Archive for July, 2009

Question of the Week: I have had to “aim” my satellite dish to a satellite for my TV to work. If satellites are in orbit around the Earth, how does satellite TV work?

Reader Questions | Posted by Drew
Jul 26 2009

This is a great question and its answer is not real obvious.  The three assumptions that are made in asking this question are true.  First, in order for a satellite dish to work and have TV reception, the dish must be pointed directly at a satellite.  Secondly, satellites orbit the Earth at a velocity that is specific to their altitude.  Thirdly, there is something special about a satellite that does not appear to move in the sky while at the same time orbits the Earth.

Motion in space is a tricky thing, to say the least; especially when you are talking about orbital velocities and altitude.   There is a paradox when talking about altitude, velocity, and apparent velocity.  The fact is, the faster you go, the higher will be your orbit, but the longer it will take you to orbit the Earth.  So, if you want to go around the Earth faster, you slow down.  If you want to slow your apparent ground speed, you increase your actual velocity.  The reason for this is, as you increase your actual velocity, your altitude from Earth increases and the distance around the Earth is greatly increased.  Since the orbit is higher and distance is much longer, it takes longer to make the orbit.  Therefore, higher the orbit, longer it takes.

To simplify the discussion, I am assuming the satellite is above the equator and is moving in the same direction as the Earth’s rotation.

Now, if we look at the orbit of a satellite and look at the spinning of the Earth, we find something interesting.  Low orbit satellites appear to move forward.  Extremely high orbit satellites appear to move backward because the Earth spins underneath them.  There is a magic altitude where the satellite orbits the Earth at the same rate that the Earth spins on its axis.  This is the geostationary orbit.  Communication satellites are placed in this geostationary orbit so the antenna dishes can be pointed to them and they appear to, as their name suggests, remain stationary.

There is an interesting website that you will want to read on this: http://en.wikipedia.org/wiki/Geostationary_orbit.

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Celestial Feature of the Week: Southern Delta Aquarid

Celestial Feature of the Week | Posted by Drew
Jul 26 2009

The Southern Delta Aquarid meteor shower peaks on Monday, July 27th, although you can view these meteors all week long.  This meteor shower has two branches (northern and southern components) that peak at different times.  The southern branch or component is the most active of the two with a zenithal hourly rate (ZHR) of around 20 meteors per hour.  This is under ideal conditions with the “radiant” at the zenith under very dark skies.

It is a good week for the shower’s peak because the Moon will be First Quarter.  This means that the early morning viewing of this shower will be unhampered by the Moon’s glare.   The one promising thing about the Southern Delta Aquarid meteor shower is, it represents the preamble to the famous August Perseid meteor shower (one of the best showers of the year).  We will be discussing the Perseid shower in the next issue or two.

If you wish to observe a Southern Delta Quarid meteor, your best bet is to get out early in the morning, before sunrise, and observe while you are facing in a southerly direction.  These meteors tend to be very faint so you will need to be in a fairly dark location while observing.
You do not need a telescope or pair of binoculars when observing meteors but in this case you might want to bring one along so you can do some deep sky observing as you look for meteors.

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Today in History: 7/26/09 – 8/1/09

Space History | Posted by Drew
Jul 26 2009

July 26, 1971: Apollo 15 launched.  It was the fourth lunar landing mission and the first mission to use a lunar rover.

July 28, 1851: First recorded photograph of a solar eclipse was taken.

July 29, 1958: President Eisenhower signed the National Aeronautics and Space Administration Act, creating NASA.

July 31, 1964: The U.S. space probe Range 7 transmitted photos of the moon’s surface.  The Ranger program was first U.S. attempt to take close-up images of the Lunar surface. The Ranger spacecraft were designed to fly straight down towards the Moon’s surface and send images back until the moment of impact. This is the first close-up picture of the Moon taken by Ranger 7 about 17 seconds before impact.  This image has a resolution of .5 meters.

July 31, 1971:  Apollo 15 astronauts Scott and Irwin drive the first lunar roving vehicle (LRV) on the Moon.  The LRV carried two astronauts, tools, scientific equipment, communications gear, and lunar samples.  The four-wheel, lightweight vehicle greatly extended the lunar area that could be explored by humans. The LRV could be operated by either astronaut.  To get the LRV into the spacecraft it must be folded up into a very small package.  After landing on the Moon, the LRV unfolded itself from its stowed configuration and deployed itself onto the lunar surface in its operational configuration, all with minimum assistance from the astronauts.

August 1, 1818: Maria Mitchell was born on the island of Nantucket in Massachusetts. She became the first acknowledged woman astronomer in the United States. In 1848, Maria became the first woman to discover a comet and in that same year she became the first women member of the American Academy of Arts and Sciences, and later became a fellow of the society. She served as professor of astronomy at Vassar College from 1865 to 1888. In 1875 Mitchell was elected president of the American Association for the Advancement of Women.  Maria Mitchell died on June 28, 1889.

