Monday, April 30, 2012

Saturn

Many observers consider Saturn to be the most spectacular planet. Its magnificent rings, seen clearly with even small telescopes, provides Saturn a great for over other planets such as Jupiter with its clouds or Mars and its surface features. Saturn is the sixth planet in the solar system and is the furthest away from the sun that we can see with the naked eye.
For the ancients, Saturn was the seventh and last planet. The list included the sun and moon as planets and the Earth was not included. Uranus, though may be seen with the unaided eye was not considered to be a planet in ancient times since it is too faint and moves very slowly. For these reasons Saturn had the honor to be the last planet.
Saturn's movement is slow, completing its orbit around the sun every 30 years. To see Saturn movement in the sky you should watch it every two weeks. At this duration its movement will be noticeable. Currently (May 2012) Saturn is in Virgo near the bright star Spica. Using Spica as a reference fixed star will help to identify the slight movement of Saturn. Saturn is the second largest planet, however its mass is not high (relatively) and its density is only 0.7 (g/cm2) which means that Saturn will float in a very (very) big ocean just like wood.


General information on Saturn (from Wikipedia)
Saturn information
Saturn orbit
Mean distance from sun 1,426,725,413 km
(9.537,070,32 AU)
Orbit time 10,832.327 days (29.657296 years)
Axis tilt 2.488°
Number of moons 60 and some more which are not named yet
Physical attributes
Radius 60,268 Km
Surface area: ‎4.27×1010‎ Sq. KM
Mass: ‎5.6846×1026‎ Kg
Density: 0.6873 g/cm2
Gravity: 8.96 m/sec2,
or 0.914 g
Rotation period: 10 hours, 47 minutes, 6 second
Rotation speed: 9.87 Km/Sec (Equator)
Rotation Axis tilt: 26.73°
Escape velocity: 35.49 Km/sec
Atmosphere
Pressure: 140 K Pascal
Hydrogen More than-93%
Helium More than-5%
Methane 0.2%
Water vapor 0.1%
Ammonia 0.01%
Ethane 0.0005%

Saturn was one of the planets that Galileo watched with his telescope in 1610. Galileo's telescope was not sharp enough and Galileo did not see the rings very well. Galileo saw something like two ears, and that is how he draw it.
Saturn in a draw by Galileo
Saturn in a draw by Galileo
After some years the ears (rings) disappeared and then re-appeared. The reason for this is that the rings plane was parallel to the earth and although the rings are large, there thickness (height) is just about 10 meters. Look from a distance on a sheet of paper with its narrow thin edge toward you, and you will hardly see it. Turn the paper toward you and you will see it clearly. It is the same with the rings which becomes invisible when they face exactly toward earth. The cycle of the rings plane movement is 14 years. After some years Galileo draw the rings of Saturn again, in a way which is more similar to what we usually see.

Saturn in a draw by Galileo
Saturn in a draw by Galileo

Only when telescopes were improved the fine details of the rings were discovered. The origin of the rings is unknown but the best theory is that an old icy moon of Saturn was crashed to millions of small pieces. The real beauty of the rings was discovered only when Pioneer and then Voyager came close enough to Saturn during the late seventies and early eighties.

Saturn from Pioneer 11
Saturn from Pioneer 11. Credit: NASA
Voyager images were much better. The next photo from Voyager 2 taken 21 Million KM from Saturn and shows 3 of its moons.

Saturn from Voyager 2
Saturn from Voyager 2. Credit: Nasa

These days Cassini is orbiting Saturn sending even more amazing photos. We will dedicate Cassini a special article next week.

Monday, April 16, 2012

Sundials in Israel


Sundials were a very important mean in the past to measure and show the time. Today, sundials are regarded more as architectural and design artifacts. Most sundials contain a gnomon which is usually a rod which casts a shadow, and a table which shows the time. There are various types of sundials, simple and complex, and they can be very accurate. This article will show some examples of the many sundials that can be found around Israel.


For a tourist, one of the best places to look for sundials is the Eretz Israel Museum in Tel-Aviv. The museum has a yard with replicas of ten sundials, old and new, from several places around Israel. Also, there is a planetarium in the museum which you should visit.


