On Monday morning at 7:34 a.m. ET the planet Mercury will begin to cross the suns disk. This is not going to be the easiest astronomical event of 2019 to witness, but it is easily the rarest. It last happened 2016, and it won't happen again until 2032, but why does the Transit of Venus get more attention than the Transit of Mercury? Since Venus is much larger than Mercury, it's much easier to see as it occasionally traverses the suns disc. However, the next transit of Venus will not happen for another 98 years. That makes Monday a big, important astronomical event.
The only way to see the Transit of Mercury is through a telescope or mounted binoculars with a solar filter attached. You can try using any eclipse glasses you have, but dont expect to see much, if anything since Mercurys disc is very small. NEVER look at the sun without eye protection (and that does not ever include sunglasses!). The best and safest way will be to attend an organized event at an observatoryand I will write a separate post on that.
Meanwhile, heres a bunch of things to know about Mondays super celestial event:
A transit of a planet across the sun is one of the rarest predictable celestial events. A transit of Mercury happens 14 times in the 21st century. A Transit of Mercury last occurred in 2016 and will happen next on November 13, 2032, though the next one to be visible from North America wont be until May 7, 2049. They always occur in either May or November.
Mercurys disk it 150 times smaller than the sun, so it takes a while to transit. The process will begin with first contact and second contact, also known as ingress, when the black dot of Mercury begins to cross the suns disk at 12:34 p.m. UTC on November 11, 2019. It makes third contacts and fourth contact, also called egress, at 6:04 p.m. UTC, to end the event.
Along with South America, the east coast of the USclear skies allowinghas the best view of the Transit of Mercury in that its possible to witness the entire event (though you only really need a quick peek). It happens after sunrise, occurring from 7:34 a.m. ET through 1:04 p.m. ET. On the west coast it beings at 4:34 a.m. PT, before the sun is up, though observers there will be able to see the transit ongoing at sunrise through 10:04 a.m. ET. From the UK, it begins at 12:37 p.m. and will still be happening at sunset at around 16:15 p.m. You can get the exact timings for the transit of Mercury for wherever you are in the world here.
Mercury is currently in a period of apparent retrograde motionappearing to go backwards in the sky (from October 31 through November 20, 2019)something that concerns astrologers who like to believe that communications are disrupted during this time (thats based purely on Mercury being named after the Romans Messenger of the Gods). Thats complete fiction; all thats happening is that Mercury is overtaking Earth in its inner orbit.
By taking measurements at precisely the same time of exactly where Mercury appears from two sites in different locations in the world, its possible to calibrate Mercurys orbit, figure out the distance between the Sun, Earth and Mercury, and calculate the size of the solar system. Its much easier to do that at a Transit of Venus than at a Transit of Mercury, but thats not stopping amateur astronomers from trying.
At least, they do for now. Mercury takes 88 days to orbit the Sun, which is four orbits every 352 days. Thats close to the length of an Earth year at 365 days, so Mercury is classed as being in an orbital resonance with Earth. Consequently, the transits occur in the same months, always in May (when Mercury is closest to Earth, and appears slightly larger) and November (when its further away, and appears slightly smaller). However, that 13 days interruption to the orbital resonance means that in future, transits of Mercury will drift into April and October.
A Beaver Moon, Frosty Moon or Long Nights Moon occurs officially on Tuesday, but its on Monday evening at dusk that the moonrise occurs closest to sunset, so when it will look at its most spectacular. So after youre done with the Transit of Mercury, come back a few hours later and look to the eastern horizon to see a majestic moon rise in pale orange hues.
Wishing you clear skies and wide eyes.