Monthly Archives: July 2014
At the beginning of last year I was taking some pictures of the open cluster M67, in the constellation of Cancer, when I noticed that I had an additional slow-moving object appearing in the frames that I had recorded. To capture the star cluster I was using a 102mm (4 inch) aperture Celestron NexStar telescope with a digital SLR camera at prime focus (an old Fuji S2 Pro). I was taking short ten second duration frames at ISO 800 and subsequently went on to process these frames in DeepSkyStacker (an astronomical imaging software package). The final image can be found here on the Society’s Imaging Group Flickr page.
Figure 1, above, shows a composite of five of the frames. M67 is the cluster of stars at the bottom left of the picture, and north is roughly up. The unidentified object is seen as the elongated streaks and is heading eastwards towards M67. The trail is not complete, not because the satellite was intrinsically fading in and out, but because the camera was preparing to take the next 10 second frame in the sequence and so didn’t record the motion of the satellite.
So what is this object? I was initially puzzled because I am used to seeing earth satellites moving across the sky at a reasonable lick. Anyone who has seen the International Space Station will tell you that this bright object moves across the sky in a matter of minutes, and if you do happen to get such an object in your telescope it will cross your field of view in a flash! So what was happening here? The picture shown above is in fact a crop of the full frame of the camera which is 2.0 x 1.3 degrees. The angular distance travelled by the object is similar to the distance between the two stars HD75700 and HD75299, marked in Figure 1, and this is 0.62 degrees. The first frame started at 21:57:51 and the last ended at 22:00:27 GMT, a timespan of 2 minutes 36 seconds. So the object is moving at just under a 1/4 degree per minute. This is slow! What’s more, it is quite faint. I have marked the magnitudes of a couple of other stars in Figure 1, one at 9m.4 and one at 10m.5, and you can see that the object’s brightness is somewhere in between these two values.
I initially had a brief discussion about this with our expert on satellites at the ASE, Alan Pickup, and he suggested that this might be an earth satellite in a geosynchronous orbit. These orbits are used for communications satellites, and these objects orbit the earth once every sidereal day (which is 3 minutes 56 seconds shorter than a ‘normal’ day of 24 hours). So these satellites, approximately, move through 360 degrees in 24 x 60 = 1440 minutes, or 360/1440 = 1/4 degree per minute, in rough agreement with what I observed.
Later I showed these pictures to the Imaging Group and Alan said that he might be able to identify exactly which satellite this was – and he was successful! It turns out that this object is the remains of a Chinese Long March 3C rocket that was used to place a Beidou (or Compass G3) communications satellite into geosynchronous orbit on the 2nd June 2010. Its initial orbit measured 35582 x 202 km and had an orbital period of 627 minutes. By the 6th February 2013 (when I detected it) its orbit was 27080 x 168 km and its period was 469 minutes. Because of the highly elliptical nature of this orbit, this rocket will be moving slowly across the sky when it is further from the earth, and faster when it is close by. I think it is fortuitous that I happened to observe it move at 1/4 of a degree per minute (which happens to match the average speed of a geosynchronous satellite).
Figure 2, above, shows a map of the sky near M67 where the rocket was observed (this was produced by Alan using SkyMap Pro). Using the date and timings of my five frames he produced a prediction of the position of the rocket using the Heavensat software (green dots). My observations of the rocket have been roughly drawn on this map and are shown as red dashes. You can see that there is a pretty good agreement between the two! Alan reckons that there is an along-track residual error of about 10 seconds between the observed and predicted positions. I am not really surprised by this as I don’t think the clock on my camera would have been set that accurately. He notes also that the rocket would have entered the earth’s shadow at a point near the end of the final trail at the left of the figure, and sure enough the object does not appear in the frames that I took of M67 seconds after this.
So it just goes to show how things can turn up unexpectedly in astronomy, and how a bit of research can lead to an interesting result. Who would have thought I would have seen a Chinese rocket through my telescope!
Many thanks to Alan Pickup for suggesting that I look into these observations in more detail, and for providing predictions of the rocket’s positions, as well as his analysis.
Duncan is currently on the Council of the ASE and is also a member of the Society’s Imaging Group. Thanks to Duncan for sharing his account of how he, with Alan Pickup’s assistance, identified the UFO in Cancer!
I visited the City Observatory on Calton Hill on the 1st of July 2014. The Open Gallery and Edinburgh City Council had opened the site during the course of the day for stakeholders, in order to provide an update on the development of the observatory. It proved to be an excellent evening! It was rather like the old Doors Open days but, instead of concentrating on the past, this was looking to the future with great optimism. I met Kate Gray, Director of The Collective Gallery who run the site, and she said that they have secured the majority of the required funding for the next stage of the development. This will hopefully mean that there should be access to the dome and telescope by 2017.
I was pleased that the condition of the building hadn’t deteriorated as much as I had feared and it was a walk down memory lane as I looked round the Playfair building. I met David Williams and Frank Little from the City Council and was given the go-ahead to open up the dome! The door opened easily, after the usual climb to unlock the padlock, and the dome rotated quite smoothly. The Cooke telescope seems to be in perfectly good condition and I was able to unlock and move it.
