Transit of Mercury
2019 November 11
Monday, 7:35 a.m. - 1:04 p.m. EST
During the transit, Mercury appears as a tiny dot slowly gliding across the face of the sun. To witness this phenomenon, you need to view a magnified image with proper solar protection. Unlike Venus in transit, in which the planet is big enough for the human eye to discern without magnification, Mercury is smaller and more distant. On Nov. 11 the planet diameter appears a mere 10 arc-seconds across. For comparison, Venus is about 60 arc-seconds (one arc-minute) across, and the sun is about 30 arc-minutes (half a degree) across.
In 1677, at age 20, astronomer Edmond Halley witnessed a transit of Mercury from the island of St. Helena. Decades later, in 1716, Halley wrote of his new method using the transit of an inferior planet (i.e., Mercury or Venus) to measure the size of the solar system. Because Venus is closer and yields a larger parallax, Halley appealed for global expeditions to time the next transit of Venus.
Do not observe Mercury near the sun without proper eye protection. See Eye Safety column at Eclipse 2024 page.
Here is an authoritative talk about eye safety by Dr. Ralph Chou:
He notes, #14 welder's glasses are falling out of favor, for polycarbonate filters must have gold filter to attenuate the dangerous UV rays, and not all have the gold filter.
Or read Dr. Chou's summary of eye safety excerpted from my transit of Venus website:
Image: NASA SOHO
Purchase Black Drop Effect coffee from Victorian Pantry in Granger, IN.
These websites may help you prepare for the next transit of Mercury, including images and other content from previous transits of Mercury.
These links take you to content I made for previous transits of Mercury. They may be pertinent for 2019.
Images from previous years
Blogs tagged "transit of Mercury"
Until start of 2019 transit of Merury at 07:35 a.m. EST, as seen from center of earth (geocentric). Your time will vary.
Dr. Edmund Halley
Philosphical Transactions Vol. XXIX (1716)
A New Method of Determining the Parallax of the Sun,
or His Distance from the Earth, Sec. R. S., N0 348, p. 454
Translated from the Latin
"While I was making my observations in the island of St. Helena, about 40 years since, on the stars round the south pole, I happened to observe, with the utmost care, Mercury passing over the sun's disk: and contrary to expectation, I very accurately obtained, with a good 24-foot telescope, the very moment in which Mercury, entering the sun's limb, seemed to touch it internally, as also that of his going off; forming an angle of internal contact. Hence I discovered the precise quantity of time the whole body of Mercury had then appeared within the sun's disk, and that without an error of one single second of time; for, the thread of solar light, intercepted between the obscure limb of the planet, and the bright limb of the sun, though exceedingly slender, affected my sight, and in the twinkling of an eye, both the indenture made on the sun's limb by Mercury entering into it, vanished, and that made by his going off, appeared. On observing this I immediately concluded, that the sun's parallax might be duly determined by such observations, if Mercury, being nearer the earth, had a greater parallax, when seen from the sun; for, this difference of parallaxes is so very inconsiderable, as to be always less than the sun's parallax, which is sought; consequently, though Mercury is to be frequently seen within the sun's disk; he will scarcely be fit for the present purpose.
There remains therefore Venus's transit over the sun's disk..."