Archive for January, 2009

Telescope Corner: What is the magnification of my telescope?

Telescope Corner | Posted by Drew on Behalf of Dr. Bob.
Jan 25 2009

Determining the magnification of a telescope is not difficult although it does take a little division.  Every telescope has a focal length that is prominently written on the side of the telescope.  The common department store refracting telescopes have a focal length of 1,200 millimeters (mms).  Some of your Newtonian reflectors have similar focal lengths.  When we say that the focal length of a telescope is 1,200 mms, we are saying that the primary lens or mirror of the telescope has that focal length.  Often this lens or mirror is referred to as the “objective.”

When you buy at telescope you also get some eyepieces that go along with the telescope.  These eyepieces attach to the end or side of the telescope and they are what you look through to see celestial objects.  Each of these eyepieces have a specific focal length engraved on them as well.

To determine the magnification or power of your telescope, take the focal length of the objective and divide it by the focal length of the eyepiece.  Say the telescope objective focal length is 1,200 mms and you use a 12 mm eyepiece.  You take 1,200 mms and divide by 12 mms.  This gives you a 100 X magnification.  Say you change the eyepiece to a 24 mm eyepiece.  By doing so, you change the magnification or power of the telescope from 100 X to 50 X (1,200 mms / 24 mms).    Now you change to a 6 mm eyepiece.  The magnification then becomes (1,200 mms/ 6 mms = 200 X), twice as powerful!

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Why is Venus so bright?

Fun Space Facts | Posted by Drew on Behalf of Dr. Bob.
Jan 25 2009

Venus: Why So Bright?

Venus: Why So Bright?

I’ve noticed, as most folks have, that Venus is very bright.  Why is Venus so bright?

Venus is one of the brightest objects in the night sky. Venus can often be seen within a few hours after sunset or before sunrise as the brightest object in the sky (other than the moon). It looks like a very bright star. It is for this reason that it is often called the Morning Star or Evening Star.

When you “Google” the question, “Why is Venus so bright?”  The answer you always seem to get is: Venus is the brightest planet because it has the highest surface reflectivity.  That is to say, its thick clouds reflect most of the sunlight that reaches it, about 70% reflects back into space.  The other factor that is often mentioned is that Venus is the closest planet to Earth.  If Venus were deep in our solar system, then the reflectivity would be overcome by the remote distance.

As I ponder this question, I wonder if the size of the planet and the distance it is from the Sun and Earth may also have an effect on its brightness in our night sky.  The answer is, of course they do.  If the reflectivity of all of the planets were identical then the distance from the Sun and Earth and their relative size would definitely affect the planet’s relative brightness.

I created a spreadsheet which listed each planet and its relative distance to the Sun and its relative diameter (see attached).  We know that the surface area of a circle with a diameter of “d” is equal to Pi times ½ d squared: (area = π ½ d2).  Therefore, everything else being equal (reflectivity and distance), the larger the planet, the brighter it would appear.  In fact, if it had twice the diameter, it would reflect four times the light or 2 squared.

Now we have the relative size of the planets computed for brightness, we need to figure in the relative distances from the Sun to the planet and then the planet to the Earth.  This is where we must consider the way light radiates out from an object.  In Physics we learn the light radiates out in all directions, in a sphere.   Calculating the area of a sphere at a certain radius “r” we find that it is equal to four times pi times the radius squared (area = 4 π r2).  This appears similar to our surface area formula but this time, greater the radius (distance from the sun) the dimmer the planet will be by squared the radius ratio.  That is to say, if a planet (A) is three times further away than planet (B), planet A will be one-ninth (1/9) as bright as planet B.

Given this notion, I took the relative distances from the planet to the sun and calculated the relative sunlight that struck the planet’s surface.  Taking into consideration the planets relative size, I calculated the amount of sunlight that would be reflected from its surface; the further out the planet, less sunlight that would strike it by the relative distance squared.  Next I took the amount of sunlight reflected from the planet and calculated the amount that would head to Earth, using a mean relative distance from the planet to the Earth.  This relative distance will also follow the inverse squared law with respect to the amount of light that would reach Earth.

