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Wednesday, June 27, 2012

Observing Satellites

Orbiting around our planet are thousands of electronic satellites that make great targets for urban astronomers like ourselves. And, there are a number of useful tools and apps that will help you locate them.

A common misconception is that the easiest satellites to spot are those in geosynchronous orbit (GSO) which  stay positioned above the same place on Earth. This is not true, as these satellites orbit at a distance of 35,786km, from which they cannot be seen as they have no light of their own.
The easiest satellittes to spot are those closest to us in low earth orbit (LEO), orbitting between 200km-2000km above the Earth. Such low orbits cause them to travel around the Earth 10 or 15 times every day, occassional travelling above Singapore.

A good website to find dates and timings of visible satellittes is Heavens-Above.
Once there, the first thing you must do is set your location. This is done under the "Configuration" menu: click "from database" and type in and select your city .i.e. Singapore.

You can be more precise by manually inputting your longitude and latitude or selecting from the map, however I often found these options give you the timings in UT (universal time/GMT) which is minus 8 hours from Singapore time,which is a be a bit confusing. Selecting your city from the database gives the local timings.

Once your location is set, just click on a satellite name. The brightest satellites are usually the International Space Station (ISS), Hubble Space Telescope (HST), Iridium Satellites (very bright communication satellites) or maybe China's Tiangong 1 space station.

After making a selection you will be presented with a table of information for all the visible passes for that particular time period.
This information includes the brightness or magnitude. The lower the number the brighter the object will be. Negative numbers indicates that the satellite will be brighter than most stars.
Satellites with magnitudes greater than 2 or 3 maybe difficult to spot in a light polluted environment.
The timings are given in 24hour format (HH:MM:SS) along with the altitude (height) and azimuth (direction) of the satellite at that particular time. Some satellites are visible for several minutes, so their start and end timings/positions are stated separately.
The highest possible altitude is 90 degree (directly overhead). Altitudes below 30 degrees may not be visible from some locations due to trees or tall buildings.

Iridium Satellites ( only visible for a few seconds so usually only one time period is stated. Because of the shape of their solar panels, they only reflect the sunlight for short period of time but the reflection is very intense and quickly fades from view, this is known as an Iridium Flare. 
Iridium satellite 
Apps for Satellite Tracking

One of the most useful ways to find satellites is using a smartphone app. I've only tried one so far called SatTrack for Android phones from Goggle Play Store:
Again, the first thing is to set your location using your GPS, once that's done you'll get a list of all visible satellites passing over your location. This even includes various rockets and other space junk left behind in orbit. Its best to use the settings to filter the most visible ones. Basically, anything brighter (lower) than magnitude 2.5 and higher than 30 degrees in altitude should be easy to find.

Once you select a satellite, you'll be presented with the magnitude, timings, altitude and azimuth as well as a handy compass which indicates the location and direction in which the satellite will travel across the sky (the purple line).

The app sometimes sends you notifications, when a satellite pass is due to start but you can also select an extra alarm/vibrate setting for those satellites you do not want to miss.

SatTrack app is free and there's also a paid version (without ads) but there many other satellite apps on the android market. There are also some on iTunes for iPhone users, this include: GoSatWatch and Satellites although they're not free,

Look out for those bright Iridium Flares and ISS sightings over the coming week.

Wednesday, June 20, 2012

June Solstice in Singapore

This week is June Solstice week, where the Sun reaches its most northerly point in the sky. Of course, this event is not due to the Sun's actual movement but instead the movement and tilt of Earth. Every year around 21st June, Earth's north pole points more towards the Sun than at any other time of year. This causes a number of significant effects here on Earth.

June Solstice signifies the start of summer in the northern parts of the Earth as well as the longest daylight hours for the whole year. At the same time, it also marks the start of winter and the shortest daylight hours in the southern hemisphere.
There's often a great deal of excitement and sometimes celebelation associated with solstice particularly in places like stonehenge in the UK, where crowds gather from sunrise (around 5am) to sunset (around 9:30pm). The stones themselves also mark the Sun's position at solstice.
Stonehenge - Credit: Pete Strasser -
In Singapore, the effects of solstice are a little harder to spot as near the equator the Sun's position varies only slightly throughout the year.
However, here are some of the signs to look out for in order to notice the solstice from 1 degree north of the equator:

1. Longest daylight hours and shortest night. As Singapore is technically in the northern hemisphere by 1 degree, we also experience the longest number of daylight hours for the year. How long? Exactly 12hours 11minutes 48seconds, from sunrise to sunset. Compare this to the shortest daylight hours of 12hours 3minutes 2seconds in December, the difference is only 8 minutes. Not much to celebrate about, but it is noticeable particularly if, like me, you find yourself reaching home around 7pm. Whilst walking home from the MRT station, bus stop or waiting for a ride, look up at the sky and see if it looks any brighter than usual. A slightly later sunset at 7:16pm should make the sky look brighter than at other times of the year.
Sunset/dusk in June - Longer daytime, later sunset, slightly brighter sky.

