Archive for June, 2009

Question of the Week: Why does the Moon shine?

Reader Questions | Posted by Drew
Jun 28 2009

That is a great question.  The answer is, the light from the Sun strikes the surface of the Moon and it is reflected back out into space.   We see the reflected sunlight that heads toward the Earth.  There is a technical term, “albedo”, that is a measure of the reflectivity of an object.  To be specific, albedo is a ratio of the incident light and the reflected light.  The greater the albedo, the brighter an object would appear.

When we look at the Moon, we see light and dark areas.  The dark areas on the Moon are the lakes or Maria.  When you look at the Moon through a small telescope or pair of binoculars you can see that these are smooth areas.  These areas are relatively young regions on the Moon that were formed by volcanic flows of basalt.  The albedo of the basalt rock is relatively low.

The lighter regions on the Moon are the mountain areas with old and jagged rocks.  The albedo of the mountain areas is fairly high.
It is also interesting to note that we see all the planets by the reflection of sunlight.  We see the stars by the light that they give off themselves.

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Celestial Feature of the Week: Jupiter

Celestial Feature of the Week | Posted by Drew
Jun 28 2009

Jupiter is the fifth planet from the Sun and by far the largest. It is more than twice as massive as all the other planets combined (the mass of Jupiter is 318 times that of Earth).

The Ring of Jupiter

The Ring of Jupiter

The planet is the fourth brightest object in the sky (after the Sun, the Moon and Venus), partly because of its size and its reflective gaseous atmosphere. It has been known since prehistoric times as a bright “wandering star”. But in 1610 when Galileo first pointed a telescope at the sky he discovered Jupiter’s four large moons Io, Europa, Ganymede and Callisto (now known as the Galilean moons) and recorded their motions back and forth around Jupiter. This was the first discovery of a center of motion not apparently centered on the Earth. It was a major point in favor of Copernicus’s heliocentric theory of the motions of the planets (along with other new evidence from his telescope: the phases of Venus and the mountains on the Moon).
Jupiter was first visited by Pioneer 10 in 1973 and later by Pioneer 11, Voyager 1, Voyager 2 and Ulysses. The spacecraft Galileo orbited Jupiter for eight years. It is still regularly observed by the Hubble Space Telescope.

This gas giant is about 90% hydrogen and 10% helium (by numbers of atoms, 75/25% by mass) with traces of methane, water, ammonia and “rock”. This is very close to the composition of the primordial Solar Nebula from which the entire solar system was formed. Saturn has a similar composition, but Uranus and Neptune have much less hydrogen and helium.  Jupiter probably has a core of rocky material amounting to something like 10 to 15 Earth-masses.  Above the core lies the main bulk of the planet in the form of liquid metallic hydrogen.
At last count, Jupiter has 63 known satellites: the four large Galilean moons plus many more small ones some of which have not yet been named.  Io, Europa and Ganymede are gravitationally locked together in a 1:2:4 orbital resonance and their orbits evolve together. Callisto is almost part of this as well. In a few hundred million years, Callisto will be locked in too, orbiting at exactly twice the period of Ganymede (eight times the period of Io).

Jupiter's Family

Jupiter's Family

Jupiter (a.k.a. Jove; Greek Zeus) was the King of the Gods, the ruler of Olympus and the patron of the Roman state. Zeus was the son of Cronus (Saturn).  Jupiter’s satellites are named for other figures in the life of Zeus (mostly his numerous lovers).
We can see Jupiter in the late night in that it rises above the eastern horizon around 11 p.m. EDT.  It is easy to spot and you can see its four Galilean moons and equatorial cloud belts with just a pair of binoculars.

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Today in History: 6/28/09 – 7/4/09

Space History | Posted by Drew
Jun 28 2009

June 30, 1868: George Ellery Hale, founding father of the Mt. Wilson Observatory, was born on this day. He was the force behind the founding of Palomar Observatory and the building of the 200-inch Hale telescope.

June 30, 1908: is the 100th anniversary of that ferocious meteor impact near the Podkamennaya Tunguska River in remote Siberia that leveled eight hundred square miles of remote forest.  It is estimated that the space rock, about 120 feet across, entered the atmosphere of Siberia and then detonated in the sky.  It is also estimated that the asteroid entered Earth’s atmosphere traveling at a speed of about 33,500 miles per hour and during its quick plunge through the atmosphere heated the air surrounding it to 44,500 degrees Fahrenheit.

