Sept. 3: Frits Paerels Talk and Remote Observing

On Friday, Sept. 3 some 140 people attended a lecture by Dr. Frits Paerels about missing matter in the universe. Dr. Paerels described how astronomers came to understand that most of the matter in the universe was unaccounted for. Showing beautiful images of clusters of galaxies and simulations of the large-scale structure of the universe, Dr. Paerels described how only 4% of the universe was made out of normal matter and how fully 50% of it hasn't yet been detected.

After this great talk, we were treated to a remote observation by graduate students Neil Zimmerman and Andrew Brown who imaged Stephan's Quintet using the website slooh.com. These observations were a big hit with our regular visitors. Other newcomers were treated to a tour of the observatory on the roof with an exhortation to return soon!

This past Friday, recent graduate of the Columbia Astronomy doctoral program, Stephanie Tonnesen, gave a talk entitled, "Hubble Deep Field: Looking back in Time." In her talk, Stephanie gave us a detailed background on the nature of the Hubble Deep (HDF) and Ultra Deep fields (UHDF). She also gave us a sense of just how difficult an exposure of 150+ hours is in low Earth orbit due to the glare of the Sun. However, the biggest problem in terms of getting a great picture of the past was finding a patch of sky where few Milky Way stars existed. Too many foreground stars would actually outshine the very distant, and hence, faint galaxies that were the precise interest of that survey.

After showing us great pictures of these galaxies, Stephanie went on to explain the why astronomers are so interested in objects whose features we can barely make out. One main question addressed in the HDF & UHDF pictures is, "How do galaxies form?" Stephanie pointed that there are two main theories for galaxy formation: monolithic collapse and hierarchical merging. In monolith collaspe, different- sized gas clouds collapse due to self-gravity and form tight clumps of stars and/or stellar disks that constitute galaxies. In hierarchical merging smaller galaxies merger together to form larger galaxies that then feed off of remaining smaller satellite galaxies to grow. Occassionally these galaxies would run into another massive galaxy to form elliptical galaxies.

One observational fact that Stephanie pointed out that may favor monolithic collapse (at least in the early universe) is that the light Hubble observes in the visible here was redshifted from the ultraviolet (UV) light emitted from the HDF/UHDF galaxies. She showed us a UV picture of a nearby galaxy and we found that the picture looks clumpy due to the clusters of young star formation in the galaxy. Since massive blue stars in young star clusters emit predominately in the UV, could it be that the "blue dots" that we originally claimed to be merging proto-galaxies are actually starbursts in a single galaxy?

The audience asked many questions about galaxy formation and about the prospect of sorting the "blue dots" issue out. Stephanie explained that telescopes like James Webb and other projects will target visible light from these galaxies in the infrared (IR) to possibly solve this issue. This issue also highlighted why astronomers try to view objects by collecting all wavelengths from the electromagnetic spectrum. Once again, our speaker fielded a myriad of good questions from our audience and we ended our Q&A session only in the interest of observing time.

Thanks to the 7 volunteers and the 85+ people who attended our lecture and observing night!

Astronauts and Moon Landings

Yesterday, we provided a free screening of the film Apollo 13 to an audience of around 120. Erika Hamden and Cameron Hummels introduced the film with a short history of the Space Race along with a few definitions of some jargon terms that were used in the film (e.g. burn, gimbal lock, LEM). The film lasted about 2:20, and the auditorium thermostat seemed broken so the audience got an accurate experience of how cold it was in the broken command module of Apollo 13.

After the film, Erika and Cameron spoke for 20 minutes about how scientifically accurate the film was (very), and then discussed what broke in the actual Apollo 13 service module and why. They presented information about the remainding days of the Apollo program and the followup Shuttle program. Lastly, they gave information on how to go see the remaining shuttle launches and tips for youngsters on how to become an astronaut.

Unfortunately, the sky was cloudy, so we were unable to observe. NASA swag of Hubble Space Telescope photos and stickers for the HST-servicing mission were given out to audience members.

Thanks to everyone who turned out!

--Cameron

Supernovae Lecture and Stargazing: July 2, 2010

This past Friday, recent post-baccalaureate of the Columbia Astronomy program, Nicholas Hunt-Walker, gave a talk entitled, “Supernovae: Going out with a Bang!” In his talk, Nick gave a clear overview of the main points of stellar evolution that lead up to two different types of supernovae: mass-accretion and core-collapse. He told us that mass-accretion type supernovas (also known as Type Ia) arise from binary systems where one star has already gone through all of the evolutionary phases, becoming a hot, dense stellar remnant, called a white dwarf. The other star, being less massive at birth, takes longer to evolve, eventually becoming a red giant star. When this occurs, the red giant star becomes so puffed up that its outer layers are close enough to the white dwarf companion that it becomes more gravitationally attracted to it. Thus, the white dwarf starts to siphon off the envelope of the red giant star and forms an accretion disk around itself. When enough matter has piled on the white dwarf it ignites thermonuclear burning in its core again. However, since it no longer has an envelope of mass around the core like a normal star, it can’t contain the increase in pressure and temperature and thus ignition becomes a runaway event that blows the white dwarf apart!

