Howard Community College Summer Astronomy 2016: July 2016

Newton
Moon
Sun
Moon phases
The Parsec
H-R diagram
Stellar evolution
Doppler - Red shift / Blue shift
Planets - "Which planet has _____" questions.
Eclipses
Star chart - sky tonight. Be prepared to find 10 or so objects on a "naked" star chart.
meteor showers
weightlessness
minor bodies - comets, meteors, asteroids, etc.

https://vimeo.com/167991139

http://www.physics-astronomy.com/2014/12/11-jaw-dropping-pictures-that-will-make.html?m=1#.V5Eyw0b3anN

http://www.astronomy.com/observing/sky-this-week/2016/07/the-sky-this-week-for-july-15-to-july-24-2016

Life and Death of Stars

H-R Diagram – a graph of luminosity (absolute magnitude, M) versus temperature (stellar type).

Gas and dust – nebula. Collapses. Why?

4.568 billion years ago – our solar system is born!

Protostar heated by gravitational collapse. Leftover material forms planetary system.

Too little mass - <0.1 solar masses – failed star / brown dwarf

The larger the birth mass, the shorter the time to get to the Main Sequence (MS) – tens of millions of years (less than a solar mass) to tens of thousands of years (10+ solar masses).

Nuclear fusion powers MS stars.

Low-mass stars: H to He

High-mass stars must be hotter to offset their larger gravity.

Higher temperature means larger luminosity and shorter lifetime.

Our sun:

G2 star

Absolute magnitude: M = -4.83

Apparent magnitude: m = -26.72

Compare to Sirius (m = -1.43, M = 1.47)

We’ll spend about 10 billion years on the MS, whereas a 10 solar mass star might only spend 10 million years on the MS.

Low mass evolution

H starts to run out, pressure in core begins to drop – gravity “wins”

Outer layer cools and expands, engulfing all inner planets. Sorry. Red giant phase.

Outer layers eventually “flake away” and expand more – planetary nebula, which are super pretty.

Eventually, a small hot core is left – white dwarf

For more massive stars:

H used up rapidly – expand outward

Red supergiant (Betelgeuse)

There is not enough pressure to counter the immense gravity: star explodes – supernova!

What is left in core is a neutron star (mostly neutrons), incredibly small relative to their original size – imagine a many-solar-mass star shrunk to the size of Baltimore!

What about the most massive stars? They may eventually become a black hole.

Tuesday, July 19, 2016

HW 5 - due Thursday or Monday (exam night)

1. Explain the Doppler effect, and give at least one example of its application. Use pictures, if helpful.

2. Look up the official definition for a planet and discuss why Pluto lost its status.

3. What are KBOs?

4. Look up the information for the total solar eclipse in 2017, and plan where you hope to go to see it. Give the time and location.

5. What makes Mars potentially habitable and Venus completely uninhabitable?

6. O B A F G K M ---- what exactly does this refer to?

Monday, July 18, 2016

Online Orrery FYI

https://in-the-sky.org/solarsystem.php

http://www.theplanetstoday.com/

https://www.fourmilab.ch/solar/

http://www.fourmilab.ch/earthview/vplanet.html

https://www.fourmilab.ch/cgi-bin/Solar/action?sys=-Si

Minor Worlds

Dwarf Planets

Pluto, Ceres, Eris, Haumea, Makemake

Pluto

40 AU

Highly elliptical orbit (most others are nearly circular) and greatly inclined to ecliptic

5 moons: Charon (1978), Nix (2005), Hydra (2005), Kerberos and Styx (2011/12)

Largely, Pluto and Charon are a double-dwarf system (tidally locked)

Atmosphere – Nitrogen, Carbon Monoxide, Methane

2 g/cc density - ice and rock – about twice the density of water

If we were standing on Pluto, sun would appear over a 1000 times fainter

Clyde Tombaugh, discover (in 1930) died in 1997

249 year period

Sometimes within Neptune’s orbit (20 years out of every Pluto spin around the Sun)

