Senin, 13 Agustus 2012

transit venus

Transit of Venus, 2012

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Image of transit taken by NASA's Solar Dynamics Observatory spacecraft
Main article: Transit of Venus
The 2012 transit of Venus, when the planet Venus appeared as a small, dark disk moving across the face of the Sun, began at 22:09 UTC on 5 June 2012, and finished at 04:49 UTC on 6 June.[1] Depending on the position of the observer, the exact times varied by up to ±7 minutes. Transits of Venus are among the rarest of predictable celestial phenomena and occur in pairs, eight years apart, which are themselves separated by more than a century:[2] The previous transit of Venus took place on 8 June 2004 (preceded by the pair of appearances on 9 December 1874 and 6 December 1882), and the next pair of transits will occur on 10–11 December 2117 and in December 2125.[3]

[edit] Observations of the event

Visibility map
The entire transit was visible from the western Pacific Ocean, northwesternmost North America, northeastern Asia, Japan, the Philippines, eastern Australia, New Zealand, and high Arctic locations including northernmost Scandinavia, and Greenland.[4] In North America, the Caribbean, and northwestern South America, the beginning of the transit was visible on 5 June until sunset. From sunrise on 6 June, the end of the transit was visible from South Asia, the Middle East, east Africa, and most of Europe. The phenomenon was not visible from most of South America, nor from western Africa. There were a number of live online video streams with footage from telescopes around the world. Midway through the transit one of the NASA streams had nearly 2 million total views and was getting roughly 90,000 viewers at any given moment.
In Los Angeles, crowds jammed Mount Hollywood where the Griffith Observatory set up telescopes for the public to view the transit. In Hawaii, hundreds of tourists watched the event on Waikiki Beach where the University of Hawaii set up eight telescopes and two large screens showing webcasts of the transit.[5] The transit was also observed and photographed by a flight engineer aboard the International Space Station, Don Pettit.[6]
High-definition images of the event were provided by NASA's Solar Dynamics Observatory, from 36,000 km (22,000 mi) above the Earth. Agency astrophysicist Dr. Lika Guhathakurta said, "We get to see Venus in exquisite detail because of SDO's spatial resolution, SDO is a very special observatory. It takes images that are about 10 times better than a high-definition TV and those images are acquired at a temporal cadence of one every 10 seconds. This is something we've never had before".[7] (SOHO was not in a good position to view the transit due to the size of its lissajous orbit centered about L1.)

[edit] Research

Children in Dili observing the transit of Venus
The 2012 transit gave scientists a number of research opportunities. These included:[8][9][10]
  • Measurement of dips in a star's brightness caused by a known planet transiting a known star (the Sun). This will help astronomers when searching for exoplanets. Unlike the 2004 Venus transit, the 2012 transit occurred during an active phase of the 11-year activity cycle of the Sun, and would have provided practice in detecting a planet's signal around a "spotty" variable star.
  • Measurement of the apparent diameter of Venus during the transit, and comparison with its known diameter. This will have given information on how to estimate exoplanet sizes.
  • The number of locations documenting the event will provide much data via parallax that will generate more accurate measurements.
  • Observation of the atmosphere of Venus simultaneously from Earth-based telescopes and from the Venus Express spacecraft. This gave a better opportunity to understand the intermediate level of Venus's atmosphere than is possible from either viewpoint alone, and should provide new information about the climate of the planet.
  • Spectrographic study of the atmosphere of Venus. The results of analysis of the well-understood atmosphere of Venus will be compared with studies of exoplanets with atmospheres that are unknown.
  • The Hubble Space Telescope used the Moon as a mirror to study the light reflected from Venus to determine the makeup of its atmosphere. This may provide another technique to study exoplanets.

