A note on the Hydrogen spectrum

The emission spectrum of atomic hydrogen is given by this amazing spectral series diagram:

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Let’s take a closer look at only the visible portion of the spectrum i.e the Balmer series.

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If a hydrogen lamp and a diffraction grating just happen to be with you, you can take a look at the hydrogen lamp through the diffraction grating, these lines are what you would see:

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Source

These are known emission lines and they occur when the hydrogen atoms in the lamp return to a state of lower energy from an excited energy state.

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           Representation of emission and absorption using the Bohr’s model

Here’s another scenario that could also happen:

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You have a bright source of light with a continuous spectrum and in between the source and the screen, you introduce a gas (here, sodium)

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Source: Harvard Natural sciences

The gas absorbs light at particular frequencies and therefore we get dark lines in the spectrum.

This is known as absorption line. The following diagram summarizes what was told thus-far in a single image:

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The absorption and emission spectrum for hydrogen look like so :

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Stars and Hydrogen

One of the comments from the previous post was to show raw spectrum data of what was being presented to get a better visual aid.

Therefore,the following spectrum is a spectrum of a star taken from the Sloan Digital Sky Survey (SDSS)

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                                 Plot of wavelength vs median-flux

Here’s the spectrum with all the absorption lines labelled:

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Source: SDSS

You can clearly see the Balmer series of hydrogen beautifully encoded in this spectrum that was taken from a star that is light-years away.

And astronomers learn to grow and love these lines and identify them immediately in any spectrum, for they give you crucial information about the nature of the star, its age, its composition and so much more.

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Source: xkcd

Have a great day!

*If you squint your eyes a bit more you can find other absorption lines from other atoms embedded in the spectrum as well.

On the strong 5577Å spectrum line


The above is a plot of the Wavelength(in Å) in the x-axis vs the flux of some objects from the Sloan digital survey ( consists of galaxies, young stars, Quasars, etc)

But  there is one strong peak in all of those plots that seems to stand out: 5577 Å

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And if you like, the color that it represents is the above  (Made with Stanford’s color matcher app)

A nightmare for the astronomer

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This line at 5577.338 is what astronomers refer to as a ‘skyline emission’ or a ‘mesospheric night-glow’ and arises from the recombination of atomic oxygen in the mesosphere.[2]

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                                               Source

This line is of no significance to an astronomer who is looking to find out properties about a far away astronomical object. Yet, this line pops up in every spectrum of any object that you look at in outerspace!

In addition since the line is so strong, it contaminates the nearby pixels making the nearby data unusable and also messes up the scaling of the plot.

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Example of contaminated pixel columns in an image because of bright object

Wavelength Calibration

What do you do with something that is always there but has no use for you? – Re-purpose it!

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Having noticed that this peak was consistent at 5577.338, Astronomers decided that they would use this peak line in the data as a reference to calibrate their actual data. (known as ‘zero-point correction’).

This ensures that all the spectrum lines in the data are aligned and any errors that might have occurred during observation are corrected for.

Other lines ?

There are other lines at 6300,6363, etc which are sometimes as bright or brighter than the 5577 line that are also used for calibration.

If you are interested in learning more, the following are three papers that this post was inspired from and they dive deeper into more technical details that underlie this fascinating topic:

[1] Night-Sky High-Resolution Spectral Atlas of OH and O2 Emission Lines for Echelle Spectrograph Wavelength Calibration

[2] Mesospheric nightglow spectral survey taken by the ISO Spectral Spatial Imager on ATLAS 1

[3] Variability of the mesospheric nightglow sodium D2/D1 ratio

Have a great day!

Pillars of creation, Lick Observatory, 2018 [RAW]

Having recently attended a workshop at the Lick Observatory and the opportunity to observe at the telescopes there, this is the raw data of the pillars of creation that we were able to capture using the Nickel Telescope whilst there. 

