The Monthly Sky for May 2016
Sun takes over with Mercury Transit
by Viktor Zsohar
Memories of the true night skies may fade away for Yukon astronomers during May, but the midnight Sun and the midnight Twilight will warm the hearts of all who live North of 60°. The astronomical twilight only returns to the Yukon in August. Observation opportunities therefore are limited for astronomers during the month of May. However, a few solar system objects, and a great Mercury transit event may keep the observing amateur astronomers of the Yukon busy.
THE TRANSIT OF MERCURY IN FRONT OF THE SUN
On May 9th, Mercury transits the Sun, for the first time since 2006. The transit begins with a “Contact I“, which is the instant when the planet’s disk is externally tangent to the Sun. In other words, the exact moment when the planet’s disk first touches the Sun’s perimeter. Shortly after Contact I, the notch of the planet becomes visible in front of the Sun. The entire disk of the planet is first seen at “Contact II“. At “Contact III“, the planet reaches the opposite limb of the Sun, and once again, it is internally tangent to the Sun. Finally, the contact ends at “Contact IV“, when the planet’s disk is externally tangent to the Sun, which also signifies the end of the transit. Contacts I and II are called ingress, and Contacts III and IV are called egress. Position angles of Mercury at each contact are measured counter clockwise from the northern point of the Sun’s disk. According to the RASC Observer’s Handbook 2016 (p.144) the ingress will not be visible from Whitehorse, as it occurs in the early morning hours, when the Sun is not yet above the Horizon. However, the greatest transit will occur at 7:57:38, when the Sun will be at 15° altitude above the Horizon. The internal egress (Contact III) and external egress (Contact IV) will be well visible, weather permiting, at 11:38:37 and 11:41:48, respectively.
MERCURY TRANSIT EVENT AT SHIPYARDS PARK
The Yukon Astronomical Society is celebrating the International Astronomy Week by hosting the Mercury Transit Event on May 9th, 2016 from 07:00am to 1:00pm, at Shipyards Park. We invite every member, their families, and friends to come and witness this rare event! Everybody will get a chance to look through Solar-filtered astronomical telescope, and actually see planet Mercury in front of the Sun!
A Celestron 50AZ telescope was donated by Whitehorse Canadian Tire to the Yukon Astronomical Society. It will be raffled-off, and the lucky winner will win a fully equipped beginner’s telescope!
Do you want to volunteer at this event? Let us know!
May 2016 – Yukon Sky Events
May 6. New Moon
May 9. Mercury in inferior conjunction. TRANSIT OF MERCURY
May 9. Observe the 3 day old Moon’s thin waxing crescent. Can you find the thin Moon?
May 13. First Quarter
May 19. Mercury at aphelion
May 21. Full Moon
May 22. Mars is in opposition
May 29. Lat Quarter
May 30. Mars closest to Earth
PLANETS IN MAY, 2016
Mercury is well placed in the morning sky between May 19th to 31st, favourable apparition for those who live in the South. Inferior conjunction on May 9th, when Mercury also transits in front of the Sun. Aphelion on May 19th. Brightness in the range of +3.0m.
Venus is not in a favourable position, too close to the Sun.
Mars is in Scorpius, positioned very low above Yukon Horizons. Visible all night. Closest to Earth on the 30th, only 0.5AU (4.2 light minutes) away from Earth. It shines bright with -2.1m, and its diameter is substantial: Mars displays a 19″ disk at -21° South from the Celestial Equator.
Jupiter in Leo, and visible during the first part of the “night” during May. Jupiter is among the few Celestial objects besides Mercury, the Sun and the Moon that Yukoners may still observe in May.
Saturn in Ophiucus. The Ring Planet rises late evening, and visible for the rest of the night., However, it is a difficult target with an astronomical telescope, because it stays low above Horizon
Uranus is in Pisces, in the Eastern dawn sky. Twilight interferes until late in the month.
Neptune is in the eastern morning sky in Aquarius.
OBSERVING THE SUN
ONLY USE safe and appropriate solar filters, that are designed to be used with your telescope!
Please, be properly prepared for observing the Sun,
before pointing your telescope up towards our central Star!
Any questions? Please ask us first!
As the Sun becomes our main focus during the summer months in the Yukon, it is imperative for all of our members to be properly prepared, and safe, while observing the Sun; either alone at home or during one of our observation events. The Yukon Astronomical Society advises you to read the following article carefully, as this article not only explains about safety precautions, but also introduces observation techniques, and provides useful tips.
Published by the Sky and Telescope Magazine, and also publicly available at:
Observing the Sun
By: Alan MacRobert | July 16, 2006
The Sun in a telescope is an awesome sight! It is a dynamic, living body, changing unpredictably from day to day. The Sun is also the only celestial object extremely hazardous to the observer. Without proper protection, even a glimpse of it through a telescope or a pair of binoculars can burn the eye’s retina and leave a permanent blind spot!
Two Safe Methods of Solar Viewing
There are two ways to observe the Sun safely: by direct viewing, with a proper filter over the front of the telescope, or by projecting the Sun’s image onto a piece of paper or dark background.
Filters protect the eye against both visible and invisible radiation, and also the telescope itself against heat. These aperture filters have made every other light-reducing device obsolete as far as the ordinary amateur is concerned.
