GCSE Astronomy

Observing

Size on the Celestial Sphere

The Square of Pegasus is a notoriously 'hard' object to find in the sky insofar as it looks straightforward on a star map but can prove difficult to find if you have no inherebt idea of its size in the sky. The usual advice given is to recognize that the Sun and Moon both subtend about half a degree on the sky.

Dark Adaption

To make the best use of observing time, your eyes need to be dark adapted. The usual minimum time required to adapt 'properly' would be 15 to 20 minutes.

Serious observers will avoid bright light during the day and wear sunglasses after sunset. If you are observing with a telescope, one method used by a colleague is to sit in a darkened room for about half an hour wearing an eye patch.

Advice extends to selecting the correct food. Protein-rich food is recommended as it releases its energy over a long period. Short lapses of 'tiredness' can presumably be countered with carbohydrates.

If a light is needed, use a low-power red light.

With experience, the eye (actually the brain) should 'learn' to pick out more and more details.

Biological Effects

• Faint objects can often be seen better by using averted vision, i.e. 'from an angle' than by looking at them directly.

• Fainter objects still can sometimes be brought into view by moving your eyes quickly. This effect can be simulated by jerking a pair of binoculars or telescope (if possible). You could, for example, try this technique on the tail of a comet and see whether you notice any difference.

The eye is not very receptive to red, so although photograps might show an emission nebula to be reddish, to the eye it is likely to be white. Stars can perceived to be 'red' and this is more obvious to females, apparently.

The eye is most sensitive to green. This appears to have caused problems in the past when some observers saw green colors on Mars and interpreted them as vegetation.

With experience, the eye (actually the brain) should 'learn' to pick out more and more details.

Equipment

• red light
• planisphere specific to latitude

Some Optical Double Stars

Optical doubles are stars that appear close together from our line of site but are not actually close together in reality. This is opposed to binary stars which could be classed as physical doubles.

• Mirak   in Bootes. A yellow/orange of magnitude 2.5 and a 'bluish' of magnitude 5. A binary system but period appears to be very long, of the order of thousands of years.

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  Algeiba   in the Sickle of Leo. Apparently some subjectivity with respect to the colors, varying from yellow/yellow to yellow/red, or yellow/purple.

• Albireo   in the head of Cygnus. Albireo A is yellow of magnitude 3.1, Albireo B is blue of magnitude 5.1. It is a genuine binary but the distance between them is so vast at 800 billion kilometers that no orbital motion has ever been detected.

• Almach   At the end of the line of three stars in Andromeda which form the handle of the 'Great Dipper' which some astronomers call the combination of Andromeda and the Square of Pegasus. Almach A is yellow of magnitude 2.2 and Almach B is a blue star of magnitude 5.1.

• Polaris has a 9th magnitude companion which is classed as an 'intersting test for a 7.5 cm telescope'.

Stars and Asterisms

8000 stars are visible to the naked eye, spread evenly thru the sky. Only about 2000 are potentially visible at any one time.

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  The Summer Triangle is formed by Vega (Lyra), Altair (Aquila) and Deneb (Cygnus) (it also forms the Winter Triangle in the Southern Hemisphere with the triangle inverted appropriately). Deneb and Altair point towards Sagittarius.

• This Square of Pegasus is notoriously harder to find than you might think. You need to take note of its size (and remember that the Sun and Moon subtend half of a degree) and to realise that it will be probably more 'slanted' in the sky than shown on a diagram.

• Vega and Capella are bright circumpolar stars. either side of the North Star. Vega is overhead in Summer when Capella is low down on the Northern horizion, and vice versa during winter.

• μ Cephei is known as the Garnet Star (named as such by William Herschel) because it is strikingly red.

• Sagittarius is alternatively known as the Teapot.

• Hercules Keystone

The Virgo Cluster (or Virgo-Coma Cluster) contains 13,000 galaxies - many of these can be viewed by the anmateur in Virgo and Coma Berenices.

Planets

Because Jupiter doesn't move very move its synodic period very close to earth's revolution period of 365 at 399 days. As we go out the synodical period comes closer and closer to 365. It can reach a size of 50" (cf. 60" for Venus).

Directions

Capricorn can found by following a line joining Aquila's three brightest stars downwards.

The constellation Monoceros is contained to a large extent by a triangle connecting Betelgeuse, Sirius and Procyon.

Deneb and Altair point towards Sagittarius.

Telescopes

Reflectors need to cool down before observing. It is obviously best not to store it in too high a temperature.

Condensation may form on telescopes and something like a hair drier is recommended to remove this - do NOT wipe the lens with anything.

For dust etc., wipe sparingly with tap water

keep outside

--notes--

milky way

refraction by atmosphere

shadows east or west da - 8mm if interested

size vary, smallest at apogee, largest at apogee