LIFESTYLE

Looking up: Mercury to pass in front of Sun

Peter Becker More Content Now
This is a time-elapse photograph of a past transit of Mercury across the Sun, taken every few minutes. (NASA)

A relatively rare event happens Monday, May 9, 2016. Essentially an eclipse of the Sun, this is one few people will notice.

Every several years, the little planet Mercury passes between the Sun and the Earth, visible to those with special protection to safeguard their eyes at a telescope, as a tiny round dot silhouetted against the brilliant face of the Sun.

Although it acts like an eclipse when the Moon covers the Sun, astronomers refer to this as a transit. Much more rare is when the planet Venus transits the Sun. Of all the Solar System planets, only Mercury and Venus are in position to transit the Sun, since they orbit closer to the Sun than we do. If you were to be on Mars at the right time, you could witness the Earth transit the Sun, as well as Venus and Mercury.

Transits of Mercury occur about 13 times a century; the last time was in 2006.

Watching transits such as these have become much more common since astronomers began discovering “exo-planets” in the mid 1990s. Although we cannot yet actually resolve the disc of a distant star and be able to see the black dot of one its planets in transit, careful monitoring is done of the slight dip in the star’s brightness as the planet covers a part of the star. This is a chief way of detecting the presence of other planetary systems, when the planet’s orbit happens to be aligned so we can see the event from our vantage point.

Mercury’s passage in front of the Sun blocks a minuscule amount of sunlight, and therefore causes no noticeable effect to the daylight we experience.

These transits were of much interest to astronomers, historically. Careful observation and timing of transits helped to calculate the distance of the Sun, and understanding of these planets.

Today, transits of Mercury or Venus are primarily attended to by amateur astronomers and science educators.

This time around, Mercury starts crossing the edge of the Sun at 7:12 a.m EDT. The planet takes its own sweet time, reaching half-way across the solar globe at approximately 10:47 a.m. Mercury exits the golden disk at 2:42 p.m.

Occurring on a Monday before school lets out, no doubt science classes in many school districts across the United States (as long as weather permits) will take advantage of this rare celestial phenomena to teach about the mechanics of the solar system.

It must be said clearly, NEVER endanger your eyes by looking at the Sun unless you do so safely. Direct observation through a telescope MUST be done with a properly fitted solar filter.

There are indirect methods to observe the Sun. Aiming a small telescope on a tripod, without looking through it, align the tube until its shadow becomes round. Hold a piece of white cardboard screen behind the telescope eyepiece. You should see an image of the Sun casted onto the screen. Turn the focusing knob until the Sun’s image becomes sharp. This is a perfectly safe way to view the Sun at any time. Just be extra cautious with children, that no one tries looking into the eyepiece, or the small “finder” scope attached to the telescope tube.

A couple handy solar projection devices have been marketed, which also show you the Sun. One of these I like to mention is the “Sunspotter.” It was invented in 1978 by a good friend of mine, the late Daniel R. Janosik, who lived near Hawley, Pennsylvania. He made more than 1,000 of these in his house and sold them across the country, many to schools. A science education company now produces them.

You don’t need to wait for a transit to inspect the Sun. An ever-changing display of dark sunspots may be viewed; at times there are no spots, at other times they are numerous.

NASA has more information about Mercury and the May 9 transit online, at http://www.nasa.gov/transit. NASA is also planning a live program on NASA TV and the agency’s Facebook page from 10:30 to 11:30 a.m.

— Peter Becker is Managing Editor at The News Eagle in Hawley, Pennsylvania. Send him notes at news@neagle.com.