First Light Guide #13: How to find 30 Arietis

30 Arietis

A detailed guide to finding / observing the double star

First Light Guide 13 graphicFirst Light Guides #13 is a detailed written and video reference to finding and observing the double star 30 Arietis in the constellation of Aries. This guide is ideal for beginners, but many advanced amateur astronomers may find it useful. It is designed to help you locate this double star with almost any telescope. There is a video to using a magnified finderscope, red dot finder, or setting circles along written tips on observing 30 Arietis.

Visitors who are new to this site may wish to get started here, while more advanced observers can search the First Light Guides by constellation, or by right ascension


Find Lambda Ari in the sky

30 Arietis is a double star within our own Milky Way galaxy. It consists of two F-class, white stars at magnitude 6.5 and 7.1. The slight difference in temperature and visual brightness sometimes shows an actual color difference to some observers. The separation of the two components has remained the same since they were first measured in 1835. The brighter primary star is a spectroscopic binary star with a period of 1.1 days, and the dimmer secondary star has a massive planet 10 times the size of Jupiter orbiting it every 11 months. 

If you have a magnified finderscope on your telescope, start here to find 30 Arietis:

If you have a red dot finder on your telescope, start here to find and observe 30 Arietis:


Observing tips:

30 Arietis is an easily split double star, at 38.1 arc seconds of separation between the primary and secondary components. As a zodiac constellation, Aries is visible from most anywhere on Earth, and is ideally placed for best viewing when it is at or near the meridian. In this way, it will be at it's highest point (culmination), providing the least amount of atmosphere to look through in order to find and observer the star. Use a long to medium focal length eyepiece.

Though the two stars are nearly identical in spectral type (see below), the slight magnitude difference between them causes an interesting effect at the eyepiece with respect to the colors seen. Most any F class star should appear pure white. But these are both F spectral class stars, with one slightly dimmer than the other. As a result, some observers have reported that the dimmer star may appear to have a subtle lilac color. What color(s) do you see?

Useful filter(s): None needed.

What should I see?

Below is an approximate view of 30 Arietis and the surrounding stars as seen with a 70mm telescope at 38x magnification, and a 1.40 degree telescopic field of view.  

30 Ari at 38x in 1.4 degree FOV

Details of 30 Arietis

Type: Double star

True binary: Unknown

Orbital period: Unknown

Distance: 136 ± 3 light years

Apparent separation: 38.1 arc seconds

Apparent magnitudes: 6.45, 7.10

Right ascension: 02h 37m 00.5s

Declination: 24° 38′ 50









Because telescopes and observers are all different, here are some alternate sketched/drawn views of 30 Arietis:

John Nanson, using a 6" reflector


The constellation: Aries

General information can be found here about Aries the Ram, where 30 Arietis is located.  This will help you know where to find the constellation in the sky and be able to locate and identify its brightest stars.

General information about Aries

Name of constellation: Aries

Abbreviation: Ari

Genetive form: Arietis

Common names: Ram

Associated asterisms: No major ones

Original 48 of Ptolemy: Yes

Area by size: 441 square degrees

Relative size: 39 out of 88 (Canes Venatici is next larger, Capricornus is next smaller)

First Light Guides objects: Lambda Arietis, 30 Arietis

Brightest stars in Aries, by magnitude 

First lists the Bayer designation, then the "traditional" star name (often Arabic, but not always - see each star's notes for details). Graphic shows constellation at culmination on the meridian, facing south.

  • α (Alpha) Arietis (Hamal) magnitude 2.01 it is the 49th brightest star in the sky, and resides at 66 light years distance. The traditional name comes from the Arabic phrase for "head of the ram."

  • β (Beta) Arietis (Sheratan) magnitude 2.64, and is 60 light years distant. Traditional name means the Arabic الشراطان aš-šarāţān "the two signs", a reference to the star having marked the northern vernal equinox together with Gamma Arietis several thousand years ago.