Topic 6 Flashcards
What is the appearance of a star in the night sky?
Appears to be a point of light in the sky that scintillates
What are the two types of double star and why are they different?
Binary star & optical binary.
Optical binary stars do not share a common centre to orbit.
What is a binary star?
2 + stars that shave a gravitational bond and orbit around a common centre - they appear to be two closely positioned points of light
What is an optical binary?
Two stars that appear close, and to be binary but are unrelated by gravitational attraction
What is a constellation?
A group of stars that appear to make a pattern in the sky.
We see different throughout the ones year due to our rotation and axial tilt.
What is an asterism?
A pattern of stars that may or may not be linked to a constellation
- the plough is in ursa major
- Deneb is in Cygnus
What is the difference between a constellation and an asterism
They’re both patterns of stars. However, constellations are a group of 88 recognised official patterns. Asterisms are smaller patterns within constellations, nothing official.
The asterism The big dipper / the plough is a part of the constellation called ursa Major
What is a star cluster?
Groups of stars which are gravitationally bound.
What are galaxies?
Gravitationally bound system of stars, stellar remnants, interstellar gas, dust & dark matter
What is a nebulae?
Cloud of gas & dust in outer space, visible in the night sky as either an indistract bright patch or a silhouette against other luminous matter
Appearance of a planet in the night sky
Appear as a point of light in the sky that does not scintillate due to now close they are relative to Earth
What is a comet?
Balls of frozen gases, rock, and dust that orbit the sun.
- point of light clearly noticeable over a short period of time
- vast trails of ice & dust over a large portion of sky
What is a meteor?
Small, rocky, irregular lumps of debris in the solar system
- often originating from the dust trails of comets, forming a group called meteoroid streams and are the source of meteor showers (emerging from the radiant)
- many meteoroids enter the atmosphere and friction causes them to burn up and produce a streak of light (meteor/shooting star)
- streak of light lasts a matter of seconds
What is aurorae?
Bands of coloured light in the sky, curtains of light
- when the solar wind interacts with the atmosphere
What is a supernovae?
Burst of extremely bright light in the sky, very rare
- it is the death of a massive star
How does an artificial satellite appear?
Slow moving, very faint objects orbiting in a polar orbit, viewable on the median
How do aircraft appear?
Multiple bright white & red lights slowly moving over the sky
How does the milky way appear?
Faint grey band in the sky
What is light pollution and how does it affect viewing?
Optical light from human sources.
It reduces contrast in the sky and ruins vision at night.
What things can obstruct viewing at night?
-Air pollution
-Saharan dust
-clouds
-mountains (landscape)
-other celestial bodies
can reduce clarity
What is The celestial sphere?
The imaginery sphere around Earth.
What is right ascension and where is it measured from?
Longitude of a star from the first point of Ares ( imagine a clock)
What is RA measured in?
Hours, minutes, seconds
How to and right ascension?
Find degrees that an object is east of the F.P.A.
360/x = y
24/y = RA
Find the right ascension of a Star that is 90 degrees East
360/90 = 4
24/4 = 6hr RA
What is declination and where is it measured from?
Latitude of a star from the celestial equator measured in degrees, arc minutes’, and arc seconds”
-arc minute is 1/60 degree
-arc second is 1/60 of an arc minute
-3600” in 1 degree
What position in the sky is a star with the declination +45 from the equator
45 degrees
What is the altitude of an object?
How high an object is in the sky from the horizon
-measured in degrees
-90 degrees = zenith
What is the azimuth of an object
How eastward ain object is by due north (bearing)
-measured in degrees
-90 degrees = due east
Which altitude does the latitude of an observer equal?
North celestial pole
What is the meridian
Imagine line passing through the north Pole, south pole, and the observer
What is the local sidereal time?
The LST of an observer is the RA of a star on the observer’s median.
if the RA us 5hr35min when it crosses the observer’s meridian then the LST is 05:35
True or false: a person on a meridian in London will see the sun culminate earlier than someone in Bristol (2 degrees west)?
True
What is hour angle and how is it measured?
Hour angle is the angle between the meridian of the observer and the meridian of the star
- this line is called the houn circle.
