Observation of Specific Objects


AfH provides information on how to observe specific objects and where they can be located. For example, perhaps you already know you want to take photographs through a telescope of a star with known exoplanets. This will take you down the right path.

The following types of objects can be successfully observed using robotic telescopes and can yield important scientific results. AfH provides recommendations and guidance for selecting research projects that can provide authentic research experiences, and can produce important science results.


Before the discovery of Cepheid variable stars, there was no way to accurately measure the distance to objects outside of our own Milky Way Galaxy. Learn more about these “cosmic measuring tapes” and how they’re used to define the scale to neighboring galaxies.

Cepheids are pulsating variable stars for which distances may be determined by means of the Leavitt Law. They are useful for studies of the structure of our galaxy and distances to nearby galaxies. Cepheids provide fundamental reference data for the distance ladder of the universe.

Artist’s depiction of the “cosmic distance ladder”


  • Classical Cepheids (DCEP type)
  • Type II Cepheids (CW type)
  • RR Lyrae variables (RR type)
  • RV Tauri variables (RV type)
  • Long Period Variables (LPVs, Miras, M type)

Changes in period and changes in light curve shapes provide indicators of stellar evolution for these pulsating variables.

Suggested Research Projects:

  • Search for undiscovered variable stars in a star field.
  • Determine periods and light curves for some newly discovered variables.

Suggested Research Questions:

Determine a light curve for your Cepheid.

Determine one or more Time of Maximum (ToMx) for your Cepheid.

  • Does your ToMx agree with predictions?

Determine the period (P) of your Cepheid from your data.

  • How does your period compare with the published period for your Cepheid?

Determine a phased light curve for your Cepheid.

  • How does your phased light curve compare your light curve with published data?

Use your light curve to determine the amplitude (A) for your Cepheid.

  • How does this compare with published data?
  • Are there any amplitude variations?

Use your light curve to determine the period (T) for your Cepheid.

  • Compare with published data and evaluate the possibility of changes in the period.
  • If there are period changes, determine the rate of period change.
  • Compare your rate of period change with theoretical model predictions.

Use your data and the Leavitt Law to determine the distance to your Cepheid.

  • Compare your distance with the distance determined by trigonometric parallax.

Determine a light curve for a Cepheid in another galaxy, and determine the distance to the galaxy.

     To see all Cepheids in the GORT image archive, visit https://afh.sonoma.edu/archive/objects?type=cepheid.

Cepheids pulse in size (and brightness) in a very regular pattern, which takes longer to complete the bigger they are. By watching how long it takes to go from bright to dim to bright again you can determine how bright a Cepheid star really is. By comparing that to how bright a Cepheid star looks in the sky you can figure out how far away it actually is, in the same way you can figure out how far away a streetlight is on the highway…the farther it is the dimmer it looks. Astronomers used Cepheid variable stars to determine distances to galaxies for the first time, when no one really understood just how far away they were. NASA’s Hubble Space Telescope still performs distance measurements using Cepheid stars today, in order to more precisely measure the rate at which our universe is expanding.

The Video to the above is of barred spiral galaxy Cepheidin which shows a pulsating Cepheid variable star near the left-hand edge. Credit:NASA/etc.

AfH Supernova Activity

  • 1: Select the file button at the top left, then ‘open > local file’. Use the file picker to select the FTS image you’d like to work with.
  • 2: From the ‘Scale’ tab, select ‘Log’. Adjust brightness as needed.
  • 3: Using a finder chart, locate your traget and comparison stars. Make sure to label these on your chart for reference.
  • 4: If needed, resize the circle. You should use the same size for each image and each star, so if you change this note the size and make sure it fits for all objects.
  • 5: Move the region to your target star and click ‘Target Star’. Do the same for each comparison. This will also determine background from the area around the object.
  • 6: Click ‘draw chart’ to plot the background subtracted results of your image.
  • Repeat for additional images.


Interacting Binary Stars

There are more binary and multiple star systems than single stars in the universe. Interaction effects allow sizes, masses, temperatures, luminosities, and internal structures to be determined for individual components. Such determinations cannot be reliably determined for single stars.



  • Algols (EA type)
  • Beta Lyrae variables (EB type)
  • W Ursa Majoris variables (EW type, contact binaries)
  • Double Periodic Variables (DPVs)
  • W Serpentis variables (WSER type, mass transfer, accretion disks)
  • Cataclysmic Variables (CVs, most are binary star systems)
  • Supernovae (SN type, many are binary star systems)

Activity in interacting binary stars provide direct indications of stellar evolution. Such indications are not easily detectable in single stars.

Eclipsing Binary Systems (EBs)

Eclipsing systems can have orbital periods ranging from a few hours to several decades. However, most of the known eclipsing systems have periods of a few days. This is most likely a selection effect resulting from the manner in which most variable stars have been discovered. Eclipse depths can range from several magnitudes to a few tenths or a few hundredths of a magnitude. Basic research activities involve measuring precise times of occurrence for eclipses and eclipse depths. A complete light curve can be solved to determine physical characteristics of the stars in the system.

  • Observe an eclipse and determine the Time of Minimum (ToM).
  • From multiple times of minima determine the period.
  • Search for and evaluate possible changes in the period.
  • Evaluate the O-C diagram for an eclipsing system.
    • Determine the eclipse depth and duration for an eclipse. For well observed eclipsing systems, compare with prior observations to search for variations in the shape or nature of the eclipses.
    • Determine the characteristics for a secondary eclipse. Secondary eclipses are often not regularly observed.
    • Obtain a complete light curve and solve the light curve to determine physical properties for the system. Determine a model for the eclipsing system.