When all was said and done, I found that Venus is the brightest planet when only considering distance and disc diameter, ignoring relative reflectivity.  Roughly figuring, I calculated that the brightest would be Venus by 8 times brighter than Mercury.  Mars would be third and Jupiter would be fourth.  But as we know, the reflectivity of the planet’s surface or atmosphere has a huge effect as well.  In conclusion, Venus is the brightest planet because of its reflectivity, size and relative distance from the sun and earth.

Comment: If anyone thinks they see an error in my logic or analysis, I would love to hear your comments and thoughts – please be specific.

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Planet Watch: 1/25/09 – 1/31/09

Planet Watch | Posted by Drew on Behalf of Dr. Bob.
Jan 25 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.

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

Venus is still high in the western sky and very easy to observe.  It is in third quarter phase at this time.  You can see it phase if you look at it through a small telescope or maybe even through a pair of binoculars.  We will be able to observe Venus in the evening sky for the next six (6) or seven (7) weeks.  On a point of interest: Venus will pass 1.4 degrees north of Uranus at 11 a.m. EST on Friday, January 23rd.
Neptune is too close to the sunset glare to be viewed this week and for several weeks.
Uranus is still in a good place if you have a good low western horizon at sunset.  This week may be a great time to spot the brighter of the gaseous twins (Neptune and Uranus) because the Moon can serve as a pointer for you.  Look at Moon Watch for Thursday (29th).

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

Not much to see in the late evening and early morning this week.  If this is your stargazing time of the night, prevail because it won’t be long before Saturn will be gracing the sky at this time of night.

Predawn Sky:  (4 a.m. until sunrise)

The predawn hour is the best time to view Saturn.  Look high in the south, almost overhead for the Ringed Planet.  Saturn is between Virgo and Leo.  You will need to look carefully because the rings are not as pronounced now as they have been.  The position of Saturn in its orbit around the sun is approaching the equivalent to the Earth’s equinox.  In this position we are looking into the edge of the rings, making it difficult to see them.  Mars is still too low on the eastern horizon to be observed.  It will be later in the year before we will see much of the Red Planet.
Jupiter and Mercury are also into the sun’s glare and will soon emerge into the predawn sky.

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Moon Watch: 1/25/09 – 1/31/09

Moon Watch | Posted by Drew on Behalf of Dr. Bob.
Jan 25 2009

•    Monday (26th), the Moon is New and there will be a annular solar eclipse.  The eclipse will take place in Southern Africa and Southeast Asia.
•    Tuesday (27th), the Moon passes 1.8 degrees north of Neptune at 1 p.m. EST.
•    Thursday (29th), the Moon passes 5 degrees north of Uranus at 8 p.m. EST.  This may be a good time to view Uranus.
•    Friday (30th), the Moon passes 3 degrees north of Venus at 7 a.m. EST.  This is a great time to try to see Venus during daylight hours with your naked eye.  You will easily be able to see it with a pair of binoculars.

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Celestial Feature of the Week: Crab Nebula M1

Celestial Feature of the Week | Posted by Drew on Behalf of Dr. Bob.
Jan 25 2009

The Crab Nebula, Messier 1 (M1, NGC 1952), is the most famous and conspicuous known supernova remnant, the expanding cloud of gas created in the explosion of a star as supernova which was observed in the year 1054 AD. It shines as a nebula of magnitude 8.4 near the southern “horn” of Taurus, the Bull.

Celestial Feature of the Week: Crab Nebula M1

Celestial Feature of the Week: Crab Nebula M1

The supernova was noted on July 4, 1054 A.D. by Chinese astronomers as a new or “guest star,” and was about four times brighter than Venus, or about magnitude -6. According to the records, it was visible in daylight for 23 days, and 653 days to the naked eye in the night sky. It was probably also recorded by Anasazi Indian artists (in present-day Arizona and New Mexico), as findings in Navaho Canyon and White Mesa (both Arizona) indicate; there’s a review of the research on line at: http://www.astronomy.pomona.edu/archeo/outside/chaco/nebula.html.

