astronomy review

What is a standard candle?

An object of known brightness that can be used as a distance indicator

What is an Astronomical Unit?

the average distance between Earth and the Sun

When we observe Mars going retrograde, is it actually moving backwards in its orbit?

No. Retrograde motion is seen when the Earth “laps” Mars.

Conservation of angular momentum

if no outside forces are causing it to rotate or change its rotation, the total angular momentum of the system will remain constant

What key observation did Galileo make about Venus?

Galileo saw all phases of Venus, which is not possible in a geocentric cosmology

Why do we say Venus is a morning or evening “star”?

• Venus is an inferior planet, meaning that it’s orbit around the Sun is inside that of the Earth

• Accordingly, it will always appear close to the Sun and therefore can only be observed at morning or evening

What are the two main functions of a telescope?

• increase the amount of light we collect

• resolve smaller features

What is the diffraction limit on a telescope?

The fundamental limit on a telescope’s resolution due to the wave nature of light

What are adaptive optics?

A technique of correction for deformation of light by the atmosphere via a deformable mirror

What is the ecliptic?

The yearly path of the Sun through the background stars

If the Earth’s axis had no tilt, would we still have seasons?

No, we would no longer have seasons

• The seasons are due to the tilt of the Earth’s
  axis changing the angle of the Sun over a year

• If there were no tilt, the angle would always be the same (for a given location on Earth)

• The slight change in the distance to the Sun from the slight ellipticity of Earth’s orbit would not produce much of an effect

We saw that the plane of the Moon’s orbit is inclined about 5◦ from the ecliptic.
If the Moon’s orbital plane was not inclined, so the Moon’s orbit is in the same plane as the ecliptic, how would that affect the frequency of eclipses?

It would increase the frequency of eclipses as there would be one every month

In Ptolemy’s geocentric cosmology, the planets move around the Earth in epicycles.
In this picture, when we see Mars going retrograde, is it actually going backwards in its orbit?

Yes - Retrograde motion is an actual physical backward motion in Ptolemy’s cosmology

True or false: The seasons on Earth are caused by the elliptical orbit of the Earth bring it closer or farther to the Sun

False

Imagine a hydrogen atom with its electron in the first excited state. If the electron drops down to the ground state, the atom:

emits a photon of a specific frequency

Blue light has a higher frequency than red light. Thus blue light has

Higher energy and a shorter wavelength than red light

Images of jellybeans in a jar appeared in a lecture. The point was to illustrate

the concept of binding energy

What astronomer first applied the new “quantum mechanics” to the problem of stellar spectra and classification?

Cecilia Payne-Gaposchkin

Why do O stars have relatively weak hydrogen lines in their spectra?

• O stars have the highest temperatures of any class of stars

• They are hot enough to ionize hydrogen so that there are no electronic states to produce discreet spectral lines

What will be the final fate of the Sun?

It will become a white dwarf

In the lecture, we saw two Hubble Space Telescope images of the Ultra Deep Field. One taken in UV showed several “blue” galaxies indicating strong emission in the UV. What was the conclusion drawn from the observation?

These galaxies have very active star formation as indicated by hot,
massive stars

Some spinning neutron stars emit electromagnetic radiation at their magnetic poles. These are known as

pulsars

At the end of the life of a massive star, it will have an onion-like structure with shells of different elements. What element is the core, the innermost part, composed of just as it collapses?

Iron

What is a planetary nebula?

An expanding shell of gas ejected from a low-mass star near the end
of its life

where is each region of stars located on the HR diagram?

• white dwarfs, main sequence, super giants, red giants (bottom left to top right)