The Sky This Month

By Joe Grida, Technical Information Officer

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Updated 3 June 2020

This monthly guide is designed to keep you looking up during these rather uncertain times. We can't get together for Members' Viewing Nights, so I thought I'd write this to give you some ideas of observing targets that you can chase on any clear night this coming month.

Stargazing is something that we all like to do. Cavemen did it many thousands of years ago, and we still do it. There's something rather special in looking into a dark sky and seeing all those stars. It's more meaningful now. We don't have to assign god-like powers to any of those stars for we now know what they really are, and I think that makes it even more awesome to look up at a star-studded sky.  Keep looking up!

Naked Eye Star Walk

For centuries, humans have looked up at the night sky and played games of "join-the-dots” with the stars. Today, these patterns form the 88 constellations that cover the entire sky.

The largest constellation is Hydra the water snake, which slithers across 90 degrees of the sky. To get a sense of how much sky that is, consider that the full Moon spans only half a degree. Whilst the head of Hydra is setting in the west, its tail stars are still overhead!

The smallest constellation is one of the most famous. Its correct name is "Crux", the cross, although it's better known as the Southern Cross. At this time of the year, it’s high in the southern sky. Its stars are shown on the Australian and NZ flags.

Crux is small, but it's packed with celestial wonders. For example, there's the Jewel Box Cluster, shown on this month’s starchart by its catalog number of 4755. Seen through a telescope, the stars of the Jewel Box shine diamond-white and sapphire-blue. A lone red star lies between Earth and the cluster, so it looks like a ruby against the other gems. The whole cluster is set against the glittering band of the Milky Way. Of course, you’ll need a dark sky to see the Milky Way. The light polluted skies of Adelaide hide it fairly well.

High in the sky, above the Southern Cross and the Pointers, look for a small fuzzy star. It’s labelled 5139 on the star chart. The Omega Centauri globular star cluster is a vast "city" of stars, perhaps a million stars packed into a fairly small, spherical volume of space. It's about 17,000 light-years away, in the constellation Centaurus.  It stands highest above the southern horizon around 10 p.m.

To really appreciate the cluster, though, you need some help. Binoculars will show you more of its stars. But there's nothing like a telescope to reveal Omega Centauri for what it really is; a stellar city swarming with a million stars.

High in the eastern sky is the constellation of Scorpius, the scorpion. Throughout the ages, almost all civilisations have endowed this particular group of stars with the body of a scorpion.

Over in the northwest, orange Arcturus keeps watch. The star became a famous object in 1933, when its starlight was used to trigger a switch that turned on the floodlights at the World Expo in Chicago. It is a large star, roughly 25 times the diameter of our Sun. It is some 115 times brighter than the Sun, but at its distance of almost 40 light years, the heat we receive from it is equal to the heat from a single candle at a distance of approximately 9 kilometres. Not quite enough to keep the winter chills away!

Get a star chart for the month of April here: http://skymaps.com/downloads.html

The Solar System

Planetary observers rejoice! Both Jupiter and Saturn are beautifully placed for evening observation this month.

Mercury is an evening object at the beginning of the month. You’ll find him frolicking with the twins in Gemini, low in the western sky soon after sunset. It’s probably best seen around June 4-5, when it is at its greatest elongation from the Sun. At 6:00pm ACST, it will be just below 7o elevation in the north-west, so make sure you have a clear horizon. Always nice to catch elusive little Mercury!

Venus returns to the morning sky after passing inferior conjunction with the Sun. On the 15 June, it sits right in the head of Taurus, the bull. See sky simulation below.

Mars rises around midnight, displaying a small apparent diameter of 11 arc-seconds. Wait until October, when the disk will have grown to over 22 arc-seconds.

Jupiter and Saturn lord it over the entire night. The Jovian satellites are a pleasure to watch as they transit and get eclipsed by their behemoth parent, whilst Saturn’s rings bring sheer delight to first time observers.

Uranus rises at 3:30am. Stay warm in bed.

Neptune, only about 2o from Mars in Aquarius, rises just after midnight

 

The Moon

 

Instead of highlighting a specific lunar feature this month, I’d like to recommend a few resources that you can use to augment your lunar observing.

Virtual Moon Atlas - download it for Windows or Linus here

21st Century of the Moon - purchase it from Amazon here

Hamlyn Atlas of the Moon is a classic that you will be hard pressed to find at a reasonable price. I recently saw a copy on eBay advertised for ~ $150!

