* Astronomy

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July 2011

Blobrana · L

Earth will be at aphelion, its furthest orbital distance from the Sun, around midnight on 3 July. It will then be 152,095,745 km from the Sun, compared with its minimum distance from the Sun (perihelion) of 147,103, 622 km in January.

Since the eccentricity of our planet's orbit is very small and the orbit is nearly circular, aphelion and perihelion differ from the mean Sun-Earth distance by less than 2%. If you drew Earth's orbit on a sheet of paper it would be difficult to distinguish from a perfect circle.
Since Earth is at its furthest from the Sun, average global sunlight arriving in July is about 7% less intense than it is in January. However, the average temperature of Earth at aphelion is about 2.3C higher than it is at perihelion - Earth is actually warmer when it is further from the Sun.

This is because our planet has more land in the northern hemisphere and more water in the south. During July - in the northern summer - the mainly continental northern half of our planet is tilted toward the Sun, and the land masses heat up more easily than the oceans.

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Blobrana · L

Meteor Showers

July has three main meteor shower: the Capricornids are active over July with peaks on the 8th, 15th and 26th, although the maximum rate is only about 5 meteors per hour. The Delta Aquarids are active from 15 July with a peak on the 29th of 10-20 per hour. The Alpha Cygnids will peak on the 21^stJuly when you can see up to 5 shooting stars per hour.

Shower	Activity Period	Maximum	Radiant		Velocity	ZHR
		Date	R.A.	Dec.	km/s
Beta Taurids (daylight)	June 5-July 18	29th June	79.4 °	21.2 °
Capricornids	8th	8th July		°
July Phoenicids	10th -19th July	10th July
Ophiuchids	15th	15th July	18.9h	-22.6°	13.4km/s	5
Alpha Capricornids		16th July
Perseids	17th July - Aug 24th	10-14 August
Alpha Cygnids		21st July				5
Capricornids	26th	26th July
Kappa Cygnids		27th July
S. Delta-Aquariids	July 14-Aug 18	30th July	3.9h	-51.8d	14 km/s	11.2
Scorpius-Sagittariids		31th July	20.2h	-24.6°	10.5km/s	5

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Highlights

The Summer Triangle -- Vega, Deneb, and Altair -- holds the central position, high in the south. The scorpion sits low to the south and slightly west. Directly to the arachnid's east is Sagittarius, the Archer, and between the two lies the direction toward the Milky Way galaxy's centre. The ribbon of soft light that delineates our galaxy flows up from the south, through the Triangle, and then cascades toward the northern horizon.

Trifid and Lagoon Nebulas

By mid-month the distinctive "Teapot" of Sagittarius should be hovering above the southern horizon.

Looking towards the right of the lid of the teapot and a little to the right is the delicate Trifid Nebula, "M20". A nebula is simply a cloud of interstellar dust and gas, the raw materials that stars are made of. If there are already stars embedded in the cloud it will glow with an eerie ghostlike appearance forming such vistas as the Great Orion Nebula, or this one, the Trifid. Sporting two patches of nebulosity, one red the other blue, this is one of the finest objects in the sky and very easy to find in binoculars. Just slightly below M20, is the rosy red Lagoon Nebula, which goes under the profoundly less romantic name of "M8". This is one of the best diffuse nebulas for naked eye observers, surrounding the small young star cluster NGC6530. The nebula is known for having a number small dark globules of material believed to be stars at the very beginning of formation, sometimes called protostars. Overall M8 is over 100 light years across, with its central regions a more modest 50 light years in diameter. It is also one of the largest in the sky, challenging the full moon for size.

M51 The Whirlpool Galaxy

Summer is the time for the galaxies.

As the earth swings around in its orbit the night skies are aimed away from the centre of our own galaxy, the Milky Way. No longer does the body of the Milky Way block the skies, now we can look out into the depths of space. One of the most spectacular is M51, better known as the Whirlpool Galaxy located right below the handle of the "Big Dipper". This was the first ever to be seen as in the classic spiral form, in the mid-19th century. While visible in the smallest instruments, its twisted nature will not show in anything less than an eight-inch telescope. With a luminosity of 10 billion suns and a diameter of 100,000 light years, M51 is roughly equivalent to M31, the great Andromeda galaxy and in turn, our own home. The Whirlpool is about 35 million light years away and glows at a genial eighth magnitude. In the sky it is seen face on and is about 1/3rd of the visual width of the Moon. It should be visible as a dim fuzzy patch in a pair of binoculars in a very dark sky. If you are lucky in that regard, step outside and see what you can see tonight.

Notable Messier objects

M3 is one of more heavily studied globular clusters due to its position in the galaxy, putting it far above the interstellar dust and gas that dim its light. More than 200 variable stars have been observed out of a total of near 50,000. Being one of the brightest

globulars, M3 is regarded as one of the most striking in the sky. A 60mm scope will begin to reveal hundreds of its magnitude 11 stars, while larger instruments may show arms or branches radiating from the sides.

M5 : A Nice Globular Cluster

Located in the "head" half of the split constellation, Serpens, you will find the smashing globular cluster, M5. These are round, concentrated clusters of old stars which usually collect into halos surrounding galaxies. They contain between 100,000 to 10 million stars and are typically 100 light years across. Globulars are wonderful objects in small telescopes due to their perfectly rounded shape and the delicate glistening of the nucleus.

Omega Centauri in the southern skies is by far the best. northerners can relish M13 in Hercules, M3 and now M5, which are, considered one of the finest in the sky. It's 13 billion year age makes M5 one of the oldest clusters known. Easily visible in binoculars it takes at least a four-inch telescope to be able to resolve some of its ½ million stars.