To see all eclipsing binaries in the GORT image archive, click this link: https://afh.sonoma.edu/archive/objects?type=binary

Short Period Pulsators (SPPs)

The extreme short period pulsating stars can have periods of only a few hours, so that a complete cycle can be observed in a single night. Amplitudes are less than one magnitude, and can often be only a few tenths or a few hundredths of a magnitude. Such systems can be successfully observed using CCD detectors.

The shortest period systems are either RR Lyrae variables (RR) or Delta Scuti variables (DS). Cepheid variables (DCEP) are sometimes considered part of the SPP group, even though they have periods ranging from a few days to a few weeks. Cepheid variables normally have amplitudes slightly greater than the other SPP objects.

  • Determine times of maxima (ToMx) and times of minima (ToM) from light curves.
  • Determine amplitudes by comparing magnitudes at maxima and minima.
  • Determine multiple light curves and search for variations from cycle to cycle.

Long Period Variables (LPVs)

Long period variables can have periods from several months to more than a year. Amplitudes can be up to 12 magnitudes. Light curves do not repeat exactly from one cycle to the next. Amplitudes and periods for some seem to be changing in some regular fashion. These objects are red giants, and it has been suggested that all red giants may be variable at some level. Because of the lengths of the periods, many of these objects are not regularly observed.

  • Determine times of maxima (ToMx) and times of minima (ToM).
  • Determine magnitudes at maxima and minima.
  • Determine one cycle of a light curve and compare with previous observations by other observers.

Exoplanet Transits

Continuing timing of transits of exoplanets allow the orbital periods to be determined. The shape of the transit curve permits the sizes of the planets and the orbital inclination to be determined. Variations in transit times indicate the possible presence of additional orbiting planets in the system.

Exoplanets detected by observing dips in the brightness of stars


  • Transiting exoplanets

Suggested Research Projects:

Exoplanet Transits

  • Record a transit for an exoplanet and determine the transit time.
  • Compare an observed transit time with a predicted transit time.
  • Determine a model for a planet using a transit observation.

Determine a transit light curve for your exoplanet.

  • What is the transit time (T) for your exoplanet?
  • Does your transit time agree with the predicted transit time?
  • Is there any indication of transit time variation (TTV) for your exoplanet?
  • What is the depth (d) for your transit curve?
  • Does the depth of your transit curve agree with predictions?
  • What is the transit duration (D) for your exoplanet?

Fit a model to your transit data.

  • Determine the radius for your exoplanet.
  • Determine the inclination of the orbit for your exoplanet.

Unusual stars with outbursts or other unpredictable activity

Monitor stars with known unpredictable activity. (note: Professional observatories generally do not allocate observing time for such observations.) Normally such stars are quiescent and not active. These stars should be monitored because such events are unpredictable. When such events occur, the astronomical community should be notified so specialized instrumentation at professional facilities can be used to study these events.

Stars with unpredictable activity:

Cataclysmic variables (CVs)

  • Dwarf novae
  • Recurrent novae
  • Novae
  • Polars

RCB stars (inverse novae)

YSOs (Young Stellar Objects)

Variable nebulae (likely illuminated by YSOs)

SR stars (semi-regular variables)


Follow the decline of a supernova. Supernovae (SNs) are classified as cataclysmic variables, but the outburst is far brighter than other forms of CVs.

Active Galactic Nuclei (AGNs)

The nuclei of some galaxies are variable in brightness. This variability reflects dynamic processes associated with the accretion disks surrounding the supermassive black holes at the center of these galaxies. These processes can involve matter striking the accretion disks or motions within the disks. The time scale of the variability places limits on the sizes of the structures or phenomena involved.


  • Slow, irregular variations
  • Outbursts

AGN Observing Goals

  • Long Term Goals: The goal should be to achieve a time resolution of 1 month for a number of years. Multiple filter observations for a broad range of objects should be obtained at least once a month. A relatively small collection of observatories could produce an impressive collection of data with a time resolution on the order of 0.1 years. Ideally, any unusual variations would be reported and thus serve as a trigger for more intensive observation campaigns.

  •  Interday Goals: The goal should be to establish targeted campaigns to achieve a true time resolution of 1 day for a period of several weeks. Objects exhibiting unusual variation in the long term studies, or objects selected for other reasons, can be placed on special focused campaigns. For such a campaign, cooperating observatories will attempt to obtain an observation once a night for an extended, but finite span of time. A modest distribution of observatories would be expected to produce surveillance data with a time resolution on the order of a day. Such campaigns might extend for 4, 8, or 12 weeks.

  • Microvariability Goals: The goal should be to establish targeted campaigns to achieve a true time resolution of several minutes for a period of several days. Objects exhibiting unusual night-to-night variations, or objects selected for other reasons, can be placed on special microvariability campaigns. For such a campaign, cooperating observatories with appropriate equipment will attempt to observe a designated target nearly continuously for several/many hours at a time throughout the night. Such a campaign should last for an extended but finite span of time. With proper planning and a uniform distribution of observatories in longitude, this should make it possible to keep a target under virtually continuous surveillance with a time resolution on the order of minutes. Such campaigns might extend for 5, 10, or 15 days.

To see the galaxies in the GORT archive, visit https://afh.sonoma.edu/archive/objects?type=galaxy.