Thursday, December 5, 2013
By BERNIE REIM
The month of June always marks the beginning of summer for us in the northern hemisphere. This year that will happen at 1:04 a.m., June 21. The word solstice means "sun stands still" in Latin.
That day marks the farthest north of east that the sun will rise and the farthest north of west that the sun will set for the whole year. It is exactly the opposite in the southern hemisphere, where the sun rises farthest south of east and sets farthest south of west, marking the first day of winter.
You can actually prove this for yourself as you figure out exactly where the sun stands still as part of your everyday landscape. Just pick a fixed place from which to watch. It could be a stone to sit on with a good western view, a mark on the ground, or a high, west-facing window. Starting several weeks before the solstice, watch the sun going down and sketch and mark the points near the horizon, trees, buildings or mountains.
Mark and date on your sketch exactly where the sun sets each evening. As you approach the solstice, you will notice that the difference each night will get less and less. Keep going until a week or so beyond the solstice when the sun starts moving south again. It will be easier to track this as the sun speeds up again going south and the difference gets greater each day. Then look halfway between the dates that you marked when the sun was moving north and the equal amount of time when the sun was moving south again, and that will be the summer solstice.
That may be very similar to the way the people who built Stonehenge about 5,000 years ago figured this out for themselves. Stonehenge is a wonderful, permanent marker to track the change of the seasons and probably also a great tool with which to calculate eclipses. There are tours that will allow you to go inside the circle during the solstices.
It is interesting to think that the very second we pass the summer solstice, the days are getting shorter again and we will already be on our way to the winter solstice in six short months.
You can also prove another aspect of the solstice by showing that the shadows are at their shortest for the year and point true north at local apparent noon near the summer solstice. Find the actual clock time for this moment using a planetarium program. Put a stick or rod in the ground and mark where the tip of the shadow falls at that moment. You will notice that the shadow will shrink as the summer solstice gets closer, hold still for several days, then lengthen again at a faster rate.
These little exercises will not only connect you with your ancient ancestors and help you appreciate how they figured all this out without satellites and computers and Google Earth, but it will also help you to tune in to your natural surroundings in a more detailed way.
It will make you much more aware of the continuing change of the seasons, and help you relate to the constantly changing positions of the earth and the sun and what effects these changes produce. It should also help you look beyond all these seasonal changes, and find the constant and unchanging aspects of life that go far deeper than the surface seasonal changes.
Instead of three planets dancing in our evening sky, only two will grace our western sky this month. We will lose the king of the planets, Jupiter, leaving our two innermost planets on display all month long.
This month our first planet, Mercury, will start about 5 degrees above our neighboring planet, Venus. Then they will drift closer and closer until they will be less than 2 degrees apart two days before the start of summer. Then keep watching as they switch places and Mercury ends up below Venus low on the west-northwestern horizon 45 minutes after sunset. This will be Mercury's best evening apparition for this whole year. Through a telescope, notice that Mercury starts about half lit and decreases to a thin waning crescent, while Venus only decreases to 92 percent illuminated by the end of June.
You may want to consider starting your solstice marking exercise on the evening of June 10, when a wonderful slender waxing crescent moon joins the pair of planets in Gemini the twins, about 10 degrees below Castor and Pollux, the mortal and immortal twin, respectively. The next evening the moon will be 7 percent larger and 12 degrees farther east along the ecliptic at the same time of the evening. That will add the moon into the equation as you track the precise relationship of the earth and the sun around the summer solstice to help increase your awareness of all the wonderful motions we are always involved in without our sensing any of it.
On an even larger scale, Earth is always traveling around the sun at 67,000 mph, or 18.6 miles per second, which translates to getting from New York to Los Angeles in just under three minutes. Then go even farther and realize that the sun and our whole solar system, of which we can only see a tiny part from our narrow window confined to the surface of Earth, is constantly being flung around our giant Milky Way galaxy at about seven times that speed. That means if it takes you about 10 minutes to read this column, we will have traveled about 75,000 miles through galactic space in that time, which translates to three times around the world.
Saturn rises in the east just before sunset. The ringed planet is still in retrograde or westward motion this month in Virgo, but the rate of that motion is slowing. Look halfway up in the southern sky from June 17 through June 19 to catch the waxing gibbous moon passing just below Spica and then Saturn.
Mars finally makes reappearance into the eastern morning sky late this month along with Jupiter, but you will probably need binoculars to see them.
• June 3. On this day in 1948 the 200-inch Hale telescope was dedicated on Mt. Palomar.
• June 4. On this day in 2000 the Compton gamma ray telescope was allowed to reenter our atmosphere.
• June 8. The new moon is at 11:56 a.m. On this day in 1625, Giovanni Cassini was born. The most obvious gap in Saturn's rings is named after him, the Cassini Division.
• June 10. The Mars rover, Spirit, was launched on this day in 2003.
• June 13. Pioneer 10 leaves the solar system on this day in 1983.
• June 16. First-quarter moon is at 1:24 p.m. On this day in 1963, Valentina Tereshkova became the first woman in space and still holds the only solo spaceflight by a woman.
• June 18. On this day in 1983 Sally Ride became the first American woman in space.
• June 21. The summer solstice is at 1:04 a.m., marking the shortest night of the year. On this day in 2004, SpaceShipOne was launched, the first privately funded human space flight.
• June 22. The Royal Greenwich Observatory was founded on this day in 1675. On this day in 2000, NASA announced evidence of present-day liquid water on Mars.
• June 23. The full moon is at 7:32 a.m. This is also called the Strawberry or Rose Moon. This will also be the largest full moon of the year, so try to watch it rise out of the ocean.
• June 26. Charles Messier was born on this day in 1730. He developed a catalogue of 110 objects that turned out not to be comets because they did not move from night to night. He also discovered about a dozen comets.
• June 29. George Ellery Hale was born on this day in 1868. He designed the four successively largest telescopes in the world, starting with the 40-inch Yerkes refractor in 1893 and ending with the 200-inch Mt. Palomar telescope.
• June 30. On this day in 1908 a comet or asteroid exploded with the force of 20 megatons of TNT about five miles above Tunguska in Siberia, leveling 80 million trees over nearly 1,000 square miles. In comparison, the recent Chelyabinsk meteor was about five times smaller, but still potentially very dangerous if it had entered at a steeper angle. That occurred only a few hundred miles west of Tunguska and just over 100 years later.
Bernie Reim of Wells is co-director of the Astronomical Society of Northern New England.