Supernovae: Dying Stars

Star Death

Lifetime of a Star

It is true that all living things come from stardust. In about 5 billion years, our Sun will have swelled to a red giant and engulfed the inner planets, ready to explode in a supernova. Supernovae enrich the interstellar medium with high mass elements, like iron and calcium. The high energy from supernovae also triggers formation of new stars. On average, supernovae occur only about once every 50 years in the Milky Way Galaxy. They are rare events— so rare that the last one in the Milky Way was discovered in 1604 (SN 1604, or Kepler’s Supernova)— spectacularly luminous and extremely destructive. In fact, supernovae can cause bursts of radiation more luminous than entire galaxies and emit as much energy as the Sun will in its entire lifespan! In a supernova, most of the star’s material is expelled into space at speeds up to 30,000 m/s. The shock wave passes through the supernova remnant, a huge expanding shell of gas and dust. Supernova are caused either by the sudden gravitational collapse of a supergiant star (Type I Supernova) or a white dwarf accreting enough mass or merging with a binary companion to undergo nuclear fusion (Type II Supernova). White dwarfs are very dense stars that do not have enough mass to become a neutron star (formed from supernova remnant, stars comprising almost entirely of neutrons). Supernovae can be used as standard candles (objects with known luminosity). For instance, the dimming luminosity of distant supernovae supports the theory that the expansion of the universe is accelerating. Now, with powerful telescopes like Hubble, many supernovae are discovered each year. How perfectly supernovae represent the circle of life: from death comes life!

History of Supernova Observations (Milky Way)

  • SN185 by Chinese astronomers
  • SN1006 by Chinese and Islamic astronomers
  • SN1054 (caused Crab Nebula)
  • SN1572 by Tycho Brahe in Cassiopeia
  • SN1604 by Johannes Kepler

* Supernova (SN) are named by the year they are discovered; if more than one in one year, the name is followed by a capital letter (A, B, C, etc.), and if more than 26, lowercase paired letters (aa, ab, etc.) are used

Below is a video on supernovae! Enjoy.


Fun Facts Cluster 2: From Space Rocks to Drones (AskAstro)

1. SPACE ROCK SUICIDE: Scientists can detect a comet or asteroid colliding into the Sun’s surface. The self-destructing comet or asteroid will explode due to pressure of traveling into the Sun’s photosphere. The brightness and impact of the collision depends on the mass of the object. A collision as such is high unlikely, however, because: 1) most comets and asteroids would to dust and vapor in the sizzling atmosphere of the Sun 2) objects will lose most of its mass as they approach the Sun 3) objects normally orbit the Sun, so the objects’ orbit must be altered or the object may be from another planetary system.

2. STELLAR DONATIONS: In a binary star system, if stars are close enough, tides can become so strong that the more gravitationally strong star call pull gas from the surface of its companion. Though the “tidal transfer” depends on the mass of the donor star, if two stars have equal mass, the accretor (the star gaining mass) will steal mass if the donor star’s radius exceeds 38 percent of the binary separation (distance between the stars) no matter the separation.

3. COLOR CODE: The dark and light horizontal bands depend on the organization of winds in Jupiter’s atmosphere. The light bands have a eastward jet on the side closest to the pole, and vice versa in the dark bands. The zones (light bands) appear bright because of colorless high-altitude clouds that contain ammonia ice. The belts (dark bands) have much thinner high altitude clouds and darker particles.

4. DANGEROUS FLYBY: NASA calculates the planetary flybys with nothing but Newton’s laws of motion. The desired closest approach depends on the mission and how much added velocity boost the mission requires.  The mass and closeness of the planet determines the bending of trajectory the probe must undergo. The approach distance can range from a few hundred to several thousand kilometers.

