Some photos of last night’s “Blood Moon" total lunar eclipse. From here in Tucson, we had a perfect view of the entire event unspoiled by clouds. The middle photo is a stack of 10 iPhone frames with an average dark frame subtracted to reduce the camera noise. The special guest star above the Moon is 76 Virginis (magnitude 5.2). The bottom photo is a wide-field context shot, showing the planet Mars as the bright “star” above and to the right of the Moon during the event.
Mark your calendars: the next such total lunar eclipse is on 8 October 2014, which will be best viewed in Europe and Africa. (Western) North America’s next chance is the next eclipse in the series: 4 April 2015.
(Images by the blogger)
Tonight sees the first lunar eclipse in the ominous-sounding “Blood Moon Tetrad” series. The first lunar eclipse of 2014 will be a doozy, and North America is well-positioned to see the entire event. Around 1AM EDT this morning, the Moon will begin to transit through the shadow of the earth; by 3AM, it will be deeply immersed in the dark, inner shadow cone, leading to “totality”. Turned red by the scattering of light by small particles in the Earth’s atmosphere, a totally-eclipsed Moon is truly an awesome sight to behold.
Tonight’s lunar eclipse is slightly unusual in that it begins a series of eclipses. As Universe Today puts it, “The April 15th total lunar eclipse is the first in series of four total eclipses spanning back-to-back years, known as a tetrad. There are eight tetrads in the 21st century: if you observed the set total lunar eclipses back in 2003 and 2004, you saw the first tetrad of the 21st century." While the Moon will turn red like blood tonight, that’s where the similarities end. The cycles of eclipses can be explained by the nature of the Moon’s orbit around the Earth — neither something more mystical or nefarious.
As a bonus, tonight is also the closest approach of Mars to the Earth in six years. It’s the bright red “star” north (above) and west (to the right) of the Moon. Nearer still is the blue star, Spica, the brightest star in the constellation Virgo.
Chance alignments make for a pair of celestial ‘diamond rings’. Today the European Southern Observatory released the above Very Large Telescope (VLT) image of the planetary nebula Abell 33 (top), appearing as a ghostly blue circle. By pure chance, our line of sight toward the nebula is almost perfectly aligned with the bright foreground star HD 83535; the off-center arrangement is reminiscent of a glittering gem in a metaphorical ring setting. Were the solar system located in a slightly different region of our galaxy, the alignment might be spot on, putting the bright star at the center — or it could bring these objects nowhere near each other in our skies.
This isn’t the only such diamond ring in the sky. A similar phenomenon, produced by entirely different means, is seen at the beginning or end of the total phase of total solar eclipses, such as in this 22 July 2009 eclipse seen from Japan (bottom image). Here, as the total phase ends and the first rays of sunlight peek through mountain valleys along the edge of the Moon’s disc, a blindingly-bright spot lights up a corner of the eclipsed Sun. It is known as the “diamond-ring effect”. Where the diamond ring occurs around the Moon’s disc in any given total eclipse is due to chance: the path the Moon takes across the Sun in our sky combined with the irregular profile of the Moon’s limb.
(Image credits. Top: European Southern Observatory. Bottom: Wikimedia Commons user ComputerHotline)
Mars reaches opposition tonight. On the evening of 8 April, the Earth and Mars will reach points in their respective orbits that put Mars and the Sun exactly opposite each other (i.e., about 180º apart) in Earth’s sky. As a result, as the Sun is setting in any particular location, Mars is rising on the other side of the sky, and vice versa at sunrise. Mars will be up all night. If the orbits of Mars and Earth were perfectly circular, tonight would also be the date of the Red Planet’s closest approach to Earth. However, planetary orbits are elliptical so the actual date of closest approach doesn’t come until next week (14 April).
Look for Mars in the southeastern sky after dusk. It’s so bright relative to the stars around it’s unlikely to be mistaken for a star, but note that the fainter, bluish star Spica (α Virgo) is not far away. Through binoculars, Mars remains a small, bright orange dot, but a small telescope can show surface features including clouds and the white ice of the planet’s polar caps. Alternately, view it online either at the Virtual Telescope or Slooh Observatory.
(Image credits. Top: Space.com. Bottom: NASA)
Meet a galactic serial killer. This new image from the MPG/ESO 2.2-meter telescope at La Silla Observatory in Chile shows two rather different galaxies: NGC 1316 (center), and it’s smaller neighbor, the small spiral galaxy NGC 1317 (right). This pair is close to one another in space, but their past histories are very different. NGC 1317’s life has been quiet and otherwise “normal”, but NGC 1316 shows the signs of having swallowed other galaxies whole. The glow of stars thrown out into intergalactic space from previous encounters, to the left and below NGC 1316, tells part of the story. Read the ESO press release for details.
