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Rotation period. Study the photometric curve. Shape. Is it binary?. Asteroids Rotation Period. spectroscopy. Surface composition. Observations reveal:. Time-dependent brightness variations. Rotation period of the asteroid around its axis. Due to:.

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Rotation period

Study the photometric curve


Is it binary?

Asteroids Rotation Period


Surface composition

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Observations reveal:

Time-dependent brightness variations

Rotation period of the asteroid around its axis

Due to:

Different reflectivity across the asteroid

Non spherical shape of the asteroid

Average rotation period: 10 h

Typical brightness variation : 0.2 mag

Fast rotators period: 2 h

Slow rotators period: few weeks

Most rotators period: 7 h –30 h

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Asteroid Rotation Period Determination

Non spherical shape-

rugby ball

Time-dependent brightness variations

for most asteroids are due to:

Cross section changes (as seen by the Earth)

Light reflected towards us varies-

Brightness appears to vary

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Asteroid Rotation Period Determination

Shape is 180 degrees symmetrical around an axis perpendicular to its greatest dimension

Rugby-ball shaped asteroid

Other side of the asteroid






same side of the asteroid-full revolution

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Asteroid Photometry



Magnitude system

The scale that traditionally has being used to denote the brightness of an object


Based on the eye

Brighter stars : 1st mag

Dimmest stars : 6st mag

The intensity becomes 10 times larger every -2.5 magnitudes eg. 6st mag staris 100 times fainter than1st mag star

Real intensity:

Or in mathematics :

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Known brightness



Asteroid photometry process:

  • Every certain interval of time take a picture

  • in each picture measure the signal from the asteroid

  • Measure the signal from at least onecomparison star of similar color in the vicinity of the asteroid

Is the comparison star


Pick 2 or more comparison stars and use the average intensity

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Asteroid photometry process-continued :

  • Calculate Δm from each measurement (we need to know the brightness variation and not the actual brightness of the asteroid )

  • Plot Δm vs time (eg. pictures are 3min apart)

  • Calculate the period by measuring the time between consequitive maxima or minima of the same amplitude

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Exercise procedure

Short period : < 4h

Bright enough

Be observable most of the night

  • Pick an asteroid

  • Plan an observation

  • Submit a request to the telescope

  • Analyse the data

List of asteroids

1727 Mette

Cartes du Ciel