Moon and Jupiter close midnight to dawn September 8
See the Moon pass very close to Jupiter tonight.
“he darkness after midnight and before daybreak belongs to the waning gibbous moon and the planet Jupiter tonight. These two beautiful worlds – Jupiter and our companion moon – will appear in the east after midnight on Friday night. They’ll steadily climb upward until dawn breaks Saturday morning. Jupiter outshines all the true stars in the sky, and is only exceeded in brilliance by the planet Venus, which you’ll also find before dawn tomorrow – closer to the horizon than Jupiter and the moon.”
“The moon will be very close to its last quarter phase tomorrow morning as seen in the U.S. This month’s last quarter moon falls at 8:15 a.m. CDT (13:15 UTC) on Saturday, September 8.”
Turning Blue: Friday’s Full Moon a ‘Blue Moon’
For the first time since March 2010, we’ll gaze upon a blue moon this Friday.
(A “blue” moon. Credit: Getty Images)
“This Friday, Aug. 31, might not be all that much fun for you, especially if you’re someone who vows to only do obligatory tasks once in a blue moon. Then again, if you’re a believer that good luck comes your way only once in a blue moon, Friday might be just the day you’ve been waiting for. After Friday, you’ll have to wait another 36 months — until July 2015 — for the next one. So, it’s time to loosen up Friday and do all those things you say you do ‘once in a blue moon.’”
“Once in a blue moon” is a colloquialism that has come to mean some kind of event that only happens incredibly rarely. Real ‘blue moons’ aren’t that rare at all, despite the association our culture has made with them. The period of the Moon’s orbit around the Earth is about 29.5 days, which (importantly) is very nearly the length of the months in the Gregorian calendar we use. However, the month isn’t defined to be 29.5 days in length, for a variety of reasons. Some months are longer, and one is always shorter. That means every now and then — quite by accident — the Moon and our calendar sync up in a weird and coincidental way.
A “blue moon” is defined as two full moons occurring in the same calendar month, or alternately, the third full moon in a season with four full moons. Because the period of the Moon’s orbit doesn’t exactly match either the length of our months, and the Earth’s year isn’t an integer number of lunar orbital periods, the date that a given phase of the Moon occurs wanders through the calendar. Quite by accident, the lunar cycle and our calendar line up in a way that appears to produce an “extra” full moon (or any other given lunar phase) in some defined period of time. Every two to three years, that “extra” full moon appears, leading to the colloquial expression. The important thing to keep in mind is that the Moon doesn’t actually appear bluish in color during one of these events.
The exact origin of the term is unclear, historically, but there have been instances in history when various atmospheric effects on Earth have caused the Moon (or even the Sun!) to appear blue in color. These instances are coincident with situations where a great number of very small particles were injected into the atmosphere; notable examples are after volcanic eruptions such as Krakatoa in 1883, and a series of large wildfires in Alberta, Canada in September 1950. When particles of anything — drops of water, bits of pulverized volcanic rock, or ash from wildfires — are comparable in size to the wavelengths of light passing through them, they preferentially scatter those wavelengths. Particles of about 1 micron in size are highly efficient at scattering long wavelengths of visible light, while transmitting longer and shorter wavelengths. Under exceptionally rare circumstances, the right-sized particles are aloft long enough to “deredden” moonlight and render it truly “blue”. -JCB
See The Moon And Two Planets Tonight (August 22)
“The moon has been awesome these past few nights in the western twilight sky! It’s been moving past the very noticeable triangle there, consisting of two planets – Mars and Saturn – and the star Spica in the constellation Virgo. But of course the moon never stops moving. As darkness falls this evening in North America, the rather wide waxing crescent moon appears to the south of the constellation Libra, and to the east of the planets Saturn and Mars. In the Eastern Hemisphere – Europe, Africa, Asia, Australia and New Zealand – tonight’s moon will be closer to Mars and Saturn than it is in the Western Hemisphere.”