Frozen planet: -391 F

Mountains, 2-3 km high

Chaotic orbit

Possibly from Kuiper belt in outer solar system

New Horizons (fastest spacecraft ever launched) did a fly-by in 2015

Roughly magnitude 13.5

Very hard to deduce basic info about Pluto – some is done by effects on Uranus

Roughly 1/500 Earth mass

From albedo, bright polar caps were discovered; dark band near equator

Low atmospheric pressure (1/100,000 Earth’s) – layered atmosphere - some methane, and a gas heavier than methane - carbon monoxide or nitrogen

Highly eccentric orbit, highly inclined to ecliptic

I love this quote from NASA: “The New Horizons mission is one of the great explorations of our time; there's so much we don't know, not just about Pluto, but about similar worlds as well. Scientists won't be rewriting textbooks with this historic mission - they'll be writing them from scratch.”

Asteroids

Asteroid belt between Mars and Jupiter

Assigned a number in order of discovery: 1 Ceres, 16 Psyche, 433 Eros

Rarely come within a million km of each other, though there are occasional collisions

Larger asteroids are the same size (roughly) as some of the minor moons

Saturn’s outermost moon, Phoebe, is probably a captured asteroid

Mostly stony, though some are high in carbon

Not the result of a destroyed planet between Mars and Jupiter - old theory

There may be millions of asteroids

Some orbit each other, apparently – Ida and Dactyl

Hayabusa (Japan) landed on Itokaka, sampled it, and returned to Earth in 2010

Named in honor of people, alive or dead

Meteoroids

Small chunks of matter in interplanetary space - up to 10’s of meters across

When one hits the atmosphere, it heats up – meteor (shooting star); around 100 km up, 30 km/s or so

If a part hits the earth, we call it a meteorite

We are bombarded ALL the time - usually these disintegrate, but we’re still hit by tons of stuff per day (micrometeroites). We can actually sample stuff in the upper atmosphere.

Barringer Meteor Crater in Arizona, formed 25,000 years ago or so

On occasion, we’re hit - once in a while by a meteoroid from Mars or the moon

Most meteorites originate from asteroids

Large asteroid impact, some 65 million years ago, is thought to have created the huge crater on the Yucatan Peninsula, and eliminated much life on Eaerth

Meteor Showers - when we pass through comet debris

Regular showers:

Perseids ~ August 12 (Swift-Tuttle)

Leonids ~ November 17 (Tempel-Tuttle)

Geminids ~ December 14 (Phaethon)

Orionids ~ October 21 (Halley)

Kuiper Belt

30-50 AU

KBO = Kuiper Belt Object

The probable home of short-period comets

Predicted in 1951

Several found so far, but there may be as many as 70,000 over 100 km in diameter, between 30 and 50 AU from sun

KBOs: Quaoar, Sedna, Makemake (“Easterbunny”), Haumea (“Santa”)

These may give clues to the history of our solar system, since they are among the oldest objects in it

Oort Cloud

Proposed by Jan Oort, 1950

Comprised of trillions of comets (formed or forming)

A sphere some 100,000 AU in diameter!

On occasion, comets break free of the cloud and orbit the Sun (or elsewhere)

Huge cloud, but again – hypothetical, used to explain long-period comets

Comets

Appartently from Oort Cloud

Periods vary widely (a few years to thousands of years and more)

Tail directed away from Sun

~ 1 dozen discovered each year; most are new, and only

A few are naked eye

Nucleus

Dirty snowball (Whipple theory)

Few km wide

H20, CO2, NH3, CH4, Dust

Hale-Bopp, the most viewed comet of all time, was 40 km wide

Nucleus rotates

Coma

The rest of the comet’s head

~million km across

Surrounded by H-cloud (breakup of water molecules by UV)

Tails can be > 1 AU

Dust Tail - dust particles vaporized from nucleus, left behind, blown slightly away from Sun

Gas Tail - ions fairly straight behind comet

The tail can be sampled

Total mass of comet < 1 billionth Earth mass

Originates from Oort Cloud (probably the long-term comets, at least)

Famous comets: Halley (76 year period), Hyakutake, Kohotek, Shoemaker-Levy 9, Hale-Bopp

Planet Notes - 2

The Gas Giants!