More recently the nova remnant was discovered in 1731 by British amateur astronomer John Bevis.  Bevis added it to his sky atlas, Uranographia Britannica.  Independently Charles Messier found the nebulosity on August 28, 1758, when he was looking for comet Halley on its first predicted return, and first thought it was a comet. Of course, he soon recognized that it had no apparent proper motion, and cataloged it on September 12, 1758: thus its designation M1!

Crab Nebula as seen from Spitzer

Crab Nebula as seen from Spitzer

To see this beautiful object, look close to your meridian at 9:00 p.m. at Taurus, the Bull.  From the “red eye”, Aldebaran, look up the southern horn, the Crab Nebula will be just 1 degree northwest of the horn star, Zeta Tauri.  It will take good dark skies and a telescope to see it.  On a note, I was looking on and off for about a year before I first spotted this wonder.  If you have a 6” telescope of larger, I am sure you will spot it more readily than I.  I promise that we will look for it at our next star party on February 21st, so be sure to come out and join us.

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This Week in History 1/25/09 – 1/31/09

Space History | Posted by Drew on Behalf of Dr. Bob.
Jan 25 2009

Joseph Lagrange

Joseph Lagrange

January 25, 1732:

Joseph Lagrange was born in France.  He was a French astronomer, skilled mathematician and observer and “popularizer” of astronomy, who became director of Paris Observatory in 1768.

January 25, 1959:

American Airlines opened the jet age in the US with the first scheduled transcontinental flight of a Boeing 707.

Ranger 3

Ranger 3

January 26, 1962:

The US launched Ranger 3 to land scientific instruments on the moon, but the probe missed the target by some 22,000 miles.  (Must have given the first astronauts scheduled to make that trip a world of confidence).

January 27, 1967:

Astronauts Virgil “Gus” Grissom, Edward H. White and Roger B. Chaffee died in a flash fire during a test aboard the Apollo One spacecraft at Cape Kennedy (Canaveral), Florida.

January 28, 1611:

Johannes Hevelis was born in Danzig (modern Gdansk, Poland).  He was the first astronomer to describe the bright features of the solar photosphere known as faculae, which he found were connected with the formation of sunspots.  Hevelis was the last major astronomer not to use a telescope.

January 28, 1986:

The space shuttle Challenger exploded 73 seconds after liftoff from Cape Canaveral.  Of the seven courageous astronauts who perished in the accident, the one that many remember the most is Sharon Christa McAuliffe, the first teacher to fly in space. She was selected from among more than 11,000 applicants from the education profession for entrance into the astronaut ranks.

The Brave Crew

The Brave Crew

January 30, 1964:

The US launched Ranger 6, an unmanned spacecraft carrying television cameras, designed to crash land on the Moon.

Explorer I Design Team

Explorer I Design Team

January 31, 1958:

The US entered the Space Age with its first successful launch of a satellite into orbit, Explorer 1. Explorer-I, officially known as Satellite 1958 Alpha, was the first United States earth satellite and was sent aloft as part of the United States program for the International Geophysical Year 1957-1958. It was designed and built by the Jet Propulsion Laboratory (JPL) of the California Institute of Technology. The satellite was launched from Cape Canaveral (now Cape Kennedy) in Florida at 10:48 P.M. EST on 31 January 1958 by the Jupiter-C vehicle–a special modification of the Redstone ballistic missile–that was designed, built, and launched by the Army Ballistic Missile Agency (ABMA). The Jupiter-C has its origins in the United States Army’s Project Orbiter in 1954. The project was canceled in 1955, however when the decision was made to proceed with Project Vanguard. Following the launch of the Soviet Sputnik I on 4 October 1957, ABMA was directed to proceed with the launching of a satellite using the Jupiter-C.

January 31, 1971:

Astronauts Alan B. Shepard Jr. (commander), Stuart A. Roosa (CM pilot), Edgar D. Mitchell (LM pilot) blasted off aboard Apollo 14 (Command Module, Kitty Hawk and Lunar Module, Antares) on a mission to the Moon.