Exposure time: 300 seconds

Location : M16 (Eagle Nebula)

This image needs to reduced even further to correct for the anomalies in
color that one can observe on the image and that’s something we are
currently working on.  We hope to share the entire data with you in a month’s time after post-processing.

Have a good one!

There are the Sketches of the four moons of Jupiter (Io, Europa, Ganymede and Callisto), as seen by Galileo
through his telescope.

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                                                 Source

The drawing depicts observations from the time period January 7 to 24, 1610.

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The above is the sequence of photographs taken by JunoCam aboard the Juno
spacecraft, in June 2016, of Jupiter and the motion of the four Galilean
moons, as the spacecraft approached the planet.

* There are 79 known moons of Jupiter.

** Jupiter has 4 rings.

Emojis of the cosmos

Pareidolia  is a psychological phenomenon in which the mind responds to a stimulus, usually an image or a sound, by perceiving a familiar pattern where none exists.

These are merely some images of stars and galaxies taken by the Hubble Space Telescope. But what do you see ?

One of the striking aspects of our solar system is that the orbital plane of all the planets are similar i.e Its like the following:

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                                                  Source

And not like so:

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                                                Source

But if you are puny human sitting on earth, how would one visualize this ? It’s easy!

Step out and look at the trajectory taken by the  sun and planets in the sky:

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                                                    Source

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You will notice that the trajectories taken by the sun and the planets are similar in the night sky.

This gives you a visual validation of the fact that the orbital plane of all the planets and the sun are similar. Just a little something that you may or may not have realized about the cosmos.

Go ahead, give it a shot and have fun!

* The ecliptic plane is the name given to the mean plane in the sky that the Sun follows over the course of a year; 

Van Gogh’s The Starry Night is a stunning painting that artistically brings out the effect of turbulence in our atmosphere on stargazing.

And this turbulence of air in addition to the effect of increasing refractive index causes the twinkling of stars:

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     Source: Enhanced Learning

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But if you are an astronomer trying to study the cosmos from the earth, this turbulence of air and twinkling of stars is a nightmare.

The last thing that you want the light that painstakingly took millions of years to get to the earth is be wiggled away from your telescope through refraction and turbulence.

Adaptive Optics

Have you ever seen time lapses like these of the Keck observatory with laser beams coming out of it ?

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Those lasers serve a purpose: to account for the atmosphere disturbances in the night sky in real time and correct the images that they observe dynamically.

This is known as Adaptive optics. This video by the RoyalObs explains the essence of Adaptive optics really well. Do watch it

With and Without Adaptive Optics

Prof. Andrea Ghez and her research team at UCLA whose research on what is at the center of our galaxy that was featured in our previous post has contributed a lot in using Adaptive optics for astronomical observations.

And using this technique, the following is the difference between capturing an image with and without adaptive optics.

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And it is with the aid of adaptive optics that the group was able to track the trajectories of the galaxies surrounding the proposed center of our galaxy to conclude that there is most likely a Super Massive Black Hole at the center of it.

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      Trajectories of stars surrounding the proposed center of our galaxy.

So, the next time you go out to gaze at the cosmos, just remember that whatever you are seeing in the night sky right now is through the looking glass of our beloved atmosphere.

And astronomers put in immense effort to nullify the dynamic atmospheric effects that it loves to entertain us with.

Have a great day!


All images/animations featured in this post were created by Prof. Andrea Ghez and her
research team at UCLA and are from data sets obtained with the W. M.
Keck Telescopes

What is at the center of our galaxy?

Here’s a very interesting question: What exactly is at the center of our galaxy? Is there a black hole ? How do we go about studying it?

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A group of researchers from UCLA’s Galactic center group were inspired by the same question and decided to look at a region in the sky where they believed was the center of our milky way galaxy.

And this is what they found of the trajectories of stars surrounding the proposed center of the galaxy:

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The star in the middle is the proposed center of our galaxy.These images were taken through the years 1996 – 2016 (see top right of gif).

The first thing that you notice about these stars is that they are orbiting a point in space. This is very similar of how planets in our solar system are orbiting the sun.

