Posts Tagged ‘observing’

Happy Birthday Hubble! Top Five Spring Telescope Targets

April 23, 2013 Leave a comment

The iconic Hubble Space Telescope (HST) was launched 23 years ago on 24 April 1990, and ever since has been returning breathtaking images of the cosmos as well as world-changing science. It is, without a doubt, one of the most successful scientific instruments ever built.

To celebrate its 23rd birthday here is a list of five stunning celestial objects visible over the next couple of months that you can find for yourself using a small earth-based telescope. Most of these objects will look like nothing more than diffuse grey smudges in the field of view of your eyepiece, but I’ve illustrated this post with some HST images of the same objects, to show you what they really look like. Despite the fact that your telescope can’t ever show anything as stunning as an HST image, there’s something even more wonderful about seeing these objects in real time, for yourself, not mediated via a computer screen.

1. Saturn

Hubble view of Saturn
Hubble view of Saturn

Rising around 2030 local time at the end of April, and 1800 local time at the end of May, Saturn is visible in the evening skies throughout the Spring and into Summer. At the moment Saturn’s rings are tilted very favourably towards us, presenting a striking view. Through a very small telescope – or binoculars on a tripod – Saturn might appear as nothing more than a oval, or at best a circular disk with handles, but most modest telescope should show the disk of the planet and the rings, and even Saturn’s largest moon, Titan.

2. Sombrero Galaxy, M104

Sombrero Galaxy, M104
Sombrero Galaxy, M104

The stunning Sombrero Galaxy in the constellation Virgo gets to its highest above the horizon around 2330 in late April, and 2130 in late May. It’s one of the brighter galaxies in the sky, and so even a medium sized telescope should show up the dark dust lane obscuring the view of the central bulge of the galaxy. This dust lane is actually a ring that surrounds the galaxy, and is probably where most of the star-forming takes place, as it is composed of atomic hydrogen and dust.

3. Ring Nebula, M57

The Ring Nebula, M57
The Ring Nebula, M57

Located in the constellation of Lyra in the Summer Triangle, the Ring Nebula (Messier number 57) is a striking object in medium or large telescopes. It rises from low in the NE mid evening to almost directly overhead by the time dawn begins to brighten the sky. The Ring Nebula is a great example of a planetary nebula, so-called as it looks like the disk of a planet when seen through modest telescopes. However this name is completely misleading, as the gas in this nebula was puffed off by a red giant star just before it died and collapsed into a white dwarf, a fate that awaits the Sun in 5 billion years or so.

4. The Great Globular Cluster in Hercules, M13

The Great Globular Cluster in Hercules, M13
The Great Globular Cluster in Hercules, M13

This spherical collection of around 300,000 stars is one of the best examples of a globular cluster in the sky. It’s high in the SE sky during the evenings of April and May, and continues to be visible into the Summer. M13 is at the very limit of naked eye visibility, and small telescopes show it off beautifully. In fact, this is one object where a smaller earth-based telescope gives you a better overall view of the object than the mighty HST. Hubble has such a high magnification that its field of view is very small. This is fine when you’re looking for tiny faint galaxies millions of light years away, but a nearby globular cluster presents problems; it’s simply too big to fit into the field of view. Nevertheless, this spectacular HST image shows the heart of M13, and the stunning array of stars that make up this beautiful object.

5. The Eagle Nebula, M16

Pillars of Creation in The Eagle Nebula

OK, OK, so maybe this is more strictly speaking a late summer object, but it is visible pre-dawn in late May, low in the south, in the constellation of Serpens. Despite the unsocial hours it keeps at this time of the year, it still has to be included in any top-5 list of Hubble objects. The iconic “Pillars of Creation” image, taken by HST in 1995, is one of the most widely viewed of all Hubble images. It shows giant pillars of gas within the Eagle Nebula within which new stars are being born. However it’s a pretty tricky nebula to see through a telescope. There’s a star cluster within it that you’ll make out even in light polluted skies but to see it best you’ll need to head to a dark stargazing site and be patient.

For maps and tips about how to find these objects, and hundreds more like them using binoculars or a telescope check out my book, Stargazing for Dummies.

UPDATE: I just realised; there are people alive today with degrees in astrophysics who weren’t yet born when the Hubble Space Telescope was launched in 1990!


