How to Observe and Analyze a Spiral Galaxy: A Step-by-Step Guide Using Hubble Data

Introduction

Have you ever gazed at a spiral galaxy and wondered what secrets it holds? With the help of the NASA Hubble Space Telescope, you can dive into the details of a nearby spiral like NGC 3137, a glittering galaxy located 53 million light-years away in the constellation Antlia. This guide will show you how to observe, capture, and study a spiral galaxy step by step—perfect for amateur astronomers, students, or anyone fascinated by the cosmos. By the end, you’ll understand the techniques astronomers use to reveal a galaxy’s star clusters, dust lanes, and central black hole, just as Hubble did for NGC 3137.

What You Need

• Telescope – A 8-inch or larger aperture telescope for visual observation; a Go-To mount helps for tracking.
• Camera – A CCD or CMOS astronomy camera for imaging (optional for visual only).
• Filters – Broadband filters (e.g., B, V, R) or narrowband filters to capture different wavelengths.
• Mount – Equatorial mount with tracking capability for long exposures.
• Software – Image processing software (e.g., Siril, DeepSkyStacker, Photoshop) and analysis tools (e.g., SAOImage DS9).
• Internet Access – To access Hubble data via the Mikulski Archive for Space Telescopes (MAST).
• Reference Materials – Star charts, galaxy catalogs (e.g., NGC catalog), and scientific papers on NGC 3137.

Step-by-Step Instructions

Step 1: Choose Your Target Galaxy

Start by selecting a spiral galaxy visible from your location. NGC 3137 is an excellent choice because it’s relatively bright and well-studied. It lies in the constellation Antlia (the Air Pump), which is best observed from southern or equatorial latitudes during autumn. Check the galaxy’s coordinates: Right Ascension 10h 07m 10s, Declination -29° 51′ 08″. Use a planetarium app (e.g., Stellarium) to confirm when it’s highest in the sky. NGC 3137 is part of the NGC 3175 group, a collection of galaxies similar to our Local Group—including two large spirals (the other being NGC 3175) and many dwarf galaxies.

Step 2: Set Up Your Telescope for Observation

Align your mount and ensure it’s balanced. If you’re using a Go-To system, input the galaxy’s coordinates. Before observing, allow your telescope to acclimate to the outdoor temperature (30 minutes minimum). Start with a low-power eyepiece (e.g., 25 mm) to locate the galaxy—NGC 3137 will appear as a faint, elongated smudge. Then switch to higher magnification (e.g., 10 mm) to see its inclined, feathery spiral arms. Note that the galaxy is highly tilted from our point of view, giving it a unique shape. Record your observations in a logbook.

Step 3: Capture Images with a Camera

For detailed study, attach your camera to the telescope. Use a focal reducer if needed to widen the field. Focus carefully on a bright star near the galaxy. Take a series of sub-exposures: try 15–30 seconds each (with tracking) for at least 15–20 frames per filter. NGC 3137’s center is bright, but its fainter arms require longer total exposure (30–60 minutes). Use a filter wheel to capture images in different color bands—Hubble used six bands for its final image. If you lack a filter set, capture in monochrome and later combine with online Sloan filters for color. While exposing, keep an eye on guiding accuracy.

Step 4: Process Your Image Data

Stack your sub-exposures using software like DeepSkyStacker (free). Calibrate with darks, flats, and bias frames to remove noise. Then debayer (if using a one-shot color camera) or align monochrome frames. Use Siril or Photoshop to stretch the histogram to reveal the galaxy’s structure. For a multicolor image, combine your red, green, and blue channels—this mimics Hubble’s color composite. In your final image, you should see a bright core surrounded by dusty clouds. The core of NGC 3137 hosts a supermassive black hole estimated at 60 million solar masses—though not directly visible, its influence on surrounding gas is key.

Step 5: Analyze the Galaxy’s Structure

Use analysis software (SAOImage DS9) to measure the galaxy’s dimensions. NGC 3137 spans about 2.5 arcminutes visually—convert that to light-years using its distance. Identify the spiral arms: they appear loose and feathery due to the galaxy’s high inclination. Overlay your image with published Hubble data from MAST (search for NGC 3137 in the archive). Compare the distribution of star-forming regions (bright blue knots) and dust lanes (dark patches). The galaxy is a member of the NGC 3175 group, which has over 500 dwarf galaxy candidates—see if any faint companions appear in your frame. Note that the Local Group, containing the Milky Way and Andromeda, has a similar structure with two large spirals.

Step 6: Interpret and Document Your Findings

Now it’s time to draw conclusions. Write a report describing the spiral pattern, the presence of dust, and any visible star clusters. Compare your results with professional studies of NGC 3137. In the NGC 3175 group, astronomers study galaxy interactions—can you see any evidence of tidal distortions? Also, consider the dynamics: since NGC 3137 is only 53 million light-years away, it’s a nearby system for studying the stellar lifecycle. Include a table of your measured values (e.g., apparent magnitude, angular size) and link to the Hubble image for reference. This step turns your observation into science.

Tips for Success

• Plan Your Observation Night – Check weather and moon phase; darkest skies are best (new moon). NGC 3137 is best high in the south if you’re in the northern hemisphere.
• Use Dark Sky Sites – Light pollution washes out faint details; drive to a Bortle 4 or better location.
• Start with Shorter Exposures – If you’re new to astrophotography, begin with 10-second subs to avoid tracking errors.
• Explore the NGC 3175 Group – While imaging NGC 3137, look for its companion NGC 3175 (visible in the same field with a wide-angle setup).
• Consult Hubble Data – The official Hubble image of NGC 3137 was created from six color bands. Download the FITS files from MAST and reprocess them to match your own—great for learning image calibration.
• Share Your Results – Post your image on astronomy forums (e.g., Cloudy Nights) or on the Hubble Community Science page to get feedback.

By following these steps, you’ll not only capture a striking image of a spiral galaxy but also gain insight into the science behind Hubble’s observations. The same techniques used for NGC 3137 can be applied to countless other galaxies, helping you explore the universe from your own backyard.