s crossing. Solar radiation, solar wind and meteorites cause Mercury’s atmosphere to billow into a cometlike tail that stretches for 1.2 million miles. However, this tail is invisible to the naked eye.
Mercury, named after the swift Roman god, orbits the Sun about 60 percent faster than the Earth does. However, its daily rotation is much slower. It takes 59 Earth-days for Mercury to spin once on its axis. If you’re planning a trip, then you might want to pack sunscreen, shorts and a sweater. Daytime temperatures are six times hotter than the warmest spot on Earth, while at night, temperatures are as much as two times colder than our chilliest location.
Launched on November 3, 1973, Mariner 10 was the first human-made object to visit Mercury. Thirty years went by before a second spacecraft — NASA’s MESSENGER — repeated the feat. MESSENGER flew by Mercury in 2008, settled into orbit in 2011 and then smashed into the planet’s surface in autumn 2015.
Last week, the U.S. Geological Survey released a map of Mercury’s surface created with images snapped by MESSENGER. The map offers the first high-resolution, comprehensive view of Mercury’s entire surface, depicting the planet’s craters, volcanoes and tectonic landforms.
Can’t catch today’s crossing? Mercury’s next solar transit is scheduled for November 11, 2019, while a follow-up is slated for November 13, 2032.