- measured in hours, minutes, seconds
What is the hour angle of a Star if an observer is looking at a star due west of their position, at 9pm The Star transits the observers meridian at 11:30pm
2hr30min HA
What direction do we calculate hour angle? How far is a Star 1 hour East of the meridian(2hr30min HA)
23 hours, Westwards
What is the formula for Hour angle
HA=LST-RA
The Star Betelgeuse rises from London at 20:03 on the 23rd November. What time will it rise on the 30th November (stars rise approx. 4 mins earlier each day)
23/11 to 30/11 = 7 days
7x4=28
20:03- 00:28=19:35
Betelgeuse rise at 19:35 on the 30th November
What are cardinal points
North, south, East, west on compass
What is culmination?
Culmination is when a star reaches the observer’s meridian
What is upper culmination? And what is lower culmination
- when a star is at its highest point in the sky
- when a star is at its lowest point in the sky
What is a circumpolar star?
A star that reaches both upper and lower culmination above the horizon
What is co-declination? what is the formula?
The distance between the north celestial pole and a star,
Co-dec = 90-declination
What is a seasonal star?
Stars seems at various points in the year due to axial tilt and orbit of Earth
How do you determine whether a Star is circumpolar or not?
90 degrees- declination < latitude of observer
What is co-latitude and How do you work it out?
The distance between the latitude of the observer and the celestial pole
Co-dec = 90- latitude of star
Betelgeuse has a right ascension of 05hr55min. It culminates at 02:03 on the 6th January. Rigel culminates at 01:23 on the 6th January, what is Rigel’s right ascension?
01:23 minus 02:23=difference of -40 minutes
05:55-40 minutes = 05:15min= right ascension of Rigel
Betelgeuse has a right ascension of 05hr55min. It culminates at 02:03 on the 6th January. Rigel culminates at 01:23 on the 6th January. On the same day Sirius has a right ascension of 06h45m What time does it culminate?
06:45 - 0:55 = difference of +50 minutes
62:03 +50 minutes =02:53
The Star Betelgeuse rises from London at 20:03 on the 23rd November. A person 3° west sees the star culminate at What time?
1° West = difference of +4 minutes
3° = 12 minutes
Star culminates at 20:03+0:12=20:15
As saying Polaris has a declination of 90° north At what angle in the Sky would it be visible from these locations?
A) Beijing 40°N
b) Bombay 19°N
C) Wellington 41°S
A) 40°
B) 19°
C) it is not visible as it would be 41° below the horizon when culminating
A star seen from London (51°) culminates at 30° above the horizon . What is the star’s declination
90-51=39
30-39 =9°N
A star culminates at 50° it has a declination of +20° - What is the latitude from where it’s observed?
The altitude is equal to the declination + (90 ° -latitude) the latitude is the declination - altitude +90°
20°-50° +90° =+60°
A person on the Tropic of Cancer measures the angle of the Sun at midday on different days. What angle is it at on these dates?
a) March 21st
b) June 21st
c) september 21st
d) december 21sr
a)66.5 degrees
b) 47 degrees
c) 66.5 degrees
d) 90 degrees
It is midday on December 21st. What angle is the Sun in the sky at these locations?
A) tropic of cancer ( 23.5° North)
B) Sydney ( 34° South)
C) South Pole ( 90° South)
D) London (51° North)
Bear in mind the sun has a declination of -23.5 (South) above the equator. It is at the zenith from the tropic of capricorn
A) 90- 23.5 = 43 degrees
B) 90- (34 + 23.5)= 79.5 degrees
C)90-(90+23.5)=23.5 degrees
D)90-(51-23.5)=15.5 degrees
Geoff and Billy observe the Star Capella at different places. Geoff sees Capella Cross the meridian at 19:00. Billy is 3° East of Geoff.
What time does Billy see Capella Cross the median.
A year later the same happens, only Billy sees Capella 10 minutes later than Geoff. How far has Billy gone?
1° = 4 minute difference. 3°=12 minutes, East means the number is negative so sees it sooner
19:00 - 12 minutes = 18:48
4 min difference= 1 degrees, 10 minutes = 2.5° difference. Seeing the star later means he is now west so he is 2.5° west of Geoff.
When does upper culmination take place?
Right acsencion= LST
