3.2:observing The Night Sky Flashcards
Go do astronomers locate objects in the sky
Use a system of grid lines similar to those of longitude and latitude on a conventional map.the astronomical equivalents are called right ascension and declination
Do seas, nebulae and galaxies have fixed co-ordinates
Yes
What are the co-ordinates for the sun, moon and planets
They aren’t fixed due to the various orbital motions of the Earth and planets around the sun and the moon around the earth
What was zero right ascension chosen to be
The celestial equator at which the sun moves from the Southern to the Northern Hemisphere (this occurs around march 21st every year
What is right ascension expressed in
In hours and minutes eastwards (1 hour is equivalent to 15°)
What is polaris’ declination and why is it used for navigation
+90° and is useful since it not only indicates the northerly direction but also can be used to determine latitude. This is because the angular elevation of Polaris above the northern horizon is equal to the observers latitude
What are circumpolar stars
Stars that dont dip below the northern hemisphere and so are always visible
If looking in a northern direction why to stars appear to rotate in a anti-clockwise sense about Polaris
Due to the earth’s rotation from west to east
How can we determine if a star will be circumpolar
Declination > 90 - observers latitude
Where do stars in the south rise and set
Rise in east, set in west;in northern hemisphere this makes them appear to move across sky from left to right
Where do stars appear at their brightest
When they reach their highest elevation during their motion around sky as light received from them has least amount of atmosphere to pass through
What does culminate mean
Cross the observers meridian
How can you calculate the time a star will culminate
If a star whose right ascension is known is crossing an observers meridian the subtracting the RA from the desired stars RA will give an angle in hours and min
The equivalent time difference will give the interval if tune before desired star crosses meridian
What 4 things should you consider when planning a suitable naked-eye observing date
- phase of the moon ideally new
- weather forecast ideally clear
- likelihood of meteor shower
- visibility of a comet,planets or interesting Messier objects
Equipment needed for naked-eye observing
- torch with red filter
- warm clothes and refreshments
- clipboard,prepared star chart
- comfortable chair