Look to the southwest tonight at dusk and find the Moon, then use the chart above to lead you on to Saturn and Mars. And when you find Mars, think about the fact that right now, there’s a rover from Earth there with a laser beam strong enough to vaporize solid rock… -JCB
Of course, check your local listings here, here, or here.
Spectacular Meteor Shower Should Be Visible to Most
One of the best meteor shower events of the year will be happening this weekend, peaking late tonight. Most of the country should have at least a decent view.
How To Observe The Perseid Meteor Shower
As a follow-up to my previous post about watching golfballs hit the moon at 100,000 miles an hour, here’s a guide to the Perseids and how to enjoy them.
- What are the Perseids? They are particles shed by Comet 109P/Swift-Tuttle, a periodic comet that last passed near Earth in 1992. Composed of mostly silicate minerals, the typical meteor particle, or meteoroid, is about the size of a grain of sand. The motion of the Earth through its orbit carries us toward “streams” of these particles left behind in the comet’s wake; our relative motion toward them makes the particles encounter the Earth at a relative velocity of tens to hundreds of thousands of miles per hour. They meet the upper atmosphere and vaporize as they reach temperatures of thousands of degrees for a few brief seconds; we see their remnants as bright streaks of light commonly known as “shooting stars”. The Perseid shower is one of the year’s more notable events, leading sometimes to hundreds of meteors per hour being seen.
- How often do they happen? The Perseids are an annual event each August, and has been happening at least since antiquity. Last seen exactly 150 years ago during the Civil War, Swift-Tuttle was somewhat considered “lost” because its observations in 1862 were not sufficiently precise to nail down its orbit. The comet “announced” its coming return to the inner solar system during the 1991 Perseid shower with a huge burst of activity during the early morning hours over East Asia. Speculation as to whether this feature represented material recently shed by the comet was well founded; the comet re-appeared in Earth’s skies about a year later. Each time the comet returns, a new stream of particles is shed and the shower is replenished.
- Why are meteors important? There’s a lot of science involved. So many comets have come and gone over the history of the solar system that the inner part is chock full of dust particles. These particles constantly rain down on the Earth and other terrestrial planets, bringing many tons of cosmic material per year; early in the solar system’s history, this may have included the essential components needed in the chemistry of life. The particles are thought to be relatively pristine, in the sense that they avoided the thermal shocks and chemical mixing that occurred in the solar nebula. So a meteor seen streaking across our skies is a glowing messenger from the earliest times of our planetary system, telling us what conditions were like then.
- Do I need a telescope to observe the Perseids? Nope! Meteor showers are a phenomenon requiring no special equipment at all; in fact, binoculars and telescopes allow views of such relatively small parts of the sky that they’re mostly ineffective for meteor observing. Rather, showers like the Perseids contain many larger particles, which make for brighter meteors, and the best instruments to observe them are unaided human eyeballs. Our eyes are pretty sensitive once dark adaptation has occurred, and we can see a very large area of sky at a time with them, increasing the chances of seeing meteors.
- When should I look for Perseid meteors? The shower peaks in intensity around August 11-13, so it’s going on right now — even during daylight hours. However, for nighttime observing, the hours between midnight and dawn are best, because of the relative speed difference between the meteors and the Earth. Before midnight, we’re facing away from the direction the Earth moves in its orbit around the Sun, so to be seen the meteors have to “catch up” to us. After midnight, we’re facing the direction of motion and the relative speeds are highest. Speed correlates with meteor brightness (for a given particle size), so you’re likely after midnight to see fainter meteors as a result.
- What part of the sky should I look toward? The Perseids can be seen in any part of the sky, but they appear to “radiate” from a point in the constellation Perseus. In August, that constellation is rising in the northeastern sky toward midnight in the Northern Hemisphere. So facing northeast aligns the observer with the direction from which the meteors appear to originate and increases the chances they’ll be seen before burning out. Also, choice of seating is important, and a reclining lawn or lounge chair is highly recommended. Staring upwards for hours at a time is otherwise rough on the neck muscles!
