Astro 89: Celestial Sphere, Motions, and Powers of Ten

Flashcards reviewing celestial sphere concepts, astronomical coordinates, seasonal solar movement, telescope fields of view, scientific notation, orders of magnitude, and astrophysical scales.

What imaginary line on the celestial sphere divides the sky into a northern and a southern half?

The celestial equator

How many degrees are equivalent to $360''$ (arcseconds)?

$0.1^\times10^0$ degrees (or 0.1^\bar{\text{ }} = 0.1^\times10^0 = 0.1^\text{o})

On the celestial sphere, which coordinate corresponds to latitude and which corresponds to longitude?

Declination corresponds to latitude, and Right Ascension corresponds to longitude.

What is the approximate angular size of both the Sun and the Moon as seen from Earth, which can be covered by an outstretched pinky finger?

About $0.5^\times10^0$ degrees ($0.5^\text{o}$)

How does an official astronomical constellation differ from an asterism?

A constellation is a precisely defined region of the celestial sphere (there are 88 official constellations defined by the IAU), whereas an asterism is a prominent pattern or group of stars ("connect the dots" shape) smaller than a constellation.

What is the angle of Earth's axial tilt with respect to its orbital plane (the ecliptic)?

$$23.5^\text{o}$$

In the Northern Hemisphere, on what dates do the summer solstice and winter solstice occur, and where does the Sun rise on those days?

The summer solstice occurs on June 21 (Sun rises at its northernmost point); the winter solstice occurs on December 21 (Sun rises at its southernmost point).

What is the figure-8 pattern called that maps the position of the Sun at noon over the course of a year?

An analemma

How does a sidereal day compare in duration to a solar day, and why?

A sidereal day (1 full $360^\text{o}$ rotation of Earth relative to the stars) is about 4 minutes shorter than a solar day (time from one apparent noon to the next).

What is the furthest north latitude at which the Sun will pass directly through the zenith at least once per year?

Tropic of Cancer ($23.5^\text{o}\text{ North}$)

How does the field of view of the Nancy Grace Roman Space Telescope compare to that of the Hubble Space Telescope (HST)?

Roman's field of view is approximately 100 times larger than Hubble's.

In the class numerical conventions, what numbers correspond to 1 million, 1 billion, and 1 trillion?

1 million = $1,000,000$ ($10^6$), 1 billion = $1,000,000,000$ ($10^9$), and 1 trillion = $1,000,000,000,000$ ($10^{12}$).

Which metric prefixes correspond to the factors $10^{12}$, $10^9$, $10^{-6}$, and $10^{-12}$?

$10^{12}$ is tera (T), $10^9$ is giga (G), $10^{-6}$ is micro ($\mu$), and $10^{-12}$ is pico (p).

By how many orders of magnitude is the radius of the Sun ($7.0 \times 10^8\,\text{m}$) larger than the radius of the Earth ($6.4 \times 10^6\,\text{m}$)?

2 orders of magnitude (a factor of $10^2 = 100$ times larger).

In Centaurus A ("CenA"), what are the physical length scales in meters for the supermassive black hole's jets, the spinning gas disk, and the Schwarzschild radius?

The jets extend across ~$4 \times 10^{20}\,\text{m}$ (~$40,000\,\text{ly}$), the spinning gas disk is ~$10^{17}\,\text{m}$ (~$10\,\text{ly}$), and the Schwarzschild radius is ~$10^{11}\,\text{m}$.

What is the duration of the silicon-burning stage in the life of a massive star before it explodes?

1 day (~$0.003\,\text{years}$)

What is the approximate order of magnitude distance in meters between the Milky Way and the Andromeda galaxy?

$$10^{22}\,\text{m}$$