“The new Moon in the old Moon’s arms”. Have you ever noticed that when viewing a thin crescent Moon, you can see the rest of the disc (the “missing” part)? It’s been known for a long time; Leonardo da Vinci drew it, and correctly explained it, more than 500 years ago:
People once argued over the course of centuries as to whether it was real or an optical illusion, not understanding the source of the illumination.
Now we know it is very real — a phenomenon called earthshine. When we see a crescent Moon, an observer on the Moon would see a nearly-“full Earth”. For all its dark oceans and land, there are are a lot of clouds in Earth’s atmosphere. The clouds, and ice, reflect much sunlight back into space, illuminating the otherwise “dark” face of the Moon:
(Diagram by Gary Seronik)
The human eye has a large dynamic range, so even while the crescent gets bigger over the next few nights, the faint earthshine will remain evident for nearly a week. Eventually the crescent becomes too wide, overwhelming the eye, but the contribution of reflected light from Earth drops. By quarter Moon, most observers can no longer see it.
(Photo by the blogger)
Brazilian astronomers have discovered the first ring around an asteroid. Researchers affiliated with the European Southern Observatory today announced they have gathered observational evidence supporting a thin ring of water-ice particles around the asteroid (10199) Chariklo. It is the first instance known of a planet-like ring around a small solar system body.
At a diameter of about 250 km, Chariklo is (probably) the largest representative of a class of asteroids known as Centaurs. By definition, they orbit in the space between Jupiter and Neptune, and probably represent icy bodies from the more distant Kuiper Belt that have been nudged inward by periodic kicks from Neptune’s gravity. The ‘dwell time’ in these orbits is a few million years, after which Centaurs likely get deflected either in toward the Sun or out of the solar system entirely. In the former case, they begin to superficially resemble comets in their behavior like the Centaur (2060) Chiron, which suddenly sprouted a tail about 25 years ago.
Today’s announcement was made on the basis of June 2013 observations of an “occultation" event involving Chariklo in which the Centaur passed in front of a background star called UCAC4 248-108672. Its light dimmed before the asteroid itself blocked the starlight, a clue that something in its vicinity scattered or absorbed some light. Modeling of the observations suggested it was a ring rather than a small moon orbiting Chariklo.
"We weren’t looking for a ring and didn’t think small bodies like Chariklo had them at all, so the discovery – and the amazing amount of detail we saw in the system – came as a complete surprise!" said study author Felipe Braga-Ribas.
Chariklo’s ring is small in diameter relative to the asteroid itself, and spans 12 miles with a five-mile gap between two dense rings. Careful study of the starlight transmission during the occultation revealed this detailed structure. The discovery team has suggested “Oiapoque” and “Chuí”, two rivers in Brazil, as names for the ring components.
What made the ring? We don’t know yet. The leading explanation is the past collision of two or more satellite moons orbiting Chariklo. Another possibility is that water “geysers” erupting from Chariklo’s frozen surface are feeding the ring, much as Saturn’s moon Enceladus “feeds” the planet’s E-ring. The mystery deepens.
Astronomers may have detected the signal of decaying dark matter particles. Something makes up about 84% of the matter-energy in the Universe but is utterly invisible: it radiates no electromagnetic energy, and is sensed only by its gravitational effect on electromagnetic-radiating “normal” matter. But attempts to directly detect the presence of this potentially exotic matter near Earth have so far turned up nothing. To date, dark matter’s existence is only inferred indirectly.
One approach to sensing dark matter is to watch for it to decay into other particles, releasing high-energy light called gamma rays that can be detected with special hardware. Analysis of new data from just such hardware, NASA’s Fermi Gamma-Ray Space Telescope, may have turned up the signal of dark matter particles toward the center of the Milky Way decaying and emitting light. “If our interpretation is correct, this signal would constitute the discovery of an entirely new particle that makes up the majority of the mass found in the universe,” says study coauthor Dan Hooper. “I can’t find words that are strong enough to capture the significance of such a discovery.” Based on the energy of the gamma-ray excess observed by Fermi, researchers think the radiation indicates the decay of dark matter particles in the mass range of 31-40 GeV.
Others are skeptical. There exist alternate sources of gamma radiation not produced by dark matter decay, such as pulsars. The result therefore needs validation by additional tests, perhaps by looking at dwarf galaxies, thought to be abundant in dark matter but not in other natural particle accelerators like pulsars. All sides agree: more data are required to confirm this intriguing observation.
(Image: the entire sky at energies >1 GeV based on 5 years of data from NASA’s Fermi Gamma-ray Space Telescope. Warmer/brighter colors indicate brighter gamma-ray sources. Credit: NASA / DOE / Fermi LAT Collaboration)