Astronomy Question: Change of Seasons?
Published January 31, 2011Sam writes:
We discussed the seasonal change of summer to winter when I was in school and the years required to make the seasonal change from summer to winter and back to summer was 27,000 years.
Is this the number of years for this change and is this the same time period for a polarity shift of the poles?
Thanks Sam.
Sam, the phenomenon you are referring to is known as precession, where the axis of rotation “wobbles” with a specific interval.
You are correct in that this cycle is in the neighborhood of 26,000 – 27,000 years.
Keep in mind, not only does the Earth’s rotational axis “wobble”, the amount of tilt also varies in a cyclic pattern from around 22 degrees to almost 25 degrees.
There are some theories that use the axial tilt and axial precession (along with a few other orbital factors) to explain such phenomenon as “Ice Ages” – however, there is no known correlation (that I’m aware of) between these cycles and magnetic pole reversals.
While Geology isn’t my specialty, if I remember correctly, the last magnetic pole reversal was almost 800,000 years ago, and the reversal before that was around a million years ago. Some magnetic reversals took place over many years, and there are some magnetic reversals theorized to have taken place during a decade or less!
What is interesting to know is currently, the North Magnetic Pole is drifting over thirty miles per year from it’s current location in northern Canada, towards Siberia. Another interesting tidbit, is that while the North Magnetic Pole is geographically “North”, electrically, it is a south magnetic pole, in that it attracts the north “pole” of a bar magnet!
Scale
Published January 30, 2011From Brad Goodspeed at bradblogspeed.com:
…the basic idea is, each planet you see is the size it would appear in the sky if it shared an orbit with the moon,
380,000 kms from earth. I created this video in After Effects, and because of certain technical considerations had to keep the field of view at 62 degrees.
That means the foreground element is not precisely to scale. I realized this after the fact and may update the video at some point in the future. All planets are to correct scale with one another in any case.
Scale from Brad Goodspeed on Vimeo.
Statement by the President on NASA Day of Remembrance
Published January 27, 2011Fifty years ago, a young President facing mounting pressure at home propelled a fledgling space agency on a bold, new course that would push the frontiers of exploration to new heights. Today, on this Day of Remembrance when NASA reflects on the mighty sacrifices made to push those frontiers, America’s space agency is working to achieve even greater goals. NASA’s new 21st Century course will foster new industries that create jobs, pioneer technology innovation, and inspire a new generation of explorers through education – all while continuing its fundamental missions of exploring our home planet and the cosmos.
Throughout history, however, we have seen that achieving great things sometimes comes at great cost and we mourn the brave astronauts who made the ultimate sacrifice in support of NASA missions throughout the agency’s storied history. We pause to reflect on the tragic loss of the Apollo 1 crew, those who boarded the space shuttle Challenger in search of a brighter future, and the brave souls who perished on the space shuttle Columbia.
Through triumph and tragedy, each of us has benefited from their courage and devotion, and we honor their memory by dedicating ourselves to a better tomorrow. Despite the challenges before us today, let us commit ourselves and continue their valiant journey toward a more vibrant and secure future.
Source:The White House – Office of the Press Secretary
Day of Remembrance
Published January 27, 2011
Apollo 1 Mission Patch - Image Credit: NASA
At NASA’s Johnson Space Center in Houston, Center Director Michael L. Coats will be joined by astronaut family members to lay a wreath at the Astronaut Memorial Tree Grove at 11:30 a.m. on Jan. 27.
Friday, Jan. 28, marks the 25th anniversary of the Challenger accident. At 9 a.m. EST, the Astronauts Memorial Foundation will hold a remembrance service honoring the STS-51L crew members at the Kennedy Space Center Visitor Complex in Florida.
NASA Television will provide live coverage of the event, which will take place at the visitor complex’s Space Mirror Memorial.
STS-51-L Mission Patch - Image Credit: NASA
Challenger’s seven astronauts died shortly after launch on Jan. 28, 1986. The crew consisted of Commander Scobee, Pilot Michael J. Smith, Mission Specialists Judith A. Resnik, Ellison S. Onizuka, and Ronald E. McNair, and Payload Specialists Gregory B. Jarvis and Sharon Christa McAuliffe.
STS-107 Mission Patch - Image Credit: NASA
The Astronauts Memorial Foundation, a private, not-for-profit organization, built and maintains the Space Mirror Memorial. The memorial was dedicated in 1991 to honor all astronauts who lost their lives on missions or during training. It since has been designated a National Memorial by Congress.
To view an online tribute, including photographs, videos and information about the crew members on Apollo 1 and shuttle Challenger and Columbia, visit: http://www.nasa.gov/externalflash/dor11/
Source(s):NASA Press Release , NASA Day of Remembrance Page