July 2, 1947: an object crashed near Roswell, New Mexico.  The US Army Air Corps insisted that it was a weather balloon, but eyewitness accounts gave rise to speculation about an alien spacecraft.  That speculation persists to this day, though the US Air Force continues to disclaim it.

July 4, 1054: Chinese astronomers observed a “guest star” in and area of the sky that is now called Taurus, the Bull.  This “guest star” was actually a supernova that was as bright as Venus with a duration of 24 months.  It was reported that it could be seen in the daylight sky.   The remnant of this supernova is the Crab Nebula, M1, and can be viewed through a small telescope.

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Weekly Stargazers’ Rating: 6/28/09 – 7/4/09

Stargazer Rating | Posted by Drew
Jun 28 2009

With the Moon waxing from a late crescent (6-day moon) to nearly Full (12-day moon), the early evening will be drenched with light from the Moon.   After moonset the skies will again be suited for deep sky observing but this will not happen until the late night hours.  The Stargaze Rating for the week is fair (in the early evening) to good (in the early morning).

The Moongaze Rating is good as the terminator will be passing from the mid-eastern surface of the Moon across to the western limb.

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Planet Watch: 6/28/09 – 7/4/09

Planet Watch | Posted by Drew
Jun 28 2009

For a great website to locate the planets, go to www.nightskyinfo.com.  This site will tell you about the planets and give you a good star map to locate them (116).

Sunset Sky: (Sunset until 11 p.m.)

This week, Saturn is still high enough in the western sky to be a wonderful sight at sunset.  It will remain in the west until around Midnight, when it sets.  You should look for the flat view of the rings around Saturn, this is a fairly unusual view: once every 16 years or so.

Late Evening (11 p.m. until 4 a.m.):

The early evening sky holds my favorite planet, Jupiter.  Jupiter is a large and bright naked eye planet.  With nothing more than a pair of binoculars it easily shows its four Galilean moons and cloud belts.  Not nearly as easy to see is Neptune, which is right next to Jupiter.

Predawn Sky:  (4 a.m. until sunrise)

The early morning planets trail Jupiter and Neptune by an hour or so.  The first planet is Neptune’s twin, Uranus.  This gas giant is a naked eye planet under ideal conditions of clarity and darkness.
Later in the early morning we will see Mars and Venus rise in the eastern sky.  For a while we saw Venus first but now it Mars that rises higher in the sky.  As the week progress, we will see Mars rise earlier each week and Venus rise later, increasing the apparent distance between them.
By now we have lost Mercury to the early morning Sun’s glare.  It will be late July before we can see it again.  Only then it will be in the early evening low on the western horizon.

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Moon Watch: 6/28/09 – 7/4/09

Moon Watch | Posted by Drew
Jun 28 2009

Monday (29th), the Moon will be in First Quarter at 7:28 a.m. EDT.
Friday (3rd), the Earth is at aphelion its furthest distance from the Sun for the year (94.5 million miles) at 10 a.m. EDT
Saturday (4th), the Moon will pass 0.5 degrees north of Antares at 6 a.m. EDT.

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Satellite Watch: 6/28/09 – 7/4/09

Satellite Watch: Satellites of Magnitude 3.0 and brighter | Posted by Drew
Jun 28 2009

Sunday, June 28, 2009:
Tropical Rainforest Monitoring Mission (TRMM): 06:00 Hrs, 86Âș altitude in the NNW, rising from the W, heading to the E, magnitude 1.4.

Monday, June 29, 2009:
Tropical Rainforest Monitoring Mission (TRMM): 05:04 Hrs, 79Âș altitude in the S, rising from the WSW, heading to the E, magnitude 1.3.
Upper Atmosphere Research Satellite (UARS): 05:48 Hrs, 67Âș altitude in the NW, rising from the SW, heading to the NE, magnitude 2.5.
Lacrosse 4 Satellite: 21:42 Hrs, 49Âș altitude in the ESE, rising from the S, heading to the NE, magnitude 2.8.
Lacrosse 5 Satellite: 21:56 Hrs, 67Âș altitude in the SE, rising from the SSW, heading to the NE, magnitude 2.5.