From: Astronomy magazine December 2012 Vol 41 Issue 12

The 8 Planets – Part 5: Jupiter



The giant of planets and quite a monstrosity of swirling gases, Jupiter is the king of the planets. Through the asteroid belt, we arrive at Jupiter, fifth planet from the Sun. With bands of red and white falling and rising gases, Jupiter seems like a huge marble on a racetrack. Named for the Roman god of the sky, Jupiter is mighty and dominant in the solar system, with two and a half times the mass of all other planets in the solar system combined. Jupiter is known for its Great Red Spot, though all gaseous planets have storms. The Great Red Spot is an ongoing storm existing for millenia; about three Earths placed side-to-side can fit across the storm. The storm can attract and suck in weaker storms in its neighborhood. Like the other gaseous planets, Jupiter is mainly hydrogen and helium, the lightest elements. With 71% hydrogen and 24% helium, Jupiter has a composition like that of the primordial solar nebula. Because Jupiter is light for its size, it rotates very fast — its day is less than 10 hours! Though Saturn has noticeable ice rings, Jupiter has only faint rings mainly composed of non-reflective, rocky material. With the most mass, Jupiter has a strong magnetosphere. In fact, if Jupiter were seventy-five times larger, it would have enough pressure and heat inside its core to perform nuclear fusion, produce its own energy, and become a star! But the smallest red dwarfs, or the bare cores of stars, is only three times the mass of Jupiter. Jupiter produces heat in excess to the solar radiation it receives by the Kelvin- Helmholtz mechanism (no heat transfer, by contraction) . By this mechanism, Jupiter shrinks 2 cm per day; Jupiter was actually twice as its current diameter and much hotter at the time of formation. For its interior, scientists are not sure whether Jupiter has a icy or metallic core or even no core at all. Jupiter, does indeed, have a liquid metallic hydrogen layer about 78% of the radius. Droplets of helium and neon precipitate in this layer, so little to none is found in the atmosphere. The liquid metallic hydrogen layer is surrounded by a transparent, supercritical (between liquid and gas phases) hydrogen layer. Water clouds’ polarity in the atmosphere cause lightning 1000x stronger than on Earth and winds often reach 100 mph in zonal (zones and belts on Jupiter, falling and rising gases) jets. In addition, Jupiter has orange and brown clouds that change color when exposed to the Sun’s UV light. Unlike Earth, Jupiter has a low axial tilt, giving less solar radiation to the poles, but convection distributes heat to the poles, balancing the temperatures.


Jupiter has the most number of moons at 67. All four moons are named after several of many of Zeus’ lovers in Greek Mythology, which seems appropriate since Jupiter is Zeus in Roman form. First discovered in 1610 by Galileo Galilei, Jupiter’s four moons are Io, Europa, Callisto, Ganymede (or I Eat Green Carrots). Galileo’s discovery of the moons, initially called Cosmica Sidera (“Cosimo’s stars”) proved that there were other celestial objects orbiting other planets— that everything did not orbit around the Earth. With a telescope you can easily see the four Galilean moons orbiting the planet. You can usually see three or four of the moons; sometimes the moon is positioned behind Jupiter so it is not visible on some nights. Io, Europa, Ganymede, and some of the largest satellites in the solar system form the Laplace resonance; every time Io orbits Jupiter four times, Europa orbits two times, and Ganymede one time. The resonance invokes the moons’ gravitational effects to distort their orbits to be more elliptical. In contrast, Jupiter tidal force, which keeps the moons in orbit, circularizes the orbits. The push and pull heats the moon’s interiors by friction. The closer the moon, the hotter, more active, and denser the moon is; the further the moon, the colder, unchanging, and less dense the moon is.

Jupiter’s moons: Io, Europa, Ganymede, Callisto


Io is the innermost of the Galilean moons and fourth largest moon in the solar system. Its surface ever-changing, Io has over 400 active volcanoes. Some of Io’s more than 100 mountains are taller than Mount Everest! Io has a thin atmosphere comprised of sulfur dioxide and silicate rock surrounding a molten iron or iron sulfide core.


Europa is the second Galilean moon and the smallest, slightly larger than Earth’s moon. In contrast to Io, Europa has one of the smoothest surfaces in the solar system, with a layer of ice and water over the mantle of the planet. Scientists hypothesize that water may exist on Europa and that the planet may house extraterrestrials. Heat energy from tidal flexing, or push and pull of Jupiter and its moons’ gravity, keeps the water liquid. Europa has prominent reddish brown markings that may be volcanic water splitting the surface. It also has an atmosphere of oxygen.


Ganymede is the largest natural satellite in the solar system and the third Galilean moon. In fact, Ganymede is larger than even Mercury! Ganymede is icy and the only planet to have a magnetosphere, possibly created by convection with its liquid iron core. Like Europa, Ganymede may also have water (salt), but 200 km below its surface between layers of ice. Its surface comprises of highly cratered dark regions and younger regions with grooves and ridges. Its thin atmosphere includes oxygen, O², and maybe O³ (ozone) and hydrogen.


Callisto is the last and least dense of the Galilean moons. Callisto has an ancient, heavily cratered and unaltered ice surface. It has a homogenous mix of rock and ice.