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Weekly Stargazers’ Rating 1/25/09 – 1/31/09

Weekly Stargazers’ Rating | Posted by Drew on Behalf of Dr. Bob.
Jan 25 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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Satellite Watch for 1/25/09 – 1/31/09

Satellite Watch: Satellites of Magnitude 3.0 and brighter | Posted by Drew on Behalf of Dr. Bob.
Jan 25 2009
The Hubble Space Telescope

The Hubble Space Telescope

Sunday, January 25, 2009:
Lacrosse 5 Satellite: 07:07 Hrs, 56Âş altitude in the SW, rising from the NW, heading to the SSE, magnitude 2.8.
Hubble Space Telescope (HST): 18:51 Hrs, 38Âş altitude in the S, rising from the WSW, heading to the ESE, magnitude 2.8.
Lacrosse 4 Satellite: 20:03 Hrs, 54Âş altitude in the N, rising from the NNW, heading to the N, magnitude 2.9.

Monday, January 26, 2009:
Helios 1B Satellite: 06:06 Hrs, 84Âş altitude in the E, rising from the NNE, heading to the SSW, magnitude 2.9.
Lacrosse 5 Satellite: 06:13 Hrs, 72Âş altitude in the NE, rising from the NNW, heading to the SE, magnitude 2.7.
Lacrosse 2 Satellite: 06:24 Hrs, 60Âş altitude in the WSW, rising from the NW, heading to the S, magnitude 2.5.
Hubble Space Telescope (HST): 18:49 Hrs, 38Âş altitude in the S, rising from the WSW, heading to the ESE, magnitude 2.8.

Tuesday, January 27, 2009:
Lacrosse 4 Satellite: 19:36 Hrs, 71Âş altitude in the ENE, rising from the NNW, heading to the SSE, magnitude 2.5.
Upper Atmosphere Research Satellite (UARS): 19:53 Hrs, 61Âş altitude in the WSW, rising from the NW, heading to the WSW, magnitude 2.7.

Wednesday, January 28, 2009:
Lacrosse 2 Satellite: 05:33 Hrs, 70Âş altitude in the ESE, rising from the ESE, heading to the SSE, magnitude 2.7.
Lacrosse 5 Satellite: 06:06 Hrs, 62Âş altitude in the WSW, rising from the WNW, heading to the SSE, magnitude 2.5.
Lacrosse 3 Satellite: 07:13 Hrs, 77Âş altitude in the SE, rising from the SSW, heading to the NE, magnitude 2.8.
Upper Atmosphere Research Satellite (UARS): 19:01 Hrs, 52Âş altitude in the NE, rising from the NNW, heading to the SE, magnitude 2.4.
Lacrosse 2 Satellite: 19:42 Hrs, 79Âş altitude in the WNW, rising from the SSW, heading to the NNE, magnitude 2.6.

Thursday, January 29, 2009:
Okean O Rocket (Tumbling Rocket Body): 06:19 Hrs., 62Âş altitude in the WNW, rising from the N, heading to the SSW, magnitude 2.8.
Lacrosse 4 Satellite: 19:08 Hrs, 73Âş altitude in the ENE, rising from the NNW, heading to the SSE, magnitude 2.6.

Friday, January 30, 2009:
Lacrosse 3 Satellite: 06:30 Hrs, 69Âş altitude in the SE, rising from the SSW, heading to the NE, magnitude 2.9.
Tropical Rainforest Monitoring Mission (TRMM): 07:04 Hrs, 42Âş altitude in the SSE, rising from the SW, heading to the E, magnitude 2.6.
Lacrosse 2 Satellite: 18:52 Hrs, 59Âş altitude in the ESE, rising from the S, heading to the NNE, magnitude 2.6.
Lacrosse 5 Satellite: 20:22 Hrs, 59Âş altitude in the SSW, rising from the SW, heading to the SSW, magnitude 2.9.