Total Lunar Eclipse 15 June 2011

June 13, 2011 40 comments

The first total eclipse of the Moon of 2011 occurs this Wednesday evening, 15 June 2011, and it will be the longest lunar eclipse in over a decade. However the views from the UK (and Europe) will be constrained by the fact that the Moon will be below the horizon for much of the eclipse, and will rise fully eclipsed, or in some cases even coming out of eclipse. It’s still worth having a look though: just try to find somewhere with a very low and clear SE horizon, as this will be the direction in which the Moon will rise, and it will be in eclipse only while it is VERY low (only a few degrees above the horizon).

Lunar Eclipse, December 21, 2010, by Jiyang Chen

A lunar eclipse occurs when the Moon, in its orbit around the Earth, passes into the Earth’s shadow, as cast by the Sun. You might imagine that this would happen once every lunar orbit, or once a month. That it does not is due to the fact that the Moon’s orbit around the Earth is tilted by around 5 degrees compared with the Earth’s orbit around the Sun. So in most orbits the Moon passes above or below the Earth’s shadow.

However, once in a while (there are at least two lunar eclipses each year) the orbital planes will align so that the Moon passes through the Earth’s shadow, sometimes just grazing it, in which case we get a partial lunar eclipse, and at other times passing right through the shadow, when we get a total lunar eclipse.

The Earth’s shadow has two distinct regions, forming two concentric circles [correction, the shadow is two cones, not circles – need to think in 3D! (see comments)]: the inner, darker, part of the shadow is called the umbra, and objects within this part of the shadow receive no direct light from the Sun. The outer, lighter, part of the shadow is called the penumbra, and objects within this part of the shadow can receive direct light from the Sun, but part of the Sun’s disk will be obscured by the Earth, and so less light than normal falls on the object.

The umbra and the penumbra

For the lunar eclipse of 15 June 2011 the Moon will pass very deeply into the darker umbra, making this an especially dark – and long – eclipse.

There are several distinct phases of a lunar eclipse, as the Moon travels through the penumbra and umbra. For this lunar eclipse the total time during which the Moon is at least partially in the Earth’s shadow is 219 minutes, and 100 minutes of this is spent entirely within the umbra, i.e. in total eclipse.

The phases of the 15 June 2011 total lunar eclipse (via NASA's eclipse website)

These phases are given the names: P1, the time when the Moon’s disk enter the penumbra; U1, the time when the Moon’s disk enters the umbra; U2, the time when the entirety of the Moon’s disk is within the umbra; U3, the last time when the entirety of the Moon’s disk is within the umbra; U4, the last time when part of the Moon’s disk is within the umbra; and P4, the last time when part of the Moon’s disk is within the penumbra.

The timings for these instances are well known. In the following table are: the timings for P1, U1, U2, U3, U4, and P4; the time of greatest eclipse (i.e. where the Moon is closest to the centre of the umbra); and the local times of moonrise for a variety of places around the UK

Eclipse Contact Contact Description Time (UT) Time (BST) Moonrise Time (BST) (UK Location)
P1 Penumbral Eclipse Begins 17:24:34 UT 18:24
U1 Partial Eclipse Begins 18:22:56 UT 19:22
U2 Total Eclipse Begins 19:22:30 UT 20:22
Greatest Eclipse 20:12:37 UT 21:12 21:12 (Channel Islands)
21:14 (London)
21:26 (Cardiff)
21:33 (Manchester)
21:56 (Belfast)
21:58 (Glasgow)
U3 Total Eclipse Ends 21:02:42 UT 22:02
22:19 (Orkney)
21:23 (Shetland)
U4 Partial Eclipse Ends 22:02:15 UT  23:02
P4 Penumbral Eclipse Ends 23:00:45 UT  00:00

UT = Universal Time = GMT
BST = British Summer Time = GMT+1

As you can see, the UK is far from ideally placed to view this total lunar eclipse, but the further south and east you are the better your chances of seeing something. The Moon will rise well past U2 across the UK, and everywhere except the Channel Islands and SE England it will rise well past greatest eclipse. Indeed in the north of Scotland the Moon will rise after the total eclipse phase ends (i.e. past U3).

Observers in the Channel Islands and in the SE of England will have around 50 minutes of total eclipse to observe although the Moon will still only be a few degrees above the horizon at U3), and here in Glasgow I’ll have about 4 minutes between moonrise and U3!

While in total eclipse no direct sunlight will fall on the Moon, but we will still be able to see it illuminated a dull red colour. How can this be, if there is no sunlight shining on it to light it up? It is due to the fact that the Sun’s light is refracted, or bent, through the Earth’s atmosphere. The red light from the Sun’s spectrum is refracted the most, and so it is this light that will illuminate the Moon during a lunar eclipse. In effect, the light you will see on the Moon is the combined light from all the sunrises and sunsets on Earth, being focused onto the Moon by the lensing effect of the Earth’s atmosphere.