MISSIONS: Pioneer 10 and 11, Voyager 1 and 2, Ulysses, Cassini, New Horizons, Galileo, Juno (2011), JUICE (2022)


  • Order in Solar System: #5
  • Number of Moons: 67
  • Orbital Period: 11.86 years
  • Rotational Period: 9.925 hours
  • Mass: 1.8986 x 10^27 kg (317.8 Earths)
  • Volume: 1.4313 x 10 ^15 km³ (1321.3 Earths)
  • Radius: 71,492 km (11.209 Earths)
  • Surface Area: 6.1419 x 10^10 km² (121.9 Earths)
  • Density: 1.326 g/cm³
  • Eccentricity of Orbit: 0.048775
  • Surface Temperature (Average): 165 K
  • Escape Velocity: 59.5 km/s
  • Apparent Magnitude: -1.6 to -2.94

The 8 Planets – Part 3: Earth


Earth, our home planet

Imagine a blank sphere floating in the middle of space. Now picture the whole sphere flooded by blue oceans, rivers, and lakes. And seven continents, defined by low elevation green patches, high elevation brown areas, and deserts golden brown. Add white ice caps capping the North and South Poles. And white swirling clouds in the atmosphere. Then tilt the whole sphere 23.5 degrees. There. Our home planet, Earth!

Third planet from the Sun and the only planet to support life, Earth, or the Blue Planet, formed 4.54 billion years ago from accretion of the solar nebula and first hosted life approximately 1 billion years ago. Though technically not named after any Gods, the Greek god Gaea is mother of the earth. Home to millions of species, Earth has the “Goldilocks Phenomenon” since all conditions including climate and temperature support life. Earth is in the “life zone,” where water exists in all three phases: gas, liquid, and solid. Earth’s surface is 30% land and 70% water. Collectively, the biosphere and the abundance of minerals support life. Earth’s atmosphere, specifically the ozone layer, and magnetic field blocks high-energy electromagnetic radiation harmful for life. The axis of the Blue Marble, the largest terrestrial planet, tilts 23.5 degrees, causing the four annual seasons. The hemisphere tilting toward the Sun is in summer and the other is in winter. In fact, Earth’s orbit is nearly circular and Earth is actually closer to the Sun in winter than in summer. Earth’s tectonic activity, or the sliding of tectonic plates, causes volcanic activity and earthquakes that renew Earth’s surface. A viscous liquid mantle and a rigid crust surround a solid core. Earth orbits the Sun once every 365.25 days and rotates once every 24 hours. Earth has one moon, or natural satellite.


The Moon

Earth only has one moon, called the Moon. Reflecting sun light, this natural satellite orbits the Earth once every ~29 days, seen in different phases throughout every month: New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Third Quarter, Waning Crescent. Formed about 4.53 billion years ago, the Moon is an imperfect sphere bombarded by asteroids and comets during the Late Bombardment Period 3.8-4.1 billion years ago. In fact, the Near Side is much smoother than the Far Side (never observed from Earth), so one theory is that the Moon was actually two chunks of material that collided. However, the giant impact hypothesis indicates that a large object collided into Earth’s surface and while some mass fused with Earth, the rest formed the Moon. This theory explains why the Moon’s interior is similar to that of Earth. The Moon’s gravitational pull contributes the movement of ocean tides, stabilizes Earth’s tilt, and gradually slows the Earth’s rotation.


  • Order in Solar System: #3
  • Number of Moons: 1
  • Orbital Period: 1 year
  • Rotational Period: 1 day
  • Mass: 2.9736 x 10^24 kg
  • Volume: 1.08321 x 10^12 km³
  • Radius: 6,371 km
  • Surface Area: 5.10 x 10^8 km²
  • Density: 5.515 g/cm
  • Surface Pressure: 101.325 kPa
  • Eccentricity of Orbit: 0.0167
  • Surface Temperature (Average): 287.2 K
  • Escape Velocity: 11.186 km/s
  • Apparent Magnitude: N/A

The 8 Planets – Part 2: Venus



An inferno fireball on the inside, a smooth yellow marble on the outside. Venus, the two-faced planet known as “heaven and hell.” Beautiful yet dangerous, Venus is rightfully named after the Roman goddess of love and beauty. In modern culture, people associate Venus with beauty products… and Venus Williams, the world champion tennis player.

