Class notes
The suns light and life on earth
- Course
- Astro 101 (ASTRO101)
- Institution
- University Of Alberta (UofA)
The suns light and life on earth
[Show more]
Seller
Follow
Content preview
Do not look directly at the sun. The sun is bright, and our squishy, liquid- lled human eyes haveevolved for use in an average solar irradiance environment. That's a mouthful. But the lesson is
simple. Do not look directly at the sun even using sunglasses. Doing so can permanently damage
your eyes and your ability to see. In extreme cases, you may become permanently blind. There are
safe ways to look at the sun. Either by reducing the total light that we observe with our eyes or by
narrowing the spectrum of interests into a short range of colors. Common light reducing tools are
the number 14 welders glass, or an astronomy-speci c pair of solar sunglasses like this. Now, that
we're nally equipped to look at the sun, let's go ahead and have a look. Wow! The sun's surface
which is called the photosphere is a roiling inferno of activity. Bright patches mottle the surface
separated into small cells by darker boundaries. Once in a while, you encounter a very dark patch, a
sun spot. If you look closely, you can also see hot gases above the Sun's surface following
magnetic eld lines. Every detail we see on the surface of the Sun is the result of the thermonuclear
reaction at the core. The photons that eventually escape from the surface of the sun are not the
same ones that began the journey in the nuclear furnace at the stellar interior. Although the energy
was produced by fusion, that energy went through several stages in its 100,000 year journey. The
most notable was the journey through the convective zone, where our photons energy was locked
away in the vibrations of the hydrogen and helium gases as they oated to the surface. Once
exposed to the vast vacuum of space, the heat energy contained within those vibrations can now
escape freely as photons. Since these photons originate from hot dense gas, they're mostly the
result of blackbody radiation. Some sprinklings of atomic hydrogen emission and absorption are
present in the Sun spectrum. But the dominant component of the spectrum is the result of the
Sun's surface temperature. Since we can measure what the peak wavelength of the Sun's
blackbody emission is, we can use Wien's law to calculate the average surface temperature of the
Sun as well. Since the Sun's peak wavelength is about 500 nanometers, which is to say a yellow
greenish color, we'll plug that number into Wien's law in order to calculate the surface temperature.
The Sun's surface temperature is equal to Wien's constant 2.898 times 10 to the negative 3 divided
by the peak wavelength 500 nanometers. Which results in a temperature of 5,796 degrees Kelvin.
The fact that the Sun does not look green, when in fact it has a peak emission in the wavelength of
green, is due to the fact that the Sun also emits a lot of red and blue light, and when you combine
red, green, and blue light, we observe it as a white light. But what about this strange pattern on the
surface of the Sun? What causes this pattern to emerge? These are called solar granules, and are
the result of the convection in the photosphere. Hot gases rising from the stellar interior are visible
as bright patches of yellow. But what happens to them once they're at the surface? At the surface,
these gases emit light, and in doing so, cool down. The cooler gases are now more dense, and
therefore less buoyant, and they begin descending in the zones at the boundaries of the hotspots.
These cooler gases are visible as the grain-like boundaries on the Sun's surface, and this is where
the cool gases begin their descent. The Sun's photosphere is a layer of gas that becomes cooler in
the outermost layers. This image of the Sun's visible light shows all the colors of the rainbow and
corresponds to blackbody emission from the lowest region of the photosphere. As the light travels
outward through the photosphere, some of the light with special colors, is absorbed by the cooler
hydrogen gas and other elements present in the atmosphere. When the light is absorbed at these
colors, we see black lines instead of that color. We call this an absorption spectrum. The Sun
doesn't just produce good old-fashioned visible light. Wien's law tells us that it also produces high
energy UV radiation and X-rays too. These images come from NASA's Solar and Heliospheric
Observatory called SOHO for short, and show the Sun at wavelengths that our eyes can't see. This
image for example, was taken with a peak wavelength in the ultraviolet, or a 19.5 nanometers.
Revealing even more of the stellar atmosphere that wasn't visible to the naked eye. Not only that,
but in the UV, there's much more contrast. So, activity in and above the photosphere is much more
apparent. The outermost regions of the Sun's atmosphere are called the chromosphere and the
corona. The corona is much hotter than the Sun's surface, which scientists think is a result of the
tremendous energy contained within the magnetic elds that are generated by the Sun. The energy
fi
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller titaniayuki1. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for CA$4.42. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
51683 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 15 years now