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Weekly Stargazers’ Rating: 7/26/09 – 8/1/09

Weekly Stargazers’ Rating | Posted by Drew
Jul 26 2009

With the First Quarter Moon occurring on Tuesday, the Moon will be setting a little later each evening and will be getting larger and brighter.  The stargazing will be best early in the week and later in the evening.  The Stargaze Rating for the week is fine, especially in the early morning.

Moongazers will enjoy watching the terminator move across the surface from the midline toward the western limb providing good crater relief.  The Moongaze rating is excellent for the week.

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Planet Watch: 7/26/09 – 8/1/09

Planet Watch | Posted by Drew
Jul 26 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.)
The early evening sky still holds the ringed planet, Saturn.  This is an especially interesting time to view Saturn because the ring plane is nearly facing Earth.  As we look at Saturn you can see that the rings are very thin and less descript.  Although, during this time, we can’t see the rings as well, it is easier for us to see the moons that orbit the planet.

Take note, if you want to see Saturn, you have about 6 weeks before it descends into the sunset sky.  Look low on the western horizon for Saturn as soon as the skies get dark enough for some stars to become visible.

You should also be able to see Mercury low on the western horizon this week as well.  It will be very faint and small but clearly not star like in appearance.  Give it a try.
Late Evening (11 p.m. until 4 a.m.):

During this time of the evening, Jupiter will be fairly high in the southeastern sky.  It is very bright and should be easy to spot with the naked eye.  Jupiter is snuggly positioned between Capricornus and Aquarius.  Looking at Jupiter through a small telescope or pair of binoculars, you will see Jupiter’s cloud belts and four Galilean moons.
Right next to Jupiter you will see the gas giant, Neptune.  In order to spot this one, you will need a small telescope or pair of binoculars.  So when you are finished looking at the Galilean moons, pan your instrument a couple degrees eastward to find Neptune.

Predawn Sky:  (4 a.m. until sunrise)
The order of the predawn planets is Uranus, Mars, and Venus.  Neptune’s twin, Uranus, is much brighter and easier to observe.  Look about 15 degrees east of Jupiter for this planet.  You can see Uranus with your naked eye if you have good clear, dark skies, and know where to look.
The next planet is Mars, the Red Planet.  It is located in Taurus, the Bull.  It is fairly bright and with its amber hue, should be fairly easy to identify.  The only problem you may have is mistaking if for Aldebaran, the red star in Taurus.
Finally, we will spot the easiest planet of the all, Venus, Earth’s Twin.  Looking low on the southeastern horizon, you will spot a very bright light.  That will be Venus.  It is so bright because of its reflective cloud layers.  They are so dense and thick that we have to us x-ray imaging to get a view of the surface of Venus.

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Moon Watch: 7/26/09 – 8/1/09

Moon Watch | Posted by Drew
Jul 26 2009

Tuesday (28th), the Moon will be in First Quarter at 6:00 p.m. EDT.

Friday (31st), the Moon will pass 0.5 degrees north of Antares at noon EDT.

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Question of the Week: Why don’t we see more Solar Eclipses?

Rome Star Gazers Party! | Posted by Drew on Behalf of Dr. Bob.
Jul 19 2009

This is an interesting question because under a few different conditions, we might be able to see a solar and a lunar eclipse every month.  The reason the question has been raised is probably because we have a total solar eclipse on July 22nd.  The eclipse this week will be seen in parts of India, China, and the Pacific Ocean.  It has been reported that because of where it will cross the surface of the Earth, more than a billion people will be able to witness this event, depending on the weather of course.

A Total Eclipse Over Africa by Cees Bassa

A Total Eclipse Over Africa by Cees Bassa

Remember that a solar eclipse is when the Moon’s shadow falls on the Earth and blocks the sunlight from reaching us.  As things are now, we have to be at the correct location on Earth for this event to be seen because the shadow of the Moon covers only a very small portion of the Earth at a time.   That is why people travel across the planet to be in the path of the Moon’s shadow to experience the solar eclipse.

Now, a lunar eclipse is when the Earth’s shadow falls on the Moon.  The Earth is much larger than the Moon so the Earth’s shadow is much larger than the Moon and can actually completely cover it a couple times over.  When a lunar eclipse occurs, everyone on Earth that can see the Moon can see the eclipse.

For either a solar or lunar eclipse to occur, the Earth, Moon and Sun must be lined up.  Each month there is a partial alignment which occurs but because their orbits are not in the exact same plane, the Moon and Earth are too far north or south for the eclipse to take place.  Under ideal conditions an eclipse would occur each month.  As it is, we have to observe them when they happen.

In review, the alignment for a solar eclipse is fairly rare and it is even rarer that we are in the correct location on Earth to observe the eclipse when it does occur.  This is evidenced by the fact that in order to see the Solar Eclipse on the 22nd we will have to travel half way around the world.  For these reasons, it is not common to see a solar eclipse.

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Celestial Feature of the Week: Globular Clusters

Celestial Feature of the Week | Posted by Drew on Behalf of Dr. Bob.
Jul 19 2009

One of my favorite type of objects is a globular cluster.  There is something about looking at a large ball of stars and imagining just the shear numbers and distances from us that captivates my mind.   It also is a pretty sight to behold through a pair of binoculars or small telescope.