Sunset/dusk in April - slightly darker than in June.
2. Sunrise, Sunset and Northern Sun
If you're heading out to work or school around 7:30am or 8am, you may notice that the morning Sun is positioned slightly more to the left (i.e. North) than usual.

June morning Sun to the left (north) of the Science Centre entrance - After June 21st the morning Sun will gradually make its way south (towards the right)
After 21st June, take a look at the Sun every now and then over the next few months around 8am. You should find the Sun gradually moving more towards the right (i.e. south) every week, until it reaches the December solstice position on 21st December.
Similarly at sunset, the afternoon/evening Sun should be located more towards the right than usual. This can be a bit annoying if you happen to own a house, flat or condo with north-facing windows, thinking that you'll escape the brightness and heat of the afternoon/western Sun. Around June Solstice, you'll start to find what was once a nice shady spot is now lit by bright sunlight, as that north facing window is now tilted slightly towards the Sun for most of the day. Those with south-facing windows will experience the same thing in December.

3. Noontime Shadows
Between 12:30pm and 1:30pm, the Sun is at its highest point in the sky but as the June Sun is at its most northern point, midday shadows on the ground will be at their longest as compared to other times of year.
June Solstice Shadows - Longest noontime shadows. Shadows point South

Morning Shadows in June - Sun rises from north-east, shadows point south-west 
If you compare your shadow at midday over the next few months you should find it becoming gradually shorter and shorter until finally its directly below your feet around late September, when the Sun is directly overhead (Autumnal Equinox). Also, as the Sun is located towards the North, all the June shadows should point in the opposite direction towards the South.

All parts of the world, will experience the effects of solstice in one way or another, the most obvious being  in those parts furthest from the equator.In Singapore, the changes may be small, but the clues to spot them are all around us, we need only stop for a while and look around at the environment we live in.

There are a number of other times in year in which the Earth's tilt causes other seasonal effects, such as the the position of the Sun, daylight hours, sunrise, sunset, planet growth, animal migration and seasonal weather patterns. Some of these changes have even influenced the dates of well know holidays and celebrations such as May Day, Halloween, Mid-Autumn Festival, Christmas and Chinese New Year as the movement of objects like the Sun and Moon, have formed the basis of many calenders for thousands of years.
The world may be full of different cultures, but we all share the same sky.
Happy Solstice everyone!

Friday, June 15, 2012

Transit of Venus - Pictures

Its been over a week since the Transit of Venus event. There wasn't alot of time to stop and reflect as we immediately had to move on and prepare for other events and programmes going on during this busy June holiday period.
However, the event went well despite a disappointing start due to bad weather. Around 3000 people turned up at Science Centre that day. When we arrived to set up the telescopes around 7:30am there was already a  queue of 10-15 people eagerly waiting to catch a glimpse of this rare event.

Around 8am the sky was still cloudy and there was no sign of the Sun. After informing the growing number of visitors about the delayed start, we began to standby around the viewing area and wait for the Sun to appear. It was also an ideal time for some group photos.

Anticipation started to turn to disappointment as the time approached 9am and it started to rain with light drizzle.
As the crowd was growing every minute, we were starting to question whether the transit will be visible at all and at what time should announce to  visitors that viewing may have to be cancelled. During the wait, I managed to access and display a live webcast from an observatory on Hawaii's Mauna Loa, whilst other scobbers and volunteers tried to entertain visitors in the queue with some of our gallery activities sets.
By 10am, all we could see were "cloud transits" as the Sun remained covered. So it was time for a talk, two talks in fact. The first, by myself, explained some things about what was happening in the live webcast and some basic information on what else is visible in the sky this month. The second talk featuring more detailed info about the transit was by Mr Albert Ho from TASOS, who regularly helps out at the observatory.
One of the problems about conducting a talk was that not everybody could see it. The ideal location for the talk was the open terrace area in front of the observatory classroom, however the queue line was set up to run down the linkway corridor in order not to cause too much obstruction. Many visitors had to decide weather the would remain in queue for the telescope viewing area or attend the talk. Most people chose to remain hopeful about viewing the transit and kept their place in the queue. However, there were speaker set up along the linkway so that visitors could at least hear what was being said even if there couldn't see it.
After the talks there was a glimmer of hope as sunlight started to appear behind the clouds, a sign that the cloud layer was becoming thinner. Soon after, those that purchased the handheld solar filters were able to see a faint outline of the sun but it was still too faint to see Venus.

