Astronomy 1020-HSpring_2015

Day-30Stellar Astronomy

Sometimes you learn more from finding out that you do not understand a process.

Our first detections of neutrinos were not what were expected.

PROCESS OF SCIENCEPROCESS OF SCIENCE

Course Announcements

• Smartworks Chapter 14: Friday• 2 Dark night observing sessions left:

• Mon. Apr. 13 & Thurs. Apr. 16

• Reports are due Wed. Apr. 22• Solar Rotation Project due Mon. Apr. 27

• Exam-3: Fri. 4/10

Astronomy in the Fall, 2015

ASTR-1010/1011 - Planetary Astronomy + Lab (H,R)ASTR-1020/1021 - Stellar Astronomy + Lab (R)ASTR-2010 - Problems in Planet AstronomyASTR-2011 - Intro. to Observational AstronomyASTR-4000/4001 – Astrophotography & LabASTR-4170 – Special Topics in Astronomy

Photometry and Filter SystemsTR; 3:30-5:00; B310

Energy TransportMechanisms of moving energy:

Radiative transfer (photons).

Convection (rising/falling of hot/cool gas).

Inner part of the Sun: radiative zone.

Outer part: convective zone.

Surface: radiation emitted into space.

Energy from the core takes 105 years to reach the surface.

Sound waves move through the Sun. This makes surface and interior waves. Doppler shifts give the speed of wave motion.

Speeds depend on the Sun’s composition and the depth of the convection zone.

Observations agree with models. This is called helioseismology.

Temperature decreases outward in the photosphere; increases inward.

Atmosphere density drops very rapidly with increasing altitude.

Photosphere: layer where light is emitted (apparent surface).

Effective temperature: 5780 K.

Limb darkening: Because we look through less material at the edges, it appears darker.

Cooler outer layers absorb some of the light from hotter, deeper layers.

Produces a complex absorption spectrum from the presence of over 70 elements.

Chromosphere: above the photosphere.

Higher temperature than the photosphere.

Gives off a reddish emission-line spectrum.

Corona: above the chromosphere.

Very hot: T = 1 to 2 million K.

Emits X-rays. Can extend for several

solar radii. Not visible with the eye

unless there is a solar eclipse.

Concept Quiz—Regions of the Sun

From hottest to coolest, the layers in the Sun are

A. corona, photosphere, chromosphere.B. corona, chromosphere, photosphere.C. photosphere, chromosphere, corona.D. photosphere, corona, chromosphere.

Sun’s magnetic field structures the atmosphere.

The solar wind: Charged particles flow away from the Sun through coronal holes, where magnetic field lines also extend away.

Sunspots: cooler areas in the photosphere. Structure: dark inner umbra with surrounding

penumbra. Caused by magnetic fields.

Sun shows an 11-year sunspot cycle (part of 22-year magnetic cycle).

Solar maxima: most sunspots and activity. The Maunder Minimum showed a distinct

lack of sunspots between 1645 and 1715.

Concept Quiz—Sunspots

Sunspots have temperatures of about 4500 K. Why do sunspots appear to be dark?

A. They don’t emit any light.

B. They emit light, but mainly in the ultraviolet.

C. They emit less energy per square meter than the photosphere (Stefan-Boltzmann).

D. Light can’t pass through magnetic fields.

The flux of an object is the amount of energy coming out of a square meter of surface every second.

The temperature of a sunspot on the Sun is about 1500 K less than the Sun’s surface.

MATH TOOLS 14.2MATH TOOLS 14.2

Solar prominences: hot rising gas in the chromosphere constrained by magnetic fields.

Solar flares and coronal mass ejections are highly energetic, violent bursts and eruptions.

Correlate with sunspot positions.

Solar activity changes slightly over time. Solar storms can disrupt electric power grids

and satellites. Cause brilliant auroras.

Sun’s reach of influence on its environment is the heliosphere.

Solar wind pushes away material and helps protect Earth from harmful cosmic rays.

Solar magnetic fields also create other atmospheric phenomena

plagesfilaments

These features arefound in the chromosphere.

The most powerful solar flare in 14 years,... erupted from sunspot 486 in late October of 2003. The explosion hurled a coronal mass ejection almost directly toward Earth, which triggered bright auroras when it arrived on Earth.

Solar Flares

Produces a magnetosphere that deflects and traps particles from the solar wind protecting Earth

Earth’s Magnetic Field

Exam - 3