Aperture filters come in two kinds. The most economical is made of metalized Mylar plastic, which usually turns the Sun blue. (NOTE: do not stretch the Mylar to remove any wrinkles.) Metal-on-glass filters leave the Sun with a more natural tint, are more durable, but cost more.
In either case, the best filters have both sides of the Mylar, or glass, metalized. This keeps the inevitable tiny scratches and pinholes in a single coating from letting sunlight into the telescope, where it would reduce image contrast and possibly threaten the eye. Hold the filter up to the Sun. If bright pinpoints show through, they should be touched out with opaque paint. If the flaws are many or large, the filter should be thrown or properly disposed of.
Be sure to attach the filter securely to the front of the telescope, so wind or a careless finger can’t dislodge it while you’re gazing at the Sun!
Sky & Telescope image archivist Imelda Joson shows how to safely view a partial eclipse of the Sun on Christmas day, 2000. She demonstrates the projection method of solar viewing by projecting the eyepiece image onto a white card.
The projection method is preferred by many solar observers — see “Sketching Sunspots” for an example of the method’s advantages.
For a quick first look of this technique, hold a white card or paper a foot or two behind the eyepiece of a telescope, or pair of binoculars, on a tripod. The card must be shaded from direct sunlight. Focus until the Sun’s limb appears sharpest. Almost as much detail will be visible in the projected image as when the Sun is viewed directly through an aperture filter.
For more than a quick look, you’ll need a projection screen attached to the telescope to hold the paper. Such screens are sometimes supplied with small refractors. You can make your own (or better yet, a projection box to improve contrast by keeping daylight off the paper) by experimenting with cardboard, wooden dowels, bolts, and plywood. Plan the distance from eyepiece to screen to be 107d/(m – 1), where m is the telescope’s magnification and d is the diameter you want the Sun’s image to be.
Small telescopes are especially suited to the solar-projection method. Seen here is a simple projection system made from a cardboard box with a piece of white paper as a projection surface. A surprising amount of detail on the solar surface can be seen.
When viewing the Sun via the projection method, follow these precautions for safe viewing:
- Cover the finder scope.
- Don’t aim the telescope at the Sun by sighting along the tube. Rather, move the tube until its shadow on the ground is smallest, while watching at a distance for light to come blazing out of the eyepiece.
- Use a low-power eyepiece. If it has cemented lenses, as almost all modern ones do, stop the telescope aperture down to 2 or 3 inches by cutting a round hole in a piece of cardboard and fitting it over the front of the tube. More than a few inches of aperture will allow too much heat and light into the telescope. This heat can damage the clear cement between eyepiece lens elements. The best eyepiece for solar projection is an old fashioned Huygens, or Ramsden, which has no cemented lenses.
- Schmidt-Cassegrain telescopes in particular must be stopped down. Excess heat can damage the adhesive that holds the secondary mirror to its mounting in most Schmidt-Cassegrains.
One advantage of the projection method is that sunspot positions can be marked right on the paper. A circle is drawn in advance, the Sun’s image is fitted to it and focused, and a few touches of the pencil does the rest.
To record the orientation of such a drawing, mark the position of a sunspot, turn off the telescope’s drive and let the image drift, then mark the spot again; a line from the first dot to the second runs east to west. Nudge the instrument north; the Sun’s northern edge is the trailing edge. Once a spot’s position is recorded, its solar latitude and longitude (heliographic coordinates) can be calculated using data from an astronomical almanac.
When examining the image, try flicking the paper rapidly back and forth, low-contrast detail that was lost in the paper’s surface irregularities will pop into view.
A close view of the large sunspot group visible in the solar image seen here.
S&T: Craig Michael Utter
Sunspots are cooler, relatively dark areas on the Sun’s bright surface (the photosphere). Most have a central dark umbra and a lighter gray penumbra. At high resolution, the penumbra is seen to have thin fibrils radiating from the umbra. Only the smallest of sunspots, called pores, lack penumbras.
Spots tend to form in pairs, marking the “feet” of magnetic-field loops that arch above the surface. A pore appearing in a clear area is a sign that a spot group may soon be born. Pores often die out in a day or two, but sometimes one grows and develops a penumbra. More spots may appear nearby, and within about 10 days a complex active region is in full bloom, strung out between two major spots lined up east-west.
The eastern spot is usually the first to die out; the western one becomes round and smaller, sometimes persisting alone for weeks. The end of a sunspot is often signalled by a large light bridge, a finger of the photosphere that intrudes into the spot and appears to split it apart.
The Sun’s rotation quickly becomes evident with several sunspot drawings, allowing two weeks for a group to travel across the disk. Different regions of the Sun rotate at different rates. The synodic rotation period (apparent period as seen from the moving Earth) is 27¼ days, at the Sun’s equator, but about 30 days at solar latitude 40°. If you get a good run of daily drawings, you can align them and flip through the stack with your thumb to watch the Sun rotate, in an animated cartoon.
A standard index of solar activity is the relative sunspot number. Naturally this number depends heavily on the instrument, seeing conditions, and on the observer’s judgment. Standardized daily sunspot numbers range from zero, on some days near the time of minimum activity, to more than 200 near solar maximum. (For more on sunspot numbers, see S&T: November 1984, page 475.)
- Starry Night Pro7 software
- 2016 Observer’s Handbook, RASC