Why is the Very Large Array Located Where It Is?

Question: Why was the area outside Socorro chosen for the VLA?  – Mary

Answer: The following is courtesy of Dave Finley, Public Information Officer at NRAO Socorro.

One of the signs on the walking tour addresses this question.

The VLA site selection committee had a set of criteria from which they worked:

West of the Mississippi; south of 35 degrees latitude
Large, flat area, to avoid hills for the transporters
High elevation, dry climate
Natural shielding (mountains, etc.) from RFI to the extent possible
Sufficiently distant from large metro area, again to avoid RFI
Good road access
Some community sufficiently close to provide housing for staff
Land availability

They started by looking at topographic maps, and identified a number of candidate sites. Next, they had detailed aerial photos made of those sites. That narrowed the candidates down. They then flew in person in small planes over the candidates, which did some more narrowing. Finally, they did boots-on-the-ground inspections of several sites. They had three finalists — the Plains of San Agustin, a site in deep southwest NM, and a site in eastern Arizona. The Plains won out.

Jeff Mangum

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Is the Motion of the Moon in the Sky Variable?

Question: Last night with the Super Moon/Eclipse the sky was clear and the moon (in the West?) seemed to move slowly,  if at all.  Tonight the moon was moving very fast (towards the East?) and seemed to be BELOW the clouds.  A very different looking sky altogether. Please can you explain these differences?  – Jan

Answer: The orbital speed of the Moon changes only be very small amounts as it orbits Earth.  Perhaps you were using a reference point, such as clouds, which were themselves moving, thus giving the illusion of a Moon which was apparently moving more quickly than it really was?

Jeff Mangum

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Why is the New Horizons Spacecraft Slowing Down?

Question: Why is New Horizons slowing down? I check it on line every day and its speed is constant. Today its losing speed.  – Tom

Answer: I don’t know of any specific reason as to why New Horizons would have been slowing down on the particular date that you noticed it.  In general the spacecraft will need to make small course corrections as it travels to its next target, which often involve changes in speed.

Jeff Mangum

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What Makes Astronomy an Interesting Field to Study?

Question: what makes astronomy an interesting field of study?  – Shayne

Answer: I think you will likely find the answer to your question in my Careers in Astronomy page of this blog.

Jeff Mangum

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What was that Bright Light in the Sky?

Question: On September 6, in Glendale AZ, at 20:45 hrs, my husband and I thought we saw a satellite in the North Sky.  (We are sky watchers.)  We agreed it was too bright.  Then it went in circles, then east and west, sometimes fast, slow or still, u-turns, bobbing, even a kind of dancing.  Our neighbor saw it.  Her neighbor saw it Sept 5th. A group of our neighbors said they watched it a month earlier.  I contacted the National UFO Network (NUFORC) and they said it was Vega.  No way.  This has me bugged.  What do you say?  — Kare

Answer: There is really no way to know exactly what it is you saw.  Aircraft would be the most likely answer given the behaviour your note.  Other options require more complex scenarios.  It is often useful to keep Occam’s Razor in mind when evaluating situations such as this.  In the end, it is usually the least complex answer that is the correct answer.

Jeff Mangum

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How Many Miles of Fiber Optic Cable Does the VLA Use?

Question: My son and I toured the VLA about 8 years ago when you were first converting from copper to fiber. We just toured with friends on the first Saturday of September. How many miles of fiber were laid? Also, are there ancillary computing systems which assist or support the Correlator?  – Steve

Answer: I checked with the engineers at the VLA who told me that the VLA has 2557 miles of fibre in the ground, and an additional 3 miles of fiber per antenna in each antenna.  As for the computing systems used with the correlator, there is specialized computer hardware and software that collects and processes the information that the correlator gathers from the VLA antennas.

Jeff Mangum

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Introductory Information on Astronomical Techniques

Question: Hey there! I love astronomy too!! Currently I am pursuing an undergraduate degree in physics as there is no such courses in astronomy in India. I want to learn astronomy and later on pursue astronomy as a career. Can you tell me some names of a good informative book that includes all about techniques, instruments and stuff regarding astronomy?  Eagerly awaiting for a reply.  – Anshul

Answer: Rather than point to some textbooks that may or may not give you the information that you are looking for, I thought that a good place to start for you might be a Coursera course on astronomy.  One such course is hosted by Duke University called Introduction to Astronomy.  This course contains quite a nice overview of astronomy, which includes information about techniques and instruments.  There are also related courses which dive more deeply into these subjects.

Jeff Mangum

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How to Determine the Relevant Date for a Star Chart

Question: How can I find the date from a given star-chart?  – Anand

Answer: In the following I am going to assume that you are using a star chart appropriate for the mid-latitudes in the northern hemisphere.  The easiest way to determine what date a particular star chart refers to is first know the approximate dates that a few bright stars transit at midnight:

  • Pollux: January 15
  • Regulus: February 22
  • Arcturus: April 25
  • Vega: July 1
  • Deneb: August 1
  • Aldebaran: December 1
  • Capella: December 10

If your star chart has any of these stars near transit then the date for that star chart is likely very close to the relevant date listed above.

Jeff Mangum

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I Love Astronomy!

Question: I am 14 years, from India, I love astronomy, after 12th, what should I do and it
is that possible in India ?  – Pooja

Answer: Glad to hear that you love astronomy!  So do I.  Most astronomers start out studying physics in college.  That is probably a good place for you to start.  In fact, you should study as much math and science as you possibly can before college as preparation for your college-level studies.  You should also look over the Careers in Astronomy section of this blog for further tips about the career path for an astronomer.  Good luck!

Jeff Mangum


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Is Satellite Internet Service Available within the NRQZ?

Question: Is satellite internet service prohibited in the NRQZ in West Virginia?  – Ron

Answer: I believe that satellite internet service is available within the National Radio Quiet Zone (NRQZ).

Jeff Mangum

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