The Monthly Sky for February 2017
Dwarf Planet Ceres & Zodiacal Light
by Viktor Zsohar
February 2017 – Yukon Sky Events
February 1. Mars is 2° North of Moon.
February 2. Algol at minimum. Moon occults Ceres! Exit of Ceres visible from the Yukon during the dusk! If you have never seen this dwarf planet, now is the chance.
February 4. FIRST QUARTER MOON
February 5. Aldebaran 3° East of Moon, as seen from the Yukon: Occultation during daytime. Algol at minimum
February 7. Mercury at aphelion
February 8. Algol at minimum
February 11. FULL MOON: The Moon will be located on the opposite side of the Earth as the Sun and its face will be will be fully illuminated. This phase occurs at 11:34 UTC. Penumbral solar eclipse: Not visible in North-America
Regulus 0.8° North of Moon: Occultation not visible from the Yukon. Algol at minimum
February 13. Zodiacal Light is visible in Northern Latitudes in West after twilight for next two weeks
February 14. Algol at minimum
February 15. Jupiter 3° South of Moon
February 17. Venus greatest illuminated extent. Algol at minimum
February 18. LAST QUARTER OF THE MOON
February 20. Venus at perihelion. Saturn 4 ° South of Moon. Algol at minimum
February 23. Algol at minimum
February 24. Saturn 3.6°S of Moon
February 25. Algol at minimum
February 26. NEW MOON. Annular Solar Eclipse: Pacific Ocean, South America and Africa
February 27. Mercury at greatest heliocentric latitude South. Mars at ascending mode. Mars 0.6° North of Uranus
February 28. Algol at minimum
PLANETS IN FEBRUARY, 2017
February nights offer excellent observations of two planets for Yukoners. Besides the most brilliant Venus, Jupiter becomes more and more favourable position. As Mars and Uranus slowly disappear together, let us not forget about the occultation of the not-a-classical planet, the dwarf-planet Ceres by the Moon that occurred on February 2nd.
February mornings also offer a very limited visibility of Saturn and Mercury, at least for binoculars. However, Southern Canada, U.S., and Mexico are definitely better places to see these planets in the morning dusk.
Not favourable to see from the Yukon, but possible.
Reaches its maximum illuminated extent on the 17th, and continues to stand out brightly with its maximum brightness of -4.8m, after sunset. Very easy target with naked eye or a binocular pointed at the brightest spot in the evening sky towards southwest. It will considerably thins after the 17th.
Mars is in Pisces. The red planet is easy to find during February in the evening sky. It sets course to pass Uranus on the 27th, as the two planets approach each other just within 0.6 degrees. The planet’s disk size is even smaller than last month, making almost impossible to see any significant surface details.
Jupiter is well-located in the Eastern sky, dominating in Virgo during the second part of the night. Starting February, for the next four months, it will be easy to spot Jupiter’s retrograde motion, when compared to the position of Spica, as Jupiter becomes stationary on February 6th, about 3.5 degrees due North of Spica. Observe the dance of the Galilean satellites around Jupiter this month.
Saturn re-appears, but the Ring Planet just barely makes it above the Yukon horizon towards south-southeast by the time the Sun paints the morning sky light blue. Moves from Ophiucus to Sagittarius.
Uranus remains in Constellation Pisces, and sets in mid-evening. The giant gas planet is visible during the first part of the night. May be still spotted on the 27th, in the close proximity of Mars.
Dwarf Planet – 1 CERES
Ceres as NASA Spacecraft DAWN saw it – Image courtesy: NASA
Ceres is the largest dwarf planet Ceres is a so-called dwarf or minor planet in our Solar System. It is the first large object that was discovered in the asteroid belt, hence its name: “1 Ceres”. Actually, it is the largest object in the asteroid belt that lies between the orbits of Mars and Jupiter.
Its diameter is approximately 945 kilometers, making it the largest of the minor planets within the orbit of Neptune. The 33rd-largest known body in the Solar System, it is the only dwarf planet within the orbit of Neptune. Composed of rock and ice, the weight of Ceres is estimated to be approximately one third of the mass of the entire asteroid belt. Ceres is the only object in the asteroid belt known to be rounded by its own gravity. From Earth, the apparent magnitude of Ceres ranges from +6.7m to +9.3m, and hence even at its brightest, it is too dim to be seen with the naked eye, except under extremely dark skies.
Ceres was discovered, by Giuseppe Piazzi at Palermo on the 1st of January 1801. It was originally considered a planet, but was reclassified as an asteroid in the 1850s when many other objects in similar orbits were discovered.
Giuseppe Piazzi (16 July 1746 – 22 July 1826) was an Italian Catholic priest of the Theatine order, mathematician, and astronomer. He was born in Ponte in Valtellina, and died in Naples. He established an observatory at Palermo, now the Osservatorio Astronomico di Palermo – Giuseppe S. Vaiana. Perhaps his most famous discovery was the first dwarf planet, Ceres.
Ceres appears to be differentiated into a rocky core and icy mantle, and may have a remnant internal ocean of liquid water under the layer of ice. The surface is probably a mixture of water ice and various hydrated minerals such as carbonates and clay. In January 2014, emissions of water vapor were detected from several regions of Ceres. This was unexpected, because large bodies in the asteroid belt typically do not emit vapor, a hallmark of comets.
Dawn Spacecraft– Image courtesy: NASA
The robotic NASA spacecraft Dawn delves into the unknown and achieves what’s never been attempted before. A mission in NASA’s Discovery Program, Dawn orbited and explored the giant proto-planet Vesta in 2011-2012, and now it is in orbit and exploring a second new world, dwarf-planet Ceres, entering orbit around Ceres on 6 March 2015. Pictures with a resolution previously unattained were taken during imaging sessions starting in January 2015 as Dawn approached Ceres, showing a cratered surface.