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                                                 Source

One of the special stars in that animation is S0-2 which completes its elliptical orbit in only 15 years!

( it takes the sun approximately 225-250 million years to complete one journey around the galaxy’s center )

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But having this knowledge of how small the orbit is, we can use Kepler’s law to find out the Mass at the center of the galaxy:

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And we get the mass of the center as a staggering 4 million times the mass of the Sun.

Let’s take a look at the orbits once again:

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The radius of this object at the center, in order to avoid collision with the rest of the objects has to be about the diameter of Uranus’s orbit.

So, an object that has 4 million times the mass of the Sun. and diameter of Uranus’s orbit .. Hmm.. The only astronomical object that would fit this characteristic is a Super Massive Black Hole (SMBH)

And that’s why we believe that at the center of our galaxy is a SMBH.

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Hope you guys liked this post. Have a good one!


* This is how the actual data of the stars orbiting this apparent black hole looks like:

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**(Lecture) Dr. Andrea M. Ghez “The Monster at the Heart of Our Galaxy”

*** (TED Talk) Andrea Ghez: The hunt for a supermassive black hole
 

     
   
 

All images/animations featured in this post were created by Prof. Andrea Ghez and her
research team at UCLA and are from data sets obtained with the W. M.
Keck Telescopes

Astronomy From 45,000 Feet

nasa:

What is the Stratospheric
Observatory for Infrared Astronomy, or SOFIA, up to?

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SOFIA, the
Stratospheric Observatory for Infrared Astronomy, as our flying telescope is called, is a Boeing 747SP aircraft
that carries a 2.5-meter telescope to altitudes as high as 45,000 feet.
Researchers use SOFIA to study the solar system and beyond using infrared
light. This type of light does not reach the ground, but does reach the
altitudes where SOFIA flies.

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 Recently, we used SOFIA to study water on Venus, hoping to
learn more about how
that planet lost its oceans
. Our researchers used a powerful instrument on
SOFIA, called a spectrograph,
to detect water in its normal form and “heavy water,” which has an extra
neutron. The heavy water takes longer to evaporate and builds up over time. By
measuring how much heavy water is on Venus’ surface now, our team will be able
to estimate how much water Venus had when the planet formed.

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We are also using SOFIA to create a detailed map of the Whirlpool
Galaxy
by making multiple observations of the galaxy. This map will help us
understand how stars form from clouds in that galaxy. In particular, it will
help us to know if the spiral arms in the galaxy trigger clouds to collapse
into stars, or if the arms just show up where stars have already formed.

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We can also use SOFIA to study methane on Mars. The Curiosity rover
has detected methane
on the surface of Mars. But the total amount of methane on Mars is unknown and
evidence so far indicates that its levels change significantly over time and
location. We are using SOFIA to search for evidence of this gas by mapping the Red
Planet with an instrument specially tuned to sniff out methane.

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Next our team will use SOFIA to study Jupiter’s icy moon Europa, searching for evidence of possible water plumes detected by the Hubble Space Telescope. The plumes, illustrated in the artist’s concept above, were previously seen in images as extensions from the edge of the moon. Using SOFIA, we will search for water and determine if the plumes are eruptions of water from the surface. If the plumes are coming from the surface, they may be erupting through cracks in the ice that covers Europa’s oceans. Members of our SOFIA team recently discussed studying Europa on the NASA in Silicon Valley Podcast.

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This is the view of Jupiter and its moons taken with SOFIA’s
visible
light guide camera that is used to position the telescope.  

Make sure to follow us on Tumblr for your regular dose of space: http://nasa.tumblr.com

In addition to conventional means of space observation like from space telescopes(like Hubble)

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and telescopes on the ground (like the Keck Observatory)

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SOFIA (or the flying telescope) is yet another tool that Astronomers use on a regular basis to study our universe.

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Resource: 
Inside NASA’s SOFIA Airborne Astronomical Observatory