Saturn at Opposition

   Saturday May 23rd the outer planet Saturn reaches its orbital position known as opposition. This is a position which has the Earth centered between the outer planet and the Sun. Picture the arrangement with the Moon at full phase; Sun – Earth – Moon, and that is similar to the arrangement for Saturn at opposition; Sun – Earth – Saturn.

   Currently Saturn is just past opposition and so it rises around local time for sunset and is visible all night.

   
   
   
   

Caution: Objects viewed with an optical aid are further than they appear.
Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Sun Not in Gemini

may-view-from-earth-astrology  According to the pseudoscience of astrology the Sun enters the constellation of the Gemini Twins on Thursday 21 May at 9 UT (4 am CDT). When in fact the actual position of the Sun on this date is still within the boundary of the constellation of Taurus the Bull, as this graphic and the banner graphic show.

   Read a little more about how astrology has the Sun incorrectly placed in a previous blog, and in another blog discussing the effects of precession.
   
   
   
   
   
   
Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Which Way is North? Part 3

The Magnetic Compass
compass   A compass used for navigation is essentially a magnetized needle or bar mounted on a point so that it may freely pivot or swing around in any horizontal direction. In the Northern Hemisphere, the north-seeking end of the needle swings around to align itself parallel with a magnetic line of force, and in doing so, points toward the north magnetic pole. Use the link “Magnetic Effects in Space” in the Internet Resources below to watch astronaut/scientist Owen Garriott on a Skylab mission use a bar magnet to demonstrate the Earth’s magnetic field and lines of force.
   Because the north magnetic pole is not located where the true North Pole (geographic) is located, an adjustment called magnetic declination is made. The magnetic declination is the horizontal angle difference between geographic north and magnetic north. Using the magnetic-field calculator at the NOAA website (see Internet Resources below), you can easily determine the magnetic declination for your location, or any other location on Earth, for that matter. By comparing different locations and dates it becomes apparent that the angle for declination not only varies daily as the north magnetic pole migrates, but there is also a difference in magnetic declination based on both latitude and longitude. For example, at the latitude and longitude of Cambridge Bay, the magnetic declination is 8.07º; using the coordinates for Washington, DC, 39º N, 77º W, the magnetic declination is -10º51’. Negative magnetic declination values indicate that the north magnetic pole is to the west of the location, while positive values have the magnetic pole to the east of the location. From the nation’s capital, the north magnetic pole is toward the northwest, while from Cambridge Bay it would be to the northeast.

   Use this link to see a list of magnetic pole locations from 1590 through 2015 at the NOAA web site.
   Using the years above and this link to see an interactive world map where you may set the date to see the lines of magnetic declination for that time period.

compass   As previously described, a compass has a freely spinning needle balanced on the point from which it spins. When held flat in one’s hand, the needle quickly swings back and forth as it aligns itself with the magnetic lines of force. At lower latitudes, such as those within the continental United States, the compass needle mostly swings left or right as it aligns parallel with the magnetic field and lines of force. As one approaches the magnetic pole, the needle is still parallel with the magnetic lines of force and responding by swinging left or right. However, near the poles, the angle of the magnetic lines of force, with respect to the Earth’s surface, are now approaching vertical; as a result, the compass needle is pulled downward, rather than moving side to side, as would be the case at lower latitudes away from the magnetic pole. In effect, the downward pull on the needle creates increasing resistance on the formerly freely swinging horizontal motion the needle had at lower latitudes. At some point, the needle simply stops moving from side to side.

(Adapted from my January 2013 Scope on the Skies column)

Previous: Which Way is North – Part 1?
Previous: Which Way is North – Part 2?

Internet Resources
Magnetic effects in space—http://archive.org/details/skylab_magnetic_effects
Magnetic field calculators—www.ngdc.noaa.gov/geomag- web/#declination
The Magnetic Sun—http://solar.physics.montana.edu/ypop/Spotlight/Magnetic
Motion of the magnetic pole—http://image.gsfc.nasa.gov/poetry/activity/s8.htm
Planetary magnetic fields PowerPoint—http://education.gsfc.nasa.gov/nycri/units/pmarchase/3b-magnetic_field.ppt
POETRY—http://image.gsfc.nasa.gov/poetry
IMAGE–http://image.gsfc.nasa.gov/

   
   
   
   

Caution: Objects viewed with an optical aid are further than they appear.
Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Which Way is North? Part 2

Earth’s Magnetic Field
magnetic poles-lines   The Earth’s magnetic field, like a bar magnet, has a north and a south magnetic pole, with magnetic lines of force resembling meridians of longitude in that the magnetic lines of force come out of one pole and follow the curve of the Earth toward the other pole. Each magnetic pole is at a location where the magnetic lines of force converge and are vertical. This point on the Earth’s surface is also known as the dip pole, as this is the one location in each hemisphere where a compass needle, if designed to swing in all directions, would point straight down with a dip angle of 90º. Interestingly, neither magnetic pole is at the same location as its corresponding geographic pole. For example, the current location of the north magnetic pole is at approximately 81.3º N, 110.8º W. The word current has to be used because the location of the magnetic poles changes constantly due to variations in the processes that create the Earth’s magnetic field.
   There is an interesting history behind the search for the magnetic pole and you could learn about the migrating magnetic pole and practice mapping and geographic skills by using the teacher-created activity Motion of the Magnetic Pole (see Internet Resources below). This is one of many lessons and activities developed by a cadre of teachers participating in POETRY, the education outreach of NASA’s IMAGE (Imager for Magnetopause- to-Aurora Global Exploration) mission. The IMAGE mission was a six-year mission ending in 2005 that focused on a study of the Earth’s magnetosphere by imaging the magnetosphere in non visible wavelengths. Use the POETRY website (see Internet Resources below) to find lessons and activities written by classroom teachers for all grade levels.

