The Astronomical Unit Gets Fixed
The Earth–Sun distance changes from slippery equation to single number.
(The new definitive value of the Astronomical Unit, in metres. Credit: Nature)
“Without fanfare, astronomers have redefined one of the most important distances in the Solar System. The astronomical unit (au) — the rough distance from the Earth to the Sun — has been transformed from a confusing calculation into a single number. The new standard, adopted in August by unanimous vote at the International Astronomical Union’s meeting in Beijing, China, is now 149,597,870,700 metres — no more, no less.”
“The effect on our planet’s inhabitants will be limited. The Earth will continue to twirl around the Sun, and in the Northern Hemisphere, autumn will soon arrive. But for astronomers, the change means more precise measurements and fewer headaches from explaining the au to their students.”
Sun is the most perfect sphere ever observed in nature
Scaled to the size of a beach ball, say scientists, the sun’s equatorial bulge would be less than the width of a human hair
(Credit: The Guardian)
“The sun is the most perfectly round natural object known in the universe, say scientists who have conducted precise measurements of its dimensions. As a spinning ball of gas, astronomers had always expected our nearest star to bulge slightly at its equator, making it very slightly flying-saucer shaped. The planet Jupiter demonstrates this effect well. Its high rate of spin - once every 10 hours - means that it is almost 7% wider across its equator than the distance from pole to pole.”
“Now a team led by the University of Hawaii’s Dr Jeffrey Kuhn have made the first precise measurement of the sun’s equatorial bulge, or its “oblateness”. The results were a big surprise. ‘We were shocked,” says Kuhn. The sun doesn’t bulge much at all. It is 1.4m kilometres across, but the difference between its diameter at the equator and between the poles is only 10 kilometres.’”
“The results, reported in the journal Science, are the culmination of 50 years of efforts to precisely measure the sun, which have been hampered by the blurring effects of the Earth’s atmosphere. ‘Finally, from space, we have it nailed,’ says Kuhn.”
“Kuhn accepts that more surprises may be in store, noting that the sun often confounds those who try to predict its behaviour. ‘It’s fooled us every time we’ve looked.’”
Lunar Reconnaissance Orbiter Spectrometer Detects Helium in Moon's Atmosphere
A NASA satellite has confirmed from orbit measurements of helium in the extremely thin lunar atmosphere first made in the Apollo era.
(Artist’s rendering of the Lunar Reconnaissance Orbiter spacecraft. Credit: NASA’s Goddard Space Flight Center)
“Scientists using the Lyman Alpha Mapping Project (LAMP) spectrometer aboard NASA’s Lunar Reconnaissance Orbiter (LRO) have made the first spectroscopic observations of the noble gas helium in the tenuous atmosphere surrounding the moon. These remote-sensing observations complement in situ measurements taken in 1972 by the Lunar Atmosphere Composition Experiment (LACE) deployed by Apollo 17.”
“Although designed to map the lunar surface, the LAMP team expanded its science investigation to examine the far ultraviolet emissions visible in the tenuous atmosphere above the lunar surface, detecting helium over a campaign spanning more than 50 orbits. Because helium also resides in the interplanetary background, several techniques were applied to remove signal contributions from the background helium and determine the amount of helium native to the moon.”
”’The question now becomes, does the helium originate from inside the moon, for example, due to radioactive decay in rocks, or from an exterior source, such as the solar wind?’ says Dr. Alan Stern, LAMP principal investigator and associate vice president of the Space Science and Engineering Division at Southwest Research Institute, Boulder, Colo.
“‘If we find the solar wind is responsible, that will teach us a lot about how the same process works in other airless bodies,’ says Stern. If spacecraft observations show no such correlation, radioactive decay or other internal lunar processes could be producing helium that diffuses from the interior or that is released during lunar quakes.”
“‘With LAMP’s global views as it moves across the moon in future observations, we’ll be in a great position to better determine the dominant source of the helium,’ says Stern.”
A Weak Geomagnetic Storm Is Underway
A disturbance in our planet’s magnetic environment, caused by the impact of a coronal mass ejection (CME) from Active Region 1520 on the Sun, is causing the appearance of aurorae right now. The activity is indicated in the above plot of the K index, a measure of the condition of geomagnetic field. The red bars show that the disturbance is causing the field to change rapidly, which often leads to displays of aurorae.
However, this event was a little weaker than it could have been due to the glancing blow that the CME struck yesterday, so the only observations of aurorae are at high latitudes (above about 60º). However, a few observers at lower latitudes saw the lights last night, such as Brad Goldpaint who captured this image of auroras reflecting from Sparks Lake in central Oregon:
(Credit & copyright: Brad Goldpaint, courtesy of Spaceweather.com)
There are no strong active regions heading onto the solar disk now, so we’re out of the woods for a while.
Solar Flare's Red Glare: Sun Unleashes Early Fourth of July Fireworks
The sun erupted with a powerful solar flare Monday (July 2) in an early solar fireworks display just in time for the Fourth of July. A wave of plasma from the flare could reach Earth by the U.S. Independence Day holiday on Wednesday, July 4.
(An intense M5.6-class solar flare erupts from sunspot region AR1515 on July 2, 2012 in this still from a NASA video by the Solar Dynamics Observatory. CREDIT: NASA )
“The sun storm came from a large sunspot called AR1515 that is now rotating across the Earth-facing side of the sun. It unleashed an intense solar flare at 6:43 a.m. EDT (1043 GMT) today in what is expected to be one of several strong solar storms in the days ahead, space weather officials said.”
“The flare registered as a class M5.6 solar storm on the scale used by astronomers to measure the sun’s weather. The sun’s strongest storms come in three primary classes. The weakest storms are C-class flares, which have little effects that can be felt on Earth. M-class flares are moderate solar storms that can supercharge the Earth’s northern lights displays. The strongest solar storms are X-class events. When aimed at Earth, the most powerful X-class solar flares can endanger spacecraft and astronauts in orbit, interfere with satellite signals, as well as damage power lines and other infrastructure on the ground.”
(This was a powerful event, to be sure, but the geometry isn’t in our favor: the resulting coronal mass ejection (CME) will only strike a glancing blow at Earth. However, observers at high latitudes — generally above 40-50º, should be on the lookout for aurorae on the night of July 4. -JCB)
Galileo Galilei, Sunspot observations
Paper
3 May 1612http://www.loc.gov/exhibits/vatican/vatican.html#itmotpmahd
Galileo helped to create a new science partly because of his extraordinary skills as an observer, which enabled him to create and use the first telescope. These drawings represent sunspots— whose existence proved that the sun was not the perfect, unchanging body that traditional Aristotelian cosmology considered it to be. Galileo’s work received strong support for a long time from Maffeo Barberini, the future Pope Urban VIII, though his Dialogues on Two World Systems and Copernican views would eventually be condemned by Rome.
(via scientificillustration)
Source: yama-bato
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)
Sun Blasts Huge Magnetic Bubble at Earth
For the second day in a row, an active region on the sun has erupted with a coronal mass ejection, blasting the beautifully dynamic magnetic bubble of energetic plasma in the direction of Earth.
(From spaceweather.com: “The fast-moving (1360 km/s) cloud isexpected to hit our planet’s magnetic field on June 16th at 14:00 UT, possibly sparking a geomagnetic storm. High-latitude sky watchers should be alert for auroras.” That time is about 10AM EDT on Saturday, but there is always some uncertainty in the delay between the arrival of a coronal mass ejection on Earth and the onset of aurorae. -JCB)
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.