Sundial - Acre
Sundial - Acre

Sundial - Acre
Sundial - Acre
A replica of an ancient sundial

Ancient sundial - Israel
Ancient sundial - Israel
The Curved sundial does not have a gnomon, the entire shape of the sundial is the gnomon and it casts a shadow on the curved area. Such a sundial is good only for half of the day, so there is a need for more than one (which is on the other side of the stone).

An interesting Sundial on Bat Galim beach in Haifa. Notice the different of the width between the hours in the scale.
Sundial - Haifa
Sundial - Haifa
A replica of a Sundial from Jaffa.
Sundial - Jaffa
Sundial - Jaffa
 An interesting mosaic Sundial in Kfar Masaryk (Near Acre)
Sundial - Kfar Masaryk
Sundial - Kfar Masaryk
On the western wall of the great synagogue in Petach-Tikva there are 3 sundials (All have replicas in Eretz Israel Museum). As they are on the west wall they can only be used in the second half of the day.
Sundial - Petach-Tikva synagogue
Sundial - Petach-Tikva synagogue

Sundial - Petach-Tikva synagogue
Sundial - Petach-Tikva synagogue

Sundial - Petach-Tikva synagogue
Sundial - Petach-Tikva synagogue
 העתקי השעונים נמצאים גם במוזיאון ארץ ישראל
Sundial - Petach-Tikva synagogue
Sundial - Petach-Tikva synagogue - Replica
 Also in Petach Tikva, in the Twelve Tribes park, a mosaic sundial.
Sundial - Petach Tikva - Twelve tribes park
Sundial - Petach Tikva - Twelve tribes park

Sundial - Petach Tikva - Twelve tribes park
Sundial - Petach Tikva - Twelve Tribes park

Sundial - Petach Tikva - Twelve tribes park
Sundial - Petach Tikva - Twelve Tribes park
 The largest sundial in Israel is in Rishon Lezion (Moshe Dayan street)

Sun dial - Rishon Lezion
Sundial - Rishon Lezion

Sundial - Rishon Lezion
Sundial - Rishon Lezion
 Going north again to Shomrat (Near Acre), an impressive sundial which has an "environmental" problem... The sundial is in the shade most of the day
Sundial in Shomrat
Sundial in Shomrat
 A rather new type of sundial is the one without a gnomon at all. You are the gnomon and you need to stand along the middle line next to the relevant date (see the dates in the third photo). These sundials have become more and more common across the world. The sundial is in Eretz Israel Museum Tel Aviv
Sundial - Eretz Israel Museum Tel Aviv
Sundial - Eretz Israel Museum Tel Aviv

Sundial - Eretz Israel Museum Tel Aviv
Sundial - Eretz Israel Museum Tel Aviv - When you stand on it, your shadow shows the time

Sundial - Eretz Israel Museum Tel Aviv
Sundial - Eretz Israel Museum Tel Aviv - Notice the various lines for the dates in the year.
A most impressive park in Israel Ramat Hanadiv, is in memory of Baron Rothschild and is located near Zichron Yaakov.
Sundial in Ramat Hanadiv Zichron Yaakov
Sundial in Ramat Hanadiv Zichron Yaakov
In Jerusalem there are several sundials. Here is one of them, the courtesy of Yoav Avnion

Sundial on a synagouge wall, Jerusalem:
Sundial on a synagouge wall, Jerusalem: Credit: Yoav Avnion
And another famous sundial in Jerusaelm in Yafo street near Machena Yehuda market on the wall of Zoharey Chama synagouge.
Sundial on a synagouge wall, Jerusalem
Sundial on a synagogue wall, Jerusalem: Credit: Yoav Avnion

שעון שמש עם פסוק משיר השירים
שעון שמש עם פסוק משיר השירים
בחצר בית הספר האנגליקני ברחוב הנביאים 82 בירושלים
בית הספר האנגליקני תוכנן על ידי האדריכל ברספורד פייט והוקם בשנת 1897
תמונת CC שצילם והעלה לפליקר רון אלמוג ©
A sundial near the public library in Yerucham.
Sundial in Yerucham
Sundial in Yerucham - Sefi Shalev
A very interesting sundial in the IDF officers academy near Mitzpe Ramon. The reflection of the dial rings is the hour,
Sundial in the IDF academy
Sundial in the IDF academy - Tom Rosenfeld
My friend, Eden Orion - An astronomer and artist - Designed and built two sundials. The first sundial is in Kornit in the memory of Ben Sela. You can read about Kornit's sundial here (In hebrew) and even if you can't read Hebrew you will see many more photos there.

