#astronomy Citizen Science with the Transit of Mercury

October 28, 2019 - Comment

If you happen to’re planning on watching the November 11th transit of Mercury, strive kicking it up a notch — watch with a pal and calculate the gap between Earth and the Solar! English astronomer Edmond Halley realized that astronomers might make the most of the transit of Venus to triangulate absolutely the distance from


If you happen to’re planning on watching the November 11th transit of Mercury, strive kicking it up a notch — watch with a pal and calculate the gap between Earth and the Solar!

Halley transit method

English astronomer Edmond Halley realized that astronomers might make the most of the transit of Venus to triangulate absolutely the distance from Earth to Venus, and thus to the Solar. On November 11th, observers have an opportunity to make use of the same methodology with the transit of Mercury.

Our photo voltaic system is an impressively massive place. However determining simply how massive took humanity a very long time. Historic astronomers used geometry to piece collectively an image of the relative distances between planets and the Solar, however they couldn’t measure these distances in absolute phrases.

The lacking piece of the puzzle was the typical distance from Earth to the Solar – also referred to as the astronomical unit (a.u., for brief). As soon as astronomers knew the a.u., the true measurement and scale of the photo voltaic system would change into clear.

Edmond Halley

Edmond Halley devised an ingenious methodology to calculate the dimensions of the photo voltaic system by observing the transits of Venus from each hemispheres.

No one found out tips on how to measure the a.u. till Sir Edmund Halley (1656-1742). Halley decided that when Venus crossed the Solar from Earth’s perspective, observers at broadly separated places would see the planet’s silhouette in opposition to the Solar at totally different positions. By measuring the shift, or parallax, in Venus’ obvious place on the Solar’s floor, astronomers might calculate absolutely the distance between Earth and the Solar.

There have been actually just a few measurements essential:

Distance between the observing websites.
Parallax shift of the planet.
Most angle of elongation (angle between the planet and the Solar – look this worth up in planetarium software program)

Sadly, Halley died earlier than the following transit of Venus, which occurred in 1761, so he by no means noticed his method in motion. (Even then, expeditions to look at the transit failed, for numerous causes, to make the wanted measurements; expeditions for the 1769 transit had considerably higher outcomes.)

For contemporary-day astronomers and stargazers, the 2006 and 2012 transits of Venus offered a chance to recreate this historic measurement. Venus received’t transit the Solar once more till 2117, however now observers have the same alternative with the upcoming transit of Mercury.

Transit comparison

This comparability of previous transits of Mercury and Venus (in 2016 and 2012, respectively) is drawn from information collected by the Nationwide Photo voltaic Observatory’s World Oscillation Community Group.
GONG / NSO / Z. Stockbridge

Citizen ToM

On Monday, November 11th, the Citizen Transit of Mercury (ToM) Venture will use Halley’s method to measure the gap to the Solar utilizing the transit of Mercury as a substitute of Venus. Though Mercury seems a lot smaller than Venus in opposition to the Solar, the method to measuring the Solar’s distance is identical.

Greater than a dozen observing websites unfold throughout the nation and utilizing equivalent gear (from the 2017 Citizen CATE whole photo voltaic eclipse mission) will take simultaneous photographs of the transit. Most individuals are college students, who may have a uncommon alternative to make one of the vital necessary measurements in astronomy from scratch.

Citizen CATE observers

This picture exhibits observers with the Citizen CATE mission at Southern Illinois College as they recorded the 2017 whole photo voltaic eclipse. The Citizen ToM Venture will use the identical gear.
Bob Baer (SIU)

The ideas behind measuring the a.u. are easy, however as with many issues in science, implementation is difficult. With fashionable clocks and GPS, precision timing and figuring out the precise distance between places is straightforward. As an alternative, the most important problem is the spotless Solar.

Spotless Sun

If the Solar stays spotless, aligning photographs of the transit taken from a number of websites will show to be a problem. Present photographs of the Solar could be discovered right here.
SDO / HMI / NASA

The Solar is at the moment on the backside of an 11-year cycle of magnetic exercise, which is why the Solar’s face seems featureless. With out sunspots, it’s troublesome to align photographs from a number of observing websites. Picture alignment must be as exact as attainable as a result of Mercury’s obvious place will solely shift a small quantity. The utmost shift that could possibly be noticed, just below 13 arcseconds, would require observers in Antarctica and northern Canada; nearer observing websites will see a smaller parallax.

One method to make picture alignment simpler is to make use of a Herschel Wedge, a extremely specialised optical prism that refracts most daylight out of the optical path. Utilizing these as a substitute of conventional photo voltaic filters will present the clearest white-light views with the best attainable distinction. Lunt Photo voltaic Programs has donated 4 photo voltaic wedges to the Citizen ToM Venture to make use of at places close to the coasts. Taking hydrogen-alpha photographs utilizing a photo voltaic telescope is one other, albeit costlier choice.

DIY Transit Measurement

If you wish to measure the a.u. for your self, there are a number of methods to do it. It actually simply includes coordinating a precise observing time with somebody distant from you, then sharing your photographs for evaluation. Ideally, you and your pal would each have the identical digital camera and telescope so your photographs could be the identical scale, however this isn’t strictly essential. Take photos of Mercury on the identical precise time throughout the transit. Then, after the occasion, align your two photographs to see how far Mercury’s place modifications. Rotating the pictures exactly earlier than evaluating them will possible be your greatest impediment since having each cameras identically aligned is a problem.

After all, in case you can’t discover an observing companion far sufficient away or you probably have unhealthy climate, you may all the time cheat . . . Use photographs of the Solar from the Nationwide Photo voltaic Observatory’s GONG community!  The GONG H-alpha telescopes are equivalent, unfold the world over, and you may entry the info with the GONG Knowledge Archive.

If you’re thinking about discovering an observing companion and measuring the a.u. for your self, you will discover extra particulars within the Photo voltaic System Imaging & Processing discussion board on Cloudy Nights.

Whether or not or not you attempt to revive Halley’s strategies, make certain you get out to see this transit. Mercury will transit once more in 2032 and 2039 for observers in Europe, Africa, and Asia. Observers on the opposite aspect of the world who miss the November 11th transit should select between shopping for a world aircraft ticket or ready till 2049.



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