General file update.

Unit4/4_5_spectroscopy_2.ipynb

@@ -18,21 +18,18 @@
     "\n",
     "## Identifying Elements in Stars\n",
     "\n",
-    "---\n",
-    "\n",
     "### Spectral Lines as Cosmic Fingerprints\n",
     "\n",
     "Every element in the universe has a unique set of spectral lines, much like fingerprints. These lines are created by the transitions of electrons between energy levels in atoms. When light from a star passes through its atmosphere, certain wavelengths are absorbed by the atoms in the atmosphere. This absorption produces dark lines in the star's spectrum, known as **absorption lines**. These lines allow us to determine the elements present in the star, as each element absorbs light at specific wavelengths.\n",
     "\n",
-    "---\n",
     "\n",
     "### Element Identification\n",
     "\n",
     "Astronomers use spectroscopy to identify the chemical composition of stars by comparing observed spectral lines to known atomic spectra. For example, the Balmer series of hydrogen, which produces lines in the visible part of the spectrum, is often seen in stellar spectra. The positions of these lines can be matched with laboratory data to confirm the presence of hydrogen.\n",
     "\n",
     "Other elements like helium, calcium, sodium, and iron also have characteristic spectral lines. By analyzing these lines, astronomers can determine not only the presence of elements but also their relative abundance. This information is crucial in understanding the life cycles of stars, as stars of different ages and masses show varying compositions.\n",
     "\n",
-    "---\n",
+    "<img src=\"https://raw.githubusercontent.com/teaghan/astronomy-12/main/Unit4/figures/abs_emiss_spectra.png\" alt=\"Elemental Spectra\" width=\"1000\" style=\"display: block; margin-left: auto; margin-right: auto;\">\n",
     "\n",
     "### Application in Stellar Spectra\n",
     "\n",
@@ -45,12 +42,12 @@
     "  \n",
     "Each of these lines provides clues about the temperature, composition, and age of a star.\n",
     "\n",
+    "<img src=\"https://raw.githubusercontent.com/teaghan/astronomy-12/main/Unit4/figures/spectral_lines.png\" alt=\"Elemental Lines\" width=\"1000\" style=\"display: block; margin-left: auto; margin-right: auto;\">\n",
+    "\n",
     "---\n",
     "\n",
     "## Measuring Stellar Velocities Using Doppler Shifts\n",
     "\n",
-    "---\n",
-    "\n",
     "### The Doppler Effect in Astronomy\n",
     "\n",
     "The **Doppler effect** is a phenomenon where the wavelength of light changes depending on the relative motion between the source of the light and the observer. In astronomy, this is used to measure the radial velocity of stars and galaxies—whether they are moving toward or away from us.\n",
@@ -59,8 +56,6 @@
     "\n",
     "<img src=\"https://raw.githubusercontent.com/teaghan/astronomy-12/main/Unit4/figures/doppler_shift.png\" alt=\"doppler shift\" width=\"1000\" style=\"display: block; margin-left: auto; margin-right: auto;\">\n",
     "\n",
-    "---\n",
-    "\n",
     "### Radial Velocity Measurements\n",
     "\n",
     "By measuring the shift in the position of spectral lines, astronomers can calculate the velocity of a star or galaxy along the line of sight, known as the **radial velocity**. The larger the shift, the faster the object is moving. This technique is invaluable in studying the motion of stars within galaxies, the expansion of the universe, and the motion of galaxies relative to one another.\n",
@@ -81,8 +76,6 @@
     "\n",
     "<img src=\"https://raw.githubusercontent.com/teaghan/astronomy-12/main/Unit4/figures/arcturus_sun_spectra.png\" alt=\"Arcturus and the Sun\" width=\"1000\" style=\"display: block; margin-left: auto; margin-right: auto;\">\n",
     "\n",
-    "---\n",
-    "\n",
     "### Exoplanet Detection Using Radial Velocity\n",
     "\n",
     "One of the most exciting applications of the Doppler effect is in the detection of **exoplanets**—planets that orbit stars other than the Sun. As a planet orbits a star, the gravitational pull of the planet causes the star to \"wobble.\" This wobble causes tiny shifts in the star's spectral lines as the star moves toward and away from us. By measuring these shifts, astronomers can infer the presence of planets, even if they are too faint to be observed directly.\n",
@@ -95,8 +88,6 @@
     "\n",
     "## Spectral Line Catalogs and Practical Spectroscopy\n",
     "\n",
-    "---\n",
-    "\n",
     "### Line Lists and Databases\n",
     "\n",
     "Spectral lines are the foundation of spectroscopic analysis, but they are only useful if we can identify them correctly. For this, astronomers rely on **line lists** and **catalogs**, which are databases of spectral lines corresponding to different elements and ions. One well-known resource is the **NIST Atomic Spectra Database**, which provides detailed information about the wavelengths of spectral lines, their strengths, and the conditions under which they occur.\n",
@@ -106,13 +97,14 @@
     "- Checking the intensity and pattern of the lines to confirm the element.\n",
     "- Determining if any Doppler shift has occurred due to the star's motion.\n",
     "\n",
-    "---\n",
-    "\n",
     "### Real-World Analysis\n",
     "\n",
     "In practical spectroscopy, astronomers use a variety of telescopes equipped with spectrometers to capture light from distant stars, galaxies, and nebulae. These instruments spread the light into its component wavelengths, producing a spectrum. The data is then processed using software that compares the observed spectral lines with known line lists to identify the elements and infer conditions such as temperature, density, and velocity.\n",
     "\n",
     "Spectroscopy is performed at both ground-based observatories, like the **Keck Observatory** in Hawaii, and space-based telescopes, such as the **Hubble Space Telescope**. Space telescopes are particularly useful for observing in the ultraviolet and infrared parts of the spectrum, which are absorbed by Earth’s atmosphere.\n",
+    "\n",
+    "<img src=\"https://raw.githubusercontent.com/teaghan/astronomy-12/main/Unit4/figures/galaxy_spectrum.png\" alt=\"Galaxy Spectrum\" width=\"1000\" style=\"display: block; margin-left: auto; margin-right: auto;\">\n",
+    "\n",
     "---\n",
     "\n",
     "## Check Your Understanding\n",