{"id":41695,"date":"2023-02-14T14:43:17","date_gmt":"2023-02-14T14:43:17","guid":{"rendered":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/?post_type=purple_issue&p=41695"},"modified":"2023-02-16T09:19:50","modified_gmt":"2023-02-16T09:19:50","slug":"take-the-caldwell-challenge","status":"publish","type":"post","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/2023\/02\/14\/take-the-caldwell-challenge\/","title":{"rendered":"Take the Caldwell challenge"},"content":{"rendered":"\n
\"\"
The magnificent Flaming Star Nebula or Caldwell 31, one of our top 10 picks from Patrick\u2019s Caldwell Catalogue <\/figcaption><\/figure>\n\n

Take the Caldwell challenge<\/h2>\n\n

Celebrate the life of Patrick Moore with 10 deep-sky objects from his own astronomical catalogue <\/p>\n\n

The early spring nights of March are ideal for discovery, something Patrick Moore, our late Editor Emeritus, was keen to encourage. To celebrate what would have been Patrick\u2019s 100th birthday, we\u2019ve put together a special challenge based on his very own Caldwell Catalogue. <\/p>\n\n

We\u2019re inviting you to take a tour of 10 of our favourite objects from his list, all of which are visible this month. Your task is to find them all in a single observing session. Some of the targets are quite popular, and you\u2019ll have seen them in our monthly deep-sky and binocular tours, while others are a little less well-known. Hopefully you\u2019ll be discovering some of these for the first time. <\/p>\n\n

The minimum size telescope for this challenge is a 4-inch refractor: all of the objects are within reach of this size instrument under dark skies. Larger apertures will certainly help, of course, revealing hidden details that may otherwise elude you. <\/p>\n\n

We suggest that you attempt the challenge near the third week of the month to avoid interference from the Moon\u2019s light. A couple of days either side of 21 March, starting at about 20:00 UT and finishing at about 22:30 UT, would be a good goal if the clouds play fair. <\/p>\n\n

As it is spring, don\u2019t be caught out by a cold snap and be sure to wear suitable warm clothing and have some hot drinks on hand. Why not involve some friends and their telescopes in the challenge and make this a social occasion too? <\/p>\n\n

<\/div>
\n

The making of Moore\u2019s marathon<\/h4>\n\n\n\n

Why did Patrick produce his own celestial catalogue, and what targets does it contain? <\/p>\n\n\n\n

\"\"
Patrick devised his list in 1995 in response to shortcomings in the Messier Catalogue <\/figcaption><\/figure><\/div>\n\n\n\n

The Caldwell Catalogue came about because Patrick felt that the Messier Catalogue \u2013 a list of 110 objects originally created to tell comet hunters what to avoid <\/em>\u2013 was somewhat incomplete. So he drew up a list of his favourite objects, all absent from Charles Messier\u2019s magnum opus. With the \u2018M\u2019 of Moore already taken, Patrick opted to use the \u2018C\u2019 of Caldwell for the objects in his list (his full surname being Caldwell-Moore). Patrick\u2019s catalogue contains 109 objects that, unlike Messier\u2019s, are spread across both the Northern and Southern Hemispheres. It includes 28 open clusters, 18 globulars, 35 galaxies, 13 planetary nebulae, 12 bright nebulae, one dark nebula and two supernova remnants, arranged in order of declination. <\/p>\n<\/div><\/section>\n\n

\"\"<\/figure>\n\n

1. NGC 752 <\/strong><\/h4>\n\n

Also designated: C28 <\/strong>
RA 1h 56m 53s, dec. 37\u00b0 47\u2019 38\u201d <\/strong><\/p>\n\n

We start our challenge with a fine binocular object originally discovered by Caroline Herschel in 1783. Open cluster C28, also known as NGC 752, lies about one-third of the way between mag. +2.3 Almach (Gamma (\u03b3) Andromedae) and the apex star in the constellation of Triangulum, mag. +3.4 Mothallah (Alpha (\u03b1) Trianguli). It can be easily found by sweeping between the two stars and, at almost two billion years old, this is one of the oldest star clusters known. Binoculars will show in the region of 30 widely scattered stars, although a richfield telescope at low magnification is the best way to really enjoy this lovely object, revealing in excess of 60 individual member stars, more than a dozen of which are brighter than mag. +10.0. <\/p>\n\n

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Edge-on galaxy NGC 891 is our second target, C23. Bump up the aperture to detect its delicate dust lane<\/figcaption><\/figure><\/div>\n\n

2. NGC 891 <\/strong><\/h4>\n\n

Also designated: C23 <\/strong>
RA 2h 22m 36s, dec. 42\u00b0 21\u2019 00\u201d <\/strong><\/p>\n\n

Moving nearly 7\u00b0 northeast now, your second object lies one-third of the way along a line joining the stars Almach and mag. +2.1 Algol (Beta (\u03b2) Persei). We\u2019re looking for mag. +9.9 edge-on galaxy NGC 891, and although it is visible in a 4-inch telescope, its low surface brightness means you may need to use averted vision. It is worth lingering here a little, as more and more detail will be revealed as your eye becomes accustomed to the view. If you can increase your aperture and up the magnification to around 120x, with careful scrutiny you should discern a slender dark dust lane bisecting the galaxy. This object was originally discovered by William Herschel in 1784 and it is believed to be over 30 million lightyears away from us.<\/p>\n\n