By around 11:15am or so we started to see the first glimpse of Venus through the telescopes. Once it became clear enough in most of the telescopes, the doors we opened and we were ready for ACTION:

Small clusters of visitors were led out towards the various telescopes at gradual intervals to prevent overcrowding. There were around 12 telescopes, from both Science Centre and TASOS as well as a few from other volunteers like the Aljunied Astronomy Club, each equipped with strong solar filters to protect our eyes.

In addition to the telescopes, we also set up a number of large solar filters and projection boxes beside snow city and of course the Milo Van and an Old Chang Kee Stall over there as well.

After one and a half hours of hot sunshine and viewing the Venus transit, we were reaching the end of the queue line. Just in time, as around 12:40pm, Venus was almost reaching the end it's transit.
Just prior to the end we managed to take a few photos of the Transit through the telescope to at least have our own record of this historic event. I took the first image with my phone camera, which involves holding the phone at the correct point in front of the telescope lens.
 The below image was taken by our volunteer Eric Lim, who used a DSLR with a special telescope adaptor known as a T-Mount, which allows the camera to attached directly to the telescope.
At the end of the day we were all very hot and tired but it was a thrilling experience to have witnessed this event that won't happen again for another 105.5years. as I mentioned in an earlier post, its not every day we get to see something moving in front of the Sun, besides clouds that it.

Monday, June 4, 2012

Preparations for Transit of Venus Part 3 - Telescope Viewing

Previously, I shared about the various filters and projection techniques that can be used to view the Sun, however, through the course of our preparations I've often forgotten how small Venus is going to be compared to the Sun.
Its easy to get caught up in the hype about an event that won't happen again for another 105.5 years. Some of us here, have nicknamed this event "the little black dot", as this is just what we are expected to see, a tiny black dot. Recently I read some articles that say Venus will be so tiny, it will be hard to spot using just a solar filter alone, like the ones I shared in Part 1 of the series of posts.

In light of that, its probably best to use a more magnified view like telescope or binocular projection (see Part 2). Even better, would be direct viewing through a telescope which should ONLY be attempted with the aid of suitable TELESCOPE SOLAR FILTERS. Which is exactly what we'll be using for our transit event.

Here's one of our telescope filters in action last week:

The filters are almost like mirrors, reflecting most of the light, so that only a tiny amount of light from the Sun is allowed to enter the telescope. There will be quite a number of these telescopes set up around the observatory grass area by ourselves (scobbers), TASOS (The astronomical Society of Singapore) and Aljunied Astronomy Club for visitors to look through.

We will not be opening our main observatory telescope as the telescope will be too high for some (e.g. children) to reach safely due the position of the Sun. We also found that in large scale events the narrow staircase becomes too congested, such as in this photo from our 2009 solar eclipse event:
Instead, I'll be connecting a video camera to the main telescope to provide a live video feed of the event that can be shown on a TV below, near the queue line, so that visitors can get to see the transit whilst their standing in line.
Above is a photo of a solar filter attached to the guide scope on the main observatory's telescope. As you can see its just like a mirror and I can also see that I need a haircut.
During testing I took some photo of the Sun through this telescope (and filter) with my phone and got some rather nice images:

This is similar to what visitors through the telescopes on Wednesday. The top image shows some cloud moving in front of the Sun. The second one shows some faint sunspots in the centre of the Sun, caused by magnetic storms, which are often the source of solar flares.
Later I attached a DSLR camera directly to the telescope for a closer look at the sunspot:

Amongst the sunspots there were quite alot of other black dots and specks. Which turned out to be bits of dust and other marks on the lens. Despite, cleaning the accessible parts of the lens some of the marks remained. I guess when a telescope is more than 20 years old and in use every week, its bound to pick up these kind of marks. Perhaps its also time for a full service.

In addition to the telescopes we'll also have a number of solar projection boxes called Venuscopes that can display a large reflection of the Sun and hopefully Venus as well.

The transit of Venus may only be a little black dot, but its not every day that we get to observe something moving in front of the Sun, and its something that telescopes all over the world will be trying to view. In addition to Science Centre's event there will also be telescopes set up at NUS, Galaxy CC and few other places in Singapore to witness this rare event.

Finally, if the weather is cloudy or you don't want to be standing in line, the transit can also be viewed online or even from space. NASA's SOHO satellites has various solar cameras that will witness the event. The website currently shows images of Venus approaching closer to the Sun over the next few days:

Also some overseas observatories will be screening live webcasts of the event such as ExploratoriumSlooh.comBareket Observatory (Israel) and Astronomers without borders. Happy transit watching!