A Tour of Our Solar System and Beyond - University of North …n00006757/astronomylectures/ECP4e/Fir… · · 2017-08-28The Terrestrial or Inner Planets: Mercury • diameter =

A Tour of Our Solar System and Beyond

The Sun

• diameter = 1,390,000 km = 864,000 mi

• >99.8% of the mass of the entire solar system

• surface temperature 5800°C

• 600 x 106 tons H -> 596 x 106 tons He per second

– But where does it go?...

• E = mc2

• About 2 mm in diameter on the "auditorium scale"

The Terrestrial or Inner Planets:

Mercury

• diameter = 4880 km

• distance from Sun = 57.9 x 106 km

• Moon-like, with no wind, no rain, no life, no significant atmosphere

• more being learned from Messenger spacecraft

• surface temperature 425°C (797°F) day, -150°C (-240°F) night

• 7 microns on "auditorium scale", about 8.3 cm from Sun


Venus

• diameter = 12,100 km


• very dense atmosphere of carbon dioxide with sulfuric acid clouds and rain

• 450°C (850°F) day and night



Earth



• oxygen-containing atmosphere due to biological activity

• moderate greenhouse effect

• liquid H2O

• 1 moon


"Earth's City Lights" from Goddard Space Flight Center at

http://earthobservatory.nasa.gov/Study/Lights/

http://earthobservatory.nasa.gov/Study/Lights/


Mars



• CO2 atmosphere, low pressure, very cold

• Once had liquid H2O and – possibly – life…Curiosity rover investigates that possibility

• extinct volcanoes

• 2 moons (probably captured asteroids)

• 10 microns on "auditorium scale", about 33 cm from Sun

Asteroids

• rocky

• diameter < 1000 km

• Irregular shape

• millions of km separate them

• left over from formation of solar system

• some danger of impacts to us

The Jovian or Outer Planets:

Jupiter



• “Gas giant” with "rocky" core deep inside

• Massive pressures, high winds, gargantuan storms in H/He atmosphere

• Rings

• Many moons

– One of them, Europa, has a water ocean under its icy rind

– Is there life in that subsurface ocean?

• 0.2 mm on "auditorium scale", about 1.1 m from Sun


Saturn


• distance from Sun = 1427 x 106 km

• Gas giant with rocky core deep inside

• Rings

• Many moons

– Titan: bigger than Mercury, thick atmosphere, subsurface water ocean

– Enceladus: geysers from a subsurface water ocean

– Life again?

• 0.17 mm on "auditorium scale", about 2 m from Sun


Uranus



• Less proportion H and He than Jupiter and Saturn, more ices, so called “ice giant”

• Rotates on side

• Rings

• Many moons



Neptune



• Similar to Uranus

• Rings

• Many moons

– Triton: orbits in opposite direction of Neptune's rotation suggests it was captured


No longer a planet…now a dwarf planet:

Pluto



• Rock and ice

• Orbit elongated and tilted

• Sometimes closer to Sun than Neptune

• At least 5 moons – Charon, Nix, Hydra, P4, P5

• Pluto is more like a giant comet-like Kuiper belt object than like the other planets

• So it is now classified as a “dwarf planet”

• 3 microns on "auditorium scale", about 8.5 m from Sun

What are planets?

(International Astronomical Union)

• A “planet” is a celestial body that

• is in orbit around the Sun,

• has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and

• has cleared the neighbourhood around its orbit.

• The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

• A "dwarf planet" is a celestial body that

• is in orbit around the Sun,

• has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape,

• has not cleared the neighbourhood around its orbit, and

• is not a satellite.

• Currently, the dwarf planets are Ceres, Pluto, Haumea, Makemake, and Eris (previously "Xena").

• All other objects, except satellites, orbiting the Sun shall be referred to collectively as “small solar system bodies".

• These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.