\"\"
Beautiful through binoculars and a sublime sight with a scope, the Double Cluster, C14 <\/figcaption><\/figure><\/div>\n\n

3. Double Cluster <\/strong><\/h4>\n\n

Also designated: C14, NGC 869 & NGC 884 <\/strong>
RA 2h 19m 00s, dec. 57\u00b0 9\u2019 00\u201d <\/strong><\/p>\n\n

Continuing our journey into Perseus, your next target is a real treat: two objects for the price of one! NGC 869 and NGC 884 are popularly known as the Double Cluster today; in antiquity it was the Sword Handle, referencing the jewel-encrusted sword given to Perseus by Athena and Hermes to help him behead the Gorgon Medusa (the latter is represented by the star Algol). The individual clusters are a fine sight through binoculars and can be seen with the naked eye from a dark location. A binocular sweep between mag. +3.9 Tau (\u03c4) Persei and mag. +2.7 Ruchbah (Delta (\u03b4) Cassiopeiae) will easily find them. NGC 884, the more easterly of the two, contains numerous white-blue stars, whereas NGC 869 is dimmer and more compact.<\/p>\n\n

\"\"
The Owl Cluster, C13 in Patrick\u2019s list, should be an easy hop from Ruchbah <\/figcaption><\/figure><\/div>\n\n

4. The Owl Cluster <\/strong><\/h4>\n\n

Also designated: C13, NGC 457 <\/strong>
RA 1h 19m 6s, dec. 58\u00b0 20\u2019 00\u201d <\/strong><\/p>\n\n

We leave Perseus and continue into Cassiopeia, a constellation named after a queen who vainly boasted of her unrivalled beauty. There is real beauty here, though, with the aptly named Owl Cluster \u2013 although it is also sometimes referred to as the ET Cluster because its shape has been said to resemble the alien from the film of the same name. The brightest star visible in the cluster is one of the Owl\u2019s eyes, mag. +5.0 Phi (\u03c6) Cassiopeiae. It lies 2\u00b0 southwest of Ruchbah, so is quite easy to find. In truth, bright red Phi Cassiopeiae is not actually a member of the cluster at all, but a foreground star. All the same, it certainly adds to the view through binoculars or a small scope.<\/p>\n\n

\"\"
Dark skies will help you track down the soft glow of NGC 188, or C1 in the Caldwell Catalogue <\/figcaption><\/figure><\/div>\n\n

5. NGC 188 <\/strong><\/h4>\n\n

Also designated: C1 <\/strong>
RA 0h 47m 11s, dec. 85\u00b0 14\u2019 38\u201d <\/strong><\/p>\n\n

Once you tick off this next object you\u2019ll be half-way through the challenge. Located just 4\u00b0 to the south of the Pole Star, Polaris, open cluster NGC 188 is often ignored by observers with equatorial mounts as locating objects this close to the pole can be a bit fiddly. But what\u2019s an observing challenge without a bit of challenge? Unusually for an open cluster, this one comprises many older stars, more yellow than the hot, white, young stars that you might have expected. With a magnitude of +8.1, it\u2019s not a naked-eye object, but a 4-inch telescope at 30x magnification will reveal it as a stretched scattering of stars set against a brighter circular core. <\/p>\n\n

\"\"<\/figure>\n\n

<\/p>\n\n

\"\"
Larger scopes will reveal arms gleaming with new star formation in C7, the spiral galaxy NGC 2403 <\/figcaption><\/figure><\/div>\n\n

6. NGC 2403 <\/strong><\/h4>\n\n

Also designated: C7 <\/strong>
RA 7h 36m 54s, dec. 65\u00b0 36\u2019 0\u201d <\/strong><\/p>\n\n

We are half-way through, so now is a good time to take a break and warm up with a hot drink as you prepare for the second stint. Our first object in the final run is spiral galaxy NGC 2403 in Camelopardalis. It has an appearance very similar to that of the Triangulum Galaxy, with numerous HII star-forming regions within its two layers of spiral arms. Shining at mag. +8.9, this is one of the brightest galaxies in the sky \u2013 but again, like the Triangulum Galaxy it is large and that brightness is spread out. NGC 2403 is somewhat isolated in sparsely populated Camelopardalis. You can find it just under 8\u00b0 west of mag. +3.3 Muscida (Omicron (\u03bf) Ursae Majoris). A 4-inch telescope will show an elongated hazy patch, but you will need a 12-inch telescope to view the spiral arms.<\/p>\n\n

\"\"
The lonely Intergalactic Wanderer, C25, at 275,000 lightyears away is a challenge <\/figcaption><\/figure><\/div>\n\n