- What can I expect to see? In an average year, observers can typically expect about one meteor per minute during the shower’s peak. The rate is somewhat variable, and at times several will be seen per minute. The Perseid shower is known for lots of bright, slow-moving fireballs, some of which explode at the end of their travel in a “terminal burst”. At times these fireballs are bright enough to cast shadows on the ground. There is rarely obvious color in meteors, but the Perseids tend toward a pale yellow, possibly due to emission of light from ionized sodium atoms. The Perseids, one of the most reliable meteor showers of the year, rarely fail to impress!
- Will the Moon be a problem? Yes and no. This year’s shower peaks a few days after the Moon is at last quarter, meaning two things: (1) The early part of the night will be Moon-free, and (2) After the Moon rises, it will present some interference. Moonlight adds to the sky background, making the faintest Perseids difficult to see. But don’t worry — the brightest meteors will easily outshine this light. The main tip here is to not look in the direction of the Moon, to keep its light from ruining one’s dark adaptation. One of the best tricks is to keep the Moon behind some obstruction, like a building or a tree, while maintaining a clear view to the northeast. Remaining in shadow will minimize the interference.
- Are my observations useful? Yes! Meteor watching is a great citizen-science opportunity. Meteor science still relies on boots-on-the-ground observations from people, many of whom are amateur astronomers and other interested skywatchers. Ways to participate can be found here, here and here. Having multiple people at one observing site helps in collecting observations, since several individuals can cover more of the sky at once than one person. But one person can still see a lot of sky, and solo observations are quite useful.
- Finally, stay warm, as the predawn hours in August can be cold in many parts of the Northern Hemisphere. My meteor watching inevitably involves a thermos of hot coffee to help ward of the chill and drowsiness.
Additional resources:
- Sky and Telescope: “Here Come The Perseids!”
- The International Meteor Organization (IMO) Perseid page
- The North American Meteor Network (NAMN) star charts for recording meteor observations
- MeteorObs: An internet forum for meteor observers of all levels
- StarDate: “Perseid Meteors Pierce The August Sky”
Summer Solstice Brings Changing Seasons Wednesday
On Wednesday (June 20), the sun will arrive at its northernmost point in the sky and herald a season change on Earth, with summer officially beginning in the Northern Hemisphere, while the winter season kicks off in the Southern Hemisphere.
(The seasons are caused by Earth’s tilt. In the Northern Hemisphere it is summer when the Northern Hemisphere is tilted towards the sun. CREDIT: Starry Night)
“The northern summer solstice will occur at 7:09 p.m. EDT (2309 GMT). Just as the word “armistice” is defined as a staying of the action of arms, “solstice” is a staying of the sun’s apparent motion over the latitudes of the Earth. At the summer solstice, the sun stops its northward motion and begins heading south. At the winter solstice, it turns north.”
(Contrary to widely held notions by smart people, the Northern Hemisphere is not warmer in summer than in winter because the Earth is closer to the sun in July than in January. Today the Sun reaches its northernmost point in the sky for the year, before beginning its long descent toward the south, all due to the 23.5 degree tilt of the Earth’s spin axis. -JCB)
Venus 12 Days After Transit
ImageSouce CCD and 16 inch Ritchey–Chrétien telescope. 3 min video processed with Registax software.
(Credit & Copyright: Dean Salman / National Optical Astronomy Observatoroes (NOAO) / Association of Universities for Research in Astronomy, Inc.)
Venus Transit in hydrogen alpha light, 5 June 2012
(Credit & copyright: Gilbert A. Esquerdo)
Transit Of Venus 5 June 2012
Seen in projection at the UW Space Place, Madison, WI
Astronomy news, recent research results, and pretty pictures from the media along with context, commentary, and explanations for folks who dig this sort of thing. Written by a quasi-professional astronomer affiliated with the University of Texas at Austin.