Comets

• the most distant solar system bodies

• a trillion of them

• ice and dust

• Kuiper belt - Pluto-like giant comets as well as smaller ones

• Oort cloud - very large, maybe 1 ly radius, which on "auditorium scale" is about from UNF to Regency Square

Comet 67P/Churyumov-Gerasimenko

Imaged by Rosetta on 3 Aug 2014

distance = 285 km

Beyond the Solar System

• Interstellar space

• The nearest star is…

• the Sun

• But beyond the solar system the nearest is Proxima Centauri

• 4.2 ly away

• on "auditorium scale", this is 57 km, about the distance from UNF to St Augustine

• Proxima Centauri is part of the star system Alpha Centauri, which is part of the

constellation Centaurus

• An image of Centaurus follows

•How should you interpret images of the night sky like this one?

•For example, some of the stars are bigger than others

•So can you learn the size of stars from images like this?

•NO! The size in an image depends on brightness

•Stars are really the size of points

•On the auditorium scale, the nearest star is in St Augustine

•Think of it as looking at a bb—a bright one—in St Augustine!

•Can you learn how close stars are to each other?

•NO!

•Stars that are close in the sky may be far apart:

•Alpha Centauri 4.4 ly

•Beta Centauri 526.1 ly

•Can you learn how close stars are to you?

•NO!

•Closer stars are not always brighter:

•Gamma Centauri 130.46 ly

•Beta Centauri 526.1 ly

•Can you see planets?

•NO!

•Planets are very small and dim compared to stars

•even so...more than 3500 extrasolar planets have been found!

•The Extrasolar Planets Encyclopedia

http://exoplanet.eu/

The Milky Way – Our Galactic Home

From http://www.atlasoftheuniverse.com/milkyway.html

• Our Sun is located in the Orion Arm of the Milky Way…

about 28,000 light years from the center

• on the auditorium scale, that’s about the distance from

the Earth to the Moon



• The Milky Way galaxy contains about 100 x 109 stars




• In the total observable universe, there are that many galaxies





• So there are 100 x 109 x 100 x 109 = 1022 stars





• So there are 100 x 109 x 100 x 109 = 1022 stars

• more than all the grains of sand on all the beaches on Earth!

Beyond the Milky Way

The Milky Way is one of 3 dozen or so galaxies comprising the Local Group


One of these is the Andromeda Galaxy, M31


The Andromeda Galaxy, M31

2.5 million light-years away



2.5 million light-years away…to the orbit of Venus on the auditorium scale

100,000 light-years across



2.5 million light-years away…to the orbit of Venus on the auditorium scale

100,000 light-years across…2X the diameter of the Moon’s orbit

It’s interesting to think about

what we see when we look at

this galaxy…

Beyond the Local Group – The Hubble Deep Field

• In the sky, this

image spans about

the same width as a

dime viewed at 75

feet

• In the sky, this

image spans about

the same width as a

dime viewed at 75

feet

• It contains at least

1,500 galaxies

• This more recent

image of about the

same amount of sky

as the HDF was

made with a longer

exposure


image of about the

same amount of sky

as the HDF was

made with a longer

exposure

• It contains 10,000

galaxies


image of about the

same amount of sky

as the HDF was

made with a longer

exposure

• It contains 10,000

galaxies

• Multiplying this

number of galaxies

by the number of

HUDFs it would take

to cover the entire

sky is where the “100

billion galaxies in the

observable universe”

comes from

• This is a 2° slice of the sky from an Australian observatory

• It shows the location of galaxies within the slice

• They lie on filaments that extend throughout the universe

• The edge on auditorium scale is 6 times farther from the Sun than Neptune

• This tour should have given you a better sense of our place in space

• Now let’s get a sense of our place in time with…

• The Cosmic Calendar

The Cosmic Calendar.ppt

Documents

A Tour of Our Solar System and Beyond - University of North …n00006757/astronomylectures/ECP4e/Fir… · · 2017-08-28The Terrestrial or Inner Planets: Mercury • diameter =