[edit] Gallery

North America:
  • San Francisco, California, USA
    Transit of airliner with Venus
  • Anacortes, Washington, USA
  • Tempe, Arizona, USA
    01:54 UTC
  • Wichita Falls, Texas, USA
  • Fennell Observatory
    Oakland, Tennessee, USA
  • Toronto, Ontario, Canada
    23:06 UTC
Europe:
  • Nowy Dwór Mazowiecki, Poland
    06:18 UTC
  • Ragusa, Sicily, Italy
    04:11 UTC
  • Moscow, Russia
  • Helsingborg, Sweden
    04:20 UTC
  • Úvaly, Czech Republic
    04:26 UTC
  • Kecskemét, Hungary
    03:41 UTC
Asia:
  • Kuwait City, Kuwait
  • Amman, Jordan
    Combination of 3 exposures
  • Chennai, India
    03:24:56 UTC
  • Guangzhou, China
    00:41 UTC
  • Hsinchu, Taiwan
    00:05 UTC
  • Handa, Aichi, Japan
    23:36–04:50 UTC
Australasia:
  • Sydney
    23:25 UTC
  • Wagga Wagga
    00:49 UTC
  • Clayton
    01:06 UTC
Others:
  • SDO's Ultra-high Definition View of 2012 Venus Transit.ogv
    Solar Dynamics Observatory Ultra-high Definition View
  • Transit of Venus, 2012 Orbital Paths.ogv
    This visualization shows the orbital paths of Venus and Earth that led to this rare alignment on 5–6 June 2012
  • Venus transit, seen here from the International Space Station.
  • Close-up of Venus by the Japanese Hinode spacecraft on the sun-synchronous orbit.
  • GOES-15 SXI 2012 VenusTransit.ogv
    GOES-15 Solar X-ray Imager shows a 2-hour longer transit due to Venus' passing in front of the Corona.[11]
  • Venus Transit 2012.ogv
    Visualization generated by compositing the small field-of-view, high-cadence closeups of Venus with the full-disk, low-cadence imagery from SDO.

[edit] References

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Minggu, 12 Agustus 2012

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Minggu, 14 Agustus 2011

Pesawat NASA Hasilkan Gambar Badai Raksasa di Saturnus

Foto: NASA/JPL-Caltech/SSI
Cassini mulai mendeteksi badai yang berupa bintik putih yang besar di bagian utara planet Saturnus pada bulan Desember 2010.
Badan antariksa Amerika, NASA, mengatakan pesawat antariksanya Cassini, telah mengambil gambar-gambar yang paling jelas satu badai yang kuat dan sangat besar di planet Saturnus yang hampir selebar Bumi.
Pesawat Cassini yang tak berawak itu mendeteksi badai tersebut – yang disebut sebagai Great White Spot atau bintik putih yang besar – bulan Desember lalu ketika badai itu terbentuk di belahan utara. Para pakar astronomi yang memeriksa gambar-gambar yang sangat tajam itu mengatakan badai yang maha-besar itu kira-kira 10 ribu kilometer lebarnya, dan berekor awan putih amoniak yang mengelilingi seluruh planet itu.
NASA mengatakan Great White Spot itu adalah badai yang paling besar yang pernah diamati oleh pesawat antariksa yang mengorbit atau terbang dekat planet yang bergelang itu. Saturnus adalah planet kedua terbesar dalam tata surya setelah tetangganya sesama planet gas raksasa, Jupiter.
Tetapi, tidak seperti Great Red Spot Jupiter yang telah terus-menerus berkobar selama lebih 300 tahun, para pakar astronomi mengatakan Saturnus mengalami satu Great White Spot hanya kira-kira setiap 30 tahun, dan masing-masing badai itu berlangsung hanya beberapa bulan.
Terhitung badai ini, para ilmuwan telah mengamati hanya 5 Great White Spot di Saturnus sejak pertama kali ditemukan tahun 1876.
Sebelumnya, pesawat antariksa Cassini-Huygens berhasil mendeteksi adanya samudera air cair ada di bawah permukaan bulan Saturnus yang kecil dan beku, yang bernama Enceladus.
NASA mengatakan instrumen Cassini mendapati konsentrasi tinggi butiran es yang kaya garam dalam semburan uap air, es dan benda lain yang selalu menyembur ke angkasa dari retakan permukaan bulan Enceladus.
Analisa sampel yang diambil pesawat itu menunjukkan bahwa sebagian besar, kalau tidak semuanya, es yang kaya garam yang disemburkan itu datang dari air yang cair yang, menurut NASA, mempunyai komposisi seperti samudera. Air cair dianggap sangat penting bagi dasar adanya kehidupan atau makhluk hidup.

 

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