The dwarf planet may have a weak, temporary atmosphere. A temporary atmosphere would be consistent with the water vapor the Herschel Space Observatory detected at Ceres in 2012-2013. The electrons that were detected by DAWN could have been produced by the solar wind hitting the water molecules that Herschel observed, but scientists are also looking into alternative explanations.
At first glance, Ceres may not look icy. Images from NASA’s Dawn spacecraft have revealed a dark, heavily cratered world whose brightest area is made of highly reflective salts – not ice. But newly published studies from Dawn scientists show two distinct lines of evidence for ice at or near the surface of the dwarf planet. These studies support the idea that ice separated from rock early in Ceres’ history, forming an ice-rich crustal layer, and that ice has remained near the surface over the history of the solar system.
Ceres’ uppermost surface is rich in hydrogen, with higher concentrations at mid-to-high latitudes — consistent with broad expanses of water ice, according to a new study in the journal Science. On Ceres, ice is not just localized to a few craters. It’s everywhere. Researchers determined the concentrations of hydrogen, iron and potassium in the uppermost surface of Ceres. On Ceres, hydrogen is likely to be in the form of frozen water.
Rather than a solid ice layer, there is likely to be a porous mixture of rocky materials in which ice fills the pores. The spacecraft’s data show that the mixture is about 10 percent ice by weight. These results confirm predictions that ice can survive for billions of years just beneath the surface of Ceres. The evidence strengthens the case for the presence of near-surface water ice on other main belt asteroids.
Concentrations of iron, hydrogen, potassium and carbon provide further evidence that the top layer of material covering Ceres was altered by liquid water in Ceres’ interior. Scientists theorize that the decay of radioactive elements within Ceres produced heat that drove this alteration process, separating Ceres into a rocky interior and icy outer shell. Separation of ice and rock would lead to differences in the chemical composition of Ceres’ surface and interior.
Scientists closely examined hundreds of cold, dark craters called “cold traps” — at less than minus 260 degrees Fahrenheit (110 Kelvin), they are so chilly that very little of the ice turns into vapor in the course of a billion years. Researchers found deposits of bright material in 10 of these craters. In one crater that is partially sunlit, Dawn’s infrared mapping spectrometer confirmed the presence of ice.
Ceres’ brightest area, in its northern-hemisphere, is Crater Occator. At 92 kilometers wide and 4 kilometers deep, Occator displays evidence of recent geologic activity. The latest research suggests that the bright material in this crater is comprised of salts left behind after a briny liquid emerged from below, froze and then sublimated, meaning it turned from ice into vapor. NASA scientists reported that the bright spots on Ceres may be related to a type of salt, particularly a form of brine containing magnesium sulfate hexahydrite (MgSO4·6H2O); the spots were also found to be associated with ammonia-rich clays. In June 2016, near-infrared spectra of these bright areas were found to be consistent with a large amount of sodium carbonate, (Na2CO3), implying that recent geologic activity was probably involved in the creation of the bright spots.
Occator Crater as “seen” by DAWN during a close approach fly-by– Image courtesy: NASA
Thus Occator does not shine because of ice, but rather because of highly reflective salts. A new video produced by the German Aerospace Center (DLR) in Berlin simulates the experience of flying around this crater and exploring its topography. Occator’s central bright region, which includes a dome with fractures, has recently been named Cerealia Facula. The crater’s cluster of less reflective spots to the east of center is called Vinalia Faculae.
Salt deposits inside Occator– Image courtesy: NASA
Another geological feature, Ahuna Mons, is a lonely, 5-kilometer-high mountain on Ceres. Ahuna Mons is a volcanic dome unlike any seen elsewhere in the solar system, according to a new analysis led by Ottaviano Ruesch of NASA’s Goddard Space Flight Center, Greenbelt, Maryland, and the Universities Space Research Association. Ruesch and colleagues studied formation models of volcanic domes, 3-D terrain maps and images from Dawn, as well as analogous geological features elsewhere in our solar system. This led to the conclusion that the lonely mountain is likely volcanic in nature. Specifically, it would be a cryovolcano — a volcano that erupts a liquid made of volatiles such as water, instead of silicates. “This is the only known example of a cryovolcano that potentially formed from a salty mud mix, and that formed in the geologically recent past.
Ceres’ lonely mountain, Ahuna Mons, is seen in this simulated perspective view. The elevation has been exaggerated by a factor of two. The view was made using enhanced-color images from NASA’s Dawn mission. Images taken using blue (440 nanometers), green (750 nanometers) and infrared (960 nanometers) spectral filters were combined to create the view. – Image courtesy: NASA
Dawn Two distinct bright spots (or high-albedo features) inside a crater, leading to speculations about a possible cryovolcanic origin or outgassing. On 3 March 2015, a NASA spokesperson said the spots are consistent with highly reflective materials containing ice or salts, but that cryovolcanism is unlikely, however on 2 September 2016, published alongside six other studies, NASA scientists released a paper in Science that claims that a massive ice volcano called Ahuna Mons is the strongest evidence yet for the existence of these mysterious ice volcanoes.
Kupalo, which measures 16 miles (26 kilometers) across and is located at southern mid-latitudes, is named for the Slavic god of vegetation and harvest.
This image from NASA’s Dawn spacecraft shows Kupalo Crater, one of the youngest craters on Ceres. The crater has bright material exposed on its rim and walls, which could be salts. Its flat floor likely formed from impact melt and debris. – Image courtesy: NASA
Position of Ceres in relation to the stars
From the Yukon, we can only see the second part of the occultation, when Ceres re-appears from behind the Moon.
1. 2017 RASC Observer’s Handbook
2. Starry Nights Pro7 Software