Shrouded by its thick sulfuric cloud atmosphere, Venus is the second planet from the Sun and the hottest planet on average in the solar system. Also known as the Morning Star or Evening Star, Venus reflects sun light strongly, with a high albedo. Because Venus’ size is similar to Earth’s, Venus is sometimes to referred to as “Earth’s twin” or “Earth’s sister.” Other than size, however, Venus and Earth have nothing in common. Venus’ atmosphere rains sulfuric acid on the dry dessert-like surface! Its thick atmosphere (90 times thicker than Earth’s) composed of mainly CO2 traps carbon dioxide (greenhouse effect) and maintains a searing temperature on Venus. Venus may have harbored water once, but rising temperatures evaporated all liquid water, leaving a volcanically active surface.  Mapped in 1990-1991 by Project Magellan, Venus’ surface comprises of 80% smooth, volcanic plains (70% plains with wrinkled ridges and 10% smooth plains) and 20% two highland “continents” Aphrodite Terra and Ishtar Terra. Venus has little impact craters but various volcanic features such as “novae” (star-like fracture systems) and “arachnoids” (spider-web-like fractures). Scientists know little about Venus’ interior without seismic data, but Venus’ size and density suggest an interior similar to Earth’s. Scientists have attempted to build probes to land on Venus’ surface, but all attempts failed (most only enter Venus’ atmosphere then burn up and crash). Venus’ clouds reflect and scatter 90% of sunlight, so scientists can only map its surface with radar. In fact, Venus’ atmosphere has an ozone layer and its clouds can produce lightning! Unlike any other planet, Venus spins from east to west, in a retrograde motion. Because Venus spins backward, its rotational period is longer than its orbital period; a day on Venus is longer than a year! Unlike Earth, Venus has a negligible magnetic field, unable to divert most solar wind. Like Mercury, Venus undergoes phases as seen from Earth. When Venus is in a crescent phase observers can actually see a mysterious ashen light. In the 17th century, Galileo proved the heliocentric theory with observations of Venus’ phases. Though Venus has no moons, scientists believe the planet had at least one that crashed into its surface. 10 million years after the collision, another impact changed Venus’ spin. Another possibility is that strong solar tides can disturb large satellites. Recently, the Transit of Venus occurred in June, when the planet crossed over the Sun.

MISSIONS: Venera, Sputnik, Mariner, Cosmos, Vega, Pioneer Venus, Magellan, Cassini, MESSENGER, Venus Express

*Many of these missions (Sputnik, Mariner) are series with only some successful and some only fly-bys; Venera is exclusive for Venus


  • Order in Solar System: #2
  • Number of Moons: 0
  • Orbital Period: 225 days
  • Rotational Period: 243 days
  • Mass: 4.8685 x 10^24 kg (0.815 Earths)
  • Volume: 9.28 x 10^11 km³ (0.866 Earths)
  • Radius: 6,052 km (0.9499 Earths)
  • Surface Area: 4.60 x 10^8 km² (0.902 Earths)
  • Density: 5.243 g/cm
  • Surface Pressure: 9.3 MPa
  • Eccentricity of Orbit: 0.2
  • Surface Temperature (Average): 735 K
  • Escape Velocity: 10.36 km/s
  • Apparent Magnitude: -4.9 (crescent) to -3.8 (full)

The Milky Way – Timeline

The Milky Way Galaxy


1750: Immanuel Kant: advocated the “lens-shaped” distribution of stars, or an “island universe” with galaxies like the Milky Way

1785: William Herschel + Caroline (wife): made the first attempt to determine the shape of the galaxy; found few stars near the edge  and many stars toward the center; determined the galaxy to be an irregular “grindstone” or hockey puck

1900: If the Sun is at the center of the Universe, why is it not brighter at the center? Gas and gas prevent seeing far toward the center and light absorbed and refracted by Earth’s atmosphere  only allows us to see a small portion of the galaxy

Harlow Shapley and Herbert Curtis

1920: The Curtis- Shapley Debate

Harlow Shapley: rising star and “golden boy” of astronomy

  • Since globular clusters are not uniformly distributed uniformly around the Sun, the center of the Milky Way must be centered 30,000 light years away
  • Concluded that the Milky Way is much larger than previously believed (>100,000 light years in diameter)
  • The “nebulae” seen are not island universes but contained in the Milky Way

Herbert Curtis: established astronomer and respected

  • Spiral nebulae are galaxies out side the Milky Way, with high recessional velocities
  • Predicted that these spiral nebulae are the right size to be galaxies –> “huge” galaxy idea

While Shapley advanced that the Sun is not at the center of the galaxy and the galaxy is much larger than believed, Curtis argued that since spiral galaxies are external, there must be more big galaxies.

Who was right? BOTH. Who was wrong? BOTH.

Shapley was right the Sun is not at the center of the Universe. Curtis was right the Universe is composed of many galaxies. However, the size of the Milky Way was in-between their estimates.

1920s-1930s: Edwin Hubble: With the Hooker Telescope on Mt. Wilson, Hubble observed Cepheid Variable stars in the Andromeda Galaxy (M31); Cepheid Variable stars are 500-10,000 brighter than the Sun (in absolute magnitudes)

  • 1920s: Discovered that M31’s distance is too large to be within the Milky Way; M31 is a galaxy like the Milky Way
  • 1930s: Further understanding of the distances and distribution of globular clusters; the scientific community accepted that they underestimated the size of the Milky Way and the Sun is not at its center