Why Can We See Stars That Are Billions of Light Years Away?

Question:  I can’t get seem to find a thoughtful yet scientific answer to this question, I was hoping you could help.  I hope this doesn’t sound dumb, I don’t mean it to be.  When we look at the night sky, we see a blanket of stars.  They seem very close together and crowed in the sky.  I know some of them may not even still exist, just the light still coming from them over millions of  light years away, in some cases.  But how is it that we can see stars that appear to be so close together but in fact are at least light years away from one another, with the naked eye from earth, no less?  And stars from one side of the night time horizon to the other have to be billions of light years apart, right?  How can we see objects so far away with the naked eye?  If we use our suns size and scale it to stars we see in the sky, millions of light years away we should not be able to see them at all, right?   I just don’t get it!  Is there some phenomenon I’m not understanding?  – Tim

Answer:  For the most distant objects, such as galaxies and quasars, what you are seeing is not just the light from a single star, but light from a galaxy full of stars.  Now, the most distant galaxies cannot be seen with the unaided eye, though.  That is why we build large optical telescopes (basically, the equivalent of a really-big and sensitive eye!).

Jeff Mangum

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Positions of the Planets on any Date

Question:  I am making a sculpture to offer to my dad with planets position at 4 of july of 1930, his day of birth. Can you help me and tell  where i can find it?  – Sérgio

Answer:  There is a nice solar system simulator which will display the positions of the planets, as viewed from above the solar system, on any date.  I ran this simulator for July 4, 1930, shown below.

Jeff Mangum

Solar System on July 4, 1930

Solar System on July 4, 1930


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Can Black Holes Explode?

Question:  Can a black hole explode?  – Dirk

Answer:  Black holes don’t really “explode”, which implies that they generate a large outburst of energy which ultimately tears them apart, but they do have outbursts (also, unfortunately, referred to as “explosions”).  The black hole at the center of our Galaxy, for example, appears to have produced an outburst of energy about two million years ago.

Jeff Mangum

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What Software Do You Use to Control Radio Telescopes?

Question:  What software you use to put the antenna in a desire position? In what language was programmed?  – Jael

Answer:  We use a combination of several programming languages, but principally use C++ and python to control our antennas.  Historically, astronomers use whatever programming language suits their needs when they actually have to write the telescope control software.  This means that we have used Fortran and C within a variety of operating system environments to control our telescopes.

Jeff Mangum

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The Story of the Very Large Array

Question:  Toured the VLA facility in New Mexico on April 5 and was very impressed with the new public relations film narrated by Jodie Foster and, I think, named, “Beyond the Visible; The Story of the VLA”.  Is there a way to make this film available to High School science and engineering students?
Thanks for a great tour and for all the work you guys do to advance science!  – Pat

Answer:  Yes.  You can watch the complete movie (closed captioned in English and Spanish) at “The Story of the VLA”.

Jeff Mangum


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Can the VLA and VLBA be used to Detect Rouge Asteroids?

Question: I’m wondering if the VLA/VLBA dedicates any observation time keeping an eye out for rouge asteroids which might intersect near our orbit?  – Doug

Answer: The Very Large Array (VLA) and Very Long Baseline Array (VLBA) are not well suited to the task of monitoring the skies for asteroids that might intersect Earth’s orbit.  The main problem is that asteroids are not strong emitters of radio frequency emission.  Also, the areal response for a particular measurement made with the VLA and VLBA are rather small in size, making it hard for them to survey large areas of sky for asteroids.

Jeff Mangum

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Can Radio Telescopes Detect the Black Box from Malaysian Airlines Flight 370?

I have received several questions about the detectability of the black box from MH370…


Does not the Black box of Malaysian Airlines work at 37.5 kHz, if the sensors are isolated at those frequencies, wouldn’t we be able to isolate the areas?  – Joy

Has anyone suggested to use the GBT to direct its sensors and bounce it through revolving satellites to detect the possible frequency the Malaysian Airlines’ Black Box emits before the deadline/back up battery signal stops.  – Joy

I recently visited the NRAO in New Mexico and I was wondering if the radio telescopes could be used to pick up the sound waves coming from the missing Malaysia airliner which is emitting a sound at 37 Kilohertz.  If the radio telescopes can pick up sound waves from deep space, surely it can pick up radio waves from the deep ocean?   – Madison

Answer: Unfortunately, Earth-bound radio telescopes cannot be used to detect and isolate the source of an object like an aircraft’s black box for several reasons.  Since the response pattern for a radio telescopes is directional, meaning that it primarily sensitive to signals that come from the direction toward which it is pointing, the fact that we cannot point our radio telescopes directly at the area where MH370 is suspect to be makes it impossible for an Earth-bound radio telescope to see such an object.  Also, none of NRAO’s radio telescopes operate at the very low frequency of 37 kHz.

Jeff Mangum

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Which Telescope Has Higher Resolution: Hubble or VLBA?

Question:  Which telescope can see farther in space (higher resolution)? :  The Hubble Space Telescope at the optical wavelengths, OR the VLBA extending from Hawaii to VA, observing at the radio wavelengths?  – Sekar

Answer:  The Hubble Space Telescope (HST) has a highest resolution of about 0.03 arcseconds, while the Very Long Baseline Array (VLBA) makes images with a resolution smaller than 0.001 arcsec.  So, the VLBA has the HST beat when it comes to picture resolution.

Jeff Mangum


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Can Gravitationally-Lensed Objects be Studied at Any Wavelength?

Question:  As per definition, Gravitational lensing refers to bending of light rays from a distant source around a massive object (Galaxy cluster) which tends to magnify the background light source. If visible light rays bend around those massive objects then X-rays, Gamma rays, UV and IR rays which forms a part of electromagnetic spectrum must also bend around those massive objects. If true, Are there any initiative to detect those distant lensed invisible objects using the space observatories(Chandra X-ray, Spitzer IR etc.)?  – Vinod

Answer:  Yes.  In fact, just a few days ago there was a press release announcing the detection of the spin of a black hole using the gravitationally-lensed x-ray emission from a black hole in a distant quasar.  Gravitational lensing has also been used to study galaxies using the Spitzer Space Telescope.  In fact, as their is no wavelength dependence to the gravitational lens effect it is possible to study gravitationally-lensed objects at all wavelengths.

Jeff Mangum

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What is an Astrogeologist?

Question:  I am a sophomore and I have been fascinated with anything about space for as long as I can remember. I’m am currently researching about the astronomy careers. I plan to be an astro geologist and I’m still not sure what this job really involves or what it takes to pursue in this career. So can anyone tell me?  – Racheal

Answer:  Astrogeologists, as you might expect, combine the fields of astronomy and geology to study the terrain, composition, formation, and evolution of planets, asteroids, and comets.  Note that this study includes not just the planets in our solar system, but also those planets being discovered in increasing number beyond our solar system (exoplanets).  As with any field that combines aspects of two different scientific disciplines, you will need to become proficient in both astronomy and geology.  Many university astronomy and geology programs have researchers who work as astrogeologists, so you should have no problems pursuing this field in college.  For general information about careers in astronomy see the related postings in the archives of this blog.

Jeff Mangum

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