In the first part of a series that looks at urban stargazing through the four seasons, Rod Mollise reveals the wonders you can discover in spring
Urban astronomy is not for the fainthearted, but persevere and you will find a wealth of celestial treasures that await discovery, even under bright night skies. Many deep-sky objects are visible even in brightly lit urban areas. Take open clusters, nests of thousands of newborn suns, deep-sky objects which are the least harmed by light pollution. More tightly packed globular clusters are very old and light pollution takes its toll on them. While many are visible in the city with smaller aperture telescopes, most are just round smudges with no individual visible stars.
Galaxies can be challenging for urban observers to see. This doesn’t mean you can’t see them, you just won’t see much detail. But diffuse nebulae are the objects most harmed by light pollution; even with a high-quality light-pollution reduction (LPR) filter screwed onto the eyepiece, dimmer emission nebulae can be a challenge to see. Planetary nebulae are not as harmed by light pollution. If they are tricky it’s because they are difficult to distinguish from stars.
Key kit
The most important characteristic of a telescope used for deep-sky observing from any site is aperture– the size of its light-collecting lens or mirror (the ‘objective’). The superior light-gathering power of a larger telescope is even more important in the city. From a light-polluted area, you’ll need one with a light-collecting lens or mirror with a diameter of at least 200mm. Inexpensive Dobsonian reflecting telescopes are a good balance between price, performance and portability. However, a 250mm Dobsonian is almost as affordable and portable, and the extra aperture makes a difference.
When it comes to mounts, new observers will find any altaz mount less complicated to use than an equatorial mount. A Go-To mount is useful in urban areas: just enter the ID of a deep-sky object into its computer hand control and the scope will move to it. LPR filters can also help, but don’t expect even the most expensive one to pull Orion’s dim Horsehead Nebula out of an orange sky. LPR filters only work on diffuse and planetary nebulae, and they are useless for galaxies and star clusters. While they block certain light wavelengths, including those of incandescent, sodium and mercury vapour streetlights, the light of the stars is in the same range of wavelengths. Since galaxies and star clusters are made up of stars, they are dimmed by LPR filters rather than enhanced.
Top tips for urban observing
Use averted vision
Averted vision involves looking at objects out of the corner of the eye. By looking to the side of a faint object, you can make it appear brighter and more detailed.
Tap the telescope
Moving objects are generally easier to see in the night sky from a city. If a celestial target is invisible, you can gently tap the telescope tube so it vibrates.
Block ambient light
Turn off any nearby lights, shield the telescope from lights, or drape a dark cloth over your head and eyepiece to allow your eyes to become more dark-adapted.
Spring sights
Striking constellations to explore above the Milky Way…
Cancer, the Crab
The well-known constellation harbours two open star clusters
INSET: M67 is estimated to be between 3–5 billion years old
M67 (mag. +6.9, 30’ across) is located in the eastern part of Cancer, 1° 44’ west of mag. +4.2 star Acubens (Alpha (α) Cancri). While most open clusters are young, M67 is old – between 3 to 5 billion years. It may not be a spectacular sight, but it is visible from urban and suburban locations and is well-framed in a medium-power eyepiece.
M44, (mag. +3.1, 1° 10’ across), is located near the centre of Cancer’s stick figure. Also known as the Beehive Cluster, from dark locations M44 is visible as a hazy patch with the naked eye, with 20 stars glowing at mag. +8.0 or brighter. The brightest, Epsilon (ε) Cancri, is nearly visible without optical aid at mag. +6.3. M44 is not as impressive in a telescope as you might expect; with a diameter of 1° 10’, it’s too large to fit in the field of view of low power eyepieces in all but the smallest scopes.
Leo, the Lion
Full of galaxies, most of Leo’s are arranged in pairs and groups
INSET: M65 (right) and M66 are approximately 35 lightyears apart
Leo’s galaxy pair, M65 and M66, are both bright enough to shine through even badly light-polluted inner city skies. The more western and dimmer of the pair is galaxy M65 (mag. +10.5, 8’42” x 2’27”). M66 (mag. +8.9, 9’6” x 4’12”) is visually brighter than its companion, despite being larger in size. A view through a 300mm telescope will reveal a little detail, but an increased aperture won’t make a big difference in heavy light pollution – the real improvement comes with darker skies. In a more suburban location, instruments with an aperture of 250mm or larger can reveal spiral detail in M66, while magnifications of 200x or higher can show hints of mottling on M65’s disc.
A third, dimmer, nearby galaxy is NGC 3628 (mag. +9.5, 10’34” x 2’32”), which makes up the ‘Leo Triplet’ with M65 and M66. From a suburban area it is easier to see with a 250mm telescope, and on a good night you can see why it is called the Hamburger Galaxy, because an equatorial dust lane slices through its disc – the ‘bun’.
Ursa Major
Known as the Great Bear, this constellation has hordes of galaxies
Ursa Major is home to the famous Plough asterism. But it is far more than that, as it contains some stunning galaxy targets. M82 (mag. +8.4, 11’12” x 4’18”) is possibly the best galaxy in the northern sky for city observers, because of its favourable magnitude and size. Nicknamed the Cigar Galaxy, it is so-called because of its elongated, lens-shaped disc. An even better name might be the ‘Exploding Cigar Galaxy’, because it’s crossed by bright and dark lanes and is throwing off huge clouds of gas. Some of these features are visible even to city-bound telescopes. M82 is not actually exploding, it is undergoing massive bouts of star formation and other effects caused by an encounter with a nearby galaxy, most likely M81. Its gas and dust have been compressed and hordes of new stars are being born across its disc.