Jupiter

5.2 AU

11.9 year period

11.2 Earth radii

67 (17 are unconfirmed) moons, including Ganymede (which is bigger than Mercury!)

The 4 Galilean moons (Io, Ganymede, Callisto, Europa) are, by far, the biggest

318 Earth masses - it contains 2/3 of the solar system’s mass (other than Sun)

1.3 grams/cc density - this tells us that it has a small solid core

86.1% H and 13.8% He; 1% CH4 and NH3, etc.

Small rocky core (iron, silicates)

Different latitudes on Jupiter’s surface rotate at slightly different speeds - bands of clouds of different color (bright = zones; dark = belts)

10 hour rotation period - this fast rotation causes planet to be oblate (pole to pole diameter is 7% smaller than equatorial diameter)

Great Red Spot - vortex of long lasting storm, counter-clockwise rotation; probably lasted so long due to heat from Jupiter

Most of interior is in liquid form; upper atmostphere is H2

Liquid molecular H in outer core; Liquid metallic (conductive) H in inner core (generating a magnetic field)

Central temp between 13,000 and 35,000 K

Central pressure is 100 million times the pressure of earth’s atmosphere (as opposed to Earth’s 4 million x central pressure)

Radiates 1.6 times as much heat as it receives from Sun

Jupiter is still contracting, however it lacks the mass necessary to become a star

Tremendous magnetic field, some of which is associated with Io; field is opposite Earth’s polarity

Wispy ring at 1.8 times Jupiter’s radius – particles from Io’s volcanoes?

Ring is inside innermost moon; some particle extend to surface

Observed in 1970’s by Pioneeer and Voyager spacecrafts; later by Galileo craft and a probe into Jupiter’s atmosphere, New Horizons (en route to Pluto)

Just reached by the Juno craft

Jupiter radiates 1.6 times as much heat as it receives

A failed star? Maybe - not nearly massive enough

Ganymede is the largest moon in the Solar System

Comet Shoemaker-Levy 9 collided with it in 1994 – we watched from Earth

Named for main Roman god (Jovian is the adjective associated with him)

Most moons are named after lovers, daughters or conquests of Jupiter/Zeus. We do run out of names, though, so some asteroids share the same names (also true for Saturn, etc.)

Saturn

9.5 AU

9x Earth mass

30 year period

The most distant of the visible planets

Possible solid core - 20% of interior

Atmosphere - 92.4% H, 7.4% He, 0.2% methane, plus some ammonia, etc.

Density lower than that of water - it would float! - 0.7 g/cc

10.7 hour rotation period

Radiates 2.5 times more energy than it absorbs Internal heat, but mainly this comes from helium sinking through liquid hydrogen

Strong magnetic field, less than Jupiter’s but stronger than Earth’s

Oblate - 10% difference

2/3 Earth magnetic field, opposite Earth’s polarity

Many of Saturn’s moons are largely water ice

62 (9 unconfirmed) moons, named for gods (Titans, Giants, Inuit and Gallic gods – which include Janus, Mimas, Hyperion, Phoebe, Odysseus)

Observed by Voyager and by Casinni

Awesome ring system - small rocks of ice (1 cm - 1 m across) - FLATTER than a cd!

Rings about 20 m thick - imagine a cd about 30 km across

Ice-coated dust and rock

Gap - Cassini division; other divisions as well - hundreds of thousands of ringlets!!!

First seen by Galileo (“ears”), later by Huygens and Cassini

Roche Limit - inside this radius, mass cannot be held together by its own gravity - it is torn apart by tidal forces on the body; for Saturn, the RL is about 2.5 times it radius. All massive bodies have an RL.

Total mass of rings is about the size of an average moon

In the 1800s, J.C. Maxwell calculated that the only way for the rings to be "stable" was for them to be made of many little rocks

Rings have differing angular velocities

Titan is the second largest moon in the Solar System; bigger than Mercury; by far, the biggest of Saturn’s moons

Uranus

4 x Earth diameter

15 x Earth mass

Hershel discovered it in 1781, the first planet discovered by telescope.