Tuesday, June 30, 2009:
Resurs 01 Rocket Body: 05:20 Hrs, 80Âș altitude in the WNW, rising from the N, heading to the SSW, magnitude 2.8.
Tropical Rainforest Monitoring Mission (TRMM): 05:46 Hrs, 76Âș altitude in the N, rising from the W, heading to the E, magnitude 1.6.

Wednesday, July 1, 2009:
Tropical Rainforest Monitoring Mission (TRMM): 04:50 Hrs, 80Âș altitude in the N, rising from the W, heading to the E, magnitude 1.4.
GENESIS I Satellite: 04:52 Hrs, 80Âș altitude in the ESE, rising from the SSW, heading to the NNE, magnitude 2.7.
SOYUZ-TMA 14: 05:58 Hrs, 78Âș altitude in the SW, rising from the NW, heading to the SE, magnitude 1.0.
USA 129 Satellite: 22:14 Hrs, 62Âș altitude in the E, rising from the SE, heading to the N, magnitude 2.4.

Thursday, July 2, 2009:
SOYUZ-TMA 14: 05:21 Hrs, 59Âș altitude in the NE, rising from the NW, heading to the SE, magnitude 1.7.
Tropical Rainforest Monitoring Mission (TRMM): 05:32 Hrs, 83Âș altitude in the N, rising from the W, heading to the E, magnitude 1.4.

Friday, July 3, 2009:
Tropical Rainforest Monitoring Mission (TRMM): 04:36 Hrs, 77Âș altitude in the N, rising from the NNW, heading to the E, magnitude 1.4.
Lacrosse 5 Satellite: 05:37 Hrs, 86Âș altitude in the NE, rising from the NW, heading to the SE, magnitude 2.6.
Lacrosse 4 Rocket Body: 23:37 Hrs, 52Âș altitude in the NE, rising from the NE, heading to the NNE, magnitude 2.8.

Saturday, July 4, 2009:
Tropical Rainforest Monitoring Mission (TRMM): 05:18 Hrs, 71Âș altitude in the SSW, rising from the W, heading to the ESE, magnitude 1.3.
Resurs 01 Rocket Body: 05:24 Hrs, 73Âș altitude in the WNW, rising from the N, heading to the SSW, magnitude 2.8.
Envisat Satellite: 23:13 Hrs, 83Âș altitude in the ENE, rising from the SSE, heading to the N, magnitude 2.8.
Lacrosse 4 Rocket Body: 23:47 Hrs, 57Âș altitude in the WNW, rising from the W, heading to the NNE, magnitude 2.9.

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Question of the Week: Why aren’t there any green stars?

Reader Questions | Posted by Drew
Jun 14 2009

First, we need to understand that the color of light is not actually a property of light but rather how our eyes perceive the wavelengths of light energy that strikes our retina.  That may sound like a lot of mumbo-jumbo but it is an important distinction when talking about star color.

The color of a star is determined by two factors: the temperature of the star light and the sensitivity of our eyes to the various wavelengths of light.  Hotter the star, more blue the star appears.  Likewise, cooler the star, the more red the star appears.  According to star temperature and light color, the temperature that a star would have to have to produce green light is about 10,000 degrees Kelvin.  Now, there are plenty of stars with that surface temperature.  The problem comes in when we begin to talk about light color sensitivity of our eyes.

Star Colors

Star Colors

It turns out that light sensitivity of our eyes in the wavelengths of green light and red light are almost overlapping wavelength charts.  While the wavelengths of the colors are widely varied, our eyes sometimes have a hard time distinguishing them.  I am reminded about color blindness charts.  The tables I’ve seen are used to determine red / green color blindness (i.e. http://waynesword.palomar.edu/colorbl1.htm).  Getting back to star color
  If the sensitivity of red and green are nearly the same, then it follows that this means that stars that are the proper temperature to produce green light produce nearly the same amount of red light.  Evidently, this superimposed red and green light results in light that is perceived in our eyes as white.

