Topic 3 Flashcards
What do stars look like?
Stars look like points of light in the sky
They twinkle towards the horizon
They are very far away
What do true binaries look like?
True binaries are double stars that orbit each other
What do optic doubles look like?
Optic doubles are double stars that look like two very close stars, but are in fact far from each other
What do open clusters look like?
Open clusters are groups of stars that are close to each other in space.
They are usually very bright
Young stars are often found in open clusters
What do globular clusters look like?
Globular clusters are more packed than open clusters
Often spherical
Have a large concentration of stars towards the cluster’s nucleus
Old stars are usually found in globular clusters
What do nebulae look like?
Nebulae are faint, blurry, fuzzy patches of light in the sky
What do asterisms look like?
Asterisms are patterns of stars in the sky (eg the Plough)
What do constellations look like?
Constellations are a recognisable pattern in the sky.
There are 88 official constellations
How are stars labelled according to their brightness?
They are named using a Bayer Designation
The brightness is indicated by a greek letter, with the brightest star being “alpha”, followed by the constellation the star is in.
e.g. Alpha Centauri
How was the official list of constellations established? Is this list the same for all cultures?
The original list was written by Ptolemy, who based the constellations around Greek mythology.
The list was developed until eventually, the IAU designated 88 official different constellations.
Asian and Latin American cultures have different constellations
(e.g. Capricornus is a sea goat in the West, but an antelope for the Indians)
Can you draw the Plough, Orion, Cygnus and Cassiopeia?
refer to http://tinyurl.com/constellationdrawings
What are the pointer stars in Ursa Major, and where do they point to?
The two stars on the end of the “pan” shape of the plough in Ursa Major point to Polaris
The “handle” of this “pan” can be used to find Arcturus
What are the pointer stars in Orion, and where do they point to?
Orion’s belt points westwards and down to Sirius, and eastwards to Aledebaran and the Pleiades Cluster
What are the pointer stars in Pegasus, and where do they point to?
The top left star in the Pegasus square points to the Andromeda Galaxy
The bottom right star of the Pegasus square points to Formalhaut
Can all constellations be seen all year round?
No, only circumpolar constellations can. Some constellations are seasonal, and so are blocked by sunlight when they are out, and some are blocked by the sun as they are too close to the ecliptic
What is “right” ascension and “declination”?
Right ascension is the distance eastwards from the celestial prime meridian - measured in hours & minutes
Declination is the degrees north or south from the celestial equator
Why does Polaris appear fixed in the night sky?
Polaris appears fixed in the night sky as it is a pole star, with a latitude of 90 degrees, meaning it lies very close to the axis of the Earth’s rotation
What is the Altitude of Polaris equal to?
The Latitude of the Observer
What is a circumpolar star, and how do you work out if a star is circumpolar?
A circumpolar star is one that is always above the horizon and never sets below your horizon.
A star is circumpolar if its declination > 90 - latitude
Deneb has a declination of 45 degrees. Will it be circumpolar from London?
Deneb’s declination = 45 degrees
Is it circumpolar from London?
45 > 90 - 51
Deneb is not circumpolar from London as 39<45
Alpha Centauri has a declination of -61 degrees. How far south would you have to be to see it as a circumpolar star?
Alpha Centuri’s declination = -61 degrees (61 degrees South)
61 > 90 - 29
Therefore you would need to be at a latitude of 29 degrees South
What is a long exposure photograph, and how can one use it to find the length of a sidereal day?
A long expose photograph will produce a picture showing star trails.
By measuring the time taken for a full circle in a circumpolar star in a star trail, you can find the length of a sidereal day by doing:
Rotation Period of Earth / Exposure Time =
360 / Mean Arc Angle
What is a planisphere and how do you use it?
A Planisphere consists of two discs fastened to each other
Around the edge are the hours of the day
On the bottom disc is a star map showing the constellations
The edge of the round area is the horizon
e.g. to find the stars available on the 4th of September at 10pm, you would move the hour dial on the overlay next to the date on the underlay and point the planisphere north to see what stars would be in the sky
What is the ecliptic and the zodiacal band?
Ecliptic: the path of the apparent movement of the sun
Zodiacal band: a region of the sky +/- 8 degrees of the ecliptic. It is where we find the path of all the planets
