Mock Revsion Help Sheet Flashcards
Moon parts
. Sea of crisis . Apennine Mountains . Sea of tranquility . Tyco crater . Kepler crater . Copernicus crater . Ocean of storms
Constellations + pointers
. Cassiopeia
. Cygnus
. Plough- Arcturus and Polaris
. Orion - Sirius, Aldebaran and Pleiades from Orion’s Belt
. Great Square of Pegasus - Fomalhaut and Andromeda
. Southern Cross
. Summer Triangle
Celestial equator
Line on sky above the equator, 0 declination
Ecliptic
Plane on which the Earth orbits the sun, and so the line across the sky upon which the sun appears to move
Zodiacal band
Region of sky a few degrees either side of the ecliptic where the sun and all the planets are always found
Observers meridian
Imaginary line across the sky from the observers southern horizon to the observers northern horizon, also point where objects culminate
Observers zenith
The location directly above the person in the sky, 90 degrees from ever horizon, 90 degrees altitude
Autumnal equinox
Where the ecliptic and the celestial equator meet and the Sun moves from the northern sky to the southern sky (declination 0°)
Winter solstice
Sun has lowest possible declination of -23.5° so the northern hemisphere is tilted directly away from the Sun and it is furthest south from the celestial equator it will get
Vernal equinox
Where the ecliptic and the celestial equator meet and the Sun moves from the southern sky to the northern sky (declination 0°),
Summer solstice
When the Sun has highest possible declination of +23.5° so the northern hemisphere is tilted directly towards the Sun and it is furthest north from the celestial equator it will get.
Tropics
The Tropic of Cancer is L = +23.5° and the Tropic of Capricorn is L = -23.5°. This angle is because that is the tilt of the Earth from 90° away from the ecliptic. Therefore the tropics are the most northerly and southerly latitudes respectively where the Sun can appear on the observer’s zenith (which it does on 21st June for Cancer and 21st December for Capricorn).
What is the Right Ascension of the First Point of Aries, and on which date is the Sun in front of it
FPoA RA = 0 h. The Sun is in front of it at midday on the vernal equinox (about 20th March).
Dave observes that the Sun is due south at his location on a particular date when his watch (set to GMT) says 11:48. The value of the Equation of time for that date is –4 minutes.
What is his AST
1200 – Sun due south means it is on the meridian, culminating, shadows pointing due north, shadows shortest.
MST equation
MST = AST – EoT
Dave observes that the Sun is due south at his location on a particular date when his watch (set to GMT) says 11:48. The value of the Equation of time for that date is –4 minutes.
Calculate MST
MST = AST – EoT = 1200 – (-4) = 1204
Longitude equation
L = ¼(MST – GMT)
Dave observes that the Sun is due south at his location on a particular date when his watch (set to GMT) says 11:48. The value of the Equation of time for that date is –4 minutes.
Calculate Dave’s longitude
L = ¼(MST – GMT) = ¼(1204 – 1148) = ¼(16) = +4°. Positive means E, so 4°E.
What is the radiant of a meteor shower?
The radiant is the point on the sky from which all the meteors seem to come. It is there because as the Earth moves into the region of debris, the first point on the Earth’s atmosphere will be where the rocks fall in from – perspective.
How to name a meteor shower
The names of the meteor showers are from the constellation that is behind the radiant. Eg Perseids has the radiant in front of Perseus.
How to find out where a meteor’s radiant is
- Go out with a star chart or graph paper on a dark, clear night.
- Wait 20 minutes+ to get dark-adapted eyes.
- Watch for a meteor, and put the streak on the star chart (if using graph paper, you’d have to plot a good few stars first!).
- Repeat this process for many meteors.
- Feed the line of each streak backwards until you find a point where all the lines cross.
- Mark on the radiant at this point, and identify the constellation it is in front of to name the meteor shower.
How to prepare for naked eye astronomy
. You must dress warmly (clear sky = cold night)
. Spend at least 20 minutes outside without looking at light sources, so your eyes become dark-adapted (the pupils expand so that more light can enter and you can pick out fainter objects).
. Any light to help should have a red filter on it as the pupil does not respond much to red. The cells at the edges of our retina are more light-sensitive than those in the middle, so looking past/to the side of an object (averted vision) rather than directly at it means it will appear brighter.
Seeing conditions vs weather
Seeing conditions is about the stillness of an object on the sky (whether it is twinkling or not) caused by the amount of movement of air. Weather affects how transparent the sky is (clouds etc).
What is magnitude
Absolute magnitude is the brightness of an object as viewed from a distance 10 pc. Apparent magnitude is the brightness of an object as viewed from Earth. With the naked eye, we can make out apparent magnitudes down to +6 (dimmest). The brightest apparent magnitude in the sky is about 0.