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Thursday, July 5, 2012

This month's sky - July 2012

Oh no! Its raining! That's how this first week of July has been almost every day. However, the cooler weather is a welcome break from the hot sunny days of June. Unfortunately, July is a great time for stargazing, with a number of bright constellations, star clusters and other deep sky objects. I only wish the sky remains as clear as it did last month. Let's hope this thick cloud clears come Friday evenings.

Planets in July
On 1st July, Mercury was at its highest point in the sky for the year as reached its "greatest elongation east" of the Sun (i.e. at the extreme edge of its orbit as seen from Earth). As Mercury moves further around the Sun, towards the Earth, it will become lost in the Sun's bright glare.
By 10th July, Mercury may be too low to see, which makes this Friday (6th July) the last opportunity we'll get to observe Mercury before it comes back for a brief visit in October.

The brightest and best planet on view at the moment is still Saturn:
Photo of Saturn (May 2012) - Taken through Science Centre Observatory's main telescope (16" Cassegrain reflector) using Nikon D70 DSLR Camera.
Similar to last month, Saturn remains relatively high in the sky next to the bright star Spica (alpha Virginis) part of the constellation Virgo. We've been getting some amazing clear views of Saturn and its rings and moons at SCOB over the last few Fridays.

Moving closer to Saturn, the planet Mars looks like an orange star, similar to the bright orange Arcturus (alpha bootis). When it first appeared, Mars was in front of the stars of Leo. In June, it moved into Virgo. By making some casual observations throughout July, you should begin to notice Mars gradually moving closer to Saturn and Spica.
Diagram highlighting the position of Mars and Saturn during July 2012.

By end July, the three objects form a triangle that slowly breaks apart during August.
On 25th July, look out for the almost half moon, positioned just South of the Saturn-Mars-Spica trianlge.

A good time for planet watching is in the early morning. Around 6am-7am Jupiter and Venus appear very bright towards the east before sunrise, gradually moving in front of the constellation Taurus.

Moon Phases
July starts midway in the 5th month of the Chinese Lunar Calendar with Full Moon occurring on 3rd July. The New Moon does not occur until 19th July, which signifies the start of the 6th Lunar Month of the Year of the Dragon (Chinese Calender).
Dates for the four main lunar phases in July 2012. Moon phases from 1st Quarter to Full Moon are best observed in the early evening. Phases from Full Moon to Last Quarter are best observed after midnight or during early morning. Phases occurring one or two days before/after New Moon cannot  be seen.

While looking up the chinese lunar calendar month, I also found that the 6th day of 6th lunar month is known as Xi Shai Jie  (洗晒节 bathing/basking festival, a day for hanging out and airing your bedding, books etc . I'm guessing this is because of the hot, sunny weather in China at this time. However, as its always hot in Singapore, we can air our bedding everyday.... if you want to. This year, Xi Shai Jie occurs on 24th July, just before 1st Quarter Half Moon.

Anyways, if you want to see the Moon at SCOB, the best Friday to come will be 27th July.

In addition to some of the bright stars of June, such as Crux, Alpha and Beta Centauri, Arcturus and Spica, one of the brightest constellations in July is Scorpius, rising high in the south-east direction.
The most obvious part is the bright red supergiant star Antares, followed by the collection of stars that make up the tail. 
Red Supergiant Star Antares (alpha scorpii) - As seen through Science Centre Observatory's main telescope (16inch cassegrain reflector)

As the stars of Scorpius are in front of one of the brightest parts of the Milky Way (our Galaxy), there are lots of amazing deep sky objects such as star clusters located within the constellation. However, our Singapore sky is much too bright to see many of them clearly but some of the brighter objects are listed in the diagram below:

1) M6 (Butterfly Cluster) – beautiful open star cluster arranged in curved chains like the wings of a butterfly. Visible in binoculars, best in telescope using low magnification.

2) M7 large open cluster of about 70 stars. Triangular pattern. Close to M6 and other star clusters.
3) Zeta Scorpii Double star, orange and blue/white colour, unrelated (do not orbit each other). More visible in telescope.
4) NGC6231 a bright open star cluster of 100 stars. Located near to Zeti Scorpii. Binoculars may reveal more star clusters in the surrounding area.
5) M4 – large globular cluster containing thousands of stars. Difficult to spot may appear fuzzy in binoculars.
6) M80 – small, distant globular cluster. Faint, requires low magnification.
7) Omega Scorpii  – unrelated double star. Easy to spot in Binoculars.

Using a pair of good binoculars or telescope at low power may reveal some of the closest globular clusters for example M4 or M80 (NGC6093). Globular clusters are large collections of stars orbiting around the centre of the Milky Way and contain some of the oldest stars in the Galaxy.
Its unlikely that you'll see the individual stars, but each cluster will appear as a faint hazy patch, like a tiny round cloud. M4 is located nearby Antares and the star Sigma Scorpii. M80 is higher up, halfway between Sigma and Beta  Scorpii.
Diagram highlighting the position of Globular Clusters M4 & M80, near to the stars of Antares and Sigma Scorpii .

Some very nice open clusters are also located near the Scorpius' tail, for example M6 the butterfly cluster.
I wonder how many we'll get to see over this month.