84 year period

>19 AU radius

Thick methane clouds with some hydrogen - to give blue-green color; Hydrogen, Helium, Methane, Water, Ammonia

Axis of rotation is roughly parallel (8°) to its plane of rotation - almost on its side. In other words, Uranus’s equator is at a nearly right angle to its orbit. It is like the planet is “rolling” through space. Collision?

Polar regions alternate light and dark for decades - bizarre seasons?

Surface temp of 58 K - no internal heat

Rings - 1.7 to 2.1 Uranus radius; at least 11 rings (9 are prominent “inner” rings) - moons are beyond

Viewed by Voyager 2

Magnetic field, 50 x Earth’s - asymmetric and inclined to rotation axis (actually, ALL mag. fields are inclined to rotation axes of planets

- Uranus’s is by 31%; Earth’s is 8%); opposite Earth’s polarity

27 Moons, named for A. Pope and Shakesperean literature figures (Puck, Belinda, Oberon, Titania, Ariel, Umbria, Miranda)

Largely nondescript appearance to telescopes

Neptune

30 AU from sun

Similar to Uranus

Deep blue color

165 year period – Neptune completed its first orbit (in 2011) since its discovery

1.6 g/cc density

Radiates 2.7 x more heat than it receives

Triumph of Newtonian astronomy - finding it based on mathematics, 1845/6. Same with Triton.

Possibly observed by Galileo in 1613

Methane atmosphere - many clouds; blue appearance; very windy (more than Jupiter and way more than Earth)

Much data from Voyager 2 (1989)

Great Dark Spot - similar to Jupiter’s spot

59.3 K average temp

Magnetic field, also asymmetric and opposite Earth’s polarity

6 Rings - narrow in general

14 moons, largest of which is Triton (son of Poseidon) which orbits backwards! Captured by Neptune?

The 14^th moon, not yet confirmed, was discovered in 2013.

Viewed by Voyager 2

Planet 9

Suggested in 2014

Not yet actually discovered

10x Earth size (or so)

10-20,000 year period

Highly elliptical orbit, a = 700 AU (!)

Planet Notes - 1

Things I'd like you to remember are in bold italics.

Mercury

• a = 0.4 AU

• Always appears close to Sun - thus hard to see from ground-based scopes

• 59-day sidereal period of rotation - 2/3 (exactly) of its 88-day year - it rotates 3 times for each 2 revolutions - not a synchronous motion like our moon

• Temperatures range from 427 °C (800 °F) to -183 °C (-300 °F); huge temp difference (>1000 degrees F) between night and day). Even so – NOT THE HOTTEST PLANET

• On rare occasions, Mercury transits across Sun (eclipsing it) - 2016

• Albedo (ratio of reflected light to total light hitting body) = 6%

• Similarly, Moon only appears bright to use because it is surrounded by dark sky

• Mariner 10 spacecraft visited in 1974

• less than 1/2 Earth diameter, but similar density (42% iron core)

• Heavily cratered, but flatter craters

• Fine dust on surface; no water, but maybe a little ice?

• Weak magnetic field

• Iron core, 50% of volume and 70% of mass of Mercury

• Thin atmosphere, detectable from Mercury’s spectra - primarily Sodium (and some Helium, Oxygen, Potassium, Hydrogen)

• Lines of cliffs hundreds of miles long - scarps; a wrinkle in the crust

• Features named after historical ships (scarps), the name of Mercury in different languages (plains), nonscientific authors/composers/artists (craters – unlike the craters on the moon which are named for scientists)

VENUS

Atmosphere

• Sulfuric acid clouds (this takes up much water) - must use radar to “see” surface

• Carbon Dioxide atmosphere (>90%)

• Surface air pressure is 90x Earth air pressure

Rotation and Revolution

• Backwards rotation, relative to other planets (perhaps it was struck while being formed)

• 225 day year

• 243 day rotation period

Misc

• a = 0.7 AU; closest planet to us

• 750 K surface (greenhouse effect from thick clouds); hottest and brightest planet (only the Moon is brighter in the night sky)

• Similar density and features

• Venusquakes?

