Naked-eye Astronomy Flashcards
What causes light pollution?
skyglow
What defines seeing conditions?
stillness of stars
The most ‘still’ stars have an Antoniadi scale value of V and the least still have a value of I.
How can professional telescopes track changes in the atmosphere that affect seeing conditions?
A laser!
The laser is removed from the image in real time.
How does weather affect observations?
Weather affects the sky’s transparency.
Why is the sky blue?
Rayleigh scattering
Blue light has a longer wavelength so it is scattered in the atmosphere.
How can you find Polaris in the night sky?
The two ‘pointer’ stats of the Plough point to Polaris.
How can you find Arcturus in the night sky?
The handle of the Plough ‘arcs’ towards Arcturus.
How can I find Sirius in the night sky?
Orion’s belt points down and to the left to Sirius.
How can I find Aldebaran in the night sky?
Orion’s belt points up and to the right towards Aldebaran.
How can Polaris be used to find information about your location on Earth?
Polaris’ altitude is equal to the observer’s latitude.
The direction of Polaris in the night sky is due North.
How can you find the Andromeda galaxy in the night sky?
Up and to the left of the top left corner of the square of Pegasus
How are meteor showers named?
The constellation that the radiant appears to lie in. e.g: The Perseids, The Lyrids etc…
What points does an observer’s meridian lie on?
NCP, SCP, Zenith, Nadir, (direction of due North)
Which direction to stars culminate in the Northern Hemisphere?
due South
(due North in the Southern hemisphere)
What are cardinal points?
North, South, East and West.
Where is a star when it culminates?
On the meridian.
Facing South if in the Northern hemisphere and North if in the Southern hemisphere.
What is a circumpolar star?
One that never sets below the horizon.
How do you know if a star is circumpolar?
A star is circumpolar if it’s declination is greater than the observer’s co-latitude.
How can you find a star’s altitude when it is at upper transit / culminating?
altitude = latitude + co-declination
How can you find a star’s altitude at lower transit?
altitude = latitude - co-declination
What is Polaris’ azimuth?
0°
How are rilles formed?
Collapse of lava tubes under the Moon’s surface
How are ‘wrinkle ridges’ formed on the Moon?
They form when the basalt cools.
Which was more recently formed: maria or highlands?
Maria
They are formed by lava flowing into a large impact crater, which creates a darker, smoother surface.
How long is a sidereal month?
27.3 days
(must know to 1 d.p.)
How long is a synodic month?
29.5 days
(must know to 1 d.p.)
How are ray systems formed?
Streaks of ‘ejecta’ are thrown out during formation of an impact crater.
e.g: Tycho crater has a visible ray system
Why can we sometimes see the part of the Moon not illuminated by the Sun?
Earth shine (light reflected from the Earth)
What causes the Earth’s shape to be an oblate spheroid?
Centrifugal force during rotation
Identify 3 methods of safely observing the Sun.
Pinhole camera
Telescopic projection
H-alpha filter
Name the regions of the sun from inside out.
Core, radiative zone, convective zone, photosphere, chromosphere, corona, heliosphere.
Where does fusion occur during the main sequence?
The core
Where does fusion occur in a red giant?
A shell surrounding the core
What causes solar flares / sunspots?
The Sun’s magnetic field ‘penetrates’ the surface. In the case of solar flares, this can cause material to be ejected.
What effects of solar wind can be seen on Earth?
Aurorae, formation of comets’ tails, geomagnetic storms.
How can sunspot data be used to find the mean rotational period of the Sun?
rotational period / change in time
=
360 / change in longitude
Temperatures of the Umbra and Penumbra of sunspots:
3,800K at Umbra
5,600K at Penumbra
What is solar wind?
An outflow of charged particles: protons and electrons.
What protects us from solar wind?
Earth’s magnetosphere
Differences between solar maxima and minima:
solar maximum: many sunspots, high space weather, sunspots with high latitude
solar minimum: fewer sunspots, low solar weather, sunspots with lower latitude
Where is an annular solar eclipse visible from Earth?
Antumbra
Why are solar eclipses only briefly visible?
The Moon orbits the Earth, causing the Umbra to move across the surface of the Earth.
The size of the Umbra on the Earth’s surface is also quite small.
What is the inclination of the Moon’s orbit?
5.1°
Why is Jupiter’s moon Io geologically active?
Tidal forces created by the other Moons of Jupiter (Galilean moons) cause internal warming in Io.
How many high tides occur a day? (24hrs)
2
What phases of the Moon do Neap tides occur?
First and third quarter (half moon, 50% illuminated)
What is the Equation of Time?
EoT = AST - MST
(apparent solar time minus mean solar time)
What makes a good shadow stick?
vertical, reasonably thin, on a flat horizontal surface
What can a shadow stick be used for?
Finding the time of local noon and finding longitude.
What is the shape created by a graph of the Sun’s declination against the Equation of Time called?
Analemma
it looks like a bottom-heavy figure-of-eight
What is the Local Mean Solar Time of Greenwich known as?
Greenwich Mean Time (GMT)
What was the method used before the invention of the marine chronometer?
The lunar distance method
The angular distance between the Moon and certain bright stars is compared with a table of values (a nautical almanac)
Who invented the first marine chronometer?
John Harrison
Why was an understanding of astronomy useful in ancient civilisation?
The heliacal rising of a star (when a non-circumpolar star becomes visible in the night sky) could be used to predict events, significant times of year, or for religious association.
An example of this is the heliacal rising of Sirius, used to predict the flooding of the Nile in Ancient Egypt.
How many years does it take for the Earth to make one precession?
26,000 years
What phenomena disproved the geocentric model of the solar system?
Retrograde motion of planets, e.g: Mars
Ptolemy introduced the ‘Ptolemaic model’ to solve the problem of retrograde motion. Describe the Ptolemaic model.
Planets move on epicycles which themselves move on an orbit around the Earth known as the deferent. (All orbits are perfectly circular)
He also moved the Earth away from the common centre of rotation.
When does superior conjunction occur?
When a planet is the ‘opposite side’ of the Sun from the Earth.
Any planet other than Earth can exist in superior conjunction to Earth, including inferior planets.
When does inferior conjunction occur?
When a planet lies ‘between’ the Earth and Sun.
Only inferior planets can exist in inferior conjunction to the Earth.
When is a planet at greatest elongation?
When an inferior planet is observed as far away from the Sun as possible.
The Earth is at a 90° angle to the other planet relative to the Sun.
What is transit?
When an object passes ‘in front’ of another object without fully obscuring it.
This could be a planet, e.g: Transit of Venus.
What is occultation?
When a celestial object fully obscured another object.
Who introduced the idea of Heliocentrism?
Aristarchus of Samos first presented the heliocentric model, however Copernicus published his ideas later and is also credited with the idea.
How can the gravitational force between to objects be calculated?
(mass of first object x mass of other object x a constant) / distance squared
This is the inverse square law
What is Kepler’s first law of planetary motion?
A planet orbits the Sun in an elliptical orbit with the Sun at one of its foci.
What is Kepler’s second law of planetary motion?
The imaginary line joining a planet and the Sun sweeps equal areas of space during equal time intervals as the planet orbits.
(The planet does not have constant speed in its orbit.)
What is Kepler’s third law of planetary motion? (in words)
The square of a planet’s orbiting period is directly proportional to the cube of the semi-major axis of its orbit.
(semi-major axis = mean orbiting distance)
What is Kepler’s third law of planetary motion? (as a formula)
T² / r³ = a constant
or
T² ∝ r³
What does the constant in Kepler’s third law depend on?
The constant in Kepler’s third law is inversely proportional to the mass of the central body.
