Deep-Sky Tour

Surf­ing the gal­ax­ies and glob­u­lars around Ser­pens Ca­put and Virgo

Sky at Night Magazine - - CONTENTS -

Tick the box when you’ve seen each one

1 M5 M5 is a mag­nif­i­cent ex­am­ple of a glob­u­lar clus­ter and, for some, the finest in the north­ern sky. It has a vis­ual mag­ni­tude of +5.6 and is lo­cated in Ser­pens Ca­put close to the bor­der with Virgo. It is eas­ily lo­cated by ex­tend­ing a line from mag. +5.0 CU Vir­gi­nis through mag. +3.7 109 Vir­gi­nis for the same dis­tance again. M5 also lies 22 ar­cmin­utes north­west of mag. +5.0 5 Ser­pen­tis. A 150mm scope shows a 10 ar­cminute glow­ing mass of stars, many re­solved with in­creas­ing mag­ni­fi­ca­tion. A num­ber of stars ap­pear to form strings run­ning out from the core. Large tele­scopes at high power show a bright, grainy core which fills one-quar­ter of the clus­ter’s over­all size.

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2 NGC 5921

We re­main in Ser­pens Ca­put for our next tar­get, a mag. +10.8 galaxy known as NGC 5921. This is lo­cated 3˚ north and 0.8˚ east of M5 and sim­i­larly has a nearby star to guide the way. In this case, it’s a ninth mag­ni­tude star 2.9 ar­cmin­utes to the south­east of the galaxy. A small in­stru­ment shows NGC 5921 as a cir­cu­lar glow with a 12th mag­ni­tude star on its south­west edge. Larger in­stru­ments show that this star ap­pears to be­long to a group of four which form an arc guid­ing you to­ward the galaxy. Larger in­stru­ments also show the galaxy to be elon­gated with an ex­tended core.

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3 PALOMAR 5

Palomar 5 is a mag. +11.8, chal­leng­ing glob­u­lar that was dis­cov­ered by the Ger­man as­tronomer Wal­ter Baade in 1950. It is lo­cated in Ser­pens Ca­put, ap­prox­i­mately 2.3˚ south-south­west of M5 and, like the pre­vi­ous tar­gets, also has a nearby ‘guidestar’ in the guise of sixth mag­ni­tude 4 Ser­pen­tis, 0.5˚ north. A large aper­ture is re­quired and with mag­ni­fi­ca­tions un­der x100 it’s dif­fi­cult to de­tect any­thing of this 8 ar­cminute ob­ject. If you do man­age to see it, the clus­ter ap­pears as a large, faint patch of light. The best view­ing tech­nique is to use averted vi­sion. Palomar 5 is 76,000 lightyears away and es­ti­mated to be 11.5 bil­lion years old.

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4 NGC 5850

We hop across the bor­der into Virgo for our next tar­get, the galaxy NGC 5850. This lies 2.8˚ west and 0.5˚ south of M5. It’s also fairly close to the mag. +4.4 star 110 Vir­gi­nis, 1.2˚ to the west­north­west. This 11th mag­ni­tude galaxy

be­longs to the 5846 group. A 150mm tele­scope will just show it sit­ting 10 ar­cmin­utes south of the 11th-mag­ni­tude galaxy NGC 5846. NGC 5850 looks quite elon­gated through larger in­stru­ments, with a core that ap­pears to stand out well from a fainter halo, but over­all the con­cen­tra­tion isn’t that well de­fined. While view­ing, a star-like nu­cleus seems to pop in and out of vi­sion. Larger in­stru­ments still show the core as an ex­tended fea­ture thanks to two large and very faint glow­ing re­gions on ei­ther side of it. Over­all this makes the core look three times longer than it is wide.

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5 NGC 5838

Our next tar­get on this month’s deep-sky tour is 11th-mag­ni­tude NGC 5838. This is an­other spi­ral galaxy lo­cated 0.75˚ to the north­west of NGC 5850. NGC 5838 ap­pears as a small ob­ject ap­prox­i­mately 1 ar­cminute across through tele­scopes be­low 250mm aper­ture. Smaller in­stru­ments also show the cen­tral nu­cleus of the galaxy as quite stel­lar in ap­pear­ance. As your aper­ture in­creases, more of its de­tail is revealed and the outer halo ap­pears elon­gated in shape. A 300mm in­stru­ment re­veals the galaxy’s core as a cir­cu­lar af­fair sur­rounded an outer halo ap­prox­i­mately 2.5x1.0 ar­cmin­utes in size. As with our last ob­ject, this galaxy is an­other mem­ber of the NGC 5846 group.

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6 NGC 5813

We fin­ish this month’s tour with one fi­nal galaxy and an­other mem­ber of the NGC 5846 group. NGC 5813 is an 11th mag­ni­tude el­lip­ti­cal galaxy in Virgo. Vis­i­ble in a 150mm scope, it lies just over 1˚ west-south­west of NGC 5838. It’s con­ve­niently framed by three 12th mag­ni­tude stars along its south­ern and east­ern edges. Larger in­stru­ments bring a fourth, mag. +13.3, fram­ing star into view to the north. The galaxy ap­pears elon­gated and around 1x0.5 ar­cmin­utes in size, with a stel­lar nu­cleus. In­creas­ing aper­ture makes the over­all galaxy ap­pear larger and the core take on a less stel­lar ap­pear­ance, hav­ing a now more pro­nounced, elon­gated shape.

SEEN IT

Elon­gated NGC 5921, with a glow­ing arc of four stars on its south­west edge

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