This is seen when we look at a Temperature vs Star Color Chart.  The table of star color goes from the hottest stars to coolest stars: blue, blue/white, white, yellow/white, yellow, orange, and red (note- no green).  The green star color that one might expect in the mid-range star temperatures are not seen as green, but white.  This explanation is not intended to be a dissertation on the subject but rather a short thumbnail sketch of a more complex explanation that I encourage you to investigate further.
You can go to article by Philip Steffey in the September, 1992 issue of Sky and Telescope (p. 266), for a more detailed analysis of this event.
In the mean time, there are no green stars but your are encouraged to go out and look for them.

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Celestial Feature of the Week: Double Stars in Bootes

Celestial Feature of the Week | Posted by Drew
Jun 14 2009

An often overlooked pleasure in the night sky is the thrill of looking for beautiful “double stars.”  I suppose I need first to say that when I refer to the term “double stars,” I refer to the collection of stars that appear in multiples through a pair of binoculars or a telescope but to the naked eye appear to be only one.  These star pairs and groups may actually be association with each other or they may only be a visual binary pair, line of sight only.

Binary Stars

Binary Stars

The first double star we will observe is Izar (Epsilon Bootis).  It lies along the eastern leg of the vertex going north from Arcturus.  This star is actually a triple star system with beautiful color contrast.  You will only be able to detect two of the three stars through a small telescope.  The stars have a magnitude 2.5 and 5.0 with a separation of 2.9” of arc.  This triple star system lies about 150 light-years from Earth and is sometimes referred to as Pulcherram, which is Latin meaning “most beautiful.”

Another find double star system is Xi Bootis.  This star, along with three others, resides to the east of Arcturus.  In China, the four stars, as a group, were called Cho-t’I, the attendants of the Spring Star (Arcturus).  Xi Bootis is located directly east of Arcturus and south of Izar, forming a right triangle.  This double star is reported to be about 22 light-years from Earth.   They have a magnitude of 4.8 and 5.0 with a separation of 7” of arc.

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Today in History: 6/14/09 – 6/20/09

Space History | Posted by Drew
Jun 14 2009

June 15, 1819: John Couch Adams was born in Cornwall, England.  While at St. Johns College, Cambridge, as an undergraduate, he tried to explain the reason for orbital irregularities in the motion of Uranus.  He theorized that the irregular orbit of Uranus was due to the presence of an undiscovered planet. All of his calculations were worked out in his head before he ever wrote them down. He submitted his work to the director of the Cambridge Observatory who dismissed it. Several months later, Urbain Le Verrier submitted similar work to Johann Gottfried Galle, the director of the Berlin Observatory. Galle acted on Le Verrier’s work and became the first person to observe Neptune. After the discovery of Neptune, the director of the Cambridge Observatory pointed out that John Couch Adams had been the first to predict the presence of Neptune. After some discussion Le Verrier and Adams agreed to share the credit.

June 16, 1963: The world’s first female space traveler, Valentina Tereshkova, was launched into orbit by the Soviet Union aboard Vostok Six.  She returned to earth on 19 June.  She remains to this day the only woman to go on a solo spaceflight.

June 17, 1985: STS-51G Discovery (5) launched from Cape Canaveral (KSC). According to the NASA website, the mission included the deployment of three communications satellites, all attached to Payload Assist Module-D (PAM-D) motors: MORELOS-A, for Mexico; ARABSAT-A, for Arab Satellite Communications Organization; and TELSTAR-3D, for AT&T.  Also flown with the mission: deployable/retrievable Shuttle Pointed Autonomous Research Tool for Astronomy (SPARTAN-1); six Get Away Special canisters; Strategic Defense Initiative experiment called the High Precision Tracking Experiment (HPTE); a materials processing furnace called Automated Directional Solidification Furnace (ADSF); and two French biomedical experiments.

Telstar 3-D communications satellite deploying from Discovery's payload bay

Telstar 3-D communications satellite deploying from Discovery's payload bay

June 18, 1983: Astronaut Sally Ride became America’s first woman in space as she and four colleagues blasted off aboard the space shuttle Challenger, STS-7.  This was the second flight for the Orbiter Challenger and the first mission with a 5-person crew.  The shuttle coasted to a safe landing at Edwards Air Force Base, California, on June 24th.  She was accompanied by Captain Robert L. Crippen (spacecraft commander), Captain Frederick H. Hauck (pilot), and fellow mission specialists Colonel John M. Fabian and Dr. Norman E. Thagard.

Sally Ride

Sally Ride

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