Saturday, January 31, 2009:
Helios 1B Satellite: 06:21 Hrs, 65Âş altitude in the WNW, rising from the N, heading to the SSW, magnitude 2.8.
Lacrosse 3 Satellite: 06:59 Hrs, 44Âş altitude in the NW, rising from the WSW, heading to the NNE, magnitude 2.9.
Lacrosse 4 Satellite: 18:40 Hrs, 74Âş altitude in the ENE, rising from the NNW, heading to the SSE, magnitude 2.6.

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Do the moons around planets interact in anyway?

Fun Space Facts | Posted by Drew on Behalf of Dr. Bob.
Jan 18 2009

To put is another way: do they have an effect on each other’s orbits?

Last week, we learned that it is common for moons to become “tidal locked” with their parent planet and rotate on their axis at the same rate they orbit the planet.  As such, they always show the same surface to the planet.
In addition to being tidally locked to the parent planet, many moons become locked to each other.  When this happens, the moons begin to orbit the parent planet in a resonance or cyclical pattern.

The closest three of the Galilean moons of Jupiter are an example of this resonance pattern: Io, Europa, and Ganymede.  The three moons are in a 1:2:4 resonance of each other, respectively.  That means, that Ganymede takes exactly 4 times longer to orbit Jupiter than Io and Eurpoa takes twice as long as Io to orbit the planet.
Furthermore, this resonance pattern is not unique in our solar system.  The three pairs of moons around Saturn (Mimas-Tethys, Enceladus-Dione and Titan-Hyperion) interact gravitationally in such a way as to maintain stable relationships between their orbits.  The period of Mimas’ orbit is exactly half that of Tethys, they are thus said to be in a 1:2 resonance.  The orbits of Enceladus-Dione are also 1:2 and the Titan-Hyperion pair are in a 3:4 resonance.

With the tidal locking and resonance of moons, it is interesting to note how “our” understand of the heavens changes.  When each of us first began to look into the night sky, all seem peaceful and static.  Then we began to notice that the skies change.  Everthing seemed to be erratic and random.  The more we studied and observed, the more we begin to detect regular patterns and see that, frequently, there is a nice dynamic action going on in the heavens; that there seems to be some kind of plan unfolding.

One moon is locked, the other is not!

One moon is locked, the other is not!

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Planet Watch 1/18/09 – 1/24/09

Planet Watch | Posted by Drew on Behalf of Dr. Bob.
Jan 18 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.

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

Mercury is zooming between the Earth and Sun as we speak.  By the first of February, it will be visible again in the early mornings in the east.

Venus, is still high in the western sky and very easy to observe.  It is in third quarter phase at this time.  You can see it phase if you look at it through a small telescope or maybe even through a pair of binoculars.  We will be able to observe Venus in the evening sky for the next six (6) or seven (7) weeks.  On a point of interest: Venus will pass 1.4 degrees north of Uranus at 11 a.m. EST on Friday, January 23rd.

Jupiter is in conjunction with the Sun on January 24th so it will not be visible again until it pops up in the early morning near the end of February, ’09.

Neptune and Uranus are low in the west and will set by 6:45 p.m. and 9:15 p.m respectively.  It will take good clear dark skies for you to spot these two gas giants.  The best time to observe these planets will be next fall when they are high in the early evening skies.

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

Saturn is still the only planet visible during this hour of the evening.  The best time to view the Ringed Planet will be just before sunrise.

Predawn Sky:  (4 a.m. until sunrise)

This time of day is the best time to observe Saturn.   Right now, is a wonderful time to try to spot Saturn because of its orientation to Earth.  The rings are almost invisible to us now.  It makes for quite a sight for those who are accustomed to seeing Saturn’s rings.

The Red Planet, Mars, is low on the eastern horizon and is not very exciting to observe.  At a magnitude 1.3, it is fairly dim, small, and low on the horizon to be much of a view.  As this year progresses, Mars will begin to climb into the early morning, predawn sky and give a better accounting for itself.  But, for now, if you must see it, look low in the eastern, pre-sunrise sky and enjoy.

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