 

Comet C/2019 U6 Lemmon

  • Discovered by the Mt Lemmon Survey on 31 October 2019.
  • Closest approach to Sun on June 18
  • On June 7, the comet lies 2.5o south of open cluster M46 in Puppis.
  • The comet moves into Hydra on the 15th.
  • On June 23, the comet will be situated very close to Alphard in Hydra.
  • The comet may then appear at its brightest, magnitude 5.5, easily visible in binoculars and possibly naked eye from a dark site.
  • Moonlight will start to interfere from June 26
  • It will make closest approach to Earth on June 29 at a distance of 123 million kms

 

 

Easy Telescopic Target - M46 & NGC 2438 in Puppis

An easy target as long as you try to catch them in early June, before they dive too far into the sunset sky.

 Open Cluster - M46 (also known as NGC 2437)

  • discovered by Charles Messier in 1771
  • estimated distance of 4920 light years
  • Size 23 arc-minutes
  • Mag 6.1

 

Planetary Nebula - NGC 2438

  • Discovered by William Herschel in March 1786
  • Estimated distance of 2900 light years
  • Size 1.1 arc-minutes
  • Mag 10.8

 

Image Credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona

Deep Sky Challenge - Globular Cluster, Palomar 5, in Serpens

The Palomar globular clusters were discovered in the 1950s on the survey plates of the first Palomar Observatory Sky Survey (POSS). The list of astronomers who first identified the objects as globular clusters includes some famous names, among them Edwin Hubble, Walter Baade, Fritz Zwicky, Halton Arp and George Abell. Several of the Palomar globulars--including Palomar 6, Palomar 7, Palomar 9, Palomar 10 and Palomar 11--are nearby clusters of average size that just happen to be heavily obscured by dust in our line of sight.

Others, including Palomar 3, Palomar 4, and Palomar 14 --are giant globulars that are very far away in the extreme outer halo of the Milky Way. Although the objects vary greatly in degree of difficulty--from easy to nearly impossible--observing the whole list is a very challenging observing project for owners of big telescopes.

Name

RA

DEC

Constellation

Size (arcmin)

Mag

Distance from the Sun (kly)

Distance from Galactic Centre (kly)

Pal 1

03h 33m 23.0s

+79d:34m:50s

Cepheus

2.8

13.18

35.6

55.4

Pal 2

04h:46m:05.9s

+31d:22m:51s

Auriga

2.2

13.04

90.0

115.5

Pal 3

10h:05m:31.4s

+00d:04m:17s

Sextans

1.6

14.26

302.3

312.8

Pal 4

11h:29m:16.8s

+28d:58m:25s

Ursa Major

1.3

14.20

356.2

364.6

Pal 5

15h:16m:05.3s

-00d:06m:41s

Serpens

8.0

11.75

75.7

60.7

Pal 6

17h:43m:42.2s

-26d:13m:21s

Ophiuchus

1.2

11.55

19.2

7.2

Pal 7 (IC1276)

18h:10m:44.2s

-07d:12m:27s

Serpens

8.0

10.34

17.6

12.1

Pal 8

18h:41m:29.9s

-19d:49m:33s

Sagittarius

5.2

11.02

42.1

18.3

Pal 9 (NGC6717)

18h:55m:06.2s

-22d:42m:03s

Sagittarius

5.4

9.28

23.1

7.8

Pal 10

19h:18m:02.1s

+18d:34m:18s

Sagitta

4.0

13.22

19.2

20.9

Pal 11

19h:45m:14.4s

-08d:00m:26s

Aquilla

10.0

9.80

42.4

25.8

Pal 12

21h:46m:38.8s

-21d:15m:03s

Capricornus

2.9

11.99

62.3

51.9

Pal 13

23h:06m:44.4s

+12d:46m:19s

Pegasus

0.7

13.80

84.1

87.0

Pal 14

16h:11m:04.9s

+14d:57m:29s

Hercules

2.2

14.74

241.0

225.0

Pal 15

17h:00m:02.4s

-00d:32m:31s

Ophiuchus

3.0

14.00

145.5

123.6

Pal 5 in located in Serpens Cauda. It has proved to be of considerable interest because it is a typical metal poor halo cluster that appears to be in the process of tidal disintegration. Deep images show trails of stars both leading and trailing the cluster and which form a stream perhaps 30000 light years long containing perhaps 5000 solar masses worth of stars.