(Adapted from my January 2013 Scope on the Skies column)
Previous: Part 1 – Which Way is North – Part 1
Next Up: Part 3 – The Magnetic Compass

Internet Resources
Magnetic effects in space—http://archive.org/details/skylab_magnetic_effects
Magnetic field calculators—www.ngdc.noaa.gov/geomag- web/#declination
The Magnetic Sun—http://solar.physics.montana.edu/ypop/Spotlight/Magnetic
Motion of the magnetic pole—http://image.gsfc.nasa.gov/poetry/activity/s8.htm
Planetary magnetic fields PowerPoint—http://education.gsfc.nasa.gov/nycri/units/pmarchase/3b-magnetic_field.ppt
POETRY—http://image.gsfc.nasa.gov/poetry
IMAGE–http://image.gsfc.nasa.gov/

   
   
   
   

Caution: Objects viewed with an optical aid are further than they appear.
Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Which Way is North? Part 1

cambridge bay   I recently read about a small Inuit village in northern Canada that will be included in the Google Street View displays available with Google Earth. Ikaluktutiak, or Cambridge Bay, is located at approximately 69º N, 105º W and is populated by fewer than 2,000 residents. There are only a few trucks in the village and no cars, and it is only accessible by air when it is snowed in during the winter months.
When it is not snowed-in and river ice has melted, the village is accessible by barges, as well. While the village’s geography and culture are very interesting, what caught my attention while reading the article was that a magnetic compass will not work at that latitude. Village residents navigate by landmark recognition and, more recently, with the assistance of GPS. Thinking about this led to some questions:

• How is it that a magnetic compass will not work, or not work correctly, at that latitude?
• What is a magnetic pole and how is it created?
• Do other planets have magnetic fields?

Planetary Magnetic Fields
earth-magnetic_field   Using the Earth as a model, the conditions a planet needs to meet in order to have a magnetic field would include a relatively fast rotation period, an electrically charged metallic liquid interior, and for convection to take place within that liquid interior. Convection causes the vertical rising and falling motions while the rotation pulls and stretches the convection currents, disrupting the flow patterns. Throughout all of this, charged particles, or electric currents, are flowing through a metallic material and in the process creating (inducing) our planet’s magnetic field. Are there other planets with a magnetic field? Within the terrestrial planet group, there is some variation. Mercury, despite its slow rotation speed, does have a measurable magnetic field, while the planet Venus, large enough to have a molten core, does not have a magnetic field—probably because of its extremely slow rotation speed. Mars has the remnants of a magnetic field preserved in rocks, similar to what we find preserved in rocks on either side of the mid-Atlantic Ridge. However, Mars is small enough that its core may have cooled so much that it can no longer power convection, thereby losing its magnetic field.
   The giant gas planets, as a group, differ in many ways from the rocky terrestrial planets; however, the process for generating planetary magnetic fields still applies. With regard to magnetic fields, we include our Sun and stars as among the things that have planetary magnetic fields because both stars and the gas planets meet the three requirements from the Earth model for creating a magnetic field. The gas planets’ respective magnetic fields are created from interiors containing electrically conductive liquid and rapid rotation periods. All four of the giant gas planets have stronger magnetic fields than Earth. For example, Jupiter and Saturn have a liquid metallic hydrogen interior that is mixed with convection currents distorted by the rapid rotation of the planet.

(Adapted from my January 2013 Scope on the Skies column)

Next up: Part 2 – Earth’s Magnetic Field

Internet Resources
Magnetic effects in space—http://archive.org/details/skylab_magnetic_effects
Magnetic field calculators—www.ngdc.noaa.gov/geomag- web/#declination
The Magnetic Sun—http://solar.physics.montana.edu/ypop/Spotlight/Magnetic
Motion of the magnetic pole—http://image.gsfc.nasa.gov/poetry/activity/s8.htm
Planetary magnetic fields PowerPoint—http://education.gsfc.nasa.gov/nycri/units/pmarchase/3b-magnetic_field.ppt
POETRY—http://image.gsfc.nasa.gov/poetry
IMAGE–http://image.gsfc.nasa.gov/

Caution: Objects viewed with an optical aid are further than they appear.
Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

May Perigee Moon

may15-perigee   The Moon reaches perigee, (minimum distance from Earth), this month on Friday May 15th at 00:26 UT (7:26 pm CDT Thursday May 14th). At that time the Moon will more or less be at a distance of 28.70 Earth diameters (366,024 km or 227,437 miles) from the Earth.
   Does our Moon actually go around the Earth as this graphic shows? From our perspective on the Earth the Moon appears to circle around the Earth. However, in reality, the Moon orbits the Sun together with the Earth*
*Click here to read my 2006 Scope on the Sky column “The Real Shape of the Moon’s Orbit”. (PDF)

   The thin waning crescent Moon rises about one hour before sunrise local time and is about 2 days from New Moon phase on the 18th.

   
   
   

Caution: Objects viewed with an optical aid are further than they appear.
Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Moon at Descending Node

apr17-descending-node   Thursday May 14th at 20:39 UT, (3:39 pm CDT), our Moon will be crossing the plane of the ecliptic moving south. This is known as the descending node, one of two intersections the Moon’s orbital path (dark green line) has with the ecliptic.
   The Moon is currently in its waning phases and is a few days away from New Moon. The thin waning crescent Moon is conveniently lined up with the left side the Square of Pegasus, an asterism formed with three stars from the constellation Pegasus the Winged Horse, and one star from the constellation Andromeda the Princess.

   
   
   
Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.