Friday, July 29, 2016

Tuesday, July 26, 2016

Astro resources etc.

Folks - thanks for a super summer course.  You truly made me look forward to being in class!  Keep in touch and, more importantly:

KEEP LOOKING UP!


Good astronomy resources - in progress.  I will add more when I can.


Facebook feeds (Twitter as well)


IFLScience

Astronomy.com

Sky and Telescope

Physics-Astronomy

Astronomy picture of the day




Magazines


Astronomy

Sky and Telescope

Make (for those of you who like to build cool stuff)




Smartphone apps


Skyweek

MoonGlobe

Planets

Night Sky

Exoplanet

Puniverse

Phases of the Moon

GoSkyWatch



Sites















Thursday, July 21, 2016

Final Exam

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