Pal 5 is perhaps 21 kpc from us and maybe 17kpc from the galactic centre and is currently high above the galactic plane. It may well be currently at its further point in its orbit from the Milky Way (apocenter?) and has obviously undergone many disk passages in its lifetime, and its next one may be its last before it is totally disrupted.

It has been suggested that Pal 5 may have lost up to 90% of its mass during these crossings and now the tidal tails
stretch 10 degrees across the sky. Unlike most globular clusters Pal 5 does show a considerable amount of flattening.

Palomar 5 is not going to be an easy observational target as, with a concentration class of XII, it will appear like a very faint open cluster.

Whilst you are there, you might as well head to the spectacular globular cluster M5, located 2.3o to the north.

More info : https://skyandtelescope.org/observing/palling-around-with-the-palomar-globular-clusters/

Pal 5 can be seen shining faintly in the middle of this image from the Sloan Deep Sky Survey 9.

 

Planetary Nebulae

  • A type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives.
  • The term "planetary nebula" is a misnomer because they are unrelated to planets or exoplanets.
  • French astronomer Antoine Darquier de Pellepoix described in his observations of the Ring Nebula, "very dim but perfectly outlined; it is as large as Jupiter and resembles a fading planet". William Herschel described these nebulae as resembling "planets".
  • All PN’s form at the end of the life of a star of intermediate mass, about 1-8 solar masses. The Sun will form a PN at the end of its life cycle.
  • PN’s - short-lived phenomenon, lasting a few tens of thousands of years, compared to considerably longer phases of stellar evolution (millions to billions of years).

They are a great object to observe. The colour is sometimes quite intense when observing the smaller planetaries. They are also easy to spot on moon-lit nights because there light is concentrated into a small area. Whereas, the larger ones  are better left for dark skies.

Most of the ones in the table below  are visible from suburban skies with a moderately sized telescope, say 200mm or above.

Name1

Name2

RA

Dec

Mag

Type

Description

Const

NGC 6572

PK 034+11.1

18 12.1

+06 51

8.1

Pl

Small very bright planetary nebula

Oph

IC 4634

PK 000+12.1

17 01.6

-21 50

10.9

Pl

Small bright planetary nebula

Oph

NGC 6369

PK 002+05.1

17 29.3

-23 46

11.4

Pl

Rather faint annular nebula

Oph

NGC 6309

PK 009+14.1

17 14.1

-12 55

11.5

Pl

Fairly bright planetary nebula

Oph

NGC 6302

Bug nebula

17 13.7

-37 06

9.6

Pl

Very bright elongated planetary nebula

Sco

NGC 6153

PK 341+05.1

16 31.5

-40 15

10.9

Pl

Fairly bright planetary nebula

Sco

NGC 6072

PK 342+10.1

16 13.0

-36 14

11.7

Pl

Fairly bright planetary nebula

Sco

NGC 6818

Little Gem

19 44.0

-14 09

9.3

Pl

Bright large planetary nebula, PK 025-17.1

Sgr

NGC 6644

PK 008-07.2

18 32.6

-25 08

10.7

Pl

Very small bright planetary nebula

Sgr

IC 4776

PK 002-13.1

18 45.8

-33 21

10.8

Pl

Small bright planetary nebula

Sgr

NGC 6563

PK 358-07.1

18 12.0

-33 52

11.0

Pl

Delicate planetary nebula

Sgr

NGC 6567

PK 011-00.2

18 13.7

-19 05

11.0

Pl

Small planetary in fine region

Sgr

NGC 6445

PK 008+03.1

17 49.2

-20 01

11.2

Pl

Pale grey planetary nebula

Sgr

NGC 6629

PK 009-05.1

18 25.7

-23 12

11.3

Pl

Small pale grey planetary nebula

Sgr

NGC 6565

PK 003-04.5

18 11.9

-28 12

11.6

Pl

Small bluish planetary nebula in rich field

Sgr

More info here: https://en.wikipedia.org/wiki/Planetary_nebula

 

Next Month

Anniversary of the Apollo 11 moon landing. We explore the landing site.

We also explore the deep sky objects in the southern constellation of Pavo, the peacock.

Please let me know if there’s anything that you would like me to cover for you.

Happy observing, and stay safe.

Joe Grida

 

Useful Links

This section is designed to give you access to further items of interest. I’ll add or delete items as the season changes.