There were a good number of visitors and they were fascinated with the telescope and the dome. All in all, it was a great night and, hopefully, just the start of a long and fruitful collaboration with the Collective Gallery and the City.
Ken is the Society’s current President and also leads the Imaging Group. He has, along with the rest of the ASE Council, endevoured to maintain good links with Edinburgh City Council in the hope that eventually the Society will once again be able to hold observing sessions at the City Observatory.
Sun spotting in safety at solar maximum
With Scotland’s nights still awash with twilight, many people focus on the Sun during July. There are dangers involved, though, and I don’t just mean sunburn. Specifically, we must never look at the Sun directly through binoculars or any telescope. To do so invites serious eye damage. Instead, project the Sun’s image onto a white card held away from the eyepiece or obtain an approved solar filter to fit over the objective (rather than the eyepiece) end of your instrument.
The most obvious features on the solar disk are sunspots, cooler areas that are shaped by magnetic activity and last for a few hours to several weeks. Because the Sun rotates every 27 days with respect to the Earth, spots take two weeks to cross the Sun’s face, provided they survive as long.
Sunspot numbers ebb and flow in a solar cycle of about 11 years, although the actual period varies from about 9 to 14 years. The last peak in the Sun’s activity occurred in 2000 and, following an unusually prolonged minimum between 2007 and 2010 when very few spots were seen, we are back near solar maximum though at a lower level than in 2000. This also means that solar flares, and the auroral displays that they can produce, are also more frequent even if they are hard to see given our summer twilight
As I warned last time, though, silvery or bluish noctilucent clouds are sometimes visible low down in the northern quarter of the sky and Scotland enjoyed a nice display on the night of 19-20 June. They are formed by ice crystals near 82km and more can be expected until mid-August or so.
The Sun tracks 5° southwards during July and from the 12th onwards Edinburgh enjoys at least a few minutes of official nautical darkness around the middle of the night. We need to wait a few days more for the bright Moon to leave the scene, but when it does the fainter stars should once again be visible.
If light pollution is minimal, the Milky Way may be seen arching high across the east at our star map times. Marking the central plane of our galaxy, with the greater density of distant stars, it stretches from Capella in Auriga in the north through the “W” of Cassiopeia in the north-east before flowing by Deneb in Cygnus in the east and downwards towards Sagittarius near the southern horizon. Where it passes through the Summer Triangle formed by Deneb, Vega and Altair it is split into two by obscuring interstellar dust, the Cygnus Rift.
The red star Chi Cygni, 2.5° or five Moon-widths south-west of Eta in the neck of Cygnus, pulsates every 13 months or so between a naked eye object of the fifth magnitude and a dim telescopic one near magnitude 13. It reached an unusually bright peak of better than magnitude four last year and should be near maximum again about now, though recent observations suggest it may not even hit magnitude six this time.
The Earth is 152,114,000 km from the Sun, and at its farthest for the year, on the 4th. Sunrise/sunset times for Edinburgh change from 04:31/22:01 BST on the 1st to 05:15/21:22 on the 31st when nautical darkness lasts for almost four hours around the middle of the night. The Moon is at first quarter on the 5th, full on the 12th, at last quarter on the 19th and new on the 26th.
Jupiter is barely 6° above the west-north-western horizon at sunset on the 1st and is unlikely to be visible as it heads for conjunction on the Sun’s far side on 24th.
Mars, to the right of Spica in Virgo and low down in the south-west at nightfall, sinks to set in the west-south-west at our map times. Fading from magnitude 0.0 to 0.4 this month, it tracks to the left to pass 1.3° above Spica on the 14th – the final and closest of three conjunctions between them this year.
The young Moon lies below Regulus in Leo low in the west on the evening of the 1st and close to Mars on the 5th. The 7th finds it close to Saturn and even closer to the double star Zubenelgenubi in Libra, the three making for a superb sight through binoculars. Saturn dims only slightly from magnitude 0.4 to 0.5 and hardly moves against the stars, appearing telescopically as an 18 arcseconds disk with rings 40 arcseconds wide.
A brilliant morning star at magnitude -3.9, Venus rises at about 03:00 BST and stands 12° to 14° high in the east-north-east at sunrise. As it tracks eastwards through Taurus, use it as a pointer to Mercury which is less than 8° below and left of Venus from the 10th to the 23rd as it brightens from magnitude 0.8 to -0.8. Set your alarm to catch Venus 8° to the left of the 7% illuminated waning earthlit Moon before dawn on the 24th.
While many stars are larger than our Sun, including the vast majority of stars visible to the unaided eye, there are billions that are smaller. Indeed, red dwarf stars, from about half the Sun’s mass to 1/13th as massive, are thought to make up 75% of the more than 100 billion stars in our galaxy. The smallest known star, and probably close to the smallest star possible, is a red dwarf in the constellation Lepus, just south of Orion. Smaller than Jupiter, but more massive, it has surface temperature of 1,800C and a luminosity of 1/8,000th of our Sun so that we need a large telescope just to see it even though it is only 40 light years away.