This week we have three beautiful globular clusters to view along our meridian around 9:00 p.m. EDT.  The first is M13, the Great Hercules Cluster.  I guess this is my favorite because I discovered it by panning the sky.  Afterward I learned what it was.  To locate this object, find Hercules and look in the middle of the western edge of the keystone.  It is easily seen through a pair of binoculars as a large cloudy ball (large is a relative term).  By its size and appearance, it is clearly not a star or a planet.

M13: The Great Globular Cluster in Hercules

M13: The Great Globular Cluster in Hercules

The next two globular clusters are in the southern sky, in Scorpius: M4 and M80.   Many like M4 more than M13 but that is a matter of preference.  To find M4, look for the brightest star in Scorpius, Antares.  It is a nice red star so you should be able to find it nicely.  M4 is just 1 degree to the west of Antares.  You will need to look at it through a pair of binoculars to see it.

Hubble Space Telescope Finds Stellar Graveyard in M4

Hubble Space Telescope Finds Stellar Graveyard in M4

M80 is a little smaller than M4.  To find this one, look north-northwest of M4 by about 5 degrees.  You will also need a pair of binoculars to view this one.

Hubble Images a Swarm of Ancient Stars in M80

Hubble Images a Swarm of Ancient Stars in M80

Although M4 appears larger and brighter than M80, in reality it is 4.5 times farther away than M4 so M80 is actually larger and brighter than it.

These three globular clusters are fairly easy to locate and observe.  Go out on a nice clear night and view these wonders.   They will capture your imagination.

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Today in History: 7/19/09 – 7/25/09

Space History | Posted by Drew on Behalf of Dr. Bob.
Jul 19 2009

July 19, 1985; Christa McAuliffe, of New Hampshire, was chosen to be the first schoolteacher to ride aboard the space shuttle.  Years later, she was among the seven who perished when the Challenger exploded shortly after takeoff.

Christa McAuliffe

Christa McAuliffe

July 19, 1969: Apollo XI and its astronauts, Neil Armstrong, Edwmin “Buzz” Aldrin and Michael Collins, went into orbit around the Moon.

July 20, 1969: Apollo XI landed, and Neil Armstrong and “Buzz” Aldrin became the first humans to walk on the surface of the Moon.

Message left by Apollo 11

Message left by Apollo 11

July 20, 1976: the U.S. Viking I robot spacecraft made a successful first-ever landing on Mars.

Viking I Spacecraft in Cleanroom

Viking I Spacecraft in Cleanroom

July 20, 1999: The Liberty Bell was hoisted out of the Atlantic Ocean 38 years after it flooded and sank.  Once the recovery ship, Ocean Project, had Liberty Bell 7 on deck it headed back to land where it docked at Port Canaveral, Florida (see July 21, 1961).

July 21, 1961: The Mercury capsule, Liberty Bell 7, with astronaut Guss Grissom made its 15 minute suborbital flight.  In the recovery attempt the capsule filled with water and sank to a depth of 15,000 feet in the Atlantic Ocean, 3,000 feet deeper than the wreck of the Titanic.

Liberty Bell 7

Liberty Bell 7

July 22, 1784: German astronomer Friedrich Bessel was born.  Bessel is credited with being the first to use parallax in calculating the distance to a star.  In 1838 he calculated that 61 Cygni had a parallax of 0.314 arcseconds, indicating that it was 3 parsecs away.  A parsec is the distance from Earth an object is with a parallax of 1 (one) arcsecond.   That distance is 3.262 light-years.

July 22, 1994: The last fragment of Comet SL-9 impacts Jupiter. From July 16 through July 22, 1994, pieces of an object designated as Comet P/Shoemaker-Levy 9 collided with Jupiter. This is the first collision of two solar system bodies ever to be observed, and the effects of the comet impacts on Jupiter’s atmosphere have been simply spectacular and beyond expectations. Comet Shoemaker-Levy 9 consisted of at least 21 identifiable fragments with diameters estimated at up to 2 kilometers.

Shoemaker-Levy 9 on the path to Jupiter

Shoemaker-Levy 9 on the path to Jupiter

July 24, 1950: The first rocket was launched from Cape Canaveral.

The Bumper V-2 was the first missile launched at Cape Canaveral on July 24, 1950.

The Bumper V-2 was the first missile launched at Cape Canaveral on July 24, 1950.

July 24, 1975: Apollo-Soyuz crew returned to Earth and was the last splashdown recovery.  All other successful recoveries were soft landings via Space Shuttles.

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Weekly Stargazers’ Rating: 7/19/09 – 7/25/09

Weekly Stargazers’ Rating | Posted by Drew on Behalf of Dr. Bob.
Jul 19 2009

The Moon will be New on Tuesday so the Stargaze Rating is excellent for the whole week.  Moon enthusiasts can enjoy a waning crescent Moon early in the week and a waxing crescent Moon later in the week.  This will give them the opportunity to view the craters along each limb of the Moon as the terminator crosses them.

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