• No magnetic field

• Many probes have been sent to visit Venus

• Basalt surface

• Large rolling plains

• Very active cloud system

• Not highly cratered - smallest meteoroids could have burned up in atmosphere; perhaps some vulcanism

• Probably lightning and volcanic activity

• Only about 16% of Venus below plain

• Huge mountain Maxwell (11 km, 2 km higher than Mt. Everest)

• One continental plate

• Similar gravity to Earth

• No satellites

• Features named after mythical goddesses (major), mythical female figures (minor), and famous women like Sacajawea (other features)

Earth

General – the water planet (71% covered)

• Inner core - iron and nickel (about the size of our

Moon) - rotates a bit quicker than outer core (by 2/3 of a second)

• studied by seismic action

• outer core is liquid, the motion of which causes the magnetic field

• mantle (outside the core) - many silicates; this is the bulk of the Earth

• crust on top (thin)

• crust and outer mantle = lithosphere

• Below lithosphere is aesthenosphere, which is partly melted

• 1/3 of Earth mass is iron

• Gravitational acceleration (local) of 9.8 m/s/s

An active planet

• Natural radiation from within

• Continental drift from geothermal energy

• Plates about 50 km thick

• Plate tectonic activity

• Continents probably once formed Pangaea (“all lands”), which in turn split into Gondwanaland and Laurasia

• Ultimately, California may split from USA, Australia may become linked to Asia, etc.

• Two plates come together, one is often forced under another - volcanoes formed

• Tides are the result of motion around sun and lunar motion - differences between gravitational forces between Moon and Earth at different locations on Earth

Atmosphere

• Nitrogen, Oxygen (>99% total)

• Troposphere (0-15 km, 285-225K) - Earth weather occurs here

• Stratosphere (15-50 km, 225-260K) - upper strat and lower mes contain Ozone layer

• Mesosphere (50-90 km, 260-190K)

• Thermosphere (90+ km, 190-260K) - aka ionosphere; not temperature rise here

Relatively thin when compared to Earth’s radius of 6400 km

Van Allen Belts

• Like a trio of donuts made of charged particles (e-, etc.) held byEarth’s magnetic field

• When hit by solar particles, our atmosphere may glow - aurora borealis, aurora australis (hundreds of km above Earth)

• Earth has strongest magnetic field of the terrestrial planets, and it is not all that strong

Mars

• The red planet (iron oxide?)

• Possible water in its past

• Surface pressure ~ 1% of Earth’s

• 23 Earth month period

• Seasonal, since it has a 25° tilt to axis

• Polar ice cap in the winter (Carbon dioxide, some water?)

• Global dust storm - hundreds of km/hr!

• Changes in appearance possibly once thought to be due to a type of vegetation

• Four types of regions: volcanic regions, canyon areas, expanses of craters, terraced areas near poles

• Channels (some 200 km wide and 7 km deep), some thousands of km long – possibly cut by water in past

• Olympus Mons (25 km high volcano, 600 km at the base!)

• 90% Carbon dioxide atmosphere

• No tectonics

• Yellowish-brown sky, dust abounds

• Once water; once life??

• Temps from 150-300 K with great variation depending on storms

• Originally thought to have canals, but no longer

• about 1/2 Earth diameter; 1/10 Earth mass; 2/5 Earth gravity

• Length of day a bit longer than Earth’s; same for axial tilt

• Smaller core and thicker crust than Earth

• Viking landers, Mars Pathfinder, Mars Global Surveyor, Mars Observer (failed), Spirit, Opportunity, Phoenix, Mars Reconnaissance Orbiter, Curiosity,

• 2 satellites (captured asteroids?) - Phobos, Deimos; cratered asymmetric rocks (15-20 km across – smaller than some asteroids)

• Major features named for Greek mythology (Olympus Mons); smaller features have been named for cartoon and children’s literature figures; some craters name for dead people associated with Mars