Sundial in Kornit.
Sundial in Kornit. Credit: Eden Orion
Another sundial designed by Eden (Only the astronomical feature) and  artistically designed and built by Yoav Shavit is in the national park of Ramat Gan. You can see many more photos and diagrams here (Also in Hebrew but Google translate does a fair job)
Sundial in Ramat-Gan
Sundial in Ramat-Gan. Credit: Eden Orion
Back to Jerusalem and to a new sundial by the old city walls created by the artist Maty Grunberg. The physical design was done by Ilan Manulis
Sundial in Teddy Park, Jerusalem
Sundial in Teddy Park, Jerusalem. Naomi Azar
Yigal Zemer, an artist, designed and built many sundials in Israel. Here are some of his sundials.
Sundial in Beit-Shean's guest house,
Sundial in Beit-Shean's guest house, Yigal Zemer

Sundial in Rechovot
Sundial in Rechovot, Yigal Zemer

Sundial in Mandelbaum pass, Jerusalem
Sundial in Mandelbaum pass, Jerusalem. Yigal Zemer

Sundial in Raanana
Sundial in Raanana. Yigal Zemer
A sundial can be part of a memorial monument like this sundial in Kedumim which is part of the memorial park to lt. Yishai Shechter.
Sundial in Kedumim
Sundial in Kedumim. Credit: Shlomi liss
On the roof of Mitzpe Ramon visitor's center there is a very accurate sundials. The center is in memory of Ilan Ramon, the first Israel Astronaut who died in the Columbia disaster (PS: Ilan choose his last name to be Ramon because he liked the area, not vice-verse)
Sundial in Mitzpe Ramon.
Sundial in Mitzpe Ramon. Anna Levin.

Sundial in Mitzpe Ramon.
Sundial in Mitzpe Ramon. Anna Levin.
Sundials also symbolized the value of labor, and working in the files from sunrise to sunset. This sundial in Deganya (The first Kibbutz) represent this theme, The writing says: "The day is short and the labor is vast"

Sundial in Deganya
Sundial in Deganya. Saar Nudel

Sundial in Deganya
Sundial in Deganya. Saar Nudel

A unique time-field in Givatiim. Each pole shows the correct time when the sun is aligned with it.
Sundial at Givataaim
Sundial at Givataaim
At the cave of the Patriacrhs in hebron there are old engravings which was used for sundial.
At the cave of the Patriacrhs in hebron
At the cave of the Patriarchs in Hebron. Photo: Amit Mendelson

A special sundials' garden in Ashqelon by the artist Yigal Tomarkin.
גן שעוני השמש באשקלון. פיסול יגאל תומרקין. צילום:דר אבישי טייכר. מתוך אתר פיקיוויקי
Sundials in Ashqelon: Photo: Avishay Taycher

A sundial with two gnomons (I am not sure which one is correct) is located in Tel-Azekah
Sundial in Tel-Azekah
Sundial in Tel-Azekah

There are more sundials in Israel, large and small, old and new. I will try and add more from time to time.

Also look at the following sites for sundials all over the world, I will be happy to add more just comment or send me a note.





Sunday, April 1, 2012

Carnival of Space #243

Hi everybody and welcome to the 243th edition of Carnival of Space, hosted by the Venus Transit. As its name implies, the Venus Transit site has lots of articles about the upcoming rare event of Venus transiting the sun in June, and in addition  includes other articles on all aspects of astronomy.

Following are this week's articles:
Nextbigfuture covers the NASA Innovative Advanced Conference Spring meeting. One topic is the Fission Fragment Rocket Engine (FFRE). The FFRE requires small amounts of readily available, energy dense, long lasting fuel, significant thrust at specific impulse of a million seconds, and increases safety by charging the reactor after arrival in LEO. If this study shows the FFRE potential, the return could be immense through savings in travel time, payload fraction, launch vehicle support and safety for deep space exploration.

