WISE surveyed the sky in infrared light, leaving an archive that readers can explore by object name or coordinates. A useful first session compares one field across bands while recording the product and observation context. This guide walks through that comparison and explains why a colored preview, a combined image and an individual exposure answer different questions.
Choose the archive product for your question
The original Wide-field Infrared Survey Explorer observed in four bands. Later mission phases used the two shortest-wavelength channels after the cryogen was exhausted. The reactivated NEOWISE mission concentrated on repeated observations useful for moving objects. The spacecraft was decommissioned on August 8, 2024; its project archive remains a source of measurements.
IRSA's WISE mission page lists the releases and access services. Start with AllWISE Atlas images for a combined view of a fixed field. For motion or variability, choose suitable single-exposure products and retain the individual observation times. A coadd combines exposures and can average away the behavior you are trying to study.
Keep the infrared bands with the picture
| Band | Wavelength | Useful comparison |
|---|---|---|
| W1 | 3.4 micrometers | Compare compact sources and extended emission with W2. |
| W2 | 4.6 micrometers | Compare with W1 while retaining calibration and resolution context. |
| W3 | 12 micrometers | Explore longer-wavelength structures in releases that include this band. |
| W4 | 22 micrometers | Compare extended emission with allowance for its broader spatial response. |
The image-service overview describes the band coverage and differences between Atlas and single-exposure products. A three-color display assigns selected bands to visible red, green and blue. Its displayed colors are a mapping choice, and each layer may have a different brightness stretch.
Make a first comparison in the image service
- Open the IRSA WISE Image Service. Enter a recognized target such as M51, then check the resolved sky position shown by the service.
- Select AllWISE as the image set and Atlas as the product. Choose W1 through W4 for a comparison of the same region.
- Use “Image contains target.” Choose the size unit first, then request a field such as 20 arcminutes. This is a 1,200-arcsecond field. Keep the same field size across bands.
- Run the search and inspect the returned image identifiers and band labels. If multiple tiles cover the position, choose matching coverage or use the most-centered option with this single release.
- Compare one band at a time before making a color composite. Record which structures appear compact or extended and whether their positions agree.
The search documentation explains region-intersection options and coordinate formats. If there are no results, verify the resolved position and search geometry first. A requirement that an entire image fit inside a small region can exclude data that actually cover the target.
Use this session to learn the interface and describe appearance. To measure flux, download the science image with its metadata and the associated uncertainty and coverage information, then follow the release's calibration guidance. A screenshot records a display; the science file preserves the values needed for analysis.
Check artifacts before claiming a new object
Bright sources can produce saturation, diffraction spikes and persistence effects. Coverage and background quality also vary. The All-Sky release cautionary notes document examples, including issues in individual frames. Use the corresponding explanatory supplement for the release you actually selected.
A useful check is to inspect whether a suspicious feature changes with the scan or appears in repeated exposures at the same sky position. Cross-checking bands can help, but an artifact or a real source can have wavelength-dependent visibility. Keep the tests together instead of deciding from color alone.
Before comparing brightness, account for different resolution, background and calibration. A source that spreads over more pixels in one band can appear less conspicuous even when the underlying emission is significant. If you need a quantitative color, use appropriately calibrated measurements and their uncertainties.
Save enough context to repeat the result
The WISE archive reading note provides fields for target coordinates, release, bands, field size, image IDs, time coverage, display settings and artifacts. Fill it out while the search results are open. For a moving target, add the ephemeris and individual frame times; a fixed-position coadd is a different product.
Your first result can be modest and useful: “These four views cover the same field, but differ in band and spatial response; the extended emission is more conspicuous in this display.” The next step is a calibrated measurement tied to a scientific question. The infrared-telescope guide explains the wavelength and thermal-emission principles behind those differences.