M81 (mag. +6.9, 26’54” x 14’6”) is also known as Bode’s Galaxy – after Johann Elert Bode, the German astronomer who discovered it in 1774. As its orientation is between face-on and edge-on, its surface brightness is high, and it is easy to see the bright centre of M81 in a small telescope under a light-polluted sky.
In Ursa Major, you can also look for M97 (mag. +9.9, 3’24” x 3’18”), the Owl Nebula, just below the Plough asterism. It’s a large, round, planetary nebula with two dark spots that represent the Owl’s eyes.
Light pollution takes its toll on nebulae; while M97 is not overly dim or large, you will need an OIII (Oxygen) filter to see it if you are using a 300mm telescope in the city or further out in the suburbs.
Canes Venatici
This little constellation represents the hunting dogs of Boötes
INSET: M51 was discovered in 1773 by Charles Messier
M51 and its smaller companion galaxy, NGC 5195 (combined mag. +8.1, 11’12” x 6’54”) are known collectively as the Whirlpool Galaxy. Low surface brightness, caused by the orientation of M51, means it can be tricky to see, but it is always detectable. M51 is located just over the Ursa Major–Canes Venatici border, 3°51’ north of the bright star Alkaid (Eta (η) Ursae Majoris), the ‘end’ star in the Plough asterism.
M94 (mag. +8.2, 11’12” x 9’6”) is a spiral galaxy, located halfway along and 1 arcminute northeast of a line drawn between the stars Chara (Beta (β) Canum Venaticorum) and Cor Caroli (Alpha (α) Canum Venaticorum). It is so bright and prominent that it is visible on the poorest nights, thanks to an intense bout of star formation in its inner regions that results in a central area less than 1 arcminute in diameter that shines intensely.
Coma Berenices
The hair of Egyptian queen Berenice is adorned with galaxies
INSET: NGC 4565 is known for its distinctive Flying Saucer shape
M64, the Black Eye Galaxy (mag. +8.6, 10’42” x 5’7”) is one of the most beautiful objects in the northern sky, despite its unimpressive specifications. From the city it can be observed with a 100mm reflector, but there will be no hint of the dark patch of dust near its centre that earns it its Black Eye moniker.
NGC 4565 (mag. +10.4, 15’54” x 1’) the Needle (or Flying Saucer) Galaxy, has a dim magnitude value that is offset by its shape – edge-on, with a long, thin, needle-like disc. Its thin body keeps its surface brightness high.
M100 (mag. +9.3, 7’24” x 6’18”) is a face-on spiral galaxy. It’s not large and its surface brightness is low due to its face-on orientation. A good night can show some hints of detail, while a 12mm eyepiece at 150x magnification can show mottling.
One of Coma’s best objects is M53 (mag. +8.3, 13’ across). An attractive globular cluster, it’s easy to see from a city with a 150mm telescope.
Virgo
Navigate views full of galaxies despite few landmark stars
In the constellation of Virgo, the Virgin, we begin with M90 (mag. +9.5, 9’30” x 4’24”), an attractive intermediate inclination galaxy. It has a bright, large core surrounded by a slightly dimmer, dusty central region set in a still dimmer disc that features prominent spiral arms. Bear in mind, however, that from a city, even with a 300mm telescope M90 may be a dissapointing compared to its neighbours.
Not far from M90 is M89 (mag. +9.8, 5’6” across), which is a perfectly round elliptical. In the city, with a 300mm telescope, the galaxy is bright with a star-like nucleus. In the suburbs, M89 is an easy catch for a 100mm refractor.
M84 (mag. +10.1, 6’30” x 5’36”) is a giant elliptical galaxy, without spiral arms or any visual details beyond a brighter central region. Detail or not, in the eyepiece this galaxy is a wonder.
You’ll know that you’ve hit on M84 because of the presence of another, slightly dimmer, elliptical galaxy in the field, M86 (mag. +9.2, 8’54” x 5’48”). This galaxy is only 17 arcminutes to the west, so it’s easy to fit the two into the field of an eyepiece with 150x magnification, which is a good power to use in Virgo if you’re observing from a city. Looking at M86’s magnitude, you would expect it to be noticeably brighter than its companion. However, it actually appears dimmer than M84, as it is more elongated (although it looks round, visually).
The easiest galaxy to see in the constellation of Virgo is probably M86, but it’s closely followed by the huge elliptical galaxy M87 (mag. +9.6, 7’12” x 6’48”).
‘Huge’ doesn’t even begin to describe this monster, which has a mass of over a trillion suns. Despite its gigantic size, in reality it’s only a bit larger than M86 in the eyepiece. It has a brighter magnitude, but always looks dimmer.
Finally, M104 (mag. +8.0, 8’42” x 3’30”) is the famous Sombrero Galaxy. Located in the southeastern area of the constellation, it is away from the main body of the Virgo Cluster that lies between the ‘arms’ of the Maiden, within the arms of the ‘Y’ of Virgo’s stick figure. In images (see above), this edge-on galaxy features a prominent equatorial dust lane and a large central bulge that makes it look like a sombrero hat.
‘Uncle’ Rod Mollise is an American amateur astronomer and writer who lives near Mobile, Alabama. He is the author of Choosing and Using a New CAT