Nextbigfuture also covers Atomic metallic hydrogen. If metallic hydrogen can be metastable at ambient pressure and temperature, then it could be used as the most powerful chemical rocket fuel, as the atoms recombine to form molecular hydrogen. This light-weight high-energy density material would revolutionize rocketry, allowing single-stage rockets to enter orbit and chemically fueled rockets to explore our solar system. To transform solid molecular hydrogen to metallic hydrogen requires extreme high pressures, but has not yet been accomplished in the laboratory. In the proposed new approach electrons will be injected into solid hydrogen with the objective of lowering the critical pressure for transformation. If successful the metastability properties of hydrogen will be studied. This new approach may scale down the pressures needed to produce this potentially revolutionary rocket propellant. It would have an ISP of 1700 and would be usable for single stage to orbit launches (SSTO).
 
Discovery Space news writes about magnetic tornadoes measuring several Earths wide which have been spotted deep inside the sun's atmosphere. Using the high-definition eyes of NASA's Solar Dynamics Observatory (SDO), researchers from Aberystwyth University have, for the first time, captured a monster solar twister evolving deep inside the corona. But far from the phenomena just being fascinating to watch, it is thought it may help predict space weather.
 
Air and Space magazine sent us the following story: Attendees at the recently concluded 43rd annual Lunar and Planetary Science Conference had front row seats to a heated debate on new data from the Moon. As opposed to how many envision scientific debate – coolly logical, white-frocked intellectuals, dispassionately discussing points of contention in a laboratory – what they witnessed was an impassioned and stormy exchange of differing opinions. There is good reason for passion. Subsequent decisions based on these data, places the success or failure of future missions in the crosshairs.
 
AstroWOW explains what "heliopause" is in its "Ride with the Voyager probes to the edge of the solar system" article.
 
Dear Astronomer  writes about new research from the ESO’s HARPS mission that provides evidence that small, rocky, Earth-sized planets are extremely common, especially in the habitable zones around faint red dwarf stars. Based on this new research, an international team places an estimate of tens of billions of these worlds in our galaxy alone, and possible hundreds of billions in our cosmic neighborhood.
  
Chandra X-ray telescope blog shares a new X-ray study of the remains of an exploded star that indicates that the supernova that disrupted the massive star may have turned it inside out in the process.
 
Astronotes from the Armagh planetarium gives us a lookout for the coming month: "The month of April is fantastic month for stargazing and for astronomy in general with numerous dates to mark in your calendar. We get a front row seat to the beauty of Saturn visiting the bright star of Spica as well as some other yearly visitors that make the April and spring night skies so magical.
 
Cosmic blog writes about Amateur astronomers who have been marveling over a curious cloud that they spotted on Mars - and now the professionals have focused in on an explanation.
 
Cosmic blog also writes about a treasure found in the deep ocean: Amazon.com's billionaire founder, Jeff Bezos, says he's funded a successful effort to locate the mammoth rocket engines that sent the Apollo 11 mission on the first leg of its mission to the moon — and now he's planning to bring them up from the Atlantic Ocean floor.
 
The Meridian Journal updates us about the latest efforts to find liquid water on Mars: "New evidence from Mars Reconnaissance Orbiter supports the possibility of liquid water brines on Mars."

Links Through Space fol­lows an Astron­omy Club as they travel through Spain. As they travel the south of Spain they visit beautiful sites and astro­nom­i­cal landmarks to bring you very cool astro-pho­tos and sto­ries about the his­tory of Span­ish Astronomy.

Some history from Vintage Space: Just over 47 years ago, NASA learned to fly in space with the first spacecraft designed for a pilot by a pilot. Read about Gemini 3 mission with Gus Grissom and John Young.

Riding with Robots writes: "With its geysers of water ice, Saturn’s icy moon Enceladus is quite possibly the most intriguing place in the entire solar system." Last week, the Cassini probe flew right through the plumes, and sent home some beautiful pictures along the way.

WeirdSciences also writes about Enceladus in a detailed article about What’s Wrong with NASA: Evidences of Life on Saturn’s Moon Enceladus?
 
And from this site, the major observational event of this week will be Venus in the Pleiades (M45), this will happen on April 3rd.


April 2012 is Global Astronomy Month (GAM), If you are an astronomer, from the novice to the expert, you will find lots of things to do and learn in GAM. Please visit GAM site and choose your desired activity or create your own!