The second type of supernova (also called Type II) comes from the core collapsing in a massive star that is capable of fusing Hydrogen in its core up to Iron. Once this occurs, the star can no longer create enough energy in the core to support the many solar masses of matter above it. In seconds the star implodes on its self and then blows apart, usually leaving a neutron star or black hole behind. Nick received a myriad of good questions about the particulars of these processes and he patiently responded to everyone who asked.

He then went on to show us many beautiful examples of supernova remnants and how you can tell the difference between the type of supernova that created them from the characteristics of the remnants themselves. One good example of the observational difference is that a core-collapse supernova can have a compact stellar remnant in its center whereas a mass-accretion supernova can’t since the central object is totally destroyed! Nick also told us why we view the spectra of these remnants in different wavelengths like the X-Ray, Radio, and Optical. He explained that with this data we can better figure out what the progenitor star was made of and how and when it exploded.

Finally, Nick shared some historical accounts of famous supernova like the Crab supernova, seen by Chinese and Arab astronomers in 1054, and Tyco Brahe’s supernova, seen by, well, the man himself, in 1572. There continued to be many good questions from the audience about supernovae and their remnants. It was only in the interest of time for observations on the roof that the Q&A session ended.

We had a great turn out and our attendees made full use of our facilities by watching astronomy visualizations on our 3-D wall, ran by graduate student Yuan Li, and by going to the roof to stargaze. It’s cool to think that some of the stars we observed will be become supernovae in the future.

Thanks to the 9 volunteers and the 140+ people who attended our lecture and observing night!

Visitors from Manhattan East School

Today, we had a visit from the Astronomy Club of Manhattan East for the Arts and Academics in East Harlem, NY. A few of the graduate students presented several interactive activities for the club, including a solar-system walk, solar observing, an observatory tour, and a 3D flight through the Universe. In addition, we fielded several questions they had about astronomy, physics, science and college life. They were a great group of kids, and we were happy to have them here!

Thanks to all 15 of our visitors and the 4 volunteers who put this on.

--Cameron

Time Machine: June 18

The free screening of H.G. Wells classic tale “The Time Machine” (1960) drew around 45 viewers this Friday. Following this movie, graduate student Jennifer Weston led a discussion about the film with the audience, and talked about some of the implications of time travel and the ideas behind it.

Some of the topics covered included: Discussing what humans will be like in 800,000 years, with a review of how we’ve changed in the past 800,000 years. We concluded that while the human race could potentially split into two very different species, our time traveler would NOT be able to speak perfect English with them.


How to resolve the apparent paradoxes of time travel. Multiple time lines and predestination were thought to be some possible ways to prevent paradoxes when you attempt to kill your own grandfather. We also introduced the concept of closed time-like curves.


After this, we had an overview of the physics of traveling through time. We reviewed some of the background for Special and General Relativity, light cones, and black holes. Finally, we outlined how one might build a time machine with wormholes and cosmic strings.


Following the movie, telescopes were set up outside on College Walk, manned by a number of students. Passersby were able to see close up views of the beautiful quarter moon, and the planets Mars, Venus, and Saturn, and the stars Arcturus, Mizar and Alcor. Over the course of a bit more than an hour, about 90 people came by to take advantage of the clear night. Thanks to everyone who attended and to those who volunteered!

From Physics 101 to Pigeons

Around 60 people attended our first event of the summer -- a free screening of The Core. Afterwards graduate student Lia Corrales guided the audience in a discussion around two major topics:

(1) Where does the earth’s electromagnetic field come from?
We reviewed the “Physics 101” of generating magnetic fields. We debunked the idea that simple rotation generates the earth’s magnetic field, and explained how much energy it would take to ‘stop’ or ‘reverse’ the rotation. We reviewed some of the scientific research showing that the earth’s magnetic field can have a complicated interior, can change over time, and occasionally switches polarity.

(2) What effect does the electromagnetic field have on life?
We discussed what solar wind does and does not contain, as referenced in the film. The highlight of the evening was the discussion centered on pigeons! We reviewed the scientific article showing that pigeons could sense magnetic fields. However, we also learned that pigeons used landmarks like roads to navigate. We concluded that a change in the earth’s magnetic field would not be enough to disorient pigeons into a kamikaze death dive, but would be enough to force them to ask for directions on the way home.

Unfortunately, the cloudy sky prevented telescope viewing for the night. Fortunately, the summer series of events got off to a great start, thanks to all the people who attended and our five volunteers!