7. The Intergalactic Wanderer <\/strong><\/h4>\n\n

Also designated: C25, NGC 2419 <\/strong>
RA 7h 38m 6s, dec. 38\u00b0 53\u2019 0\u201d <\/strong><\/p>\n\n

A quick hop southwards into Lynx will take us to a distant globular cluster known as the Intergalactic Wanderer, as it was originally believed to be located outside the gravitational influence of the Milky Way (something we now know to be untrue). Discovered by William Herschel in December 1788, this cluster is one the remotest globulars ever found, at a distance of around 275,000 lightyears. Look for it 7\u00b0 to the north of mag. +1.6 Castor (Alpha (\u03b1) Geminorum). It\u2019s a difficult object in a 4-inch telescope, but a 10-inch or larger will reveal its condensed core and patchy halo. <\/p>\n\n

8. NGC 2392 <\/strong><\/h4>\n\n

Also designated: C39 <\/strong>
RA 7h 29m 12s, dec. 20\u00b0 55\u2019 0\u201d <\/strong><\/p>\n\n

We continue our journey south into Gemini, sweeping past Castor and onwards to a point 2.4\u00b0 southeast of mag. +3.5 Wasat (Delta (\u03b4) Geminorum) to find a fascinating planetary nebula, NGC 2392. Although visible through a 4-inch telescope, with a diameter of only 48 arcseconds you\u2019ll need at least a 6-inch telescope to show the true shape of the nebula. A 10-inch or larger instrument will reveal a host of other delicate details, including two distinct shells \u2013 abright inner mottled region with an outer faint halo, separated by a dark ring. The nebula\u2019s very distinctive appearance wasn\u2019t lost on William Herschel, who described it as \u201ca very remarkable phenomenon\u201d when he discovered it in 1787. <\/p>\n\n

\"\"
Big aperture and transparent skies will get the best from the Flaming Star Nebula, C31 <\/figcaption><\/figure><\/div>\n\n

9. The Flaming Star Nebula <\/strong><\/h4>\n\n

Also designated: C31, IC 405 <\/strong>
RA 5h 16m 12s, dec. 34\u00b0 16\u2019 0\u201d <\/strong><\/p>\n\n

Although our next object is an astrophotographer\u2019s dream, it is more challenging for observers. The Flaming Star Nebula lies 4.2\u00b0 east-northeast of mag. +2.7 Hassaleh (Iota (\u03b9) Aurigae) and is a delightful mix of both reflection and emission nebulosity. The star responsible for generating all the energy is HD 34078, which can be clearly seen at the heart of the nebula. However, this star is here by chance: it\u2019s just passing through on its long journey away from a cataclysmic interaction with the Trapezium stars in the Orion Nebula in the distant past. The roughly triangular shape of the nebula can be discerned through a 6-inch or larger telescope, but HD 34078 dominates the view. Try fitting a hydrogen-beta filter to your scope to tame the star.<\/p>\n\n

\"\"
Your final challenge is to locate the curious triangular-shaped nebulosity of Hubble\u2019s Variable Nebula, C46 <\/figcaption><\/figure><\/div>\n\n

10. Hubble\u2019s Variable Nebula <\/strong><\/h4>\n\n

Also designated: C46, NGC 2261 <\/strong>
RA 6h 39m 12s, dec. 8\u00b0 44\u2019 0\u201d <\/strong><\/p>\n\n

Congratulations, you have reached the final object! This is the enigmatic comet-shaped nebula NGC 2261, also known as Hubble\u2019s Variable Nebula from a series of images captured by Edwin Hubble in January 1949. The nebula changes in brightness and to a lesser extent shape, and although it is illuminated at its head by the T Tauri variable star R Monocerotis, its variability doesn\u2019t exactly match that of the star. This unusual behaviour is caused by dust clouds orbiting close to the star, blocking its light and casting shadows across the nebula. Located 4.4\u00b0 south-south-west of mag. +3.3 Alzirr (Xi (\u03be) Geminorum), it is visible in a 4-inch telescope, though the nebula\u2019s curved wedge shape is more clearly revealed through an 8-inch telescope at around 120x magnification. <\/p>\n\n

RA\/dec. positions are correct for J2000.0 <\/strong><\/em><\/p>\n\n

\n\n
\"\"

<\/figcaption><\/figure><\/div>\n\n

Steve Richards is an experienced astronomer, astrophotographer and our expert Scope Doctor.<\/p>\n\n

<\/p>\n\n

<\/div>\n\n

PHOTOS: HOMER SYKES\/ALAMY STOCK PHOTO, ROLF GEISSINGER\/CCDGUIDE.COM, MICHAEL BREITE\/STEFAN HEUTZ\/WOLFGANG RIES\/CCDGUIDE.COM X 2, BERNHARD GOTTHARDT\/CCDGUIDE.COM, BERNHARD HUBL\/CCDGUIDE.COM, CHART BY PETE LAWRENCE, BERNHARD HUBL\/CCDGUIDE.COM X 2, FRANZ KLAUSER\/CCDGUIDE.COM, WOLFGANG PROMPER\/CCDGUIDE.COM<\/p>\n","protected":false},"excerpt":{"rendered":"

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