A detailed information sheet for this eclipse (and others) is available (pdf) on the NASA Eclipse website.

Keeping an Naked-eye Observing Diary

November 26, 2010 Leave a comment

This post is aimed at people taking my annual Winter Night Sky and Spring Night Sky astronomy classes held at Glasgow Science Centre, and organised by the University of Glasgow. However you might find it useful even if you aren’t taking that class.

Amateur and professional astronomers keep detailed observing logs whenever they use their telescopes or binoculars to observe astronomical objects.

Many new astronomers however will be satisfied with naked-eye stargazing to begin with, before taking the big step and buying a telescope, and even for complete novices an observing diary of some kind can come in useful to help you learn your way around the sky.

In this short post I will outline some of the key things to record in a naked-eye observing log.

Time and Date

All records should include the time and date of your observation. In order to keep this in line with other astronomers’ records, you should note the start and end time of your session in UT (Universal Time). Fortunately for stargazers in the UK, UT is the same as GMT the time on our clocks over the winter months. During the Summer, when our clocks go forward our time is GMT+1, so we need to subtract an hour from our local time to get UT. You should record this time as accurately as possible by setting your watch to the pips before observing.

You date should be in a double-date format, i.e 27/28 November 2010, indicating that you were observing on the evening of 27 Nov, and possibly into the morning of 28 Nov.

Observing Location

Describe the site you’re observing from in as much detail as possible, ideally with your longitude and latitude, but at the very least by postcode. Describe also how clear your view of the sky is and whether any parts of your view are obscured by buildings, streetlights etc .

What You Observed and Where it Was

Your should describe in as much detail as you can your observation of astronomical objects, e.g. which constellations you observed, the nebulae that you saw (maybe the Andromeda Galaxy, or the Seven Sisters), any planets etc. Describe the relative positions of these objects in the sky, as well as which direction you observed them in (e.g. N, SSE, SW etc) and how high above the horizon they were (remember this easy method for measuring height of objects in degrees).

The Observing Conditions – Weather

You should note the weather conditions throughout your observing session, and how it changes, specifically the cloud cover. Estimate how much of the sky, if any, is obscured by cloud. You normally wouldn’t bother observing if a significant fraction of the sky is covered. Note also temperature and air pressure (using your own thermometer and barometer, or taking the data from a reliable local weather station).

The Observing Conditions – Sky Quality

You will most likely be observing skies that are affected by light pollution in some way, and so you should note the limits imposed by this nuisance. Estimating your limiting magnitude is a little bit tricky, but certainly worthwhile learning how to do. Astronomers would note this in terms of what magnitude of star was the faintest object visible to you. There is a relatively simple method to do just this using the stars in Orion. You can learn how to do this on the GLOBE at Night website.

You should also note whether the moon was in the sky, what phase it was in, and how high above the horizon it was. When the moon is more than half full it produces natural light pollution that imposes a limiting magnitude on the faintest objects you can see.

Daytime Venus

May 16, 2010 2 comments

Now that winter’s dark nights are far behind us, and as astronomers begin to pack their scopes away until the autumn, it’s worthwhile knowing a few daytime observing targets, and none is more elusive than a daytime sighting of Venus.

That’s right, at midday over the next few days, you can see Venus in the brilliant blue sky, assuming you have the patience (and no clouds).

Venus is the only thing other than the Moon to be visible to the naked eye against the blue daytime sky, and it really does feel quite bizarre to be looking at a bright “star” in the daytime sky.

Venus is just to the left of the Sun, and when the Sun is at it’s highest point due south it wil be around 30° to the left, at the same height above the horizon as the Sun. The crescent Moon will be further to the left. If you can see the Moon, then Venus is about 1/3 of the distance from it to the Sun. You will probably have to stand and scan the sky for some time before you see it – it certainly won’t be very obvious, but it is there.

Venus in the daytime sky - screen capture from Starwalk for the iPhone

Venus in the daytime sky - screen capture from Starwalk for the iPhone

This picture shows what you can expect to see, but please note that the stars won’t be visible – the Starwalk app for the iPhone shows what stars are up even in the daytime, when they’re not visible.

Please also note that the Sun is in Taurus, so if you were born today that would be your starsign. But of course astrology is a load of bull.

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